BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1A is a block diagram illustrating a top view of a traditional via connecting two traces, in accordance with the prior art;
FIG. 1B is a block diagram illustrating a cross section of a traditional via connecting two traces, in accordance with the prior art;
FIG. 1C is a block diagram illustrating a top view of a traditional via connecting a trace and an electrical component, in accordance with the prior art;
FIG. 1D is a block diagram illustrating a cross section of a traditional via connecting a trace and an electrical component, in accordance with the prior art;
FIG. 2 is a block diagram illustrating a system for selectively polymerizing a photoresist inside a via with a focused light source, according to one embodiment of the invention;
FIG. 3 is flow diagram depicting a process for selectively plating the inside of a via, according to one embodiment of the invention;
FIG. 4 is a block diagram illustrating a cross section of a printed circuit board (PCB) with a via, according to one embodiment of the invention;
FIG. 5 is a block diagram illustrating a cross section of the PCB with the via filled with a resist, according to one embodiment of the invention;
FIG. 6 is a block diagram illustrating a cross section of the PCB with a light beam focused in the resist filled via, according to one embodiment of the invention;
FIG. 7 is a block diagram illustrating a cross section of the PCB with the focused light beam selectively polymerizing the resist filled via, according to one embodiment of the invention;
FIG. 8 is a block diagram illustrating a cross section of the PCB after the resist in the via has been developed, according to one embodiment of the invention;
FIG. 9 is a block diagram illustrating a cross section of the PCB after the via has been plated, according to one embodiment of the invention;
FIG. 10 is a block diagram illustrating a cross section of a PCB containing a plated via that is partially filled with a polymerized resist, according to one embodiment of the invention;
FIG. 11 is a block diagram illustrating a top view of a PCB containing a via vertically divided into two parts by a polymerized resist, according to one embodiment of the invention;
FIG. 12 is a block diagram illustrating a cross section of the PCB containing the via vertically divided into two parts by the polymerized resist, according to one embodiment of the invention;
FIG. 13 is a block diagram illustrating a top view of the PCB containing the via vertically divided into two parts by the polymerized resist after the via has been plated, according to one embodiment of the invention;
FIG. 14 is a block diagram illustrating a cross section of the PCB containing the via vertically divided into two parts by the polymerized resist after the via has been plated, according to one embodiment of the invention;
FIG. 15 is a block diagram illustrating a cross section of a PCB partially filled with a polymerized photoresist;
FIG. 16 is a block diagram illustrating a cross section of the PCB partially filled with the polymerized photoresist and a dielectric material, according to one embodiment of the invention;
FIG. 17 is a block diagram illustrating a cross section of the PCB horizontally divided by the dielectric material, according to one embodiment of the invention;
FIG. 18 is a block diagram illustrating a cross section of the PCB horizontally divided by the dielectric material after the two via halves have been plated, according to one embodiment of the invention;
FIG. 19 is a block diagram illustrating a cross section of a PCB containing a via with tapered sides that is horizontally divided into two parts by a polymerized resist, according to one embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention generally provides methods and systems for selective manipulation of via plating. In one embodiment, a method for selectively plating the inside of a via formed in an object may include filling the via with a resist capable of selective three-dimensional polymerization. The resist may be selectively polymerized, and developed. When the resist is developed, only a portion of the resist is removed according to whether the portion is polymerized, thereby leaving a remaining portion in the via and forming a desired structure in the via.
In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, in various embodiments the invention provides numerous advantages over the prior art. However, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).
System for Selectively Polymerizing a Photoresist Inside a Via
FIG. 2 is a block diagram illustrating a system 200 for selectively polymerizing a photoresist inside a via with a focused light source 202, according to one embodiment of the invention. The system 200 may include a system controller 212 connected to a workstation 214. The system controller 212, interfacing with the workstation 214, may be used to control various parts of the system 200 including a light source 202, a shutter 204, an X-Y stage 208, and a Z-axis controller 210. Alternatively, the workstation 214 may not be used, and the system controller 212 may perform all operations.
In one embodiment, the system controller 212 may control the light source 202, which may be a laser, in a number of ways. For example, the system controller 202 may control the intensity of the beam 216 emitted from the light source 202, the wavelength of the beam 216 emitted from the light source 202, and/or the width of the beam 216 emitted from the light source 202.
