GB2230147A - Housing for electronic modules - Google Patents

Abstract

A unitary housing assembly for a line replaceable unit, the assembly comprising; a pair of spaced sidewall plate members (2), each having front and rear edges and top and bottom edges; first, second and third cross wall members (4, 6, 8) spacing said side plate members apart with the first (8) and second (4) crosswall members being disposed in the region of the front and rear edges respectively of the side plate members and the third (6) crosswall member being located in a central region of the side plate members, the cross wall members being secured to the sidewall plate members to provide a rigid skeletal structure for the assembly; a front panel member (22) disposed near the front edges of the sidewall plate numbers and carrying external electrical connections (24) for the LRU; and a mother board electrical connection assembly disposed near the bottom edges of the sidewall plate members for receiving electrical connections of electronics modules fitted within the skeletal structure between the side plate members and the crossmembers. <IMAGE>

Description

ELECTRONIC MODULES This invention relates to unitary housing assemblies for electronic circuitry, particularly though not exclusively intended for avionics applications.

A known type of unitary housing for avionics applications, termed a line replaceable unit (LRU) comprises an outer box structure housing electronics modules, such modules being formed in the manner of circuit cards and plugging into suitable mechanical and electrical connections within the box. The box normally incorporates cooling facilities and carries external connectors. Because of their application in avionics. such LRU must be dimensionally small, light weight and rugged. It will be appreciated that in modern aircraft there is a very great amount of electrons control circuitry, and this circuitry is normally contained in banks of LRU at suitable locations within the aircraft. Since the LRU may well be supplied by a variety of manufacturers for a single aircraft, the problem arises of different sizes and shapes of LRU from different manufacturers.

Accordingly there has been defined standards, the most common of which are known as ARINC specifications 600- and 404A (Aeronautical Radio Incorporated), to which the external size parameters of LRU's nowadays normally conform. Thus referring to Figure 10, which shows the standard dimensions of an LRU, the standard dictates a fixed height (H), a fixed length (L) but a variable width (W) which can be adjusted in steps, the steps being defined in units of ATR (air transport racking) size as one quarter, one half, one, etc, etc. Thus given a fixed rack for housing the modules a given number of modules can be fitted within the rack, regardless of manufacturer.

Within the standard, a variety of sizes may exist and the standard makes no reference to the internal construction of the LRU.

Hence a manufacturer may wish to produce a variety of LRU for different applications within the overall constraint of the standard.

In order to produce savings in manufacturing costs and to cut down on the number of different subassemblies required, the applicant has realised it would be desirable to extend the concept of modularity into the internal construction of the LRU.

The present invention therefore has a dual objective: firstly to provide a modular construction for the LRU housing assembly which can be adapted to a variety of configurations; and secondly to provide an electronics module housing electronic circuits, a plurality of which will fit replaceably within the LRU in a variety of configurations.

In a first aspect, the invention provides a unitary housing assembly for a line replaceable unit, the assembly comprising; a pair of spaced sidewall plate members, each having front and rear edges and top and bottom edges; first, second and third cross wall members spacing said side plate members apart with the first and second crosswall members being disposed in the region of the front and rear edges respectively of the side plate members and the third crosswall member being located in a central region of the side plate members, the cross wall members being secured to the sidewall plate members to provide a rigid skeletal structure for the assembly; a front panel member disposed near the front edges of the sidewall plate numbers and carrying external electrical connections for the LRU; and a mother board electrical connection assembly disposed near the bottom edges of the sidewall plate member for receiving electrical connections of electronics modules fitted within the skeletal structure between the side plate members and the cross members.

There is thus provided in accordance with the invention a structure for a line replaceable unit which may be adapted to a variety of external configurations and can fit within it a variety of electronics modules.

As preferred, a rear panel member is disposed near the rear edges of the sidewall plate members and carries within it cooling fans for cooling the electronics modules. However in some configurations the rear panel may be a blank unit or alternatively contain electronics circuitry or a battery pack, for example.

As preferred, the side plate members are formed as "cold walls" which normally comprise two spaced apart metallic sheets with a corrugated sheet therebetween securing the two external sheets together and defining longitudinal grooves for air flow from the rear cooling fans to the front of the LRU. However in some configurations the side plate members may not have this cold wall facility, and a honeycomb structure may be provided between the two external sheets.

