PLOTTING AN IMAGE ON A THIN MATERIAL HAVING VARIATIONS IN THICKNESS

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to techniques of automated plotting (writing, printing) of images on thin materials, and more particularly, to a system and method for plotting an image on a thin material having unpredictable variations or non-uniformities in thickness, via measuring thin material thickness, and adjusting the plotting as needed, to compensate for the thickness variations. The present invention is particularly applicable, but is not limited, to the fields of electronics, microelectronic and semiconductor manufacturing, requiring highly accurate and reproducible plotting (writing, printing) of images on films (as exemplary thin materials), which, for example, are usable as masks for fabricating printed circuit boards (PCBs). The present invention is also particularly applicable to the field of specialized graphic arts, for specialized applications requiring highly accurate and reproducible plotting (writing, printing) of images on thin materials (such as graphic arts writing or printing media).

Principles of thin materials (such as films), plotting (writing, printing) an image on a thin material, plotters (writers, printers) used for effecting such plotting, PCB masks made by plotting (writing, printing) images on films, and using PCB masks for fabricating printed circuit boards (PCBs), theories, and practices thereof, and, related and associated applications and subjects thereof, are well known and taught about in the prior art. For the purpose of establishing the scope, meaning, and fields or areas of application, of the present invention, the following background includes selected definitions and exemplary usages of terminology which are particularly relevant to, and used for, disclosing the present invention.

Thin Materials and Films

Herein, in the context of the field and art of the present invention, the phrase ‘thin material’ generally refers to a material whose thickness is significantly small in magnitude compared to one of its other dimensions. In general, the thickness of the thin material can be ‘relatively small’, for example, on the order of microns (or smaller), or alternatively, the thickness of the thin material can be ‘relatively large’, for example, on the order of meters (or larger), in order for the material to be considered a thin material as defined herein, and as being the work piece in the description of the present invention. In general, the thin material can be composed of essentially any single substance, or combination of substances, where a given substance consists of organic matter or/and inorganic matter.

An exemplary type of thin material is a film, being a (thin) strip or sheet of material whose thickness is significantly small in magnitude compared to one of its other dimensions. For example, fabricating a PCB typically involves using a PCB mask which is made from a thin material in the form of a film generally having a thickness within a range of between about 50 microns (μm) and about 500 microns (μm), and having a ‘standard’ thickness of about 180 microns (μm). As another example, a thin material (such as a film) used in specialized graphic arts has a ‘standard’ thickness of about 100 microns (μm). In general, a thin material need not have a thickness of on the order of microns

Plotting (Writing or Printing) an Image on a Thin Material

Herein, plotting (writing or printing) an image on a thin material generally refers to generating, producing, forming, or creating, an image on a surface of a thin material (as defined hereinabove), ordinarily by using a mechanism, device or apparatus, such as a plotter, typically, included as part of an overall system, that effects the plotting (writing or printing). It is to be fully understood that the term ‘plotting’ is synonymous with the terms ‘writing’ and ‘printing’. Moreover, it is to be fully understood that grammatical variants of the term ‘plotting’, such as ‘plot’, and ‘plotter’, are synonymous with corresponding grammatical variants of the term ‘writing’, such as ‘write’, and ‘writer’, respectively, and are synonymous with corresponding grammatical variants of the term ‘printing’, such as ‘print’, and ‘printer’, respectively. For purpose of clarity and consistency, the term ‘plotting’ is primarily used throughout the present specification. Accordingly, for example, the phrase ‘plotting an image on a thin material’, is synonymous with the corresponding phrases ‘writing an image on a thin material’ or ‘printing an image on a thin material’, and the phrase ‘plotting head’ is synonymous with the corresponding phrases ‘writing head’ or ‘printing head’ (which commonly appear in technical literature in the fields of electronic microelectronic and semiconductor manufacturing, particularly as relating to making PCB masks that are used for fabricating PCBs).

Plotters and Types Thereof

Herein, the term ‘plotter’ generally refers to a mechanism, device or apparatus, typically, included as part of an overall system, that is used for plotting an image on a thin material (as defined hereinabove). Two different general main types of a plotter are known as a drum plotter, and a flatbed plotter, which primarily differ according to the overall geometrical shape (drum, or flat, respectively) of a support element (herein, also referred to as a thin material support element) used for supporting and holding, and possibly moving, the thin material upon which the image is plotted. Moreover, two different general main types of a drum plotter are known as an external drum plotter, and an internal drum plotter, which primarily differ according to the location (external, or internal, respectively) of the thin material situated upon the support element, and according to location of operation of a plotting head relative to the support element during plotting of the image on the thin material.

An external drum plotter includes a drum whose external surface (as the thin material support element) functions for supporting and holding, and moving, the thin material upon which an image is plotted. The drum is controllably rotatable about its long axis (herein, referred to as the drum axis). An external drum plotter also includes a plotting head located and operative external to (outside of) the drum. The plotting head is connected to a plotting head moving mechanism which enables controllable movement of the plotting head along the drum axis. During operation, a thin material (such as a film), is positioned upon the external surface of the drum, the drum is made to rotate, and the plotting head moves and plots an image on the thin material.

An internal drum plotter includes a drum whose internal surface (as the thin material support element) functions for supporting and holding, and moving, the thin material upon which an image is plotted. The drum is either fixed, or is controllably rotatable about its long axis (the drum axis). An internal drum plotter also includes a plotting head located and operative internal to (inside of) the drum. The plotting head is connected to a plotting head moving mechanism which enables controllable movement of the plotting head along the drum axis and simultaneous rotation of the plotting head about its own axis. During operation, a thin material (such as a film), is positioned upon the internal surface of the drum, the drum is either fixed or made to rotate, and the plotting head moves, by traveling along the drum axis and rotating about its own axis, and plots an image on the thin material.

