Patent Publication Number: US-2019182965-A1

Title: System and Method for Applying Potting Material to a Printed Circuit Board

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of PCT Application No. PCT/CA2017/050589 filed on May 16, 2017, which claims priority from U.S. Provisional Patent Application No. 62/337,671 filed on May 17, 2016, both incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The following relates to systems and methods for applying potting material to a printed circuit board (PCB). 
     DESCRIPTION OF THE RELATED ART 
     In electronics assembly and manufacturing, potting is a process of applying a solid or gelatinous compound to a completed electronic assembly. Potting may be performed in order to provide resistance to shock and vibration, or for preventing the ingress of moisture and/or other so called contaminants, such as corrosive agents, or for thermal performance reasons. For example, it is currently required that photovoltaic solar electronic assemblies (e.g., micro inverters and rapid shut down devices) have the printed circuit board (PCB) assembly protected by at least a 1/32 inch (0.79 mm) thick layer of material applied through, for example potting, in order to achieve a pollution degree of 1 per section 25.4(f) of the UL1741 standard. This standard specifies appropriate distances between high voltage and safety low voltage signals, to ensure operator safety, and are dependent on environmental conditions (i.e. the pollution degree). The higher the pollution degree, the smaller the distance that is required between components. There are typically other government or regulatory requirements, for example, that the protective layer is achieved without having air bubbles in the potting material. These requirements may also apply to devices that are included in a junction box of a solar panel and in many other electronics applications. 
     The components on or embedded in a PCB often have different heights relative to the surface(s) of the PCB, and the potting material is in a fluid state during the manufacturing process. As such, to ensure the full coverage of potting material on the components, the potting material is applied such that it fills enough (or the entirety) of the container in order to provide the requisite layer over and above the highest components, as shown in  FIGS. 1( a ) and 1( b ) . This can, in many cases, result in the application of excessive and redundant or wasteful potting material. Since the UL1741 specification requires the components to be covered with a minimum thickness of 1/32 inch (0.79 mm), when the highest components are appropriately covered, the lower components would likely be over coated. This is also the case with PCBs that are mounted with a gap under the PCB and above the floor of the enclosure as shown in  FIGS. 1( c ) and 1( d ) . 
     One solution to the problem illustrated in  FIGS. 1( a ) and 1( b ) , is to apply a plastic separator or cover over the PCB assembly, as shown in  FIG. 2 . The plastic separator is used to adjust the fluid volume application to components of different heights by physical separation of space. In this way, the space underneath the plastic separator is to be potted, and the areas above the plastic separator would not be potted. Such a plastic separator is meant to restrain the potting material in the dedicated areas, and prevent it from over flow to the other space above the structure. However, a problem encountered with this approach is that the viscosity of the potting material can prevent it from flowing sufficiently underneath the separator, resulting in voids around the components which are further away from injection gates in the structure. As a result, the separator may require multiple inlets and vents, adding to the complexity of the structure in order to achieve a consistently sufficient layer of potting material. Moreover, because the separator is generally horizontally oriented, the application of the potting material is not visible during the manufacturing process, and thus it can be difficult to verify the effectiveness of the inlets and vents. Therefore, in some case, in order to ensure adequate potting material coverage requires section cuts in the separator and prohibitive delays resulting from design adjustment. These issues can also arise if the plastic separator was used with a PCB assembly as illustrated in  FIGS. 1( c ) and 1( d ) . 
     It is an object of the following to address at least one of the above-noted drawbacks. 
     SUMMARY 
     The following provides systems and methods to reduce the amount of potting material used in electronics assemblies. 
     In one aspect, there is provided a frame for applying potting material to a printed circuit board (PCB), the frame comprising a plurality of substantially vertically oriented walls arranged to isolate a surface of the PCB into a plurality of zones. 
     In this way, pottant can be applied to areas having differing component heights throughout the board. These walls enable pottant to be applied simultaneously or consecutively to the separate regions, in differing volumes, to achieve sufficient coverage, while minimizing excess potting material, particularly over lower profile components. 
     In another aspect, there is provided a method of applying potting material to a printed circuit board (PCB), the method comprising: aligning a frame over a surface of the PCB, the surface comprising a plurality of components having different heights, the frame comprising a plurality of substantially vertically oriented walls arranged to isolate the surface of the PCB into a plurality of zones, each zone comprising at least one PCB component; and applying the potting material into a plurality of the zones to achieve coverage of the PCB components in that zone, wherein at least two zones have potting material levels that are different. 
