MODULAR HOUSING ASSEMBLY FOR TWO IMCOMPATIBLE CIRCUITS

Abstract: A modular housing assembly is provided for two incompatible circuits, for example an RF circuit and a digital circuit, mounted on the same printed circuit board. The housing assembly has a base member and a cover member which are meshed to form two double walled compartments separated by a double conducting wall. The circuit board has at least one bridge physically and electrically connecting the two circuits on the board which bridges pass through corresponding channels in the separating wall and each contain a matrix of plated through holes which operate to extend the wall through the bridge. Interconnecting wiring is woven through the holes to pass desired signals. Filters are provided between the interconnecting wiring and each circuit to eliminate conductive interference. Conductive gaskets are provided at all junctions of the separating wall with a housing member or with a circuit board to further reduce radiation leakage between the circuits.

Description: The invention relates to a modular housing assembly for two incompatible circuits according to the generic portion of Claim 1. There are many applications in commercial, medical, military, and other fields where two electrically incompatible circuits, for example an RF circuit and a digital circuit, are required in the same device. In order to minimize manufacturing costs and to reduce the size, weight and complexity of such devices, it is desirable that the devices be formed on a single printed circuit board mounted in a single housing. However, conductive and radiated noise between the circuits frequently makes it impossible to put the two incompatible circuits on the same board. A modular housing assembly for two incompatible circuits of the type mentioned above is disclosed in WO 86/ 01 969. This prior art housing assembly comprises a housing having walls of an electrically conductive material and together defining an inner space. Partition walls extend from one of the walls of the housing into the inner space of the housing dividing the inner space into different compartments. A circuit board to be mounted within the housing is provided with apertures through which the partition wall extend which shield the individual compartments and the electronic circuits contained within the individual compartments from each other. GB 2 101 811 A describes a screening arrangement for preventing RF interference from and between a number of individual sub-circuits and which has the form of a unitary wall structure made up of integral electrically conductive walls defining a plurality of compartments each open at both ends. A printed circuit board has a pattern of conductors formed on its upper and lower surface. These conductors are electrically connected by means of plated-through holes and are matching the pattern of and being in contact with the walls of the structure and the pattern of ridges of a base, respectively. An electromagnetic shielding means for a printed circuit board is disclosed in DE 35 20 531 A 1. This shielding means comprises two metallized shell like covers sandwiching the circuit board. The shell like covers are formed with partition walls to provide compartments in accordance with the requirements of the circuits. The edges of the shell like covers are in contact with conductors printed on both sides of the circuit board which conductors are electrically connected with each other by means of through holes. A shielding device for shielding a double-sided printed circuit board used in a circuit for processing high-frequency signals, such as a TV tuner circuit, is disclosed in GB 2 200 253 A. A first conductor foil for grounding is provided on one surface of a substrate, and a second conductor foil for grounding is provided on the other surface of the substrate. The two conductor foils are connected together via a throgh-hole conductor. The through-holes may be offset relative to each other for enhancing the mechanical strength of the conductor. A shield plate is placed on the conductor foil of one surface to thereby solder the two surfaces together. The invention is based on the object of providing a housing assembly as set out in the generic portion of claim 1 which permits incompatible circuits to be mounted on the same printed circuit board and packaged in a commen housing without electrical interference between the individual circuits. This object is attained by a modular housing assembly in accordance with claim 1. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. In The Drawings : Fig. 1 is a perspective view of an assembled housing assembly in accordance with a preferred embodiment of the invention. Fig. 2 is a perspective view of the housing assembly shown in Fig. 1 with the cover member removed and turned over. Fig. 3 is a sectional view through the separating wall in an assembled housing in the area of a bridge. Fig. 4 is a sectional view through the separating wall in an assembled housing in a nonbridge area thereof. Fig. 5 is a top cutaway view, partially in schematic, of the circuit board in a bridge area. Detailed Description: Referring to the figures, the housing assembly 10 of this invention is formed of a base housing member 12 and a cover housing member 14. Base member 12 has a pair of projecting flanges 16 with screw holes 18 formed therein which may be utilized for securing the housing to a rack, other components, or the like. Referring more particularly to Fig. 2, it is seen that base member 12 and cover member 14 are parts which are machined, cast or otherwise formed, from a conductive metal such as aluminum. Base member 12 has a base or bottom 20 with an upstanding rear wall 22, side walls 24 and 26, and a forward wall 28. The walls are connected at the corners to form a continuous wall except where forward wall 28 is broken, the broken area being filled by a horizontal projection 30 and vertical wall projections 32. A connector 34 at the end