As preferred, the side plate members are secured to the cross wall members by simple screw fittings for locating and securing the walls together and in addition are bonded by an adhesive glue, preferably having a small degree of resilience for vibration damping, or alternatively a solder joint. Although the side plate members are of a fixed width and depth, the cross wall members are of a variable size to conform to the various ATR sizes and to house different configurations of electronics modules.

Normally the cross wall members will define slots for receiving electronics modules therewithin in the manner of circuit cards. As preferred, the crosswall members carry a series of "wedgelock" clamps which allow modules to be slotted into grooves between the cross piece members and once slotted in are wedged in position by internal mechanisms within the wedgelock clamps. In some configurations as will become apparent below the electronic modules may be mounted parallel to the cross piece members rather than between the cross piece members and in this case slot means preferably wedgelock clamps may be mounted along the inner surfaces of the side plate members. In this case the cross piece members may be simple wall members.

As preferred, sidewall housing units may be mounted externally of the sidewall members in order to house electrical circuitry which cannot simply be accommodated in electronic modules within the skeletal structure. For example the sidewall housing units may include power amplifiers, antenna interfaces which cannot be split up into one or more circuit cards, a power supply unit, a stand by battery pack and a cryptographic unit which for security reasons is normally formed as a large assembly and cannot easily be accommodated into an electronic module. The overall width dimension of the LRU is determined by the width dimensions of the skeletal unit and the side piece housing unit and the overall dimension will conform to the ATR scale.

Turning now to the electronics modules, it is desirable that the electronic circuitry to be fitted within the LRU is in the form of electronics modules so that they can easily be inserted and removed in the case for example where a module is faulty or alternatively where a different set of electronics circuits are to be used within the LRU.

In a further aspect the present invention provides an electronics module for use in the unitary housing assembly as set forth above in accordance with the first aspect of the invention, the electronics module comprising:a generally rectangular member having width, height and depth dimensions with upper and lower faces bounding the height dimension, front and rear edges bounding the depth dimension, and side edges bounding the width dimension with ribs extending therefrom in order to fit within slot assembly means within the LRU for mechanically locating the electronics module; the electronics module having on its lower edge electrical connection means for making electrical connection to a mother board of the LRU; The electronics module either being unscreened and containing digital circuitry or having screening plate members on the said front and rear faces and containing RF circuitry or digital circuitry; and the width and height dimensions being selected such that in relation to a given skeletal structure of the LRU, the electronics module may either be fitted within the skeletal structure in a plane perpendicular to the sidewall plate members or may be fitted together with a similar electronics module side by side in a plane parallel to the sidewall plate members between first, second and third crosswall members.

Thus there is provided in accordance with the invention in this further aspect an electronic module which may be fitted within the LRU in a variety of configurations and may contain a variety of electrical circuits. The electronic module will be hereinafter termed versatile electronic module (VEM).

The height dimension of the VEM is determined by the height dimension of the LRU and the requirement for electrical connectors on the rear face of the VEM to make connection with a mother board within the LRU.

The width dimension of the VEM is fixed being determined primarily by the distance between the first and third or second and third crosswall members. In a common configuration the crosswall members will have slot receiving "wedgelock" clamping members and the edge means of the VEM will fit within the slots. However in other configurations the VEM may be disposed parallel to the crosswall members or perpendicular to the side plate members and be mounted in slot wedging members disposed along the side piece members.

The depth dimension of the VEM is variable being determined primarily by the type of electronic circuitry housed within it.

For an unscreened digital module, the electronics circuitry will commonly be a- rectangular array of square leadless chips (normally 68 pin). These may be arranged in a say 3 by 4 or 3 by 3 configuration and the dimensions of the VEM will be such that an optimum number of chips may be accommodated in a rectangular array without leaving a large amount of unused space and without packing the chips unreasonably close together. Hence the VEM dimensions are generally similar to the common "Euro Card" dimensions but being modified by the need to provide electrical connections at the base. The leadless chip carriers are normally bonded onto a ceramic substrate and ceramic substrates may be positioned either side of a central metallic sheet member, preferably an aluminium plate.The ceramic substrates may be bonded to the aluminium plate by a thermally conductive adhesive bond which gives good vibration damping and is a visco elastic material. Where a high degree of attenuation of mechanical vibration is required, the central sheet member may be formed with two sheets of metal connected face to face by an elastomeric bonding material which gives high attenuation of mechanical vibration.

