Abstract:
Electrical components mounted onto a circuit board may be sealed within a frame tray upon the addition of a curable material that encapsulates the circuit board. The electrical components of the circuit board are positioned and sealed within the frame tray such that the cured material does not affect an airflow path which dissipates heat produced by the electrical components during use. The curing of the curable material shields the circuit board from moisture, dust and other environmental contaminates.

Description:
TECHNICAL FIELD 
   The invention relates to system and methods of sealing electrical components in a frame tray. More particularly, the invention relates to system and methods of sealing electrical capacitors in a frame tray before application of a potting compound to the frame tray. 
   BACKGROUND OF THE INVENTION 
   Many electronic devices are mounted on circuit boards, which typically include a plurality of electronic components, which are then typically sold and shipped as a unit. Whether or not mounted on a circuit board, it is widely accepted that electronic circuits are formed of a plurality of electronic components, and that such circuits are sold and shipped as a unit. The prior art, however, fails to provide adequate insulation, weatherization, encapsulation, or protection for such modern electronic devices, mounted on circuit boards that are part of exchangeable frame trays that house the printed circuit boards in various pieces of equipment such as welders. 
   A known welder unit typically consists of a number of circuit boards and subassemblies that are mounted separately inside the welder. These individual components and subassemblies perform in conjunction with each other to produce an output required for welding. The main power supply components for the welder include any or all of the following: transformers, capacitors, rectifiers, and printed circuit boards. Wiring connects the components to one another and the fan can cool the components. 
   There is a need for the sealing of electronic components which are mounted on printed circuit boards housed in a frame tray, wherein the printed circuit boards are encapsulated in a potting compound to protect the printed circuit board from environmental contaminates. However, in the current state of the art, much of the potting compound leaks out before it has sufficient time to harden or cure. The embodiments of the subject invention obviate the aforementioned problems. 
   BRIEF SUMMARY 
   In one embodiment, a method of encapsulating an electrical circuit in a frame tray, includes the steps of providing a frame tray having walls defining a region for housing an electrical circuit that has one or more electrical components, the frame tray including at least a first aperture for receiving the one or more electrical components, positioning the electrical circuit within the region thereby inserting the one or more electrical components through the at least a first aperture, wherein the distance between the one or more electrical components and the circumference of the at least a first aperture defines a gap, installing at least a first conformable band that spans the gap for sealing against the flow of fluid material, and at least partially filling the frame tray with fluid material thereby encapsulating at least a portion of the electrical circuit. 
   In one aspect of the embodiments of the subject invention, the at least a conformable band is a shrinkable band. 
   In another aspect of the embodiments of the subject invention, the shrinkable band is heat activated to shrink from a first diameter to a second smaller diameter. 
   In yet another aspect of the embodiments of the subject invention, the method also includes providing tape having at least one side coated with an adhesive. 
   In still another aspect of the embodiments of the subject invention, installing at least a first conformable band that spans the gap includes applying the tape to seal the gap between the one or more electrical components and the at least a first aperture. 
   In even another aspect of the embodiments of the subject invention, the fluid material comprises a curable material. 
   In another aspect of the embodiments of the subject invention, the curable material is a potting compound selected from the group of: a one component epoxy system, a two component epoxy system, a one component silicone system, a two component silicone system, a polyurethane system, a polyester system and mixtures thereof. 
   In another embodiment, a method of encapsulating a circuit board includes the steps of providing a circuit board having one or more capacitors extending from the circuit board, providing a frame tray configured to receive the circuit board, the frame tray defining a region for encasing the circuit board, and wherein the frame tray includes one or more apertures for receiving the one or more capacitors respectively, installing the circuit board into the frame tray whereby the one or more capacitors extend through the one or more apertures, and wherein the distance between the one or more aperture circumferences and the one or more capacitors define a gap, installing heat shrink tubing to span the gap, applying heat from an associated heat source to shrink the heat shrink tubing thereby sealing the gap, and filling at least part of the region with a curable resin for encasing the circuit board. 