A flatbed plotter includes a flat (bed-type) surface (as the thin material support element) which functions for supporting and holding, and possibly moving, the thin material upon which an image is plotted. A flatbed plotter also includes a plotting head located and operative above the flat surface. The flat bed or/and the plotting head is/are connected to one or more moving mechanisms which enable controllable movement of the flat bed relative to the plotting head. During operation, a thin material (such as a film), is positioned upon the flat surface, the flat bed and the plotting head move relative to each other, and the plotting head plots an image on the thin material.

Photoplotters

In general, any of the above stated general main types of a plotter (i.e., an external drum plotter, an internal drum plotter, or a flatbed plotter) whose structure and function (operation) are based on optics and use of a light source, and which plots an image on a thin material being a type of (light sensitive) photographic medium (such as photographic film), is considered a photoplotter (i.e., a mechanism, device, or apparatus, that photoplots an image via a photographic process). Thus, an external drum plotter, an internal drum plotter, or a flatbed plotter, whose structure and function are as just described are known as an external drum photoplotter, an internal drum photoplotter, and a flatbed photoplotter, respectively. Two different general main types of a photoplotter are known as a laser (or laser-based) photoplotter, and a light emitting diode or LED-based photoplotter, which primarily differ according to the specific type of light source (i.e., laser beam light, or diode light, respectively) used by the photoplotter for effecting the photographic process during photoplotting of an image on a thin material. As well as photo-plotting, the present invention is also applicable to electron beam, X-Ray, ink-jet and other kinds of non-photo plotting.

Photoplotters are widely used in the fields of electronics, microelectronic and semiconductor manufacturing, requiring highly accurate and reproducible plotting of images on films (as exemplary thin materials), which, for example, are usable as masks for fabricating printed circuit boards (PCBs). Photoplotters are also applicable to the field of specialized graphic arts, for specialized applications requiring highly accurate and reproducible plotting of images on thin materials (such as films).

Photoplotting for Fabricating PCBs

As is well known from prior art teachings (e.g., “Printed Circuit Board Basics”, Third edition, by Michael flat, Miller Freeman Books, ISBN 0-89730-486-3, 1997, briefly, and in general, a PCB consists of a substrate that includes at least one conductive layer and at least one insulating layer. Fabricating a PCB includes producing tracks in the conductive layer in order to provide electrical interconnections between electronic components which are then added to the board at a later stage. Following computer aided design (CAD) of the electronics and of a PCB, and computer aided manufacture (CAM) of board substrates, final artwork chosen for producing the tracks is converted into a raster (digital) image and sent to a plotter (typically, a photoplotter). The photoplotter plots a black-and-white image on a film, which is then used as a PCB mask during processes for forming a desired pattern on the PCB.

Significant Problem Associated with Plotting an Image on a Thin Material Having Variations in Thickness

Regardless of the field of application, but particularly in the fields of electronics, microelectronic and semiconductor manufacturing, and specialized graphic arts, requiring highly accurate and reproducible plotting of images on thin materials (such as on films, or on graphic arts writing or printing media), a significant problem arises when there is need for plotting of an image on a thin material having (unpredictable) variations or non-uniformities in thickness.

In general, one may consider at least three main categories of factors which affect accuracy and reproducibility of plotting an image on a thin material: (1) plotter mechanics, (2) plotter environment, and (3) thin material thickness.

Among several factors which may be considered in the category of plotter mechanics, there may exist structural (geometrical) imperfections, defects, or irregularities, in the plotter, particularly of the surface dimensions of the thin material support element (e.g., drum or flatbed, of a drum or flatbed plotter, respectively) used for supporting and holding, and possibly moving, the thin material upon which is plotted the image. Such structural effects can cause undesirable ‘wobble’ or deviations in the distance and relative movement particularly translational velocities, between the thin material support element, and therefore, between the thin material upon which the image is plotted, and a plotting head of a plotter which effects the actual plotting of the image on the surface of the thin material.

In the field of electronics, microelectronic and semiconductor manufacturing, for example, requiring highly accurate and reproducible photoplotting of images on films (as exemplary thin materials), which, for example, are usable as masks for fabricating printed circuit boards (PCBs), drum plotters, particularly external or internal drum photoplotters, are used to produce photo-tools for making PCB masks. These photo-tools require high dimensional accuracy when used as PCB masks, preferably below 10 microns (μm) (feature to feature—FTF or Feature to grid—FTG) for mask sizes exceeding 500 millimeters (mm). Drum photoplotters are highly sensitive to structural effects which can cause even minute variations in the height of the plotting surface of the film in relation to an axis around which the drum of the drum photoplotter rotates. Drum photoplotters are available (e.g., drum photoplotter models LP-7008™ and LP-9008™ from Orbotech Ltd., Israel) which make measurements of, and adjust plot timings (e.g., by adjusting a strobing frequency of an exposure beam), to compensate for, such structural (geometrical) imperfections, defects, or irregularities, in the drum photoplotter.

The category of plotter environment primarily relates to environmental factors, such as variations in temperature, pressure, or/and humidity, in the immediate or local environment surrounding or encompassing a plotter or/and a thin material during a plotting procedure, which may undesirably affect the characteristics of the plotter or/and of the thin material, during the plotting procedure.

The category of thin material thickness particularly relates to (unpredictable) variations or non-uniformities in the thickness of the thin material which typically exist under actual or real conditions of plotting an image on the surface of the thin material. Separate from, or in addition to, the preceding described structural effects, a given plotter may be highly sensitive to such variations in the thickness of the thin material, which can also cause undesirable deviations in the distance and relative movement (i.e., relative tangential or translational velocities) between the thin material support element, and therefore, between the thin material upon which the image is plotted, and a plotting head of the plotter which effects the actual plotting of the image on the surface of the thin material.

The present invention is focused on the third main category, particularly regarding those factors which are relevant to accurately and reproducibly plotting an image on a thin material having (unpredictable) variations or non-uniformities in the thickness of the thin material. An excellent way of further describing, and understanding, the preceding significant problem associated with plotting of an image on a thin material having (unpredictable) variations or non-uniformities in thickness, is provided in the following illustrative description, along with reference to FIGS. 1 and 2.

