FR2494540A1 - PRINTED CIRCUIT PLATE SUPPORT - Google Patents

Abstract

THIS INTEGRATED CIRCUIT SUPPORT INCLUDES A CHASSIS INCLUDING A BACK PLATE 47 CONDUCTING HEAT COMING FROM MATERIAL TO FORM WITH THE CHASSIS A LOW THERMAL IMPEDANCE CIRCUIT ON A LARGE PART OF THE PERIPHERY OF THE CHASSIS, THIS PLATE 47 BEING PRESSURE WITH THE CHASSIS ABOUT IN THE SAME PLAN AS A SURFACE OF THE PERIPHERY OF THE CHASSIS SO AS NOT TO INCREASE THE VOLUME OF THE LATTER WITHOUT ITS PLATE, A MATERIAL 52 ESTABLISHING A THERMAL CONTACT BETWEEN EACH OF THE COMPONENTS 21 OF THE PLATE 18 OF THE PRINTED CIRCUIT AND THE REAR PLATE 47 TO IMPROVE THE EXHAUST OF THE HEAT FROM ITS COMPONENTS TO THE CHASSIS COOLING FIN 49. THIS CONSTRUCTION ALLOWS THE CHASSIS'S HEAT DISSIPATION CAPACITY TO BE RAISED FROM 1 OR 1.5 TO 4.5WATTS.

Description

The present invention relates to plate panel supports or

printed circuit boards, and

  more particularly to a support and a module

  taking said support and panel and adapted to transfer heat from the mounted circuit components

  on the panel to a heat sink.

  Certain components of printed circuit boards, more particularly integrated circuit pads of the type with two rows of pins (DIP), are limited as regards the maximum temperature at

  which they are capable of operating. This temperature

  Operating temperature is determined by the heat dissipated in the integrated circuit element itself, the heat dissipated in other heat-producing elements, including other integrated circuit pads, and the dissipative properties of the heat of the printed circuit board support which is in thermal contact with the integrated circuit chip and with a heat sink. It is generally desirable that the volume occupied by the electrical circuit, including the support, be reduced to a minimum, which results in an increase in the heat given off per unit of volume or area. It is therefore necessary that the printed circuit board support has an appropriate configuration to efficiently evacuate to the heat sink the heat given off by the integrated circuit pads by establishing a low heat path

thermal impedance.

  The characteristics by which the improvement of the heat dissipation provided by the support according to the invention is obtained will be demonstrated by

  a description of the circuit board supports

  prints available so far as well as their

performance characteristics.

  Fig. 1 shows a prior art printed circuit board holder 10 with an exploded view of the printed circuit board 18 and an illustrative example of an integrated circuit 21 with two rows of connection pins which must be soldered to the connection holes 19 of the printed circuit board 18. The support 10 comprises a metal frame 11 having at one end a pin-carrying connector 14 made of plastic. The connector 14 carries conductive pins which are connected respectively to pins (not

  shown) located on the opposite side of connector 14.

  These pins on the opposite side correspond to connection holes 20 of the plate 18. The holes 20 are connected by printed circuit wiring (not shown) to the holes 19 connected to the integrated circuits 21 to two rows of connections or to components of the resistor or capacitor type (norn shown) which can also be mounted on the printed circuit board 18, thereby establishing electrical connections between the pins 18 and the electrical components carried by the printed circuit board. plastic material includes metal shields of pins 141 embedded in its mass. Guide pins 16 are also molded into the ends of the plastic connector body 14. The metal frame 11, the electrically insulating welding mask 17 and the printed circuit board 1-8 are assembled by rivets 22 The frame 11 and the mask 17 have slots 12 and crosspieces 13. The circuit 21 has connection pins 211 which overlap the crosspieces 13 and which protrude through the slots 12 to sink into the holes 19 of the printed circuit board 18. The underside 212 of the circuit 21 is in thermal contact with the cross member 13 of the chassis II by means of a strip 23 conducting heat and insulating electricity. After completing the assembly as described above, the electrical connection of pins 15, 211 to the circuit board is made.

  printed 18 by a wave welding technique.