In one embodiment, the shutter 204 may be used to block some or all of the beam 216 emitted from the light source 202. Controlling the shutter with the system controller 212 facilitates management of the width of the beam 216. Furthermore, the shutter 204 may completely block the beam 216, and therefore may be able to control exposure time of the photoresist at the focal point of the beam 218.
In one embodiment, the X-Y stage 208, and the Z-axis controller 210 may be used to position the focal point of the beam 218 to selectively polymerize the photoresist in the via in a printed circuit board (PCB) 104. The X-Y stage 208 may be used to laterally move the PCB 104. The Z-axis controller 210 may be used either to vertically translate a lens 206 used to focus the beam 216, or to vertically translate the X-Y stage 208 and thus the PCB 104.
In one embodiment, numerous optical devices, including light filters, beam splitters, mirrors, and photo-detectors, may be used to provide better control of the light source 202. Similar systems used for traditional lithography have achieved a resolution of 120 nanometers, although the particular resolution is not limiting of the present invention.
In one embodiment, multiple light sources 202 may be used, each having a beam 216 focused on a different plane in the PCB 104. Alternatively, the beams 216 from the multiple light sources 202 may be focused on the same plane in the PCB 104, and the beams 216 may be focused at the same point in the photoresist filled via.
Process for Selectively Plating the Inside of a Via
FIG. 3 is flow diagram depicting a process 300 for selectively plating the inside of a via, according to one embodiment of the invention. The process begins at 302, where a PCB 104 is constructed. There are many techniques for creating a PCB 104 and one skilled in the art will understand that the present invention is not dependant upon a particular method.
In one embodiment, a via may be introduced into the PCB at step 304. The via may be any shape or size fitting within the PCB 104 and is dependant upon the application of the via. There are numerous methods for introducing a via into a PCB 104, including drilling, punching, and/or chemically etching a hole into the PCB 104.
In one embodiment, the via may be filled 306 with a resist capable of selective three-dimensional polymerization. As used herein, “selective three-dimensional polymerization” generally refers to the controlled polymerization of a targeted portion of a resist (a three-dimensional substance) disposed in a via to the exclusion of the rest of the resist. An exemplary resist capable of being selectively polymerized is a two-photon absorption (TPA) photoresist.
In one embodiment, the resist in the via is a photoresist which may be selectively polymerized 308 by a focused light beam 218. The focused light beam 218 may be emitted from a light source 202, such as a laser. Selective polymerization may occur at a resolution necessary to form polymerized partitions, or other shapes, inside the via filled with photoresist. Alternatively, the resist may not be a photoresist and the resist may be polymerized in a different manner.
In one embodiment, the focused light beam 218 may not polymerize the photoresist but may induce changes in the photoresist which may lead to polymerization of the photoresist in a subsequent processing step. Alternatively, the photoresist not exposed to the focused light beam 218 may polymerize in a subsequent processing step, and the photoresist exposed to the focused light beam 218 may not polymerize.
In one embodiment, the resist in the via is developed, resulting in the removal of the non-polymerized resist and leaving the selectively polymerized resist remaining in the via 310. Development of the resist may occur by one of various methods well established in the art, such as utilizing a solution to dissolve the non-polymerized resist. Alternately, development of the resist may remove the polymerized resist, and leave the non-polymerized resist.
The resulting via, which may be partially filled by polymerized resist, may then be plated 312 by one of various methods well established in the art (e.g., electroplating).
EXAMPLE OF THE PROCESS FOR SELECTIVELY PLATING THE INSIDE OF A VIA
The process 300 describes a process for selectively plating the inside of a via, according to one embodiment of the invention. Illustratively, FIGS. 4-9 depict an example of via fabrication in accordance with process 300, and as such, the process 300 of FIG. 3 will be referenced in conjunction with FIGS. 4-9.
In one embodiment, steps 302 and 304 of the process 300 may occur, resulting in a PCB 104 with a via 102, as depicted in FIG. 4. The PCB 104 may have multiple traces 106, and the via 102 may be a cylindrical via 102.
In one embodiment, as described in step 306 of the process 300, the via 102 may be filled with a photoresist 502. The resulting arrangement may be depicted in FIG. 5, a block diagram illustrating a cross section of the PCB 104 with the via 102 filled with the photoresist 502.