FIG. 1 (prior art) is a schematic diagram illustrating a cross-section of thin material 10 positioned on the external surface of a drum 12 (for example, as part of an external drum plotter or photoplotter). Thin material 10 is characterized by a nominal length 14, and by a thin material thickness 16. Plotting of an image on thin material 10 is effected on thin material surface 18, for example, by operation of an external drum plotter. Under ideal conditions, thin material 10 has constant thickness 16. During operation of an external drum plotter, as drum 12 rotates (as indicated by direction of movement 20) about drum axis 22 (to be understood as extending above, through, and below, the plane of FIG. 1) at a certain speed, the plotter, in which drum 10 is included, plots a desired image on surface 18 of thin material 10.

However, under real conditions, a significant problem arises when thin material 10 has (unpredictable) variations or non-uniformities in thickness 16. Magnitude of such variations in thickness 16 of thin material 10 may be extremely small, for example, as small as on the order of a few microns. Due to rotation of drum 12, variations (even minute variations) in thin material thickness 16 of thin material 10 result in an actual tangential velocity of surface 18 that is different from an expected tangential velocity of surface 18. Such behavior translates to a difference between an ‘effective’ nominal length and an ‘ideal’ nominal length 14 of thin material surface 18, which, in turn, may affect one or more dimensions, or/and the contents (for example, plotted pixels being offset from a planned location), of an image plotted on thin material 10.

FIG. 2 is a schematic diagram illustrating plotting location (via a grid map) resulting from changes in velocity of a thin material surface, for example, of thin material surface 18 of thin material 10 shown in FIG. 1, while plotting an image thereupon. Along with reference to FIG. 1, as shown in FIG. 2, grid map 24 of thin material surface 18 shows the location of a plotted image 26 on thin material surface 18, for thin material surface 18 moving along direction of movement 20. An exploded view of plotted image 26 shows that plotted image 26 is actually made of swaths (strips) 28, separated from each other by an exemplary swath separation distance 30. Swaths 28 are formed when a plotting head is in an active (plotting) mode, and swath separation distances 30 appear when the plotting head is in an inactive (plotting) mode. As shown by grid map 24, a sweep distance 34 corresponds to the distance along thin material surface 18 swept by a plotting head within a selected amount of time.

Under ideal conditions, thin material 10 has a constant thickness 16 (FIG. 1), and therefore the tangential velocity of thin material surface 18 is constant throughout thin material surface 18 if the rotational velocity is given. In such a case, sweep distance 34 is also constant throughout thin material surface 18, which means that a desired image can be plotted upon thin material surface 18, having uniform swath separation distance 30. Such behavior translates to a grid map of thin material surface 18 having grids with a constant sweep distance. However, under real conditions, thin material 10 has variations in thickness 16, leading to variable translational or tangential velocity of thin material surface 18, since the local radius is different, which causes variations in sweep distance 34, as shown in grid map 24. Variations in sweep distance 34 cause variations in swath separation distance 30 and misplacement of swaths 28, resulting in plotted image 24 on thin material surface 18 of thin material 10 having one or more dimensions, or/and contents (for example, plotted pixels being offset from a planned location), being different from those of the desired plotted image.

Variation in thin material thickness can be found within a same piece of thin material, or among a plurality of pieces of thin material in a same batch or in different batches of the thin material. For a film type of thin material, magnitude of variations in thickness is typically on the order of microns, as shown in the following numerical example, which shows calculation of the limit in accuracy (in terms of plot dimension error) of a drum plotter upon which is supported or held a thin material (such as a film) having a variable thickness (due to tolerance).

The relationship between thin material thickness, which changes the surface height upon which an image or pattern is to be plotted, and plot dimension, respectively, as described above and shown in FIGS. 1 and 2, may be generally described by the following equation:

Pde=FiLe/DrCr*(ΔFiTh)·2·π,

where:

Pde=plot dimension error,
FiLe=nominal thin material length (perpendicular or tangential to drum radius and along drum circumference),
DrCr=drum circumference,
FiTh=thin material thickness (for example, of a film), and
ΔFiTh=delta (due to tolerance) in thin material thickness.

For example, for the following plotting conditions:

drum circumference: 711,000 microns (μm) (28 inch drum),
thin material thickness: 180 μm (7 mil),
thin material nominal length: 660,000 microns (μm) (26 inch thin material), and
thin material thickness change (along the thin material or among batches):
±3 microns (μm) (equal to 1.7% tolerance),
the deviation in plot dimension (plot dimension error) is:
$Pde = \frac{660, 000}{711, 000} 2 \cdot π \cdot 3 = 17.5 µ m .$

Therefore, according to the above plotting conditions, the accuracy of the drum plotter is limited to 17.5 microns (μm).

As described above, due to rotation of a drum in a drum plotter, variations (even minute variations on the order of a few microns) in thin material thickness of a thin material result in an actual translational velocity of the thin material surface that is different from an expected translational velocity of the thin material surface due to local changes in the radius. Such behavior translates to a difference between an ‘effective’ nominal length and an ‘ideal’ nominal length of the thin material surface, which, in turn, may affect one or more dimensions, or/and the contents (e.g., offset of pixels) of an image plotted on the thin material.

Although magnitude of variations in thickness of a film type of thin material can be as small as on the order of microns, in view of the preceding numerical example, even such minute variations can affect the tangential velocity of the film surface, which in turn may affect the dimension of an image plotted on the film when it is mounted on the external or interior surface (as the thin material support element) of a drum unit, as is typically used in plotter applications.

Presence of variations in thickness of a thin material may affect plotting of an image or images on the thin material, throughout the entirety of the thin material, or may be localized to one or more relatively small portions, or single locations, of the thin material. Moreover, variations in thin material thickness may exist within a same piece of thin material, or among a plurality of pieces of thin material in a same batch or in different batches of the thin material.