  A module assembled as shown in Fig. 1 is capable of dissipating a total of 4.5 watts produced by circuit elements, such as component 21 with two rows of connections while limiting the temperature rise of the circuit elements to 600 above the temperature of the heat sink (not shown) which can be a cooling fluid circulating in elastic fingers in contact with the edges 24 of the chassis 11. The heat sink is part of the mechanical and electrical assembly in which the module of FIG. 1 is inserted. Although the heat dissipation properties of the module t are satisfactory, this module is less advantageous from the point of view of production. Due to the design of the module, the assembly of the numerous parts which constitute it requires manual assembly operations and is not capable of automation so that this module is

expensive.

  -As indicated above, the assembly of the module requires that, for soldering, the printed circuit board 18 be masked by an electrical insulator 17 interposed between the plate 18 and the chassis 11. Then, shore the plate 18 on the frame 11 using the rivets 22. Next, place the heat conductive tape 23 and the circuits 21 with two rows of connections in place on the frame 11-, then

  the aforementioned wave welding completes the assembly.

  During the welding operation and when the module is in service, the shields of pins 141 tend to fall from the connector 1'4 In addition, the connector 14 being made of plastic, requires that the pins 16 are introduced using an adhesive and maintained

  in a prescribed position while setting the adhesive.

  These lugs 16 frequently take up play. It can therefore be seen that the module of FIG. 1 has significant deficiencies from the point of view of manufacturing and reliability. For circuit configurations in which the total dissipation of the components mounted on the printed circuit board is I watt or less, sufficient energy dissipation is obtained to limit the temperature rise to 600C by mounting the plate 18 on the support 31 of the open chassis type shown in FIG. 2. The plate 18 is shown equipped with circuits with two rows of connections 21 and the connector 14 put in place in the support 31 is ready to be fixed there by rivets 22. The assembly of the printed circuit plate 18 and the support 31 of FIG. 2 presents various advantages over the module of FIG. 1. The most important advantage is that the printed circuit board 18 can be soldered to its circuits 21 and to its connector 14 by conventional wave welding techniques before the assembly is riveted to the chassis. 31. The assembly process can be largely automated,

  which considerably reduces the price of manufacturing.

  The chassis 31 has a pin shield 311 made from the material and, as a result, the pin shields do not risk falling from the chassis as they do in the configuration of FIG. 1. The pins 16 are also fixed to the metal frame 31 by force fitting so that they are also very securely mounted on the frame 31, compared to the fixatbn by coating in the connector 14 of plastic material.

of Fig. 1.

  Despite the mechanical advantage and the ease of manufacture, the assembly of the chassis 31 and the plate 18 of FIG. 2 is subject to a limitation consisting in that the total admissible power dissipation of the circuits 21 with two rows of pins for the permitted temperature rise of 60 C is limited to 1 watt. Since there are many circuit configurations which exceed this dissipation rate of 1 watt, it was necessary in these conditions to resort to the more expensive assembly configuration of the module shown in FIG. 1. To increase the power dissipation capacity of the assembly composed of the printed circuit board 18 and of the chassis 31, a closure plate 32 was attached to this assembly using the rivets 22. The closure plate 32 was brought into thermal contact with the circuits 21 with two rows of pins mounted on the printed circuit board 18 by means of a heat-conducting substance (not shown) inserted

  between the components 21 and the closure plate 32.

