Circuit arrangement having contact pins

Abstract

The invention relates to a circuit arrangement having a semiconductor module with a plurality of contact pins arranged parallel to one another and a circuit carrier with a plurality of internally metallized contact openings associated with the contact pins, wherein the contact pins are inserted into the contact openings and the inner faces of the contact openings are provided with a material the melting point of which lies at a temperature of at most 150°C.

Description

[0001] Description

[0002] Circuit arrangement with contact pins

[0003] The invention relates to a circuit arrangement with one or more semiconductor modules, wherein the semiconductor modules have contact pins which are inserted into contact openings of a circuit carrier.

[0004] Due to ever-increasing power dissipation densities, power electronic semiconductor assemblies must be cooled as optimally as possible. Depending on the circuit topologies and performance requirements, several assemblies are often arranged on a common circuit carrier (motherboard). This assembly hierarchy offers advantages in terms of modularity combined with high miniaturization and is therefore frequently used.

[0005] Heat dissipation is primarily ensured on the surface of the semiconductor components opposite the motherboard, toward a heat sink. This typically involves a shared heat sink for multiple semiconductor components in a circuit arrangement. Aligning multiple semiconductor components to a shared heat sink surface represents a compromise, as, for example, the thicknesses of the semiconductor components differ from one another and their respective surface normals differ from component to component due to variations in the joining processes.

[0006] Bringing the critical surfaces closer together presents a particular challenge due to these deviations. The remaining gap to the heat sink is typically closed using thermal pastes or pads, although these must be kept as thin as possible due to their comparatively low thermal conductivity compared to metals or ceramics. The necessary thermally conductive contacts also require contact pressure from the semiconductor components towards the heat sink, which is limited by mechanical influences and the associated potential for damage to the joining partners. The following basic principle can be stated: the greater the contact pressure, the lower the thermal resistance and the greater the ability to bring the critical interfaces for heat transfer closer together, but also the greater the potential damage to the joining partners.

[0007] The disadvantage is that the thickness of the thermal paste or pads must be large enough to compensate for the almost unavoidable thickness variations and tilting of the semiconductor components at any time. This means that this thickness must be selected to be much larger than would be the case for semiconductor components of the same thickness and exact alignment, which impairs the thermal properties.

[0008] It is an object of the invention to provide a circuit arrangement of the type mentioned at the outset in which the disadvantages mentioned are reduced.

[0009] This object is achieved by a circuit arrangement having the features specified in claim 1.

[0010] The circuit arrangement according to the invention comprises a semiconductor module with a plurality of contact pins arranged parallel to one another. Furthermore, the circuit arrangement comprises a circuit carrier with a plurality of internally metallized contact openings associated with the contact pins, wherein the contact pins are inserted into the contact openings.

[0011] The circuit arrangement further comprises a cover element arranged on the side of the semiconductor assembly facing away from the circuit carrier, as well as means for generating a first force which presses the circuit carrier and the cover element towards one another. The contact openings have a material on their inside which has a melting point of at most 150°C. Several spring elements are arranged between the semiconductor assembly and the printed circuit board, which spring elements cause second forces between the printed circuit board and the semiconductor assembly, which press the semiconductor assembly against the cover element.

[0012] For simplicity, the side of the semiconductor assembly facing the cover element is referred to as the top side. The opposite side is referred to as the bottom side.

[0013] The invention corrects differences in surface, thickness, and alignment between adjacent components in the circuit arrangement, thus achieving optimal alignment of a respective surface of a component with the cover element. The differences can be caused by different thicknesses of the components, which can be intentional or unintentional, i.e., due to manufacturing variations. Furthermore, the differences can be caused by thermal stresses.

[0014] The fact that the material has such a low melting point that it is liquid at the operating temperature of the electronic assembly, or at least at a slightly higher temperature, is an advantage. The contact openings and the contact pins are expediently designed so that the liquid material allows the contact pins to move freely in the contact openings in the direction of extension of the openings. If, for example, two semiconductor modules of different thicknesses are arranged next to one another, the second forces caused by the spring elements can lift the thinner semiconductor module and thus minimize its distance from the cover element.

[0015] This ensures that the semiconductor components fit optimally against the cover element, despite differences in thickness and alignment, and thus minimizes the amount of thermal paste or pads between the elements. This improves the thermal contact between the semiconductor component and the cover element.

