DE102011113929A1 - Electromechanical circuit structure for use as rack for e.g. LED in automotive environment, has deriving device deriving heat dissipated from electrical component that is contacted with injection molding casing - Google Patents

Abstract

The circuit structure (11) has a deriving device deriving heat dissipated from an electrical component (12), which is contacted with a pot-shaped multi-shell plastic injection molding casing (13). The casing comprises electrically insulating and thermally conducting material. The electrical component is mechanically fixed and/or electrically connected to conductor patterns (14) by conductive adhesive (22), conductive paint or conductive ink. The conductor patterns are extended along the casing. An outer housing (13.2) of the casing is formed with outer and/or inner surface profiles (15). An independent claim is also included for a method for manufacturing an electromechanical circuit structure.

Description

The invention relates to a circuit structure according to the respective preamble of the main claims.

For decades, development trends have been towards finer circuit patterns with tighter placement on printed or laminated and etched circuit boards, optionally with the use of higher power electronic semiconductor devices. The latter necessitate dissipating the heat generation which increases with the higher power loss, in order to avoid as far as possible a loss of performance or even loss of function as a result of parameter changes due to overheated junction temperatures. This is particularly critical, for example, in sensor circuits for vehicle technology, in which the components are operated in hermetically sealed, small-volume plastic housings, especially under elevated ambient temperatures. At least then additional space must be provided for a mounting of critical heat-generating components on large-volume heat sinks, but whose effect is limited but only in closed plastic housings for lack of convection; and additional installation volume is required for the mechanical protection of the heatsink masses against the effect of mechanical operating stresses to reliably exclude a circuit failure due to vibration induced contact and line breakage or even tearing off the heatsink holder. In addition to this operational technical and manufacturing aspect is of practical importance: For a reliable solder joint, the parts to be soldered should have temporarily the same temperature. However, the soldering temperature is critically high for many electronic semiconductor devices, especially with modern SMD equipment; and in large-volume component carriers such as lead frames is due to the heat dissipation, the required duration of the heat input until reaching the soldering temperature at the assembly point additionally critical. So it happens that some component thermally biased goes into the rough operation, whereby the functional reliability of the circuit is already reduced a priori.

In recognition of such initially discussed circumstances, the present invention is based on the technical problem of specifying an electromechanical circuit structure which is distinguished by improved thermal management in the case of cost-effective equipment conditions and is therefore suitable in particular for operation in hermetically sealed, small-volume plastic housings which are mechanically highly stressable.

The problem is solved by the combination of the essential features specified in the main claim. Thereafter, it leads to a particularly large-scale and correspondingly effective fanning and dissipating the loss of heat emanating from a component when the heat flow is spread over the housing by the critical component is thermally conductive contacted with the injection-molded from electrically insulating but as good as possible thermally conductive material housing.

Under the injection molded housing in the present context, a z. B. cup-shaped housing part to understand that is completed or closed by another housing part or simply by a cover to the housing. The electrically insulating but thermally conductive and mechanically resistant housing injection molding material, such as PBT or the like good injection moldable polyester or a polymer such as PA, can be improved by additives to experience thermal conductivity while maintaining its electrical insulation properties. An uneven and thus enlarged outer surface of the housing promotes the heat transfer to the surrounding medium, such as air or a cooling fluid circuit.

So that the heat transfer from the component to the heat-dissipating housing takes place over a large area, it is expedient, along the Gehäuseinnenmantelfläche or in the housing running - with respect to the current density required for the electrical functionality - electrically oversized, so in cross section comparatively very large volume conductor structures provide, to which Component is contacted thermally conductive; Thus, this comparison of bulky conductor structures refers to the above-discussed fine traces of common circuit boards. This solution thus represents a radical departure from the trend in technology of ever finer interconnect structures with the inclusion of power semiconductors on voluminous heat sinks. Accordingly, by using the solution according to the invention, the electromechanical circuit structure is simplified, reduced and rendered more functional and the functionality or duration of the semiconductor components even becomes significant improved.

As the cross-sectional large-volume conductor structures can be used in multi-component injection molded into the housing electrically conductive plastic sheets, as described in our patent DE 1 00 48 680 are described in more detail for another application.