of circuit board 36, which connector is shown partially broken in Fig. 2, fits in the compartment formed by projection 30 and walls 32. The final element of housing 12 is separator wall 38 which, as may be best seen in Figs. 3 and 4, has a boss portion 40 below the circuit board and an upstanding portion 42 having a pair of channels 44 formed therein. The center section of upstanding wall 42 has a pair of enlarged support and guide studs 46 formed behind it. Circuit board 36 is divided into two portions which, for example, will be assumed to be an RF portion 48, having for example an RF oscillator 50 mounted therein, and a digital portion 52, having for example a digital clock chip 54 mounted therein. While only a few representative components are shown on each portion of circuit board 36 in Fig. 2, it is to be understood that each of these circuits would contain a variety of standard components and interconnecting wiring. Circuit board 36 has a cutout 56 formed therein and a pair of side notches 58 formed therein in the space between circuits 48 and 52. The cutout 56 and notches 58 define a pair of bridges 60 which interconnect the circuits 48 and 52 of the circuit board. As may be best seen in Fig. 5, a matrix of plated through holes 62 is formed in each bridge area, the matrix covering substantially the entire bridge area. The holes are in rows and column with alternate rows being preferably offset as shown in Fig. 5 so that there is no clear path between circuits 48 and 52 through the matrix of holes. Conductive wiring 64, a single wire of which is shown in Fig. 5, is woven between the holes 62 to interconnect the two circuits. In order to eliminate conductive noise or interference between the circuits, a filter consisting of an inductor L and a capacitor C is provided in each of the circuits 48 and 52 between interconnecting leads 64 and the remainder of the circuit. The values of the inductors and capacitors will vary with applications and may be determined by one skilled in the art. In addition to the plated through holes 62 in bridge 60, there are also ground plane areas 66 around the entire periphery of circuit 48 which have plated through holes 68 formed therein, and there are ground plane areas 70 along the sides of circuit 52 having plated through holes 72 formed therein. Each plated through hole 62, 68 and 72 forms a continuous ground plane through the circuit board, interconnecting ground planes on the two sides thereof. The arrays of closely spaced plated through holes essentially serve as extensions of the walls to prevent leakage of radiated signal through the circuit board dieletric, either between the circuits or from the assembly. Cover member 14 has a top 76 with a downwardly projecting rear wall 78, downwardly projecting side walls 80 and 82, and a compartment separating wall 84. The walls 78, 80 and 82 are connected to form a continuous wall and, in conjunction with bottom wall 20 and top wall 76, define an RF circuit compartment. Spaced slightly from the ends of side walls 80 and 82 by spaces 87 and 89 respectively are side walls 86 and 88 respectively which terminate in a front wall 90. Front wall 90 has an opening with a forward projecting flange 92 which coacts with the projection 30 and walls 32 to complete the compartment for connector 34. A conductive gasket 94 is fitted in a corresponding groove formed in the inside of top 76 and surrounding walls 78, 80, 82 and 84. A conductive gasket 96 is also fitted in a corresponding groove formed in the end of wall 84. Finally, a conductive gasket 98 is fitted in a corresponding groove in the top of boss 40, the gaskets 96 and 98 being positioned, as shown in Figs. 3 and 4, such that when the members 12 and 14 are mated, the gaskets are adjacent each other on opposite sides of circuit board 36. The assembly 10 is put together by initially mounting circuit board 36 in base member 12 as shown in Fig. 2 with the center portion of wall 42 and studs 46 passing through mating opening 56 in the circuit board and side portions of wall 42 passing through mating notches 58 in the circuit board. With the board in this position, the ground plane portion 66 of circuit 48 on the edge of the circuit board adjacent wall 38 is positioned over conductive gasket 98 in boss 40. Plated through holes 68 in this area are also over the conductive gasket. The assembly is completed by mating cover member 14 to base member 12 with walls 78, 80, 82 and 84 being inside walls 22, 24, 26 and 38 respectively to form a double walled RF compartment. The side wall segments of wall 42 fit in the grooves 87 and 89, walls 86, 88 and 90 being inside walls 24, 26 and 28 respectively to form a double walled compartment for digital circuit 52. As previously indicated, the ground portion 66 of circuit 48 adjacent wall 38 is pinched between conducting gaskets 96 and 98, when the housing is fully assembled, the wall 38 thus being continued through the circuit board by the action of the conductive gaskets 96 and 98 and plated through holes 68. Leakage of RF energy around the junction between cover member 14 and base member 12 is inhibited by conductive gasket 94 which is in all areas of this junction. As may be best seen in Figs. 3 and 4, the gasket 94 also functions to inhibit RF or other radiated leakage between the RF and digital compartments. Once assembled, the vase and cover member may be held together by screws (not shown) which pass through screw holes 100 in cover member 14 and screw holes 102 in base member 12, or by other suitable means. A modular housing assembly is thus provided which permits two incompatible circuits, such as an RF circuit and a digital circuit to be mounted on the same circuit board without resulting in unacceptable levels of radiated or conductive interference between the two circuits, while permitting desired signals to be transmitted between the two circuits. The circuit design is capable of achieving isolation between the two circuits of 60 db.