   In yet another embodiment, a system for encapsulating a circuit board includes a circuit board including one or more electrical components extending from the circuit board, a frame tray comprising one or more walls defining a volume for housing the circuit board, the one or more walls having at least a first aperture configured to receive the one or more electrical components, wherein the distance between the one or more electrical components and the circumference of the at least a first aperture defines a gap, and a band of material applied to cover the gap for sealing against the flow of fluid materials. 
   In one aspect of the embodiments of the subject invention, a dielectric material is included for at least partially encapsulating the circuit board, and wherein when the circuit board is received within the frame tray, a volume is defined for containing the dielectric material. 
   In even another embodiment, a system for encapsulating an associated electrical circuit having associated electrical components includes a frame tray having one or more walls defining a volumetric region that is configured to house an associated electrical circuit, the one or more walls including at least a first aperture for receiving an associated electrical component extending from the associated electrical circuit, wherein the distance between the associated electrical component and the circumference of the at least a first aperture defines a gap, a fluid material at least partially filling the volumetric region for covering at least part of the associated electrical circuit, and means for inhibiting the flow of the fluid material through the gap. 
   In one aspect of the embodiments of the subject invention means for inhibiting comprises at least a first band operatively configured to span the gap for inhibiting the flow of the fluid material through the gap. 
   In another aspect of the embodiments of the subject invention, the distance defining the gap varies at different points around the circumference of the at least a first aperture, and the at least a first band is generally pliable for conforming to seal the gap. 
   In yet another aspect of the embodiments of the subject invention, the at least a first band is tubular and is constructed from a polymeric material. 
   In even another aspect of the embodiments of the subject invention, the at least a first band is a thermoplastic material selected from the group consisting of: a polyolefin, a fluoropolymer, a polyvinyl chloride, a polychloroprene, a silicone elastomer. 
   In still another aspect of the embodiments of the subject invention, the at least a first band is shrinkable material for sealing the gap. 
   In still yet another aspect of the embodiments of the subject invention, the shrinkable material is heat shrink tubing that conforms to variances in distance defining the gap. 
   In another aspect of the embodiments of the subject invention, the fluid material is capable of solidifying for encapsulating the associated electrical circuit and may be curable for hardening around at least part of the associated electrical circuit thereby encapsulating the associated electrical circuit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a circuit board having electrical components mounted thereon prior to insertion into a frame tray according to the embodiments of the subject invention. 
       FIG. 2  is a cross-sectional view of an electrical component mounted onto a circuit board that is inserted within a receptacle of the frame tray according to the embodiments of the subject invention. 
       FIG. 3  is a perspective view of a circuit board having electrical components mounted thereon housed within a frame tray according to the embodiments of the subject invention. 
       FIG. 4  is a partial, cross-sectional view of an encapsulated circuit board according to the embodiments of the subject invention. 
       FIG. 5  is a block diagram of a method of encapsulating an electrical circuit according to the embodiments of the subject invention. 
       FIG. 6  is block diagram of a method of encapsulating a circuit board according to the embodiments of the subject invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings wherein the showings are for purposes of illustrating embodiments of the invention only and not for purposes of limiting the same,  FIGS. 1 and 2  show a frame  10 , also termed frame tray  10 , for housing an electrical circuit, illustrated generally at  11 . The electrical circuit  11  may include at least one electrical component  12  that may be mounted onto circuit board  14 . Examples of electrical components  12  may include resistors, transistors, capacitors, integrated circuits, logic processors, heat sinks and the like. The electrical circuit  11  may be used in an article of industrial equipment, examples of which may include welding equipment, industrial controllers and the like. 
   The circuit board  14  comprises a mounting support for the electric components  12 , which may be interconnected by physical wiring. Alternatively, circuit board  14  may be a printed circuit board  14 ′, having conductive traces  9  printed thereon for interconnecting the electrical components  12 . It is to be construed that any structure of assembling an electrical circuit  11  may be chosen without departing from the scope of coverage of the embodiments of the subject invention. 