The significant problem of variations in thickness of a thin material undesirably affecting plotting of an image thereupon has been illustratively described and exemplified for a drum type plotter, used for plotting an image on a thin material having dimensions of a film. It is clearly understood that the problem is relevant to essentially any type of plotter (e.g., external or internal drum plotter, flatbed plotter, photoplotter) used for plotting an image on a thin material having non-film dimensions, where the plotting is characterized by distance and relative movement especially translational velocities between a thin material support element, and therefore, between the thin material upon which the image is plotted, and a plotting head of the plotter which effects the actual plotting of the image on the surface of the thin material.

There are extensive prior art teachings of techniques (methods, devices, apparatuses, systems) used for measuring thickness of various types or kinds of a material, as well as for measuring a distance between a material and another object. Selected examples of such teachings are provided hereinbelow.

U.S. Pat.; No. 5,485,082, to Wisspeinter et al., entitled: “Method Of Calibrating A Thickness Measuring Device And Device For Measuring Or Monitoring The Thickness Of Layers, Tapes, Foils, And The Like”, provides a method for measuring thicknesses via a combination of eddy current sensors and inductive measuring scanners. Therein is also disclosed a method for calibrating such a thickness sensor. U.S. Pat. No. 5,629,619, to Mednikov et al., entitled: “Noncontact Distance-measuring System Having At Least One Coil And Method Of Noncontact Distance Measuring Operating Either On The Basis Of Eddy Currents Or By Inductance”, discloses a system and a method for measuring distances through eddy currents or by inductance. U.S. Patent Application Publication No. 2006-0202682, to Mednikov et al., entitled: “Non-contacting Position Measuring System”, discloses a system for measuring the position of a material.

There are also prior art teachings of detecting, for example, by using a beam projecting device, and mechanically compensating for, irregularities in a drum surface of a drum plotter, for example, as disclosed in U.S. Pat. No. 5,275,465, to Menard et al., entitled: “Plotter Drum”, and in U.S. Pat. No. 5,421,937, to Menard et al., entitled: “Methods Of Fabricating A Plotter Drum”.

However, such prior art teachings are absent of providing any solution to the significant problem of variations in thickness of a thin material undesirably affecting plotting of an image thereupon.

There is thus a need for, and it would be useful to have a system and method for plotting an image on a thin material having (unpredictable) variations or non-uniformities in thickness. Moreover, there is a need for such an invention which is particularly applicable, but not limited, to the fields of microelectronic and semiconductor manufacturing, requiring highly accurate and reproducible plotting (writing, printing) of images on films (as exemplary thin materials), which, for example, are usable as masks for fabricating printed circuit boards (PCBs). There is additionally a need for such an invention which is also particularly applicable to the field of specialized graphic arts, for specialized applications requiring highly accurate and reproducible plotting (writing, printing) of images on thin materials (such as graphic arts writing or printing media).

SUMMARY OF THE INVENTION

Thus, according to the present invention, there is provided a system for plotting an image on a thin material having variations in thickness, the system comprising: a plotter unit, suitable for plotting the image on a surface of the thin material; a control unit, suitable for controlling the plotter unit, for effecting the plotting; characterized in that the system further includes: a thickness measuring device, suitable for measuring thickness of the thin material, wherein the control unit is operative to receive measured thickness values from the thickness measuring device, and to use the measured thickness values for adjusting the plotting of the image via the plotter unit, to compensate for the variations in thickness of the thin material.

According to another aspect of the present invention, there is provided a method for plotting an image on a thin material having variations in thickness, the method comprising: measuring thickness of the thin material, generating measured thickness values of the thin material; controlling a plotter unit, to effect said plotting; and plotting the image on a surface of the thin material, said controlling comprising using said measured thickness values for adjusting said plotting of the image, to compensate for the variations in thickness of the thin material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative description of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the drawings:

FIG. 1 (prior art) is a schematic diagram illustrating a cross-section of a thin material positioned on the external surface of a drum (for example, as part of an external drum plotter);

FIG. 2 is a schematic diagram illustrating plotting location (via a grid map) resulting from changes in velocity of a thin material surface, for example, of the thin material surface of the thin material shown in FIG. 1, while plotting an image on the surface of the thin material;

FIG. 3 is a schematic diagram illustrating an exemplary generalized embodiment of a system for plotting an image on a thin material having variations in thickness, in accordance with the present invention;

FIG. 4 is a flow diagram of an exemplary generalized embodiment of a method for plotting an image on a thin material having variations in thickness, in accordance with the present invention;

FIG. 5 is a schematic diagram illustrating an exemplary specific embodiment of a system for plotting an image on a thin material having variations in thickness, wherein the plotter unit is a type of an external drum plotter, in accordance with the present invention;

FIG. 6 is a schematic diagram illustrating an exemplary specific embodiment of a system for plotting an image on a thin material having variations in thickness, wherein the plotter unit is a type of an internal drum plotter, in accordance with the present invention;

FIG. 7 is a schematic diagram illustrating an exemplary specific embodiment of a system for plotting an image on a thin material having variations in thickness, wherein the plotter unit is a type of a flatbed plotter, in accordance with the present invention;

FIG. 8 is a schematic diagram illustrating another exemplary embodiment of a system for plotting an image on a thin material having variations in thickness, focusing on the components of a plotter unit, for example, as part of the system illustrated in FIGS. 3, 5, 6, or 7, in accordance with the present invention; and

FIG. 9 is a schematic diagram illustrating an exemplary detailed embodiment of the system illustrated in FIG. 8, particularly showing structure and function (operation) of a plotter unit (of FIG. 8) being a type of an external drum photoplotter, in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The significant problem associated with plotting of an image on a thin material having unpredictable variations or non-uniformities in thickness, was illustratively described, and numerically exemplified, hereinabove, with reference to FIGS. 1 and 2. As described above, for example, due to rotation of a drum in a drum plotter, variations (even minute variations on the order of a few microns) in thin material thickness of a thin material result in an actual translational velocity of the thin material surface that is different from an expected translational velocity of the thin material surface due to a local change in the radius. Such behavior translates to a difference between an ‘effective’ nominal length and an ‘ideal’ nominal length of the thin material surface, which, in turn, may affect one or more dimensions, or/and the contents (e.g., offset of pixels) of an image plotted on the thin material. Although magnitude of variations in thickness of a film type of thin material can be as small as on the order of microns, in view of the above numerical example, even such minute variations can affect the translational or tangential velocity of the film surface, which in turn may affect the dimension of an image plotted on the film when it is mounted on the external or interior surface (as the thin material support element) of a drum unit, as is typically used in plotter applications.