Claims: A modular housing assembly for two incompatible circuits (48,52) mounted on the same printed circuit board (36) comprising: first and second compartments seperated by a conductive wall (84), at least one channel (44) through said wall (38), means for mounting said circuit board (36) with one (48) of the circuits in said first compartment and the other circuit (52) in said second compartment, said board including a bridge (60) which physically and electrically connects the circuits (48,52), said bridge (60) passing through a corresponding channel (44), characterized in that said compartments are surrounded on all sides (22,24,26,28,78,80,82,84) by conductive material, a plurality of rows and columns of plated through holes (62) are formed in said bridge (60) which holes (62) connect ground planes, electrical wiring (64) interconnecting said circuits (48,52) is passing through said bridge (60) and is woven to pass between said holes (60), and conductive gasket means (96,98) are provided between each side of said board (36) and said wall (84) at least in the area of said bridge (60). The assembly as claimed in claim 1, characterized in that filter means (L₁, C₁, L₂, C₂) are included in each of said circuits (48, 52) between said interconnecting electrical wiring (64) and the remainder of the circuit to block conductive interference between the circuits. The assembly as claimed in claim 2, characterized in that said filter means (L₁, C₁, L₂, C₂) are LC filters. The assembly as claimed in claim 1, characterized in that said wall is a double wall (84, 42). The assembly as claimed in claim 4, characterized in that one wall (38) of said double wall has at least one channel (44) formed therethrough and the other wall is in two sections (84, 40), one section above and one section below said board (36), said conductive gasket means (96, 98) being on the facing ends of said sections. The assembly as claimed in claim 1, characterized in that said assembly includes a base housing member (12) having a conductive base, four conductive side walls (22, 24, 26, 28) and said separating conductive wall (38) between two (24, 26) of said side walls at a point intermediate the ends of such sides, and a conductive cover housing member (14) sized to mesh with said housing member (12). The assembly as claimed in claim 6, characterized in that said cover housing member (14) has a conductive top (76), four conductive walls (78, 80, 82, 84), which are sized and positioned to mesh with the side walls of said base housing member (12) to form a double walled housing assembly, and a separating conductive wall (38, 84) between two of the side walls (24, 26 and 80, 82) at a point intermediate the ends of such side walls, that said separating walls (38, 84) are adjacent when said housing members (12, 14) are meshed to form a double walled separator for said compartments. The assembly as claimed in claim 6, characterized in that a conductive gasket (94, 96, 98) is provided at a junction between said housing members (12, 14) in at least the portion thereof surrounding one of said compartments. The assembly as claimed in claim 1, characterized in that there is a matrix of said plated through holes (62) which covers substantially the entire area of said bridge (60). The assembly as claimed in claim 9, characterized in that there are at least three rows of said plated through holes (62) with alternative rows being offset so that there is no straight path between the circuits through the matrix of bridge holes. The assembly as claimed in claim 1, characterized in that said plated through holes (68) are formed around the periphery of at least a portion of at least one of said circuits (48, 52). The assembly as claimed in claim 11, characterized in that said plated through holes (68) are formed about at least a portion of the periphery of both circuits (48, 52). The assembly as claimed in claim 1, characterized in that one of said circuits is an RF circuit (48). The assembly as claimed in claim 13, characterised in that the other circuit is a digital circuit (52).

Inventors: COOK, GORDON V., KOTFILA, MARK, RISLEY, CURTIS A., STANLEY, DICK, TELFORD, LARRY E.
Applicants: HEWLETT-PACKARD COMPANY
Application year: 1990
Main classification: H05K9
IPC codes: B62K21, B62K15, H05K9, H05K7, H05K5