   The frame tray  10  may generally be polygonal in configuration. More specifically, the frame tray  10  may be rectangular in shape. Although, the shape of the frame tray  10  should not be construed as limiting. In one embodiment, the frame tray  10  may be integrally fashioned as a single piece of molded plastic, like for example thermoplastic. The frame tray  10  may also be constructed from metal. Persons of ordinary skill in the art will readily understand the application to numerous other types of suitable materials. The frame tray  10  is configured having one or more walls  15  that define a generally open first side  7  for receiving the circuit board  14 . The second side  8  of the frame tray  10  may be generally enclosed for containing an encapsulating material  22  as will be discussed in detail below. 
   With continued reference to  FIGS. 1 and 2 , as mentioned above, the frame tray  10  is constructed to include an area  16  configured to receive and house the circuit board  14 . Mounting holes or fastener holes, not shown, may be included, which can be used to receive fasteners for securing the circuit board  14  in place. Although, any means of securing the circuit board  14  to the frame tray  10  may be chosen with sound engineering judgment. The first side  7  of the frame tray  10  may be open for insertion of the circuit board  14  during assembly. This is contrasted with the second side  8  of the frame tray  10 , which may be generally enclosed for holding or containing an encapsulating material to be discussed further below. The frame tray walls  15  may therefore define a volumetric region within which the circuit board  14  may reside. It will appreciated that some electrical components  12  have a length that may extend a distance outward from the circuit board  14 . These electrical components  12  may require openings in the frame tray walls  15  for accommodating the electrical components&#39;  12  size, i.e. length, and/or orientation. As such, the frame tray  10  may include at least one aperture  18  or receptacle  18  through which electrical components  12  are received. In this manner, electrical components  12  are received by the apertures  18 . It will be realized that when an electrical component  12  is received within receptacle  18  of frame tray  10 , a gap  20  may be formed between the circumference of the aperture  18 , i.e. the wall of receptacle  18  and the outer surface of the electrical component  12 , the import of which will be realized shortly. Furthermore, surface imperfections located on the exterior portion of the electrical component  12  may also contribute to the size of gap  20  between the wall of receptacle  18  and the outer surface of electrical component  12 . It will appreciated that the gap may vary at different points around the circumference of the aperture  18 . It is noted here that other openings within the frame tray walls  15  may be included for accommodating other circuit components, not shown. Such openings may be sealed by gaskets or any other suitable means for forming an enclosed frame tray  10 . 
   In order to protect the circuit board  14 , which may be a printed circuit board  14 ′, from ambient conditions or environmental contaminates like moisture and dust, when housed in frame tray  10 , an encapsulating material  22 , which in one embodiment includes a potting compound, may be applied and cured within frame tray  10  to substantially encapsulate the circuit board  14 . The encapsulating material  22  may be comprised of a curable material  22 ′ being generally fluid until exposed to the air and/or mixed with other components. Over time the curable material  22 ′ solidifies. However, in the past, when applied to the circuit board  14 , the curable material  22 ′ migrates into the gap  20  between the wall of receptacle  18  and the outer surface of the electrical component  12  and leaks or seeps down the exterior wall of electrical component  12 . The leakage of the curable material  22 ′, when cured, is unsightly and can impair the performance of electrical component  12  and may lead to damaging circuit board  14 . 
   Referencing  FIG. 3 , means for sealing around the electrical components  12  mounted to circuit board  14  and extended through the frame tray walls  15  may be provided to seal the gap  20  between the circumference of the aperture  18  and the outer surface of electrical component  12 . Means for sealing may comprise a band of material  13  capable of conforming to irregular and/or discontinuous surfaces. In one embodiment, means for sealing may include a thermoplastic material  24 . One type of thermoplastic material  24  may be composed of a polyolefin, a fluoropolymer, a polyvinyl chloride, a polychloroprene, a silicone elastomer and mixtures thereof. In another embodiment, means for sealing may comprise a material that contracts or constricts when exposed to heat at a particular temperature or other energy sources. Heat shrink tubing is one such type of material. Other embodiments may include tape, which may have an adhesive applied to one or more sides thereof. The tape may or may not constrict like the heat shrink tubing, but may be pliable for conforming to irregular and uneven surfaces, being held in place by the adhesive until the encapsulating material  22  cures. 