     In yet another aspect, there is provided a device for applying potting material to a printed circuit board (PCB), the device comprising a removable frame having a contour that substantially follows contours defined by components of the PCB to enable a gap to be defined between the contour and the PCB components to enable the potting material to be injected into the gap to generate a layer of potting material over the PCB components after removing the frame from the cured potting material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described by way of example only with reference to the appended drawings wherein: 
         FIG. 1( a )  is a cross-sectional view of a printed circuit board (PCB) housed in an enclosure; 
         FIG. 1( b )  is a cross-sectional view of the PCB and enclosure shown in  FIG. 1( a )  with potting material added according to a prior art technique; 
         FIG. 1( c )  is a cross-sectional view of a PCB housed in an enclosure with a gap between the underside of the PCB and a floor of the enclosure; 
         FIG. 1( d )  is a cross-sectional view of the PCB and enclosure shown in  FIG. 1( c )  with potting material added according to a prior art technique; 
         FIG. 2  is a cross-sectional view of the PCB and enclosure shown in  FIG. 1( a )  with potting material adding according to another prior art technique; 
         FIG. 3  is a perspective view of a frame for separating a PCB housed in an enclosure, into zones of differing heights to facilitate the application of potting material; 
         FIG. 4  is a perspective view of a frame for separate a PCB into zones of different heights to facilitate the application of potting material, wherein the PCB is not housed in an enclosure; 
         FIG. 5A  is a cross-sectional view of a PCB housed in an enclosure, with a frame for separating the PCB into multiple zones; 
         FIG. 5B . is a cross-sectional view of the PCB and enclosure shown in  FIG. 5A  after potting material has been applied; 
         FIG. 5C  is a cross-sectional view of a PCB housed in an enclosure with a gap between the underside of the PCB and a floor of the enclosure, with a frame for separating the PCB into multiple zones; 
         FIG. 5D  is a cross-sectional view of the PCB and enclosure shown in  FIG. 5C  after potting material has been applied; 
         FIG. 6A  is a cross-sectional view of a PCB housed in an enclosure, with a frame similar to that shown in  FIG. 5A  but with walls that do not extend fully to the PCB surface; 
         FIG. 6B  is a cross-sectional view of the PCB and enclosure shown in  FIG. 6A  after potting material has been applied; 
         FIG. 6C  is a cross-sectional view of the PCB and enclosure shown in  FIG. 6A  after potting material has been applied and the frame removed; 
         FIG. 7  is a cross-sectional view of a PCB without an enclosure with a frame for separate the PCB into multiple zones, after the potting material has been applied; 
         FIG. 8  is a cross-sectional view of a removable jig for controlling the application of potting material to a PCB according to differing component heights; 
         FIG. 9  is a cross-sectional view of the jig shown in  FIG. 8  inserted in an enclosure; 
         FIG. 10  is a cross-sectional view of the jig shown in  FIGS. 8 and 9  after application of potting material and during removal of the jig; and 
         FIG. 11  is a flow chart illustrating steps that may be performed in using a frame for applying potting material to a PCB. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the figures,  FIG. 3  illustrates an electronics assembly  10  that includes a PCB  12  housed in, or otherwise supported by or contained within, an enclosure  14 . The PCB  12  includes a number of components  16 , including surface mount and/or embedded components  16 , that protrude or extend from one or more surfaces of the PCB  12 . In the example shown in  FIG. 3 , both relatively high profile components  16   a  are present, as well as relatively low profile components  16   b . To enable potting material to be applied to different areas, without having to use excessive potting material in order to ensure the highest component(s) are covered, a frame  18  is inserted into the enclosure  14 , to create a number of regions or zones  20 . In this way, whether the potting material is applied concurrently, or sequentially, the volume of potting material applied in each zone is only as much as needed to cover the components  16  in that zone  20 . 
     In the embodiment shown in  FIG. 3 , the frame  18  is designed to be constructed of any suitable material, such as various plastics, and includes a series of separation walls to isolate zones  20  having components  16  with different heights, thereby dividing the components  16  into separate “vessels”, without potting material fluid connections therebetween. Therefore, for the zones  20  with lower profile components  16   b , less volume of the potting material can be applied (than would occur without the frame  18 —e.g., per  FIG. 1( b ) ), and for areas with higher profile components  16   a , a sufficient quantity of the potting material can be applied to cover those higher components  16   a . This would typically result in a higher fluid level in that zone  20 , however, not necessarily a higher volume of pottant, since the components  16  being potted may themselves have higher volumes. 