Technologically less demanding and advantageous in terms of thermal conductivity, at least one, the conductor structure to enclose or pour in a reproducing, comparatively thick stamped grid in the course of the injection molding of the housing; with, in such known manner, formed on the lead frame cutting clamps or holes for mounting of wired components and ending in plug baskets pins. For high current connections additional screw connections are appropriate.

In the interest of a flexible circuit design, at least two punched grids bordered in substantially parallel planes in the housing inner wall are provided. Of these, one is, in turn advantageously in two parts, formed from cost-effective copper alloys such as CuSn 2 or CuZn 37, geometrically designed to connect, for example, an SMD transistor; and at least one further grating, preferably consisting of relaxation-optimized CuNiSi, has openings for pressing in separately prepared and populated small circuit boards.

In order to avoid soldering temperature stresses, non-wired components are expediently electrically and mechanically connected with conductive adhesives to areas of the stamped grid that are left free from the sprue. This also facilitates handling when loading the circuit directly into the housing.

From a procedural point of view it is even more expedient to free grooves embedded in the housing wall during injection molding of the housing or to project channels elevated into them, into which relatively thick strands of conductive ink or similar conductive paste can be injected or otherwise introduced as electrical and thermal conductors , This leads to extremely low production costs to geometrically exactly against each other delimited, so reliable insulated cable runs and circuit technology is especially critical where it does not depend on high accuracy and consistency of line resistance. In this case, only those of standard more complex gradients of the grooves or channels need to be filled, which are needed for a current of several prepared circuit variants. Where these courses are not filled to their upper edge with conductive material, problem-free isolated intersection curves open up by applying simple wire or punched grid pieces. For example, they can bridge an interruption in such a course or the distance between adjacent courses by simply being pressed into the conducting paste with their ends running at an angle on both sides, especially in blind holes filled with conductive paste.

It is particularly advantageous in this context, conductive pastes with adhesive properties, so electrical conductive adhesive, such as based on copper or silver-containing epoxy or polyamide, use. The adhere particularly reliable in the groove or channel bottom; and components that are pressed with their connections before curing of the conductive adhesive in this, are connected without any effort equal mechanically and electrically reliable to the heat-spreading conductor structure along the inner circumferential surface of the housing. To connect wired components are filled with conductive adhesive blind holes appropriate. On the other hand, especially for the assembly of small components, a low-viscosity conductive adhesive is preferred, or even conductive ink or ink with additives based on precious metal, metal or carbon (preferably in nanotechnology) to improve the electrical and thermal conductivity of this then only thinly applied conductor material.

According to a particularly effective development of the invention, the injection-molded housing is formed at least two shells, with injected into a preformed outer housing inner housing or with a molded from the outer housing, preformed inner housing. In this case, the inner housing is designed with the thinnest possible wall thickness in order to transfer as much as possible to the heat sink in the form of the large-area outer casing, especially in the case of electrically insulating injection-molded material, by means of the conductor structure along the housing inner wall surface. This consists of good heat-conducting injection molding material with a wall thickness which is substantially greater than that of the inner housing, ie a larger wall volume. A wave, rib or pillar geometry on the outer circumferential surface of the inner housing and complementary on the inner circumferential surface of the outer housing promotes contact surface enlargement, the heat transfer from the conductor structure via the inner housing to the heat sink in the form of the outer housing. A comparably structured geometry whose outer circumferential surface promotes the convective heat transfer to the surrounding fluid. If the material of the outer casing is also electrically conductive, as in the case of a PA-based injection molding material, the function as a heat sink is accompanied by a desirable electromagnetic shielding effect for the electrical circuit inside the housing.

The equipped with the components inner housing can finally be sprayed with insulating varnish or with thermosetting or thermosetting plastic or completely shed, thereby achieving an additional protection against environmental influences such as moisture in particular by increased mechanical stability.

If individual profiles such as pillars on the inner circumferential surface of the outer housing locally penetrate the wall of the inner housing, then the front ends can be designed for heat-conducting but, if necessary, electrically insulating recording of components to dissipate their heat loss directly bypassing the poorer heat-conducting inner housing in the outer housing , This recording can be done depending on the nature of the component as material fit by means of adhesive and non-positively by means of screws or clamping aids such as bending springs. The latter can be injection-molded on such profiles, in the case of a stamped grid also be realized by it bent sheet metal strips.

