Patent Application
20210125869
The disclosure relates generally to a method for fabricating electronic components and, in particular, to a method of producing a strip of electronic components in a roll-to-roll format. Individual electronic components having a polymeric substrate are often formed as part of a large group contained on a wafer, typically having a size in the range of 200 mm to 300 mm. The group of electronic components comprising the wafer is then diced into the individual electronic components. In applications requiring a large number of electronic components, the electronic components are attached to a rolled strip for ease of dispensing at the consumer end. However, creating electronic components from wafers is a batch process, whereas attaching them to a strip is generally a continuous process. Because of the difference in processing techniques and speeds, disruptions in the overall process often arise.
In one aspect, embodiments of the disclosure relate to a method for creating a strip of electronic components. In the method, a ribbon of ceramic substrate is provided. The ceramic substrate defines a thickness of no more than 200 μm between a first outer surface and a second outer surface opposite of the first outer surface. A conductive layer is applied to at least one of the first outer surface or the second outer surface of the ceramic substrate. The ceramic substrate is then singulated into individual slabs, and the individual slabs are laminated to a strip of polymeric carrier. The polymeric carrier has a flexural rigidity less than the flexural rigidity of the ceramic substrate.
In another aspect, embodiments of the disclosure relate to a roll of electronic components. The strip includes a plurality of electronic components in which each of the electronic components includes a ceramic substrate. The strip also includes a strip of polymeric carrier. The plurality of electronic components is adhered to a surface of the strip of polymeric carrier. Each ceramic substrate has a first thickness and a first flexural rigidity, and the strip of polymeric carrier has a second thickness and a second flexural rigidity. The first thickness is less than the second thickness, and the first flexural rigidity is at least five times the second flexural rigidity.
Additional features and advantages will be set forth in the detailed description that follows, and, in part, will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and the operation of the various embodiments.
Embodiments of the present disclosure relate to a method of preparing strips of singulated electronic components. In particular embodiments, the method is performed in a roll-to-roll fashion. That is, each fabrication step is performed in continuous and sequential steps from an initial roll of raw material, such as a ribbon of ceramic substrate, to the final singulated electronic components attached to a strip and rolled on a spool that is delivered to the customer. The roll-to-roll fabrication method has the potential to reduce the packaging cost for certain electronic components, especially electronic components that conventionally utilize polymeric substrates, such as printed circuit board. In particular, the roll-to-roll fabrication method eliminates the need to dice large wafers of electronic components produced in batches. A variety of embodiments of the method and electronic components produced according to the method are provided herein. These embodiments are presented by way of example only and not by way of limitation.
In order to introduce the processing steps, a completed electronic component mounted on a carrier will be described first. In particular,
As can be seen in
The number of slabs 14 that a strip 10 can hold is dependent on the size of the slabs 14. Further, the size can vary widely depending on a particular application, and therefore, the slabs 14 can be quantified in lot sizes. On the strip 10, a marking can be made to demarcate each lot of slabs 14, which allows easier tracking of production. Table 1, below, provides exemplary lot sizes for strips 10 of various sizes that contain slabs 14 of various types.
Having described the components of the strip 10, embodiments of methods for constructing the strip are now provided. In particular embodiments, the strip 10 is constructed in a “roll-to-roll” format on a single process line; that is, the slab 14 is constructed and attached to the carrier 12 in a continuous process beginning with a ribbon of ceramic substrate 16 and ending with a roll of the finished strip 10. However, in other embodiments, the method is not continuous, and certain steps of the method can be carried out across two or more process lines.
As mentioned, the method begins with constructing the slab 14 from a ribbon of ceramic substrate 16. In embodiments, the ceramic substrate 16 is sintered alumina, partially-stabilized or fully-stabilized zirconia, titanates (especially for capacitor applications), ferrites (especially for applications involving magnetic shielding), or another ceramic material. It should be noted that, during fabrication, multiple slabs 14 can be formed across the width of the ceramic substrate 16 as well as along the length of the ceramic substrate 16. As will be discussed below, individual slabs 14 are singulated from the ribbon of ceramic substrate 16. In embodiments, the ribbon of ceramic substrate 16 has a thickness of no more than 200 μm. In another embodiment, the ribbon of ceramic substrate 16 has a thickness of no more than 100 μm, and in still another embodiment, the ribbon of ceramic substrate 16 has a thickness of at least 10 μm. In a particular embodiment, the ceramic substrate 16 has a thickness of 40 μm.
