Patent Publication Number: US-RE29683-E

Title: Encapsulation housing for electronic circuit boards or the like and method of encapsulating

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to housings for electrical or electronic components and more particularly to an improved method and apparatus for housing and encapsulating such components. 
     Without affecting any limitations as to other applications, the present invention is set forth and described in the environment of protective housings intended for control devices in vehicles such as, for example, electronic voltage regulators. 
     With the advent of semi-conductors and the development of companion technologies, such as the thick film art and the like, many new applications are being found for solid state control devices of one sort or another. This includes voltage regulators and other control circuits. .,.!. for electronic ignition systems for automotive and other motor vehicles. 
     Because of the relatively hostile environment in which such control devices, e.g., voltage regulators, must operate, some sort of weather or environmental protection is necessary for the desired reliability of operation. The corrosive fluids and other undesirable ambient factors encountered under the hood of an automobile are much too detrimental for such electronic components without some environmental protection. The same is true with respect to high velocity air movements that very likely will be encountered. At the same time, however, there must be an opportunity for adequate heat dissipation for these components or breakdown will occur at some given elevation in ambient temperature. 
     In the past, protective housings or enclosures employed for these . .type.!. .Iadd.types .Iaddend.of control devices, such as a voltage regulator for example, have comprised a simple metallic enclosure, usually open at the bottom, and in which the associated electrical or electronic control circuit board is intended to be placed. Customarily, the interior is then encapsulated with a suitable material for full-range protection. Nevertheless, such encapsulation was more often than not accomplished by hand, one unit at a time. In addition, some means was necessary to position and then maintain the associated circuit board internally of the housing in the required relation before and.Iadd., .Iaddend.of course.Iadd., .Iaddend.during the encapsulation process. 
     The result was a unit unduly expensive and time consuming to fabricate, particularly in view of the cadmium or zinc coating required for the metallic housing and the hand operation required for the encapsulation process. Additionally, the finished unit was more often than not oversized when considering the control circuit board that it housed. This translates into even greater expense when considering the cost of the extra encapsulation material required. In many cases, the heat dissipation capacity has been deficient in that the encapsulation material effectively isolated the internal components from the outside ambient. 
     Accordingly, it is one object of the present invention to provide a protective housing for electrical components operative in a hostile environment which does not exhibit the foregoing deficiencies. 
     A more particular object of the present invention is to provide a protective housing for an electronic voltage regulator or the like for underhood operation in a motor vehicle which is less costly to produce, more compact in size, and insures more reliable operation. 
     Another object of the present invention is to provide an improved method of final assembly and encapsulation for such voltage regulator unit or other control device which is adapted to automation, or at least multi-unit production as contrasted to hand operation. 
     Yet another object of the present invention is to provide a protective housing for a voltage regulator or other device which is non-metallic, yet stabilized in configuration notwithstanding being subjected to relatively high ambient temperatures in operation and further which is non-reactive to other ambient factors. 
     Still another object of the present invention is to provide a protective housing of the foregoing type wherein internally positioned guide rails insure the associated circuit board is optimally positioned within the housing for proper heat dissipation action. 
     It is another object of the present invention to provide a protective housing of the foregoing type which contemplates vertical assembly of the associated control circuit boards and permits proper positioning therein by the action of gravity. 
     A further object of the present invention is to provide a protective housing of the foregoing type suitable for stacking in a vertical, side-by-side relation wherein one portion of each such housing effectively overlaps a portion of an adjacent housing so as to permit a continuous encapsulation process therefor. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a protective housing is provided for accommodating a circuit board with components comprising a voltage regulator or other like control device. The housing is designed to accept the insertion of the circuit board from a vertical direction with tracks or guide rails on opposing side walls which serve to guide or steer the circuit board to its intended position within the housing by the action of gravity. 
     The housing itself is formed of a non-metallic, thermosetting plastic material which remains stabilized in its set condition despite elevated temperatures to which it may be subsequently subjected. The finished, i.e., encapsulated, unit is designed for mounting on the fire wall or interior wall of a fender with the associated heat sink interior of the housing positioned adjacent thereto for appropriate head dissipation action. Alternatively, the housing may be mounted directly on the motor vehicle&#39;s alternator unit. 