  The heat conducting material was also placed between the covering regions 33 ′, 33 "between the closure plate 32 and the chassis 31. Due to the limitations imposed on the size of the chassis 31 and on the surface occupied by the circuits 21 , the contact surface available between the closing plate 32 and the frame 31 ′ was only along the edges of these elements. Since the width of the regions 33 ′, 33 ″ of the frame 31 is only about 1.25 mm, the total area available for heat transfer from the cover plate 32 to the frame 31 was not large and the total power which could

  be dissipated for a 60 ° C rise in temperature

  erasing using the closing plate 32 was only about 1.5 watts, which is only a slight improvement compared to the power dissipation of 1 watt that was obtained without the

  closure 32 for the same temperature rise.

  An object of the invention is therefore to provide an improved support for a circuit board which has the great energy dissipation capacity of the support of FIG. 1 without presenting the difficulties and costs of

  corresponding manufacturing. Such perfect support-

  born should have the characteristics of economy of manufacture of the support of FIG. 2 without being affected by the limitations of this support which relate to its energy dissipation properties. This object as well as others are achieved by the circuit plate support according to the invention thanks to the fact that the circuit plate support is manufactured in such a way that it comprises a heat conducting plate brought into thermal contact. with circuits with two rows of connections which give off heat and which is made up of an element made in one piece with the circuit plate support, which brings to a maximum value the capacity for transfer of heat between the closing plate and the part

  of the support which is in contact with a heat sink.

  The heat conducting plate may also have inwardly projecting fins integrally formed with the plate, which further increase the heat transfer capacity of the support and also serve as reinforcement for the plate while providing shielding. electrical for the terminals of

  circuits with two rows of connections.

  Other features and benefits of

  the invention will appear during the description which

  go follow. In the accompanying drawings, given only by way of example: FIG. 1 is an exploded perspective view of a module of the prior art for circuits with two rows of connections;

  Fig. 2 is a partial perspective view-

  Another exploded view of another embodiment of a module for a circuit with two rows of connections; Fig. 3 is a partially exploded perspective view of the support according to the invention; Fig. 4 is a perspective view in part

  in section of the support according to the invention.

  A preferred embodiment of the printed circuit panel support according to the invention is shown in Figs. 3 and 4. Also shown in these Figures is a set conical component 21 consisting of circuits with two rows of connections, a resistor or a capacitor 21, a connector 14 and a printed circuit board 18 to which the components 21 and the connector 14 have been wave welded to form a complete circuit 41. The complete circuit 41 is shown separately from the plate support 40 in FIG. 3 so that the details of the support 40 are not hidden by the printed circuit board. The complete circuit 41 is placed in the support 40 as indicated by the return lines 42, 44, 43. After the insertion of the circuit 41 in the support 40, the rivets 22 fix

  the completed circuit 41 in the support 40.

  Referring to FIG. 3, it can be seen that the support 40 is a unitary assembly comprising two sides 45 ′, 45 "connected to a third side 46 at the edges of a plate 47. The plate 47 has an extension located at the end of the support 40 which is opposite the side 46 and which forms the pin shield 141. Another pin shield 141 'faces the shield 141 and covers the space between the sides 45. The height of the opening made between the shields 141 is slightly larger than the height of the connector 14, to allow this connector 14 to be put in place but it is insufficient to allow the total thickness of the assembly of the connector 14 and of the printed circuit board 18 penetrate therein, so that a stop is formed at the edge 181 of the panel. The support 40 is preferably made of a material with high thermal conductivity such as aluminum or copper, and it can be of preferably formed by casting. The back or bottom plate 47 has alveoli 48 in

  which the components 21 are partially engaged.

  The cells 48 make it possible to give the bottom plate 47 a greater thickness than would otherwise be possible and, in this way, the plate 47 establishes a better thermal conduction between the cells 48

  and the guides 24 which serve to transmit the heat.

  The height of the support shoulder 33 above the surface of the plate 47 is smaller than the height of the circuits 21 above the surface of the panel 18 so that in the absence of the cells 48, the height of the circuits 21 would prevent the assembled circuit 41 from bearing on the shoulder 33. The

  sides 45 and 46 and the pin shields 141 defi-

  in combination create a peripheral limit of the

support frame 40.