[0016] In other words, height tolerances are compensated for and leveled with respect to a base plane by permanent adjustment through retraction and extension of the sliding contact pins. The electrical contact between the contact pin and the contact opening is maintained. There is no need for compromises to balance the various top surfaces of the semiconductor assemblies with respect to the plane of the heat sink, as each individual semiconductor assembly is adjusted with respect to its position. This also works continuously under operating conditions, as the sliding support of the pins remains intact even after assembly of the assembly, once the melting temperature of the material is reached.

[0017] The semiconductor assembly advantageously comprises at least one semiconductor component with contact pins or a structure comprising such a semiconductor component, for example a diode, an IGBT, or a MOSFET. The semiconductor assembly may also comprise multiple semiconductor components. The upper side is advantageously planar to enable good thermal connection to the cover element.

[0018] The contact pins are preferably metallic and are aligned perpendicular to the plane of the circuit board. Therefore, they are preferably all parallel.

[0019] Advantageous embodiments of the circuit arrangement according to the invention emerge from the dependent claims. The embodiment of the independent claims can be combined with the features of one of the subclaims or, preferably, with those of several subclaims. Accordingly, the following additional features can be provided:

[0020] The spring elements can be arranged such that the second forces can cause the semiconductor assembly to tilt. Tilting is achieved by the spring elements experiencing different degrees of stretching, thereby raising or lowering the semiconductor assembly at its edges by different lengths.

[0021] This advantageously ensures that good contact between the top side of the semiconductor module and the underside of the cover element is maintained even when the circuit carrier and the cover element are tilted or bent relative to one another, for example due to thermal stresses or other deformations in the area of ​​the semiconductor module.

[0022] The spring elements can be arranged at the edge of the semiconductor assembly. Spring elements positioned as far outside as possible on the semiconductor assembly have the advantage of best and most precise alignment of the top side of the semiconductor assembly with the underside of the cover element. This minimizes the remaining distance between the two elements and thus optimizes thermal and / or electrical contact.

[0023] The circuit arrangement can comprise a paste for heat conduction and / or electrical conduction between the cover element and the side of the semiconductor assembly facing the cover element. The paste brings about a thermal connection and / or electrical connection between the semiconductor component and the cover element in a known manner, in which the remaining gaps between the surfaces are filled and the contact is therefore significantly better than without the paste. Compared to known circuit arrangements, the amount of paste required to ensure contact is lower. Since pastes always have poorer properties with regard to heat conduction or electrical conduction than solid materials such as copper or aluminum, a smaller thickness of the paste is advantageous for the properties of the circuit arrangement.

[0024] The cover element can be a heat sink. The heat sink can be made of aluminum or copper, for example. Alternatively, the cover element can be a second circuit carrier. In this case, the semiconductor module can have one or more load terminals on its top side. The cover element can have matching metallizations on its underside, which ensure contact with the load terminals.

[0025] The material can be liquid at room temperature. In this case, movement of the contact pins in the contact openings is possible even at room temperature. This also compensates for deformations within the circuit arrangement that occur at room temperature. Such deformations arise, for example, because manufacturing steps for parts of the circuit arrangement take place significantly above room temperature. However, the means for exerting the initial force hold the structure securely together.

[0026] Alternatively, the material can be solid at room temperature. This material has the advantage that the semiconductor assembly cannot easily become detached from its anchorage in the contact openings at room temperature, i.e., outside of operating hours. At the same time, however, the material allows the contact pins to move at operating temperature. It also advantageously prevents the material from escaping from the contact openings during transport.

[0027] The material can, for example, contain a gallium component. With its melting point of approximately 29 °C, gallium offers a good starting point for materials that are liquid at operating temperature and simultaneously exhibit good electrical conductivity. The high surface tension is also advantageous for keeping the liquid material in the contact openings.

[0028] The material can, for example, be a eutectic alloy with gallium, indium, and tin. Such an alloy is known for a melting point in the range of -10°C to -20°C and otherwise exhibits suitable properties with regard to electrical conductivity and surface tension. If the material is liquid even at room temperature, this advantageously prevents thermal stresses from occurring after operation at elevated temperatures and cooling, which cannot be compensated for by movement of the semiconductor component. Rather, the semiconductor component always remains mobile, so that thermal stresses due to heating and cooling do not occur, at least in this range.