   Accordingly, as shown in  FIG. 3 , the gap  20  may be sealed by applying the band of material  13  onto a portion of the outer surface of electrical component  12  and over the wall of receptacle  18 . In one embodiment, a source of heat may be applied to the band of material  13  to shrink and thus seal gap  20  between the wall of receptacle  18  and the outer surface of the electrical component  12 . It is noted that other sources of energy, e.g. radiation or light, may be used to activate, in this instance shrink, the band of material  13 . In another embodiment of the subject invention, a source of ultra-violet light may be applied to shrink the band of material  13  and substantially seal the gap  20  between the wall of receptacle  18  and the outer surface of the electrical component  12 . In this way, the band of material  13  constricts and conforms to any uneven exterior surface found on the electrical components  12  and substantially eliminates leakage of the potting compound through the gap  20 . 
   With reference to  FIG. 4 , the curable material  22 ′ may include a one-component epoxy system, a two-component epoxy system, a one-component silicone system, a two-component silicone system, a polyurethane system, a polyester system and mixtures thereof, or any encapsulating material as is appropriate for use with the embodiments of the subject invention. 
   In one embodiment of the invention, two-component epoxy materials may be used as the curable material. Two-component epoxy materials may include one or more epoxy resins that are selectively combined with one or more curing agents or hardeners, such as a variety of active hydrogen compounds including polyamines, polyacids, polymercaptans, polyphenols, polyamides and polyureas. Additional materials and additives, such as extenders, fillers, reinforcing agents, colorants (e.g., pigments or dyes), organic solvents, plasticizers, flexibilizers, tackifiers, diluents, adhesion promoters, thixotropic agents, rheological agents, and the like, may be incorporated into either of the two components, as is known in the art. 
   Two-component epoxy-based materials are typically readily curable at room temperature, but can be inconvenient to use and store. The components of two-component systems must be accurately measured and properly mixed just prior to use. Thus, the various components to be mixed must be separately stored until use and have uniform properties. 
   In another embodiment of the invention, a one-component epoxy-based material may be used as an alternative to the two-component epoxy material. These one-component materials are typically available for industrial application in two basic forms: rigid epoxy adhesives and frozen pre-mix, flexible epoxy adhesives. Rigid epoxy materials may include such compounds as bisphenol-A epoxy materials and novolac-based materials. These rigid epoxy materials exhibit strong adhesion for many materials and may be conveniently stored at room temperature. Flexible epoxy materials form more pliable bonds that are capable of successfully adapting to stresses between dissimilar materials caused by differing rates of expansion. However, in contrast to rigid epoxy materials, frozen pre-mix flexible epoxy materials must be stored in a frozen state and must be thawed prior to use. 
   With further reference to  FIGS. 1 through 6 , the circuit board  14  may be positioned within area  16  of frame tray  10  that is open and configured to receive and house circuit board  14  such that electrical component  12 , that is mounted onto a portion of circuit board  14 , may be received and housed within receptacle  18  of frame tray  10 . Since gap  20  may be formed between the wall of receptacle  18  and the outer surface of electrical component  12  when electrical component  12  is housed within receptacle  18  of frame tray  10 , means for sealing may be used to cover a portion of electrical component  12  mounted to circuit board  14  and wall of receptacle  18  to substantially seal gap  20 . The use of the means for sealing has the advantages of being able to compress and conform to the irregular exterior surfaces commonly found on electrical component  12  and eliminate the problems caused by the size variation of gap  20 . Subsequently, a curable material may be applied and cured within frame tray  10  to substantially encapsulate circuit board  14  within curable material  22 ′. The curable material  22 ′ may then be allowed to solidify or harden. 
   Based upon the foregoing disclosure, it should now be apparent that the system and methods of sealing electrical components as described herein will carry out the objects set forth hereinabove. It is, therefore, to be understood that any variations evident fall within the scope of the claimed invention and thus, the selection of specific component elements can be determined without departing from the spirit of the invention herein disclosed and described.