     For facilitating the required encapsulation process, the housing includes a laterally projecting lip for overhanging an edge of an adjacent housing when both are stacked together in a vertical side-by-side relation. The housing units are maintained in this relation by tubular rods or other fastening means passing through apertures extending therethrough and which subsequently serve as the holes necessary for mounting the individual finished units. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof, may be better understood by reference to the accompanying drawings, in which: 
     FIG. 1 is a front elevational view of a protective housing constructed in accordance with the present invention; 
     FIG. 2 is a cross-sectional view of the housing of FIG. 1 taken generally along lines 2--2; 
     FIG. 3 is a view in perspective of an associated circuit board forming an electronic voltage regulator and which is intended to be encapsulated in the housing of FIG. 1; 
     FIG. 4 is a view in perspective of the finished and encapsulated voltage regulator unit; and 
     FIG. 5 is a view in perspective of a plurality of such housing units of FIG. 1 shown in a vertically stacked, side-by-side relation for encapsulation in multiple-unit assembly. 
    
    
     BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring now to the drawings, the finished voltage regulator unit 10 is shown in FIG. 4, which regulator includes a protective housing 12. The housing 12, in one aspect in accordance with the present invention, is shown in vertical plan view in FIG. 1. As seen in FIGS. 2, 4 and 5, the housing 12 is in the form of an upright, narrow-based enclosure defined by upstanding walls 12a, 12b, 12c and 12d, in conjunction with the bottom wall or base 12e. Support members 13a, 13b are formed on the bottom of the housing. Front and back walls 12a and 12b have a substantially wider dimension than the respective side walls 12c and 12d, say, for example, by a ratio of some 4:1. However, it is to be understood that this is no way critical to the present invention, and the dimensions of the housing 12 will be, and indeed are expected to be, tailored to best accommodate the interior-placed circuit board arrangement to be discussed subsequently. 
     In any event, housing 12 further includes a pair of apertures 14 and 16 intended for mounting the overall control device, in this case the voltage regulator 10, under the hood, or elsewhere, in its intended application environment. Apertures 14 and 16 serve a further purpose which likewise will be covered in more detail herein below. However, it may be noted that apertures 14 and 16 extend entirely through housing 12 on respective sides immediately above the base portion 12e. As best seen in FIG. 2, apertures 14 and 16 are closed off from the interior of housing 12. In addition, while aperture 14 is essentially circular in cross sectional area, aperture 16 is somewhat elongated, as will be appreciated upon reference to FIG. 1. With this particular hole configuration, the control unit 10, when fully assembled, may be mounted directly on the alternator assembly (not shown) of the associated vehicle or, alternatively, on an appropriate location on the fire wall or interior wall of the fender. 
     Housing 12 is constructed to accommodate an associated circuit board, such as that identified at 20, comprising a control device of some sort or another, such as . .a.!. .Iadd.an .Iaddend.electronic voltage regulator. Circuit board 20 includes substrate element 22 and heat sink 24. Heat sink 24 is formed as a flat board having a front and rear major surface area. The regulator preferably is designed using thick film techniques. This permits a substrate element or base 22 to be utilized on which various of the circuit paths, as well as the necessary resistance elements, may be formed directly therein. The associated discrete transistor devices and capacitor elements may then be mounted physically thereon and suitably interconnected, such as by solder reflow techniques or the like. The entire substrate assembly may then be cemented.Iadd., .Iaddend.taped or otherwise attached to the front major surface of a metallic heat sink 24 of a suitable material, such as aluminum, for optimum heat dissipation capabilities. Additional circuit components may be separately attached or cemented to heat sink 24 as well, for example, the power switching transistor 26. The necessary external control leads 28 are then attached directly to the substrate element 22 at appropriately terminal points. 
     It is of course to be understood that the actual circuit design of the voltage regulator device is in no way critical nor effective as any limitation on the present invention. The operation of a voltage regulator of this or any other conventional type is readily understood by those skilled in the art such that further detailed description is deemed unnecessary. 
     As will be appreciated upon reference to FIG. 2, a track or guide rail 18 extends downwardly along the interior of each of the side walls 12c and 12d. Guide rails 18 are shaped to define a flared or tapered opening, wider at the top than at the bottom, such that the circuit board assembly 20 may be easily inserted from a vertical direction into housing 12 and permitted upon release to be guided to its proper position by the pull of gravity. The intended position contemplates the heat sink 24 lying immediately adjacent to and in substantial contact with the upstanding wall 12b, as best seen in FIG. 5. In this referenced position, maximum heat transfer will be permitted between the heat sink 24 and the wall 12b of housing 12 and thus out to the ambient. It also prevents the isolation of the heat sink and circuit component parts by the subsequently added encapsulation material which may otherwise get between the heat sink and wall 12b. 