Sidewall members may be provided around the edges of the sheet member of the VEM for protection and where screening is required, metallic sheet members may be positioned on top of the sidewall members so as to form an enclosed box assembly electrically screened from the exterior. Screened VEM may house either RF circuitry or digital circuitry.

The depth of the modules may be varied to suit the components within the module. For example for RF modules a precision quartz crystal may be required which is a relatively bulky member and requires considerable depth. However normally where the depth dimension of the electrical circuits is not considerable, the depth of the VEM will be determined by the electrical connectors at the base. As regards RF circuitry the circuitry will normally be formed by hybrid circuits formed on ceramic chips which are bonded to the aluminium extrusion.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a first line replaceable unit (LRU) according to the invention having an external width dimension of three quarters ATR; Figure 2 is a perspective view of the LRU of figure 1 with a top cover removed and showing adjacent to the LRU a versatile electronics module (VEM) according to the invention for positioning in the LRU; Figure 3 is a partial perspective view of the LRU of figure 1 showing the underside of the LRU with the botton cover and mother board removed; Figure 4 is a diagramatic view of the LRU figure 1 showing internal construction of the LRU; Figure 5 is a perspective view of a sidewall of the LRU formed as a "cold wall" heat exchanger;; Figure 6 is a perspective rear view of the LRU of Figure 1 showing cooling fans incorporated in a rear module of the LRU; Figure 7 is a diagramatic view of an alternative version of the LRU; Figure 8 is a perspective partially broken away view of the VEM of Figure 2, the VEM housing RF circuits; and, Figure 8 is a perspective view of a second form of the VEM according to the invention carrying digital circuitry in the form of leadless chips; and, Figures 9a and 9b are a diagram and table respectively indicating the basic dimensions of standard ATR cases conforming to ARINC standard 404A.

Referring now to the drawings and to Figures 1 to 4 in particular, there is shown an LRU conforming to the ARINC standard and having a width dimension of 3/4 ATR. The module includes two sidewall plate members 2 spaced apart by first, second and third crosswall aluminium alloy members 4, 6, 8. Crosswall members 4, 6, 8, are connected to sidewall plate members 2 by screw connections and by a thermally conductive adhesive glue in order to form a strong bond with the crosswall members. The sidewall plate member 2 is shown in more detail in Figure 5 as comprising two metallic sheet pieces 12 formed as aluminium alloy sheets having an intervening corrugated aluminium alloy member 14 secured to each sheet 12 and spacing the sheets apart.The corrugations 14 form longitudinal channels for airflow therethrough so that the sidewall plate member forms a "cold wall" heat exchanger for conducting heat away from the central part of the LRU. Each cross piece member has disposed thereon "wedgelock" slot members 16 having longitudinal slots 18 and wedge members 20 extending parallel to the slot. After insertion of edge members of an electronics module into the slots 18, as will be described below, wedge member 20 is forced into engagement with the edge member when a clamping screw is tightened to a pre-determined tightening torque using a torque limiting screwdriver. Since these clamping members are of known construction and do not form part of the inventive concept, they will not be described in greater detail.

The combination of the sidewall plate members 2 and crosswall members 4, 6, 8 form a skeletal structure for the LRU and define the basic structural rigidity of the LRU together with vibration damping means and defines the area for insertion of versatile electronics modules.

-A front panel member 22 is connected at the front face of the LRU between sidewall plate members 2 by screw connections adjacent to crosswall member 4 and carries various electrical connectors indicated generally at 24 for making external connection to the LRU. Member 22 also carries a handle 26. A rear panel member 28 is mounted at the rear of the LRU adjacent to crosswall member 8 and is of generally rectangular construction, housing two rotary fans 30 as indicated in Figure 6. These fan devices blow cooling air out through the longitudinal grooves in sidewall members 2. Module 30 extends across the entire width of the LRU and is secured by screw members not only to crosswall member 8 but also by screw members 32 as shown in Figure 4 to two sidewall panel members 34, 36 disposed on opposite sides of the LRU adjacent to sidewall plate members 2 and secured thereto by suitable screw connections 36. These sidewall members carry electrical circuitry which cannot conveniently be located within electronics modules disposed within the central skeletal structure, such as for example power amplifiers, cryptographic units, power supply units and battery packs. The sidewall members have external electrical connectors generally indicated as at 38.