[0029] In certain embodiments, the melting temperature of the material is below 120 °C or 100 °C. For example, the material can also be a low-melting solder. In certain embodiments of the invention, the melting temperature is above the typical operating temperature. In this case, local temperature increases, which occur, for example, due to a momentarily increased load on one of the semiconductor components, cause the material to melt and thus allow improved alignment of the semiconductor assembly and the cover element.

[0030] The spring elements can be leaf springs, coil springs, or pieces of an elastic material such as an elastomer or silicone. These pieces are preferably cuboid-shaped. They can, for example, be glued to the surface of the circuit carrier and / or the semiconductor assembly.

[0031] The invention will now be described and explained in more detail with reference to the exemplary embodiments shown in the figures. Figure 1 shows a first schematic sectional view of a first exemplary embodiment of a circuit arrangement in an operating situation,

[0032] Figure 2 Contact pins and contact openings in the circuit arrangement in different operating situations.

[0033] Corresponding parts in the figures are provided with the same reference symbols.

[0034] Figure 1 shows a schematic sectional view of an exemplary embodiment of the invention. The circuit arrangement 1 comprises a circuit carrier 30 and a heat sink 50. For example, the circuit carrier 30 is a DCB substrate (DCB: abbreviation for Direct Copper Bonded) or an AMB substrate (AMB: abbreviation for Active Metal Brazing).

[0035] In this example, the heat sink 50 is a copper heat sink. Fluid lines 51, through which, for example, water can be conducted for heat dissipation, are arranged penetrating the heat sink 50. In alternative embodiments, the heat sink 50 can also be made of aluminum or another material. The heat sink 50 can also include an electrically insulating layer on its underside.

[0036] Furthermore, the circuit arrangement 1 comprises a first and a second semiconductor module 70, 80. The semiconductor modules 70, 80 are arranged side by side between the circuit carrier 30 and the heat sink 50. The underside of the heat sink 50 is the side facing the semiconductor components 70, 80.

[0037] The semiconductor assemblies 70, 80 are essentially planar assemblies, each comprising one or more semiconductor components. The semiconductor components can be, for example, bipolar transistors or insulated-gate bipolar transistors (IGBTs). Alternatively, they can also be field-effect transistors, in particular metal-oxide-semiconductor field-effect transistors (MOSFETs). In other embodiments, the semiconductor components can also be thyristors or diodes. The semiconductor components can be of different types.

[0038] The semiconductor components are assembled in the semiconductor assemblies 70, 80 to form a structure having a substantially straight top and bottom surface. On the top side, which faces the heat sink 50, the semiconductor assemblies 70, 80 comprise a thermally conductive layer 75, 85, for example, a copper layer. This thermally conductive layer 75, 85 serves to thermally connect to the heat sink 50. In this example, the thermally conductive layer is electrically conductive, but need not be.

[0039] On their undersides, the semiconductor assemblies 70, 80 each have a plurality of metallic contact pins 31, 32. These serve to electrically contact the control and load connections of the semiconductor assemblies 70, 80 and can be partially electrically connected in parallel. The contact pins 71, 81 run parallel to each other, at least toward their ends, in a direction perpendicular to the plane of the circuit carrier 30 and facing toward it.

[0040] The circuit carrier 30 has a plurality of contact openings 31, 32 (also referred to as vias). The contact openings 31, 32 are assigned to the contact pins 71, 81 and arranged such that the semiconductor modules 70, 80 can be inserted into the contact openings 31, 32 with the contact pins 71, 81. The semiconductor modules 70, 80 are inserted into the circuit arrangement 1. The contact openings 31, 32 are designed as bores penetrating the circuit carrier 30. They have a metallization on their inner surface. This metallization extends a distance in the millimeter range on the outer surfaces of the circuit carrier 30 in a circle around the bore as a collar and serves to make electrical contact with other circuit elements on the circuit carrier 30 by means of conductor tracks extending from the collar on a respective surface of the circuit carrier 30.

[0041] Figure 1 shows a sectional view of only five contact pins 71, 81 and contact openings 31, 32. Semiconductor assemblies 70, 80 typically have more contact pins 71, 81, which are arranged circumferentially around the edge of the respective semiconductor assembly 70, 80, thus forming a rectangle or square. The same applies to contact openings 31, 32.