Protection is also sought after for manufacturing processes for creating the described circuitry. In any case, such a circuit design is used in the automotive environment, for example as a subrack for headlights and other lights (especially each with LED equipment), inverters and amplifiers, but also for switching and the like modules such as reversing bridges, especially for modules equipped with IGBT , Transistor, diode or Hall sensor devices.

Further modifications and additional alternatives to the inventive solution will become apparent from the other claims and, with regard to the advantages thereof, from the following description of an enlarged scale in the single figure of the drawing in aborted representation on the functional essentials outlined sketched, schematic implementation example for carrying out the invention.

The sketched longitudinal section through an electromechanical circuit structure 11 shows an electrical component 12 placed in an electrically insulating injection-molded housing 13 into on ladder structures 14 is mounted. The housing 13 consists of an inner housing 13.1 and an outer casing 13.2 , which are sprayed directly onto each other and therefore contact each other over a large area. To increase the mutual, heat-transferring contact surface, these have mutually intermeshing, for example rib-like or channel-like, mutually complementary profilings 15.1 . 15.2 on. By comparable profiles 15 is also the heat-emitting outer surface 16 of the outer casing 13.2 increased.

The strength of the wall 17.1 of the inner casing 13.1 is essentially designed only for sufficient electrical insulation and therefore much less than the wall serving as a heat sink 17.2 of the outer casing 13.2 , From its inner surface 18 protrudes from the sketched implementation example a pillar 19 the inner casing wall 17.1 , On his forehead 20 is the component 12 thermally conductive mounted.

The derivation of the heat loss from the device 12 takes place for present invention explanation by way of example on the comparatively massive electrodes 21 , One of his electrodes 21.3 lie on the underside of the component 12 ; It is by means of conductive adhesive 22 electrically and thermally conductive on a branch of a first stamped grid 23.3 the ladder structure 14 glued, which here on its part thermally conductive on the pillar-forehead 20 glued. A second electrode 21.4 of the component 12 is otherwise using conductive adhesive 22 electrically and thermally conductive to the conductor structure 14 connected, namely in this example to a branch of a second punched grid 23.4 glued.

About the comparatively massive stamped grid 23 There is a widespread fanning of the heat dissipation from the device 12 in the inner casing wall 17.1 , to large transfer from there to the heat sink in the form of the outer housing 13.2 ,

Also a third electrode 21.5 of the component 12 is electrically and thermally conductive to the conductor structure 14 connected, namely in this example, immediately in one of a thick strand of conductive adhesive 22 formed trace of the ladder structure 14 inside the inner housing 13.1 immersed. The strand runs in this example trap at the bottom of a in the inner wall surface 24 of the inner casing 13.1 molded groove 25 preferably not (as explained above) in full height with conductive adhesive 22 is filled. Also on this conductive adhesive trace 14 again a spread of heat dissipation from the device 12 into the thin inner casing wall 17.1 into, to large-scale transfer from there to the heat sink in the form of contrast, the much more massive outer casing 13.2 ,

For a large spreading of an electrical component 12 dissipated heat loss this is thus according to the invention in heat-conducting contact preferably initially to a heat-conducting, in cross-section electrically oversized conductor structure 14 in the form of a stamped grid, in particular partially encapsulated 23 and / or one in a groove 25 or running in a channel, relatively thick strand of preferably adhesive conductive paste, so conductive adhesive 22 brought. Thus fanned out, a large-scale transfer takes place in serving as a heat sink housing 13 ,

Such a the electrical conductor structure 14 resulting course of the conductive material, so the conductive adhesive 22 or by contrast, thinner Conductive lacquer can be needle-metered, jet-metered or printed (in particular in tampon or screen print) onto the inner wall of the housing in easily available technology 17.1 be applied. in the not yet end-cured material are thereby electrically and mechanically and thermally connected components 12 with their electrodes 21 and pressed the bent ends of conductor bridges.