In embodiments of a method 100, such as the embodiment shown in the flow diagram of
In a third step 103, the conductive layer 18 or conductive layers 18 are plated onto the ceramic substrate 16 (or adhesion layer, if applied). In embodiments, the conductive layers 18 are selected to be at least one of copper, silver, or nickel, and in embodiments, the thicknesses of the conductive layers 18 are from 2 μm to 20 μm in thickness. In a particular embodiment, the conductive layers 18 are formed from copper and have a thickness of 10 μm to 12 μm. In embodiments, the conductive layers 18 are applied by electroplating the copper onto the ceramic substrate 16 (or adhesion layer). After the third step 103 of electroplating with copper, the copper plating is then covered with a mask in the portions defining a circuit pattern for the conductive layer 18, and in a fourth step 104, an etchant is applied to dissolve the regions of the copper plate outside of the circuit pattern. The mask is then removed. In embodiments, the mask is applied by laminating a dry film over the ceramic substrate 16 or adhesion layer and then exposing the dry film to ultraviolet light to create the circuit pattern. After electroplating, removal of the mask can be accomplished using a caustic solution. In an alternate embodiment, the mask is applied prior to electroplating such that copper is only applied in regions defining the circuit pattern.
After the fourth step 104, soldering pads (not shown) are formed on or adjacent to the conductive layers 18 in a fifth step 105. In embodiments, another dry film mask is applied over the surface of the plated ceramic substrate 16 to define open regions where the soldering pads are to be located. In embodiments, nickel and/or gold is deposited in the open regions to form the soldering pads. In certain embodiments, the soldering pads are formed through electroless plating. Further, in embodiments, the steps 103, 104, 105 are repeated as necessary to provide one or more layers of conductive layer 18 on one or both sides of the ceramic substrate 16.
In an alternate embodiment that is shown in the flow diagram of
Advantageously, through printing on the ceramic substrate 16, components having various functionalities are able to be formed on the ceramic substrate. For example, the printing technique can be used to apply various functional layers, such as conductive layers 18, resistors, multilayers of conductive circuitry separated by dielectric layers, piezo-resistors, potentiometer resistors, heater resistors, and/or NTC (negative temperature coefficient) thermistors, among others. In embodiments, up to twenty layers can be applied to one or more sides of the ceramic substrate 16. As with the previous embodiment, solder pads are also deposited in a fourth step 204 to provide connection points.
After forming the soldering pads in step 105 of
In step 108 of
In order to laminate the slabs 14 to the carrier 12, the adhesive 24 is sprayed, coated, deposited, or otherwise applied to the slabs 14 and/or to the carrier 12. Exemplary methods for applying the adhesive include slot die coating, printing, chemical vapor deposition, or physical vapor deposition. In embodiments, non-limiting examples of the adhesive 24 include at least one of an epoxy, silicone rubber, polyimide, phenylenebenzobisoxazole (PBO), or benzocyclobutene (BCB). In embodiments, the adhesive 24 and the carrier 12 are selected for their ability to maintain their properties throughout various operations. For example, the adhesive 24 and carrier 12 should be able to withstand reflow soldering temperatures (e.g., up to 250° C.) and curing cycles (e.g., up to 150° C.) without losing adhesive strength or substantially degrading in mechanical properties, respectively.
Further, because the slabs 14 are intended to be removable from the carrier 12 so as to facilitate use of the slab 14 in an electronic component, the adhesive 24 is selected such that it is strong enough to hold the slab 14 securely to the carrier 12 but not so strong as to make removal difficult for a user. In a particular embodiment, adhesion strength of the slab 14 to the carrier 12 is at least 1.6 N/cm as characterized by the 90° peel test as defined by ASTM D6862. In particular, the adhesion strength reduces to less than 0.5 N/cm at the time of debonding. As will be discussed more fully below, the reduction in adhesion strength for debonding can be accomplished through heating the tape to a high temperature; applying local ultrasonic energy, applying photo excitation (e.g., ultraviolet radiation), chemical activation or solvent swelling, or laser activation, among other means.