In the field of microelectronic and semiconductor manufacturing, for example, requiring highly accurate and reproducible photoplotting of images on films (as exemplary thin materials), which, for example, are usable as masks for fabricating printed circuit boards (PCBs), drum plotters, particularly external or internal drum photoplotters, are used to produce photo-tools for making PCB masks. These photo-tools require high dimensional accuracy when used as PCB masks, preferably below 10 microns (μm) for mask sizes exceeding 500 millimeters (mm).

The present embodiments relate to techniques of automated plotting (writing, printing) of images on thin materials, and more particularly, to a system and method for plotting an image on a thin material having (unpredictable) variations or non-uniformities in thickness, via measuring thin material thickness, and adjusting the plotting as needed, to compensate for the thickness variations. The present embodiments are particularly applicable, but are not limited, to the fields of microelectronic and semiconductor manufacturing, requiring highly accurate and reproducible plotting (writing, printing) of images on films (as exemplary thin materials), which, for example, are usable as masks for fabricating printed circuit boards (PCBs). The present embodiments are also particularly applicable to the field of specialized graphic arts, for specialized applications requiring highly accurate and reproducible plotting (writing, printing) of images on thin materials (such as graphic arts writing or printing media).

An exemplary generalized embodiment of a system for plotting an image on a thin material having variations in thickness, includes the following main components and functionalities thereof: a plotter unit, for plotting the image on a surface of the thin material; a control unit, for controlling the plotter unit, for effecting the plotting; and a thickness measuring device, for measuring thickness of the thin material. In the exemplary generalized embodiment of the system, the control unit receives measured thickness values from the thickness measuring device, and uses the measured thickness values for adjusting the plotting of the image via the plotter unit, to compensate for the variations in thickness of the thin material.

An exemplary generalized embodiment of a method for plotting an image on a thin material having variations in thickness, includes the following main steps or procedures, and, components and functionalities thereof: plotting the image on a surface of the thin material, by a plotter unit; controlling the plotter unit, for effecting the plotting; measuring thickness of the thin material, for generating measured thickness values of the thin material; and using the measured thickness values for adjusting the plotting of the image, to compensate for the variations in thickness of the thin material.

Generalized and specific embodiments of a system and method for plotting an image on a thin material having variations in thickness, according to the present invention, are better understood with reference to the following illustrative description and accompanying drawings. Throughout the following illustrative description and accompanying drawings, same reference notation and terminology (i.e., numbers, letters, or/and symbols), refer to same components, elements, or/and parameters.

Referring now to the drawings, FIG. 3 is a schematic diagram illustrating an exemplary generalized embodiment of a system, herein, referred to as system 40, for plotting an image on a thin material 42 having variations in thickness 44. As shown in FIG. 3, system 40 includes the following main components and functionalities thereof: a plotter unit 46, for plotting the image on a surface 48 of thin material 42; a control unit 50, for controlling plotter unit 46, for effecting the plotting; and a thickness measuring device 52, for measuring thickness 44 of thin material 42. In the exemplary generalized embodiment of system 40, control unit 50 receives measured thickness values from thickness measuring device 52, and uses the measured thickness values for adjusting the plotting of the image via plotter unit 46, to compensate for the variations in thickness 44 of thin material 42.

FIG. 4 is a flow diagram of an exemplary generalized embodiment of a method, for plotting an image on a thin material having variations in thickness. As shown in FIG. 4, along with reference to system 40 shown in FIG. 3, the method includes the following main steps or procedures, and, components and functionalities thereof: (a) Measure the thickness 44 of thin material 42; (b) Generating thickness values of the thin material 42 and creating a map of thickness values; (c) using the measured thickness values for adjusting the plotting of the image, to compensate for the variations in thickness 44 of the thin material 42; (d) plotting (with compensation) the image on a surface 48 of the thin material 42, by a plotter unit 46

As shown in FIG. 3 (of the system), along with reference to FIG. 4 (of the corresponding method), in system 40, plotter unit 46 includes a plotter control subunit 54, a plotting subunit 56, and a thin material support element 58, upon which thin material 42 is positioned. Thickness measuring device 52 measures a thickness at surface 48 of thin material 42, and sends the resulting thickness measurement to control unit 50. Control unit 50 receives the thickness measurement and adjusts one or more plotting parameters according to pre-programmed algorithms. Adjustment data of the plotting parameters from control unit 50 are received by plotter unit 46 and sent to plotter control subunit 54 for processing, for compensating for the variations in thickness 44 of thin material 42. Plotter control subunit 54 then sends the processed data to plotting subunit 56, which includes a plotting head, which then plots an image on surface 48 of thin material 42.

Plotter Unit

The plotter unit 46 includes a thin material support element 58, for supporting thin material 42 and plotting subunit 56, which can move relative to each other. Plotter unit 46 also includes a plotter control subunit 54, which regulates the relative movement between thin material support element 58 and plotting subunit 56, as well as the timing in the plotting of plotting subunit 56. Plotter unit 46 further includes control unit 50, which calculates compensation parameters according to input data sent to control unit 50, which, in turn, is sent to plotter control subunit 54. Exemplary types of plotter units commonly used in PCB mask production, are drum photoplotters, which are readily commercially available (e.g., drum photoplotter models LP-7008™ and LP-9008™ from Orbotech Ltd., Israel).