The conductive material is preferably designed for thermal curing under convection at room temperature, possibly promoted by ultraviolet or infrared radiation or by thermal sintering. A curing or drying process at temperatures below 250 ° C., in particular between room temperature and 180 ° C., is to be preferred. For this purpose, the so-called low-temperature sintering can be used, but also a chemical or physical oxidation or drying reaction.

Instead or in addition to such conductive materials can also stamped grid 23 on the inner wall surface 24 of the housing 13 be injected or retrofitted.

The ladder structure 14 at least runs on or in the wall 17 of the heat sink serving as an injection-molded Umgehäuses 13 , This is preferably sprayed with at least two shells, with a thin-walled inner housing 13.1 especially for electrical insulation function and a thicker-walled outer housing 13.2 in any case good heat-conducting material than the actual heat sink. The locally can the inner housing 13.1 penetrate to the device 12 there also heat-conducting on the outer housing 13.2 to assemble. At the same time, the outer housing provides 13.2 a desirable electromagnetic shield and thereby an improvement in the electromagnetic compatibility of the housed circuit structure 11 if its injection molding material not only has good heat-conducting properties, but also at least slightly electrically conductive.

LIST OF REFERENCE NUMBERS

11

circuit design

12

Component (on 14 )

13

casing

14

Ladder structures (out 22 . 23 )

15

Profiles (on 13 )

16

Outer jacket surface (from 13 )

17

Wall (from 13 )

18

Inner circumferential surface (from 17.2 )

19

Pillar (up 18 , by 13.1 )

20

Forehead (from 19 , within 13.1 )

21

Electrodes ( 21.3 - 21.5 from 12 , on 14 )

22

Conductive adhesive (also conductive ink or ink)

23

Punching grid ( 23.3 . 23.4 )

24

Inner wall surface (from 13 )

25

Groove (in 24 , With 22 )

x.1

Inside-...

x.2

Outside-...

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10048680 [0007]

Claims (10)

Electromechanical circuit construction ( 11 ) with means for deriving the heat loss of at least one electrical component ( 12 ), characterized in that the component ( 12 ) heat-conducting with an injection-molded housing ( 13 ) is contacted from electrically insulating but thermally conductive material. Circuit structure according to the preceding claim, characterized in that the component ( 12 ) by means of conductive adhesive ( 22 ), Conductive ink or conductive ink along the housing ( 13 ) ladder structures ( 14 ) is mechanically attached and / or electrically connected. Circuitry according to the preceding claim, characterized in that the conductor structures ( 14 ) on the housing inner wall surface ( 24 ) In some areas molded punched grid ( 23 ) and / or longitudinally molded grooves ( 25 ) or channels extending strands of conductive pastes, webs of conductive ink or ink and / or plastic material molded plastic sheets are. Circuit structure according to one of the two preceding claims, characterized in that bridges or wired components ( 12 ) with their angled ends in holes initially filled with not yet hardened conductive material holes, channels or grooves ( 25 ) are pressed. Circuit structure according to one of the preceding claims, characterized in that the housing ( 13 ) mehrschalig created in plastic injection molding. Circuitry according to the preceding claim, characterized in that the housing ( 13 ) with the ladder structures ( 14 ) equipped inner housing ( 13.1 ) made of especially good electrically insulating material and an outer housing ( 13.2 ) in particular has good heat-conducting and preferably also electrically conductive material. Circuit structure according to the preceding claim, characterized in that the outer housing ( 13.2 ) with external and / or internal surface profiling ( 15 ) and optionally with the latter locally into the inner housing ( 13.1 ) intervenes. Circuit structure according to the preceding claim, characterized in that the outer housing ( 13.2 ) the inner housing ( 13.1 ) penetrated locally and there with components ( 12 ) is equipped. Method for producing a circuit structure according to one of the preceding claims, characterized in that at least one conductor structure ( 14 Needle or jet metered from conductive material or applied in a printing process to a housing interior and with at least one component ( 12 ) is fitted, which undergoes the conductive material a thermal final curing. Application of a circuit structure according to one of the preceding claims as a rack for, in particular LED-equipped, lights, for inverters, for amplifiers or for switching modules, especially for use in the automotive environment.

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