Referring now to Figure 7 this shows a further LRU having a width dimension of one half ATR and wearing similar parts to those of Figures 1 and 2 as indicated by the same reference numeral. A principal difference is that no sidewall units are provided and sidewall plate members 2 form the outer boundary for the LRU.

Another principal difference is that the VEM 50 mounted within the LRU are mounted perpendicular to the sidewall plate members and parallel to the crosswall members 4, 6, 8. In this embodiment the crosswall members are formed as simple plane members, and the wedgelock receiving slot members for the VEM are mounted along the sides of the sidewall plate members as indicated at 52. In this embodiment, it is not possible to force air between the VEM since they are mounted across the LRU and although it is possible to force air through the sidewall plate members, the embodiment of Figure 7 is generally useful for housing electronic circuitry which does not require forced cooling. Accordingly the rear module 28 may house for example a power supply and battery pack unit.

Referring now to Figure 8, this shows a versatile electronic module (VEM) according to the invention constructed to house RF circuitry which requires shielding. The VEM comprises a main structural member 60 formed as an aluminium extrusion and having a central plate portion 62 together with a central longitudinal rib 64 and wall members 64, 66 extending along left and right edges of the VEM on both sides of the plate member 62. Sidewalls, 64, 66 define the width dimension of the VEM, which in this embodiment is chosen to be 23 millimeters. The width is naturally determined by the components to be mounted within the VEM and may be of any width.

As shown in Figure 8, a crystal oscillator assembly 70 is provided which requires a considerable width of VEM and is mounted in a slot 72 within plate portion 62. However, as shown in Figure 8 and in most cases where the electronic circuitry within the VEM does not occupy considerable width, the main constraint on the width dimension is caused by the electrical connectors indicated generally at 76 at the lower face of the module. As shown these connectors for an RF module are of two types namely D type signal connectors 78 and slide type coaxial connectors 80. These connectors naturally also have a certain depth and the total depth of the VEM is chosen to be a hundred and fifty two millimeters to allow for the depth of the electrical connectors.The width of the VEM is chosen to be a hundred millimetres and thus the overall dimensions of the VEM are somewhat similar to a Eurocard assembly (160mm x 100mm). The left and right sidewall members 66 carry upstanding edge members 80 which engage within the slots of the wedgelock receiving members within the LRU. The circuitry within the module is normally formed as hybrid circuits 82 printed on a ceramic substrate 84 to which is subsequently secured to the aluminium plate member 62. Aluminium screening covers 84 are provided for screening circuitry from the exterior.

Referring now to Figure 9 this shows another VEM which is adapted for digital circuitry. The width and height dimensions of the VEM Figure 7 are the same as that of Figure 8 but the depth is slightly different being 15.5 millimetres and being determined by two off 65 way connectors 90 mounted at the base of the VEM. The main structural member of the VEM comprises of a metallic plate 92 constructed of a material which is designed severely to attenuate mechanical vibration. Thus plate 92 comprises two outer aluminium alloy plates 94 bonded together by an elastomer material 96 which serves to attenuate mechanical vibration. The left and right outer edges 98 form edge pieces for insertion into the wedgelock slot members of the LRU. Mounted upon the major portion of plate 92 is a ceramic substrate 100. A similar substrate is mounted on the other side (not shown) of the plate 92. Each ceramic substrate 100 carries a rectangular array of leadless chip carriers 102 which are connected to the substrate by solderbump -on technology. The chips 102 are arranged in a rectangular array having three columns and four rows, making 12 chips in all. This digital circuitry is shown unscreened since screening is unnecessary. If desired, a cut out portion 104 is provided for interconnection of one ceramic substrate at its end remote from the mother board end to the adjacent ceramic substrate via a flexible interconnect.