     With the circuit board assembly 20 properly seated and positioned within the housing 12, encapsulating material 30 may then be poured into and thereby fill the remainder of the interior space. The material 30 is then allowed to set or harden. The finished or assembled unit is shown in FIG. 4. The result is a hermetically sealed voltage regulator unit 10 with only the control leads 28 protruding therefrom, as indicated, for subsequent interconnection at appropriate terminal or reference points within the alternator and ignition systems (not shown). 
     The housing may be fabricated from any suitable material. In its preferred form, however it is compression molded from a non-metallic, but permanently stabilized plastic compound. By permanently stabilized, it is meant that once formed by the thermosetting material, it remains substantially in that form notwithstanding that the housing may be subjected to elevated ambient temperatures during subsequent operation. One such compound found to provide satisfactory operational characteristics is an alkyd material. Presently, it is marketed by the Cyanamid Company under the trade designation Alkyd 3001. However, it is to be understood that other thermosetting materials are available and which provide satisfactory operation and, in any event, the present invention is in no way limited to any particular brand or type of fabrication material nor to the way it is formed or processed. 
     METHOD OF ENCAPSULATION 
     A significant design feature of the housing 12 is its adaptability to multi-unit assembly, including the desired encapsulation process therefor. As indicated in FIG. 5, a plurality of housings 12 may be arranged in an upright, side-by-side relation. A lip or ledge 12f extends laterally and outwardly from the top of wall 12a and overhangs a top edge portion 12g of wall 12b of the next adjacent housing 12. A shallow channel or trough 12h is located centrally in the top of ledge 12f, as shown in the drawings. 
     As seen in FIG. 2 the underside or bottom edge 12k of the lip 12f lies in a horizontal plane which includes the top edge 12g of the rear wall 12b. Thus, when the housings are ganged or stacked in vertical side-by-side relation as shown in FIG. 5, the bottom edge 12k of the lip 12f overlies the top edge 12g of the rear wall 12b. The portion .Iadd.12i .Iaddend.of the side wall . .12i.!. which extends to the top edge 12j of the ledge is a smooth extension of the channel . .12e.!. .Iadd.formed between the guide rails 18 and back wall 12b .Iaddend.to assist in inserting the board 20 into the guide rails and starting to move it rearwardly toward the rear wall 12b of the housing. 
     The plurality of housings 12 are maintained in the afore-described side-by-side, vertically stacked, position by a pair of rod-like members or shafts 36, extending through apertures 14 and 16. In this referenced position, the circuit board assemblies 20 may be inserted into an associated housing 12 from essentially the vertical direction. As previously described, the action of gravity in conjunction with the referenced internal guide rails 18 at respective sides thereof is then effective to correctly position and maintain the circuit board assembly 20 within the housing 12. 
     With the completion of the insertion of circuit board assemblies 20, the interior of housings 12 may be suitably encapsulated. In the preferred form, the encapsulation will be accomplished by an automated process. However, even where a hand operation is utilized, the encapsulation itself may be effected on a multi-unit basis. 
     In operation, the encapsulating material may be dispensed into the vertically stacked housings from a stationary vessel (not shown) as the housings 12 themselves are transported or moved along a predetermined path as a group or assemblage. Troughs 12h are effective to maintain the liquid encapsulation material 30 within a prescribed area as defined by such troughs. The overlapping of the housings, i.e., ledge 12f positioned on top portion 12g of the next adjacent housing, serves to prevent the encapsulating material from spilling between housings. As a consequence, the pouring of the encapsulating material may be effected on a continuous basis, rather than a start and stop action for each individual housing. This is a particularly attractive feature, and especially with regard to adapting to a suitable automated process. 
     Alternatively, it may be preferred to first partially fill the interior of housing 12 with sand or like material, and then fill the remaining space with the usual encapsulation material. The latter permeates the sand or filled material before hardening to its final state. This procedure is attractive because the sand is far less in cost than any encapsulation material which can be used. Further, the sand enhances the heat dissipation capabilities of the assembly as a whole. 
     While certain specific embodiments have been disclosed and described herein, it is.Iadd., .Iaddend.of course.Iadd., .Iaddend.to be understood that other and further modifications and alternative constructions or procedures may be effected without departing from the true scope and spirit of the present invention. For example, it may be preferred to maintain the assemblage of housings 12 . .and.!. .Iadd.as .Iaddend.depicted in FIG. 5 in a stationary position while moving the vessel from which the encapsulation material is poured along a predetermined path. This.Iadd., .Iaddend.of course.Iadd., .Iaddend.would be the method employed when utilizing a hand operation. In any event, the appended claims are intended to cover all such modifications and alternative constructions that may fall within the true scope and spirit of the present invention.