     Since the dividing walls of the frame  18  restrain the potting material from flowing between the different vessels, both high and low profile components  16  would be able to be applied with an appropriate volume of potting material, such that both “void space” and over-coating problems can be prevented. Moreover, it can be appreciated that since the walls of the frame  18  are vertically (or substantially vertically) oriented, an improved amount of visibility for problem checking is provided when compared to, for example, the prior art implementation shown in  FIG. 2 . For example, cutting or dissection can be prevented, in order for potting material checks to be made, to ensure that the potting material level reaches the requisite targets. 
     In the embodiment shown in  FIG. 3 , the frame  18  is sized to fit within an enclosure  14  in order to create the zones  20 . However, as shown in  FIG. 4 , for PCBs  12  that need to be potted, but are not in an enclosure, the frame  18  can be adapted to include a peripheral wall  22  to effectively contain potting material within the zones  20  that are adjacent the edges of the PCB  12 . As such, it can be appreciated that the frame  18  can be configured to suit any electronics assembly  10  in order to isolate the zones  20  as herein described. 
     Depending on the material used to construct the frame  18 , the frame  18  is typically inserted and kept in the enclosure  14  (see  FIG. 3 ) or as part of the PCB  12  (see  FIG. 4 ) and becomes fixed after the potting material is cured. The frame  18  can have walls that are of the same height (as illustrated in  FIGS. 3 and 4 ), or having different heights, e.g., to generally correspond to the heights of the components in different zones  20 . 
     However, it can be appreciated that with appropriate materials that enable the frame  18  to be separated from the potting material, the frame  18  can be removed post-curing with the above-noted effect in place. For such an implementation, which is shown in  FIG. 6  and described below, a gap (e.g., of approximately 1 mm) can be established between the bottom of the frame  18  and the surface of the PCB  12 , with the frame  18  being supported above the PCB surface using any suitable method such as attachment to the enclosure  14 , a spandrel, jig, or other supporting structure. The potting material  30  would fill into this gap, and because of the viscosity of the potting material  30 , this can be done with a limited amount of flow through the gap(s). It can be appreciated that such a removable frame  18  can include all zones  20 , or smaller individual frames (not shown) can be applied successively for each zone  20 , and removed after that zone  20  has cured. Moreover, the frame  18  can be constructed, e.g. with walls of different heights, such that the frame  18  is not visible after the potting material  30  has been applied since the framed element is at a different height than the pottant trace or unframed portion. 
     The frame  18  can be constructed from a plastic as mentioned above, or from one or more various other materials, such as composite materials, paper, cardboard, etc.; or any other material that is found to be economical to leave behind after applying the potting material, or can be removed from the potting material post-curing. Also, the frame  18  can be constructed as a single unit, or can be assembled from multiple frame pieces (not shown). 
       FIG. 5A  provides a schematic cross-sectional view of an example of a PCB  12  having both higher profile components  16   a  and lower profile components  16   b , wherein the PCB  12  is supported or contained within an enclosure  14 . In this example, the frame  18  separates the PCB&#39;s surface area into four zones, and each zone includes a fill marker  34  that can be applied to a wall of the frame  18  or the enclosure  14  in order to indicate to an operator (or machine vision/detection function), to what level the potting material  30  should be filled. The potting material  30  can be applied as shown in  FIG. 5A , on a zone-by-zone sequential basis, or multiple material sources/sprayers/applicators can be used simultaneously. 
     As shown in  FIG. 5B , after application of the potting material  30 , each zone  20  includes sufficient coverage of cured potting material  32 , but at different levels. For example, the cured potting material  32   a  in a first zone  20   a  has a lower level than the cured potting material  32   b  in an adjacent zone  20   b , but with similar overall volumes applied and excessive potting material coverage minimized. In this example, the frame  18  is left behind as part of the potted PCB  12  and enclosure  14 . It can be appreciated that the walls of the frames  18  could have different heights or portions thereof removed to minimize frame portions extending above the potted portions. 
       FIGS. 5C and 5D  illustrate the same technique and structure as shown in  FIGS. 5A and 5B , but for a PCB  12  that is mounted in the enclosure  14  such that there is a gap between the underside of the PCB and the floor of the enclosure  14  into which potting material is filled.  FIGS. 5C and 5D  also show potting material being filled around the side edges of the PCB, which may also be applicable in the scenario shown in  FIGS. 5A and 5B . It can be appreciated that the applicability of the principles discussed herein to both PCB mounting configurations (i.e. directly to the enclosure  14  or slightly above the enclosure) is similar for all embodiments shown herein, and duplicate illustrations are omitted only for the sake of brevity and in view of the variations shown in  FIGS. 5C and 5D . 