Referring to Figure 3 there is shown cut out portions 110 in the edge of sidewall plate member 2 at its bottom edge adjacent with mother board (not shown) which cut out portions 110 house insert members 112 coupled to sidewall 36. These insert portion carry electrical contacts which may be of variable configuration and are indicated as at 114.

Claims (17)

1. A unitary housing assembly for a line replaceable unit, the assembly comprising; a pair of spaced sidewall plate members, each having front and rear edges and top and bottom edges; first, second and third cross wall members spacing said side plate members apart with the first and second crosswall members being disposed in the region of the front and rear edges respectively of the side plate members and the third crosswall member being located in a central region of the side plate members, the cross wall members being secured to the sidewall plate members to provide a rigid skeletal structure for the assembly; a front panel member disposed near the front edges of the sidewall plate numbers and carrying external electrical connections for the LRU;; and a mother board electrical connection assembly disposed near the bottom edges of the sidewall plate member for receiving electrical connections of electronics modules fitted within the skeletal structure between the side plate members and the cross members.

2. A housing assembly as claimed in claim 1 comprising a rear panel member disposed near the rear edges of the sidewall plate members and carrying within it cooling fans for cooling the electronics modules.

3. A housing assembly as claimed in claim 1 or 2, wherein the side plate members are formed as cold walls comprising two spaced apart metallic sheets with a corrugated sheet therebetween securing the two external sheets together and defining longitudinal grooves for air flow.

4. A housing assembly as claimed in claim 1 wherein the side plate members are secured to the crosswall members by screw fittings for locating and securing the walls together and in addition are bonded by an adhesive glue, having a small degree of resilience for vibration damping or alternatively soldered.

5. A housing assembly as claimed in claim 1 wherein the cross wall members define slots for receiving electronics modules therewithin in the manner of circuit cards.

6. A housing assembly as claimed in claim 1, wherein the electronic modules are mounted parallel to the cross piece members and including slot means mounted along the inner surfaces of the side plate members for receiving the modules.

7. A housing assembly as claimed in claim 1, wherein one or more sidewall housing units are mounted externally of the sidewall members in order to house electrical circuitry.

8. Housing assemblies substantially as described with reference to Figures 1 to 7 of the accompanying drawings.

9. An electronics module for use in the unitary housing assembly as claimed in claim 1, the electronics module comprising: a generally rectangular member having width, height and depth dimensions with upper and lower faces, front and rear edges bounding the depth dimension, and side edges bounding the width dimension with ribs extending therealong in order to fit within slot means within the LRU for mechanically locating the electronics module; the electronics module having on its lower edge electrical connection means for making electrical connection to a mother board of the LRU; the electronics module either being unscreened and containing digital circuitry or having screening plate members on the said front and rear faces and containing RF circuitry or digital circuitry.

and the width and height dimensions being selected such that in relation to a given skeletal structure of the LRU, the electronics module may either be fitted within the skeletal structure in a plane perpendicular to the sidewall plate members or may be fitted together with a similar electronics module side by side in a plane parallel to the sidewall plate members between first, second and third crosswall members.

10. A module as claimed in claim 9, comprising an unscreened digital module, the electronics circuitry comprising a rectangular array of rectangular leadless chips.

11. A module as claimed in claim 9 or 10 comprising a plate member forming the main structural member of the module.

12. A module as claimed in claim 11 including ceramic substrates positioned either side of the central plate member for carrying electrical circuits, preferably bonded to the plate member by a thermally conductive adhesive bond which gives good vibration damping and is a visco elastic material.

1 3. A module as claimed in claim 11 wherein the plate member is formed with two sheets of metal connected face to face by an elastomeric bonding material which gives high attenuation of mechanical vibration.

14. A module as claimed in claim 11, including sidewall members provided around the edges of the sheet member of the VEM for protection.

15. A module as claimed in claim 14, including metallic sheet members positioned on top of the sidewall members so as to form an enclosed box assembly electrically screened from the exterior and housing either RF circuitry or digital circuitry.

16. A module as claimed in claim 11, including RF circuitry, the circuitry being formed by hybrid circuits formed on ceramic substrates which are bonded to the plate member.

17. An electronics module substantially as described with reference to Figures 8 or 9 of the accompanying drawings.