After laminating the slabs 14 to the carrier 12, in embodiments, the slabs 14 are covered by the protective film 26 (step 109 of
Having described an embodiment of the method for producing electronic components in a roll-to-roll format, certain attributes that contribute to the effectiveness of the overall method are now discussed. These attributes contribute to the overall efficiency of the method as well as to the quality of the final product.
In certain circumstances, the strip 10, which, in embodiments, is provided in a roll, may be transported over various rollers during subsequent operations, such as during surface mounting of components onto the ceramic substrate 16. In such instances, a peeling stress may develop when the flexural rigidities of the ceramic substrate 16 and the carrier 12 are different. The magnitude of the peeling stress developed is a function of the radius of curvature over which the strip 10 travels. A larger radius of curvature will develop lower peel stress than a smaller radius of curvature. The magnitude of the peeling stress is also dependent on the differences in the flexural rigidities between the ceramic substrate 16 and the carrier 12. Flexural rigidity of a material is defined by the following formula:
where D is the flexural rigidity, E is the Young's modulus, d is the thickness of the layer, and v is Poisson's ratio. A higher difference in the flexural rigidities of the ceramic substrate 16 and the carrier 12 will lead to higher peeling stress. If the peeling stress exceeds the adhesive strength of the temporary adhesive layer 24, the ceramic substrate 16 (or completed slab 14) may delaminate from the carrier 12. Such delamination can be avoided by selecting an adhesive that has a high enough peeling stress for the particular application. However, in circumstances where selecting such an adhesive is not possible, then delamination can be avoided by lowering the difference between the flexural rigidities of the ceramic substrate 16 and the carrier 12 or by increasing the radius of curvature for the rollers over which the strip 10 travels.
Further, in embodiments, thickness of the ceramic substrate 16 is selected to be less than the thickness of the carrier 12. In doing so, the carrier 12 is able to be handled more efficiently because there is uniform stress on the carrier 12 when it undergoes the web-handling process. Second, in embodiments, the elastic modulus of the slabs 14 should be high so that circuits with fine lines and spaces can be patterned on the substrate. Third, in embodiments, the ceramic substrate 16 is designed so as to have a flexural rigidity of at least five times greater than the flexural rigidity of the carrier 12. In further embodiments, the flexural rigidity of the ceramic substrate 16 is at least ten times greater than that of the carrier 12, and in still further embodiments, the flexural rigidity of the ceramic substrate 16 is at least twenty times greater that of the carrier 12.
The third attribute, in particular, enhances the ability to handle the slabs while in a roll. In particular, it is difficult to handle the slabs 14 and separate them from the carrier 12 unless the ceramic substrate 16 of the slab 14 is rigid. Table 2, below, provides the flexural rigidity of an alumina ceramic substrate 16 as compared to a conventional polyimide substrate. Table 1 also provides the rigidity ratio of the ceramic substrate 16 to the carrier 12 for polyimide carriers 12 of different thickness.
As can be seen from Table 1, a 40 μm alumina ceramic substrate 16 has approximately the same flexural rigidity as a much thicker polyimide substrate (205 μm). In particular, the thickness and the flexural rigidity of the ceramic substrate 16 enable the ceramic substrate 16 to undergo subsequent component mounting processes and module handling processes after being separated from the carrier 12.
Table 3, below, provides instances in which the thickness of the carrier 12 is manipulated such that the carrier 12 has the same flexural rigidity as the ceramic substrate 16. As can be seen in Table 3, to achieve the same flexural rigidity as an alumina ceramic substrate 16 with a thickness of 40 μm (i.e., a rigidity ratio of 1), a carrier 12 of polyimide would have to be 205 μm thick, a carrier 12 of aluminum 6061 would have to be 68 μm thick, and a carrier 12 of stainless steel 304 would have to be 50 μm thick. If the rigidity ratio is raised to 5, the thicknesses of these materials can be much lower. As discussed above, however, the thickness of the ceramic substrate 16 is thinner than the thickness of the carrier 12 in embodiments to facilitate subsequent handling and processing of the strip 10.