       FIGS. 6A to 6B  illustrate another implementation wherein the frame  18  is supported above the PCB  12 , with a gap  36  established therebetween as illustrated in  FIG. 6B . As illustrated in  FIG. 6B , the applied potting material  32  can flow under the frame  18  to ensure complete coverage of the PCB  12 , while additionally achieving different heights of potting material in different zones  20 . It can be appreciated that the application of potting material  30  in this example can be done in a continuous or sequential process in which a first layer is applied to achieve a minimum layer to ensure coverage of the PCB  12 , and one or more additional layers that achieve the differing heights within the zones  20 , with the frame  18  being inserted either at the beginning or after application of the first, baseline layer. As such, it can be appreciated that various steps can be used in different order.  FIG. 6C  illustrates the removal of the frame  18  and the desired coverage of the PCB  12 . 
       FIG. 7  illustrates the same effect as in  FIG. 6 , but with a frame  18  that includes an outer or peripheral wall  22 . That is, the peripheral wall  22  is included to provide the same functionality as the enclosure  14  in that the individual vessels are created, without potting material flow therebetween. 
     As noted above, it can be appreciated that while the walls of the frames  18  shown in  FIGS. 3 to 7  are uniform in height, such walls can have different heights, for example, according to the heights of the components  16  within a particular zone  20 . 
     As illustrated in  FIGS. 8 to 10 , when a suitable potting material  30  and frame material are chosen, such that the frame  18  can be separated from the potting material  30  post-curing, a removable contoured frame, hereinafter referred to as a “jig”  40  could instead be constructed, which has a PCB-facing profile  42  that follows the profile of the components  16  of the PCB  12 , including both higher components  16   a  and lower components  16   b .  FIG. 8  illustrates the jig  40  which is lowered towards the PCB  12  such that it is held in place with a sufficient gap  44  between the profile  42  and the PCB components  16  as illustrated in  FIG. 9 . A potting material  30  of a suitable viscosity to enable it to flow through the gap  44  in a consistent manner, is applied at either or both ends of the jig  40 , but may also be applied using any suitable number of injection openings in the jig  40  (not shown). As shown in  FIG. 10 , in this way, after the potting material  30  has cured, and the jig  40  has been removed, a suitable layer  50  of potting material  30  is achieved. 
     Turning now to  FIG. 11 , an example of a method for applying potting material  30  to a PCB  12  is shown. At step  100 , a plurality of zones  20  on the PCB  12  to which potting material  30  is to be applied are identified, based on the profiles of the components  16  that are protruding from the surface of the PCB  12 . It can be appreciated that the layout of the PCB  12  can also be designed with the potting frame  18  in mind, such that relatively higher components  16   a  are grouped together, to the extent possible, while the relatively lower components  16   b  are likewise grouped together, to the extent possible; in order to minimize the number of zones  20 . Based on these layout considerations, at step  102 , a frame  18  is created that provides separation between zones  20 . At step  104 , the frame  18  is then inserted into the enclosure  14  containing the PCB  12 , if applicable, or supported on the PCB  12  such that the surface of the PCB  12  is covered and divided into the zones  20  with the peripheral wall  22  in place. The potting material  30  is then injected at step  106 , which can be done according to any of the various implementations discussed above. As indicated above, the injection of potting material  30  can be done simultaneously or sequentially, and can be done manually, or automatically by programming a pottant injection machine. In the example shown in  FIG. 11 , it is determined at step  108 , whether or not there are more zones  20  into which potting material  30  should be applied. If so, step  106  is repeated. If not, it is determined at step  110 , whether or not the frame  18  is removable. If so, the frame  18  is separated from the PCB  12  at step  112  and the process ends at step  114 . It can be appreciated that some or all of the steps shown in  FIG. 11  can be implemented as computer executable instructions, executed by software and/or hardware included in, or provided by, the manufacturing equipment. 
     For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein. 
     It will be appreciated that the examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles. 
     It will also be appreciated that any module or component exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media may be part of any suitable manufacturing equipment performing at least part of the methods described herein, any component of or related thereto, etc., or accessible or connectable thereto. Any application or module herein described may be implemented using computer readable/executable instructions that may be stored or otherwise held by such computer readable media. 
     The steps or operations in the flow charts and diagrams described herein are just for example. There may be many variations to these steps or operations without departing from the principles discussed above. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. 
     Although the above principles have been described with reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.