  Ribs 49 integrally with the main body of the support 40 have an edge in common with a thick part 50 of the plate 47 and another edge in common with a handle 5T. The ribs 49 serve as heat conducting elements between the plate 47 and the handle 41, which conducts the heat to the sides 45 and the edges 24. In certain applications, the handle 31 can be cooled by

  air to further increase the pro-

  heat dissipation properties of the support according to the invention. The ribs 49 also give a

  greater strength to the thin bottom plate 47.

  Orn places a heat conducting liquid 52 in

  the cavity 48 of the plate 47, at the place which corresponds to

  lays at the position of an element 21 which gives off heat. Therefore, when the assembled circuit 41 is placed in the support 40 and riveted to form with the latter a complete module, the liquid 52 is in - thermal contact with each element 21 which gives off heat and in thermal contact with the plate _9- bottom 47. The fluid 52 which conducts heat is preferably non-conductive of electricity, in order to avoid causing short-circuits with the pins of the components 21 or of the plate 18. The material 52 conductors of heat can optionally be an epoxy-like substance that hardens when the

  circuit 41 has been mounted in the support 40.

  An assembled module 60 is shown in partial section in FIG. 4. Fig. 4 shows how the circuit board 18, with its components 21, is housed in the support 40 to produce a module 60 which has the characteristics of dissipation of the

  heat of the assembly of FIG. t but with the sim-

  flexibility in manufacturing the assembly of FIG. 2.

  In certain applications such as in military equipment, it is required that the printed circuit board and its components be coated to protect the finished panel from the effects of the environment in which the circuit can be used. For the cases where a power dissipation of 4.5 watts is required and where the configuration of FIG. 1t representing the prior art, we had to start by assembling the module of FIG. 1, after which it was necessary to mask the sides 24, the upper face 241 and the connector 14 before being able to apply the coating, or the coating matching the shape of the assembly. These masking phases considerably increase the manufacturing cost of the module of FIG. 1. On the contrary, in the module according to the invention which is shown in FIG. 3, the coating conforming to the shape of the printed circuit board 18 and of its components 21 is carried out after the assembly and soldering of the components 21 and of the connector T4 on the printed circuit board 18. For the circuit 41 finished, it suffices to apply a rubber cuff (not shown) to the connector 14 before proceeding with the

- 10 -

  coating of the complete circuit assembly. We remove the rubber cuff before putting the circuit

  complete 41 in place in the support 40 of FIG. 3.

  Compared to the operations which were necessary in the case of the modules of the prior art, the simplicity of the coating operation of the circuit assembly 41 according to the invention once completed results in a considerable saving on the price of

returns from its manufacture.

  The dimensions of a support that has been studied as a Standard Electronics Module (SEM) by the Government of

  United States of America is shown in Fig. 4.

  The external dimensions indicated are the same

  for all the supports shown in the drawings.

  To make maximum use of the width of a circuit plate 18, the width of the shoulder 33 intended to support the circuit plate is limited to a value as small as possible. In Fig. 4, a value of around 0.75 mi has been indicated for this width. The shoulder 33 has a width equal to that of the shoulder 33 'of FIG. 2, which supports the heat-conducting closing plate 32. The closure plate 32 is overlapped with respect to the handle 311 of the support 31 over a distance 33 "having approximately the same value, as shown in FIG. 2. It can be seen that the closure plate 32 is limited in its contact surface with the support 31 and that the thermal resistance between these two elements is high, so that only a small increase in the maximum admissible energy dissipation of the printed circuit board components is obtained when the closing plate 32 is used, compared to the admissible dissipation when the closing plate is not used in the case shown in Fig. 2 (the power dissipation

- he -

  admissible only passing from t watt to 1.5 watts).

  Since the overlap regions 33 of the closure plate 32 with respect to the support 31 are limited by the limitations imposed on the standardized dimensions and by the need to use as large an area as possible of the printed circuit board, the usefulness of a cover plate 32 is limited due to the small increase in energy dissipation compared to the standard chassis module

  open from Fig. 2 without cover plate 32.