Thin Material Support Element

The thin material support element 58 is for supporting and holding, and possibly moving, thin material 42 upon which an image is plotted. Thin material support element 58 may be fixed or movable. For example, as shown in FIG. 8, hereinbelow, if thin material support element 104 is movable, then thin material support element 104 is controllably movable by a support element moving mechanism 118. In such an embodiment, signals of movement of support element moving mechanism 118 are sent to an encoder reading head 120, which sends out signals to synchronization controller 106 indicating the position of thin material support element 104. Encoder reading head 120 sends data to plotter control subunit 54, whereby support element moving mechanism 118 is controllable by synchronization controller 106. Thin material support element 104 can be, for example, the outer surface of a drum roller of an external drum plotter, the inner surface of a drum roller of an internal drum plotter, or a flat surface of a flatbed plotter.

Plotter Control Subunit

The plotter control subunit 54 regulates the relative movement between thin material support element 58 and plotting subunit 56 of plotter unit 46, as well as the speed and timing in the plotting by plotting subunit 56. In some plotters for PCB photo-tool manufacture, inaccuracies in geometric dimensions of the drum (the thin material support element) and wobble, resulting in velocity changes of the drum surface, are measured and plot timings are adjusted, for example by adjusting a strobing frequency of an exposure beam, to compensate for these inaccuracies. This compensation mechanism can be enhanced according to the presently preferred embodiments to further compensate for the variations in thickness 44 of thin material 42, also resulting in velocity changes of surface 48 upon which an image or pattern is plotted, for example by further adjusting plot timings on-the-fly (i.e., during real time operation of plotter unit 46.

Plotting Subunit

Operations of plotting subunit 56 are controlled by plotter control subunit 54. In the exemplary specific embodiment of the present invention shown in FIG. 8, plotting subunit 56 includes a plotting head moving mechanism 112, which provides for movement of plotter subunit 56, and a plotting head 114, whereby plotting head 114 directly plots an image on surface 116 of thin material 42. Examples of plotting head 114 are lasers or diodes, emitting specific wavelengths of light.

Thickness Measuring Device

The thickness measuring device 52 preferably operates according to a non-contacting, measuring process. Thickness measuring device 52 may comprise: an optical sensor using a suitable optical measurement method, such as a triangulation method, or an interferometry method; a mechanical sensor using a suitable mechanical probe; a capacitor based sensor to make a measurement based on dielectric characteristics of thin material 42; or any other type of sensor, such as, but not limited to, x-ray based, ultrasound based, and depth of focus based, sensors. Thickness measuring device 52 may be positioned as follows: externally, to measure thickness 44 of thin material 42 before or prior to loading onto plotter unit 46, or, alternatively, embedded inside plotter unit 46.

Thin material thickness measurements carried out by thickness measuring device 52 include, but are not limited to, online sampling of thickness 44 of thin material 42 during the plotting process, and offline generation of a three-dimensional grid map of thin material 42 before the plotting process. Thickness measurements may be carried out either on a batch basis, or for each individual sheet of thin material before the image plotting, or in accordance with a suitable periodic quality control sampling schedule.

For implementing the present invention, an exemplary suitable thickness measuring device 52 is the Combisensor™, available from Micro-Epsilon corporation of Ortenburg, Germany.

Control Unit

Control unit 50 includes computing subunits that receive thickness measurements from thickness measuring device 52 and adjust at least one plotting parameter, according to pre-programmed algorithms. Control unit 50 processes data transmitted to it, both online (i.e., real time, during a plotting process) and offline (i.e., before or prior to a plotting process), depending on the specific mode of operation of thickness measuring device 52, as described above.

In exemplary specific embodiments of the present invention, the system, and method, are optimized for plotting on a film. The film can be photosensitive. A non-limiting example of photosensitive film is silver-halide film. A non-limiting example of photosensitive silver-halide film is the Kodak ACCUMAX™ film family, which offers sensitivities to light of wavelengths of 488 nm (from Argon-Ion laser), 532, 543, 565, 633 nm (from Helium-Neon laser), and 670 nm (from red laser diodes).

In additional exemplary specific embodiments of the present invention, the plotter unit is a photoplotter. The plotting subunit of the photoplotter can be based on, but not limited to, LEDs or lasers.

In additional exemplary specific embodiments of the present invention, the plotter unit includes a thin material support surface corresponding to an external drum, or an internal drum, or a flatbed.

In additional exemplary specific embodiments of the present invention, the thickness measuring device is included within, or part of, the plotter unit.

In additional exemplary specific embodiments of the present invention, the thickness measuring device is located outside of, or external to, the plotter unit, and includes a map generator, for generating three-dimensional maps of the, thin material thickness variation as a function of (x, y) position or location of the thin material, before the thin material is inserted into the plotter. Though this embodiment may lead to slower plotting, it can increase accuracy of the plotting of the image on the surface of the thin material.

In additional exemplary specific embodiments of the present invention, the thickness measuring device includes one or more of the following features: an optical sensor, to determine the thickness of the thin material, a mechanical probe to determine the thickness of the thin material, and a capacitor-based sensor to measure at least one dielectric characteristic of the thin material and to compute therefrom at least one thickness value of the thin material.

In additional exemplary specific embodiments of the present invention, the plotting parameter to be adjusted to compensate for the thickness, may be one or more of the following parameters: a plotter scaling factor, a plotter timing factor, and an image size parameter.

The plotter scaling factor is a set of parameters that defines the scaling between the original image dimension and the plotted image dimension. The plotter timing factor is based on: (i) the velocity of the thin material support element, or/and (ii) the velocity of the plotting head moving mechanism, or/and (iii) the plotting speed or/and plotting timing. The image size parameter is a set of numerical data that corresponds to the physical size of the plotted image.