In one embodiment, as described in step 308 of the process 300, a light beam 216 may be focused in the photoresist filled via 102, as depicted in FIG. 6. Polymerization substantially occurs at the focal point of the light beam 218. Thus, by adjusting the location of the focal point of the light beam 218 within the via 102, the photoresist 502 in the via 102 may be selectively polymerized, resulting in a pattern of polymerized photoresist 702 as is depicted in FIG. 7.
In one embodiment, as described in step 310 of the process 300, the photoresist 502 in the via 102 may be developed, resulting in the PCB 104 and polymerized photoresist 702 combination as is depicted in FIG. 8. The polymerized photoresist 702 in FIG. 8 represents a disc separating the via 102 into two separate halves 102a, 102b.
In one embodiment, as described in step 312 of the process 300, the halves of the via 102a, 102b may be plated, which may result in a split-via 102a, 102b depicted FIG. 9. The plated via half 102a may electrically connect traces in the first and second planes of the PCB 104, the plated via half 102b may electrically connect traces in the third and fourth planes of the PCB 104, and the polymerized photoresist 702 may electrically isolate the plated via halves 102a, 102b from one another. Optionally, the via may have a via pad 110 on the top and/or bottom of the PCB 104 which may connect to the plating 108 in the via 102.
Exemplary Embodiments
In one embodiment, the process 300 may accommodate fabrication of a variety of via configurations. For example, FIG. 10 is a block diagram illustrating a cross section of a PCB 104 containing a plated via 102 that is partially filled with a polymerized resist 702. The via 102 configuration in FIG. 10 is a blind via since the plating 108 on the via 102 does not pass through the entire PCB 104. Blind vias are frequently used in high frequency circuits to reduce signal reflection caused by excess via length.
In one embodiment, the process 300 described above with respect to FIGS. 4-9 may be used to vertically divide a via 102 into two parts. FIGS. 11 and 12 illustrate a PCB 104 containing a via 102 vertically divided into two parts by a polymerized resist 702. FIGS. 13 and 14 illustrate the PCB 104 containing the vertically divided via 102 after the via 102 has been plated. The plated via half 102c may electrically connect traces in the first and fourth planes of the PCB 104, the plated via half 102d may electrically connect traces in the second and third planes of the PCB 104, and the polymerized photoresist 702 may electrically isolate the plated via halves 102c, 102d from one another, as is illustrated in FIG. 14. In this configuration, a via pad 110 would need to be omitted or modified so that the two via halves 102c, 102d are not electrically connected, potentially negating the effect of the polymerized photoresist 702.
In one embodiment, the process 300 described above with respect to FIGS. 4-9 may be used to selectively add a dielectric material to the via 102. FIG. 15 illustrates a cross-sectional view of PCB 104 containing a via 102 partially filled with selectively polymerized photoresist 702. A dielectric material 1602 may be added to the via 102, which may result in the configuration depicted in FIG. 16 as a cross-sectional view. The dielectric material 1602 may be added in a variety of ways. For example, the dielectric material 1602 may be deposited in the via 102 by a three-dimensional printing process. FIG. 17 illustrates the cross-sectional view of the via 112 after a second developing process where the polymerized photoresist 702 may be removed from the via 102. The via 102 may be horizontally divided into two halves 102e, 102f by the dielectric material 1602. The via halves 102e, 102f may be plated, which may result in the configuration depicted in the cross-sectional view of FIG. 18. The plated via half 102e may electrically connect traces in the first and second planes of the PCB 104, the plated via half 102f may electrically connect traces in the third and fourth planes of the PCB 104, and the dielectric material 1602 may electrically isolate the plated via halves 102e, 102f from one another. Alternatively, the polymerized photoresist may not be removed, and one half of the via 102e may be plated.
In one embodiment, a via 102 may have tapered sides, as is illustrated in FIG. 19, which also illustrates the via 102 filled with photoresist 502. The tapered configuration may facilitate easier access to the sidewall of the via 102 when polymerizing the photoresist 502 with the light beam 216.
One skilled in the art will recognize that the processes described and contemplated herein may be used to selectively plate the inside of a via resulting in configurations not depicted above.
Conclusion
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Patent Application
20070298601