  The thickness of the heat conducting plate 47 is limited by the maximum admissible thickness of the support 40 and it is approximately 2 mm except in the regions of the cells 48, where the thickness of the plate 47 is only about 1 mm. As explained above, the cells 48 are provided in the region in which the components 21 of the integrated circuit are closest to the rear plate 47. The cells give additional play without significantly reducing the transfer capacities heat from the back plate 47. The depth 331 of the support flange 33 is just sufficient to prevent the printed circuit board 18 and the solder beads 411 formed on the connection wires of the components 21 from overflowing upper faces 451 of part 45. In a typical example, this

dimension is approximately 1 mm.

  The marked improvement in dissociation capacities

  pation of energy (which goes from 1 to 4.5 watts) of the module according to the invention, as shown in Figs. 3 and 4, while still respecting the limitations

  of the standard electronic module is noted

  quable if we consider its resemblance to the module of the prior art shown in FIG. 2. The following single piece support

2 2494540

- 12 -

  the invention which is shown in Figs. 3 and 4 provides better thermal conduction between the part 52 of the support 40 to which the heat is transmitted by the components 21 of the printed circuit board 18 and the part of the support, constituted by the guide bars 24, from where the heat is removed by the elastic fingers cooled by the water from the heat sink which is incorporated into the rack

  for which module 60 is designed.

Claims (4)