In additional exemplary specific embodiments of the present invention, the measuring step of the above method includes generating a plurality of thickness values for each of a plurality of thin material sheets on a per-sheet basis.

In additional exemplary specific embodiments of the present invention, the measuring step includes generating at least one thickness value for each of a plurality of thin material batches on a per-batch basis.

The present embodiments thus provide a combination of a plotter unit, including a control unit, and a thickness measuring device, which allows compensation for the variable thickness of the thin material. Compensation may be performed in two ways: real-time and off-line. In the off-line compensation mode, the thickness of the thin material is measured before the thin material is fed into the plotter unit, and correction tables are calculated offline for subsequent use in the plotting. In the real-time compensation mode, the thickness of the thin material is measured and compensated for, while the thin material is in the plotter unit and being plotted upon.

Use of the above embodiments may provide a relatively improved level of accuracy in the plot, due to the compensation for the variable thickness of the thin material plotted upon.

One feature of the present embodiments is the short amount of time that passes between the thickness measurement and the plotting after compensation, allowing for ‘on-the-fly’ dynamic compensation. More specifically, the compensation process may be fast enough not to cause deterioration in performance (in terms of throughput) of the plotter unit.

FIG. 5 is a schematic diagram illustrating an exemplary specific preferred embodiment of system 40 illustrated in FIG. 3, herein, in FIG. 5 referred to as system 70, for plotting an image on a thin material 42 having variations in thickness 78, wherein plotter unit 72 is an external drum plotter. As shown in FIG. 5, plotter unit 72 is an external drum plotter. Plotter unit 72 includes a plotter control subunit 54, a plotting subunit 56, and a drum 74. Drum 74 corresponds to the thin material support element which can rotate around its axis (in FIG. 5, indicated by 76). Thin material 42 is positioned on the outer surface of drum 74. Thickness measuring device 52 measures thickness 78 of thin material 42 at surface 79 of thin material 42, and sends thickness measurements to control unit 50. Control unit 50 receives the thickness measurements and adjusts one or more plotting parameters according to pre-programmed algorithms. Adjustment data of the parameters sent from control unit 50 are received by plotter control subunit 54, which adjusts the plotting according to the adjusted parameters, through its connections to drum 74 and plotting subunit 56. Plotting subunit 56 plots an image on surface 79 of thin material 42, according to the instructions plotting subunit 56 receives from plotter control subunit 54.

FIG. 6 is a schematic diagram illustrating another exemplary specific preferred embodiment of system 40 illustrated in FIG. 3, herein, in FIG. 6 referred to as system 80, for plotting an image on a thin material 42 having variations in thickness 88, wherein plotter unit 82 is an internal drum plotter. Plotter unit 82 includes a plotter control subunit 54, a plotting subunit 56, and a drum 84. Drum 84 corresponds to the thin material support element, which is usually fixed and unable to rotate or translate. In specific embodiments, drum 84 may rotate around its axis (in FIG. 6, indicated by 86). Thin material 42 is positioned on the inner surface of drum 84. Thickness measuring device 52 measures thickness 88 of thin material 42, and sends thickness measurements to control unit 50.

Control unit 50 receives the thickness measurements and adjusts one or more plotting parameters according to pre-programmed algorithms. Adjustment data of the parameters sent from control unit 50 are received by plotter control subunit 54, which adjusts the plotting according to the adjusted parameters, through its connections to plotting subunit 56. Plotting subunit 56 plots an image on surface 89 of thin material 42, according to the instructions plotting subunit 56 receives from plotter control subunit 54. If drum 84 is able to rotate, plotter control subunit 54 is also connected to drum 84 (in FIG. 6, indicated by the dashed line between plotter control subunit 54 and drum 84).

FIG. 7 is a schematic diagram illustrating another exemplary specific preferred embodiment of system 40 illustrated in FIG. 3, herein, in FIG. 7 referred to as system 90, for plotting an image on thin material 42 having variations in thickness 96, wherein plotter unit 92 is a flatbed type of plotter. Plotter unit 92 includes a plotter control subunit 54, a plotting subunit 56, and a flat thin material support element 94. Thin material support element 94 may be fixed or is controllably movable. Thin material 42 is positioned on the surface of thin material support element 94. Thickness measuring device 52 measures thickness 96 at surface 98 of thin material 42, and sends thickness measurements to control unit 50.

Control unit 50 receives the thickness measurements and adjusts one or more plotting parameters according to pre-programmed algorithms. The adjusted parameters may be, but are not limited to, plotting speed and/or timing, plotting head movement, and thin material support element speed.

In the case of a fixed thin material support element 94, adjustment data from control unit 50 is received by plotter control subunit 54, which performs the adjustments via its connection to plotting subunit 56. Plotting subunit 56 plots an image on surface 98 of thin material 42, according to the instructions it receives from plotter control subunit 54.

In the case of a movable thin material support element 94, plotter control subunit 54 is also connected to thin material support element 94 (in FIG. 7, indicated by the dashed line between plotter control subunit 54 and thin material support element 94). Plotter control subunit 54 can therefore perform further adjustments to thin material support element 94, by regulating movement of thin material support element 94.

FIG. 8 is a schematic diagram illustrating another exemplary embodiment of a system, herein, in FIG. 8 referred to as system 100, for plotting an image on a thin material 42 having variations in thickness 122, focusing on the components of a plotter unit 102, for example, as part of any of the systems 40, 70, 80, or 90, illustrated in FIGS. 3, 5 (external drum plotter), 6 (internal drum plotter), or 7 (flatbed plotter). FIG. 8 particularly shows integrated layout and operation of thin material 42, a thin material support element 104, control unit 50, plotter control subunit 54, plotting subunit 56, and thickness measuring device 52. Plotter control subunit 54 includes a synchronization controller 106, a plotting head moving mechanism controller 108, and a plotting-head controller 110. Plotting subunit 56 includes a plotting head moving mechanism 112, which provides for movement of plotter subunit 56, and a plotting head 114, whereby plotting head 114 directly plots an image on surface 116 of thin material 42.