A particular embodiment of the strip 10 is now described. In this embodiment, the carrier 12 is a flexible polymer with a thickness of 75 μm. A layer of adhesive 24 is applied to the carrier 12 and has a thickness of 6 μm. The slabs 14 each include a ceramic substrate 16 with a thickness of 40 μm and conductive layers 18 on both the top and bottom sides with the conductive layers 18 being 10 μm thick. The slabs 14 are covered with a protective film 26 having a thickness of 25 μm. Accordingly, the strip 10 has a total thickness of 166 μm. A standard reel that is used in packaging electronic components in a tape-on-reel system has a hub diameter of 150 mm and outer diameter of 330 mm. Using the aforedescribed strip 10 and the standard reel, 400 m of strip 10 can be stored on the reel, which facilitates low-cost mass production of electronic components. Indeed, as demonstrated above in Table 1, several million slabs 14 can be provided on a strip 10 that is 400 m long (depending, in part, on the particular type of electronic component).
In the remaining figures, embodiments of electronic components that are capable of being fabricated using the above-described roll-to-roll method are provided. In
In
In
In still other embodiments not depicted, additional complex circuit elements can be created. For example, the slab can include an antenna that is printed on the ceramic substrate. Resistors, inductors, capacitors, and other tunable elements can also be patterned on the ceramic substrate. The bottom side of the slab can include a conductive layer functioning as a ground plane. In other embodiments, the top side of the slab can have integrated circuits and other passive components mounted thereon. The slab can also contain printed sensors that sense, e.g., temperature, capacitance, pressure (piezoelectric), humidity, and/or gas.
Referring to the slabs 14 as described above,
The strength of the ceramic substrate 16 is influenced by flaws and/or defects in the material that, in some circumstances, can be introduced during the fabrication process, such as during via drilling, metallization, singulation, or handling during component assembly. Such flaws and/or defects can be decreased by using high-speed lasers, such as femto-second lasers, during via drilling and singulation and by preventing the ceramic substrate 16 from contacting hard materials, such as other ceramics or metals, as it goes through various processing steps. For example, as shown in
The bending stress is influenced by the elastic modulus of the ceramic substrate 16, the thickness of the ceramic substrate 16, the size of the slab 14, and the speed at which the slab 14 is separated from the carrier 12. In general, a higher elastic modulus will lead to a higher magnitude of bending stress. Further, in general, a thinner ceramic substrate 16 will develop more bending stress than a thicker ceramic substrate 16 of the same material. Also, in general, a larger slabs and higher separation speeds will lead to a higher bending stress. By taking into account the elastic modulus of the ceramic substrate 16, the thickness of the ceramic substrate 16, the size of the slabs 14, and the speed of separation, the bending stress can be managed so as to avoid exceeding the strength of the ceramic substrate 14.
With respect to the peel force, damage to the ceramic substrate 16 can be reduced by using an adhesive (high- or medium-tack) during the processing steps. However, in order to facilitate removal of the slabs 14 from the carrier 12, the adhesive can be weakened just prior to separation. For example, depending on the type of adhesive, the strip can be exposed to UV light, increased temperature, moisture, magnetic fields, ultrasonic energy, and/or electrostatic forces. In embodiments, the specific technique for weakening the adhesive minimizes or eliminates adhesive residue left behind on the slab 14 after separation. In embodiments, the adhesive strength, as measured by the 90° peel test defined in ASTM D6862, is greater than 4 N per 25 mm wide carrier and, after the weakening technique is performed, reduces to less than 0.4 N per 25 mm wide carrier.
Accordingly, manipulation and/or optimization of the strength of the ceramic substrate 16, the bending stress in the ceramic substrate 16, and the peel force can enhance the ability of the slabs 14 to separate from the carrier 12 when desired by the manufacturer or end user.
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein, the article “a” is intended to include one or more than one component or element, and is not intended to be construed as meaning only one.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.
This application claims the benefit of priority of U.S. Provisional Application Ser. No. 62/625,023 filed on Feb. 1, 2018 the contents of which are replied upon and incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/016181 | 1/31/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62625023 | Feb 2018 | US |