  1 - Plate panel support or printed circuit board of the type comprising a heat conducting chassis having a peripheral edge, one side of this edge being adapted to transmit heat to a heat sink and one side of said edge being adapted to serve handle for the support, this chassis being adapted so that a printed circuit board (18) having connection pins (15) can be fixed to one end so that, when the panel is fixed to the chassis, the   connection pins are adjacent to the peripheral edge   that in a position diametrically opposite to the handle (51) said peripheral edge of the chassis defining a volume roughly equal to the product of the surface surrounded by this edge by the thickness of said chassis, said printed circuit board having elements which dissipate of heat mounted on one of its faces, the plate and the elements releasing heat having together a   total thickness roughly equal to the thickness of the frame   sis, this plate support being characterized in that said chassis further comprises a rear plate (47)   conductive of the material heat with the frame   located and intended to form a circuit with low thermal impedance with the chassis along at least a significant part of the periphery of this chassis, this plate   heat conducting being at least roughly   ne and situated roughly in the same plane as a surface of the periphery of the chassis, and this plate forming, in combination with the chassis, a volume roughly equal to that of the chassis without said plate, a material (52) insulator of electricity and conductor of heat in contact with the elements (21) generating heat   which are mounted on the printed circuit board and also   in contact with said backplate so that the   heat generated in said elements (21) either faci-   transmitted to the plate and then transmitted   to cooling fins (24) of the chassis.   2 - Plate panel support or printed circuit board of the type in which the support comprises a heat conducting chassis which has an edge   peripheral, a first part of the peripheral edge for-   mant a cooling fin (49) j said chassis being adapted to support a printed circuit board (18) provided with connection pins (15) at one end   so that when the plate (18) is held by the   said chassis, the connection pins (15) are located near and within the limits of a second part of the peripheral edge which is diametrically opposite to said   first part of the peripheral edge, the peripheral edge   that of the chassis delimiting inside thereof a volume roughly equal to the product of the surface delimited by said edge and the thickness of the chassis, the printed circuit board (18) having an available volume located at l inside the chassis volume and carrying elements   (21) releasing heat mounted on one of its fac-   these, the plate (18) and the elements (21) having a thick-   seur total approximately equal to the thickness of the chassis, this support being characterized in that the chassis (40) further comprises a rear plate (47) conductive of heat, integrally formed with it, to establish a   heat conductor circuit with low thermal impedance   that along at least the part (24) of the peripheral edge   which serves as a cooling fin, said heat conducting plate (47) being at least approximately flat and located in the same plane as a surface of the peripheral edge of the chassis and that said printed circuit plate, said plate rear (47) having a thickness which combination with the chassis has approximately   the same volume as the chassis without its plate.   3 - Plate panel support or circuit board   printed baking intended to support a heat-releasing element mounted on a printed circuit board, this support comprising a peripheral frame which surrounds a hollow region adapted to receive said circuit board (18) a closing plate (47) made of material with said chassis to delimit said hollow region and adapted to conduct the heat given off by said element inside the hollow region to a part (24) of the chassis which is adapted to be put   in heat exchange relationship with a heat sink.   4 - Plate panel support or printed circuit board intended to carry elements releasing heat mounted on a printed circuit board, this   support being characterized in that it comprises: a frame   sis peripheral which surrounds a cavity adapted to receive said printed circuit board, a closing plate (47) integrally formed with the chassis to delimit said cavity and adapted to be in thermal contact with said elements (21) which give off heat and which are mounted on a surface of said printed circuit board (18) so as to conduct the heat given off by said elements inside said cavity to a part (24) of the chassis which is adapted to be put in thermal connection with a well heat.   - Plate panel or printed circuit board support, characterized in that it comprises: a chassis comprising a peripheral part adapted to be brought into thermal contact with a heat sink and a closing part (47) made integrally with the chassis , said peripheral part and said closing part delimiting in the support a cavity   adapted to receive a circuit board (18)   award-winning bearing elements (21) which release heat   mounted on one of these faces, said part of   closure (47) having a cell (48) adapted to receive   see the elements (21) releasing heat which are mounted on the surface of the printed circuit board, said closure part (47) comprising transverse ribs (49) integrally formed therewith and with   said peripheral part of the chassis.   - 6- Electronic module characterized in that it comprises: a printed circuit board (18) carrying electrical wiring, a pin conductor (14) fixed to one end of the plate (18), the pins (15) of this connector being in electrical connection with said wiring, electrical components - (21), these components being connected to said wiring, the assembly of the connector (14) and components (21) on said plate (18) forming a complete circuit ( 41); a heat conducting support (40), this support being adapted   to contain the complete circuit and including a plate   that rear (47), a cdté and three other sides conti-   gUs fixed to the periphery of said rear plate, this side extending transversely to the rear plate to   form with the latter a box open to a former   end, the side opposite to said open end constituting a side with cooling fins (49)   and the other sides (45) constituting guide sides   dage, the rear plate (47) extending beyond said guide sides, at the open end of the box to form a first guard (141) for the pins (15) of the connector (14), a second guard (141 ') being fixed to said guide sides and opposite to said first guard, the connector pins being housed between the first guard (141) and the second guard (141'); each of the guide sides (45) having   a projection (24) which extends transversely towards the ex-   trière, each projection forming a guide for the establishment of the support and associated connection pins in a complementary socket intended to receive these   pins, each of the guide sides (45) having a thick   LEMENT (33) provided on the inner part of said guide side, this shoulder extending inward over a distance sufficient to support the complete circuit (41) when the latter is placed in the support; the height (331) of said guide side (45) above the height of said shoulder (33) being greater than the thickness of said complete circuit (41) including its   wiring and its welded junctions which connect this ca-   to said components (21), the height of said shoulder   lying above said rear plate (47) being equal to the thickness of the connector (14), said electrical components comprising an integrated circuit (21) with two   rows of connections which upstream, a higher height   re at the height of said connector (14) above the printed circuit board (18), said rear plate (47) being hollowed out by a cell (48) at the location of said integrated circuit (21) to allow this integrated circuit to be embedded in said cell when said plate (41) is in abutment against said shoulder (33) in the assembled configuration, and a heat conducting material (52) placed between said integrated circuit (21)   and said honeycomb back plate (47).