Thin material support element 104 can be, for example, the outer surface of a drum roller of an external drum plotter, the inner surface of a drum roller of an internal drum plotter, or a flat surface of a flatbed plotter. Thin material support element 104 may be fixed or movable. For example, as shown in FIG. 8, if thin material support element 104 is movable, then thin material support element 104 is controllably movable by a support element moving mechanism 118. In such an embodiment, signals of movement of support element moving mechanism 118 are sent to an encoder reading head 120, which sends out signals to synchronization controller 106 indicating the position of thin material support element 114. Encoder reading head 120 sends data to plotter control subunit 54, whereby support element moving mechanism 118 is controllable by synchronization controller 106.

Following measuring thickness 122 of thin material 42 by thickness measuring device 52, and computation of compensation parameters by control unit 50, synchronization controller 106 receives the compensation parameters from control unit 50. If thin material support element 104 is movable, then synchronization controller 106 controls movement of thin material support element 104, via its connection to support element moving mechanism 118. Synchronization controller 106 further verifies the position of thin material support element 104, by receiving the signal transmitted by encoder reading head 120. Plotting head moving mechanism controller 108 controls movement of plotting head moving mechanism 112. Plotting head controller 110 controls plotting speed and timing of plotting head 114. Synchronization controller 106 also regulates the timing for conveying instructions from plotting head moving mechanism controller 108 to plotting head moving mechanism 112 and from plotting head controller 110 to plotting head 114.

FIG. 9 is a schematic diagram illustrating an exemplary detailed embodiment, herein, in FIG. 9 referred to as embodiment 130, of the system 100 illustrated in FIG. 8, particularly showing structure and function (operation) of plotter unit 102 (of FIG. 8) being a type of an external drum photoplotter. In FIG. 9, embodiment 130 includes a rotating drum 132, for example, of an external type drum photoplotter, where drum 132 rotates at an exemplary rotational speed of about 900 rounds per minute (rpm). Embodiment 130 also includes a thickness measuring device 52 included in, as part of, plotting subunit 56 (FIG. 8). Embodiment 130 also includes a drum encoder 134 which sends signals to encoder reading head 120, which monitors rotation of drum 132. Encoder reading head 120 generates encoder pulses 136 and encoder index pulses 138, according to tangential speed of drum 132.

Encoder pulses 136 are sent to a Phased Locked Loop Mechanism (PLL) 140, which generates pulses 142 with improved resolution (typically 50 MHz). Typical encoder pulse 136 frequency is 0.75 MHz, depending upon rotation speed and number of encoder counts. PLL output pulses 142 are sent to a Y-synthesizer 144 and to an X-synthesizer 146. Y-synthesizer 144 regulates operation of plotting head movement mechanism 112, via a plotting head moving mechanism controller (PHMMC) 108. X-synthesizer 146 regulates timing of the turning ON and OFF of plotting head 114 in accordance with raster data 148. Encoder reading head 120 generates an encoder index pulse 138 that serves two purposes: (1) for setting reference points for the starting positions of image slice plotting; and (2) for verifying that drum 132 is in the right position. X-synthesizer 146 and Y-synthesizer 144 generate output signals whose frequencies are determined by X-scale calibration look-up tables (LUT) 150 and Y-scale calibration look-up tables (LUT) 152, respectively.

Such look-up tables are prepared in advance during plotter calibration by measuring constant (repeatable) geometrical distortions (determined by environmental and mechanical factors, as described hereinabove in the Background section). Thickness measuring device 52, which is mounted on the same plotting head moving mechanism 112 as plotting head 114, sends thin material thickness measurement data and information 154 to X-synthesizer 146, Y-synthesizer 144, and data unit 156. Film thickness information 154 is used for generating additional adjustment type corrections in the timing of plotting head movement mechanism 112 and timing of the turning ON and OFF of plotting head 114, in accordance with the thickness of thin material 42 at a particular location along thin material 42.

Thin material thickness measurements can be performed in advance, before the plotting (including the option to perform thickness measurements outside the plotter, i.e., ‘offline’), or, alternatively, ‘on the fly’ during real time plotting of the image on thin material 42. For an ‘on-the-fly’ (real time) embodiment, thickness measuring device 52 measures thickness of thin material 42 a short time prior to plotting head 114 plots an image on the surface of thin material 42. Such synchronization provides for the time required for the signals of film thickness information 154 to be processed by Y-synthesizer 144, X-synthesizer 146, and data unit 156, and time for the output signal from Y-synthesizer 144 to be received, via plotting head moving mechanism controller (PHMMC) 108, by plotting head movement mechanism 112. Such synchronization also provides for the time required for the output signal from X-synthesizer 146 to be received, via data unit 156 and plotting head moving mechanism controller (PHMMC) 108, by plotting head 114. Based on the just described ‘compensation’ signals received by plotting head 114, then, plotting head 114 effects the plotting of the image on thin material 42.

The components of embodiment 130 of FIG. 9 can be mapped onto the corresponding components of system 100 of FIG. 8, as follows. X-scale LUT 150, Y-scale LUT 152, and data unit 156 are part of control unit 50. Y-synthesizer 144 and X-synthesizer 146 are elements shared between control unit 50 and synchronization controller 106.

It is appreciated that certain aspects and characteristics of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various aspects and characteristics of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

While the invention has been described in conjunction with specific embodiments and examples thereof, it is evident that many alternatives, modifications, and variations, will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations, that fall within the scope of the appended claims.

All patents, patent applications, and publications, cited or referred to in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual patent, patent application, or publication, was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

PLOTTING AN IMAGE ON A THIN MATERIAL HAVING VARIATIONS IN THICKNESS

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