[0042] In contrast to known circuit carriers of the type described, the contact openings 31, 32 comprise an electrically conductive material 100 that is liquid at the nominal operating temperature of the circuit arrangement 1. The nominal operating temperature can be, for example, 40°C or 80°C. At room temperature (25°C), the material 100 can be liquid or solid, provided the operating temperature is not room temperature. An example of such a material 100 is a eutectic comprising gallium, indium, and tin. Such a material 100 is liquid at 0°C and above, i.e., at any typical operating temperature, but also at room temperature.

[0043] In other embodiments, the material 100 may be, for example, gallium or another mixture that may include, for example, gallium. Gallium itself has a melting point of approximately 30°C and is therefore just solid at room temperature, but liquid at realistic operating temperatures.

[0044] The contact pins 71, 81 and the contact openings 31, 32 are designed such that, when plugged in, there is a slight clearance of less than 0.1 mm between the surfaces. Capillary forces cause the T1000 material to remain in the space between a contact pin 71, 81 and the inner wall of the respective contact opening 31, 32 and wet both surfaces. This ensures good electrical contact between the contact pins 31, 32 and the metallization of the bore. Furthermore, slight lateral movement and / or tilting of a contact pin 71, 81 within the respective contact opening 31, 32 is possible. A particularly advantageous feature is that this configuration permits axial movement of the contact pins 71, 81, where axial refers to the bore direction of the contact openings 31, 32.The contact pins 71, 81 are therefore not firmly anchored in the contact openings 31, 32, for example by means of a soldering material, as in known embodiments, but rather are relatively freely movable.

[0045] To prevent the contact pins 71, 81 from moving out too far or even falling out, means are provided to define a maximum distance between the circuit carrier 30 and the heat sink 50 or to generate a force between these elements that presses them together. For example, the circuit arrangement 1 can be arranged in a housing that enforces a maximum distance, or suitable screw connections, for example, with spacer sleeves, are provided.

[0046] This means determines the greatest distance by which the contact pins 71, 81 can be withdrawn from the contact openings 31, 32 in the installed state. This distance is advantageously small compared to the thickness of the circuit carrier 30 in order to ensure sufficient electrical contact in every operating state. A situation in which a contact pin 71, 81 is withdrawn the greatest possible distance from the contact opening 31, 32 is shown in Figure 2 for the contact pin 71, 81 shown in the middle.

[0047] Further penetration of the contact opening 31, 32 by a contact pin 71, 81 is prevented by a collar on the contact pin 71, 81, i.e., a thickening whose diameter is larger than that of the contact opening 31, 32. The situation in which a contact pin 71, 81 is inserted as far as possible into the contact opening 31, 32 is shown on the right in Figure 2.

[0048] Figure 2 also shows, on the left side, a contact pin 71, 81 at a medium insertion depth. Between the maximum insertion depth and the minimum insertion depth, a maximum compensation capacity h of a contact pin 71, 81 results. The maximum compensation capacity h extends in the direction of the surface normal of the circuit carrier 30.

[0049] In order to utilize this compensation capacity h, the circuit arrangement comprises a plurality of spring elements 72, 82 in the edge region of the semiconductor assemblies 70, 80. Figure 1 shows only two such spring elements 72, 82, but there may be eight or a different number of spring elements 72, 82 for each of the semiconductor assemblies 70, 80. They are preferably evenly distributed over the edge of the respective semiconductor assembly 70, 80, being arranged between the semiconductor component 72, 82 and the circuit carrier 30. The spring elements 72, 82 are designed such that they push the respective semiconductor component 72, 82 away from the circuit carrier 30 and thus ensure a pressing force against the heat sink 50. They allow the movement of the semiconductor assemblies 70, 80 to such an extent that the maximum compensation capacity h can be utilized.

[0050] In this exemplary embodiment, the spring elements 72, 82 are cuboid-shaped blocks made of an elastomer. They are clamped outside the rows of contact pins 71, 81 between the circuit carrier 30 and the edge of the respective semiconductor module 70, 80 that projects beyond the contact pins 71, 82, and thus exert a force on the semiconductor module 70, 80 that acts to pull the contact pins 71, 81 out of the contact openings 31, 32. This force is counteracted by the means that determine the greatest distance between the heat sink 50 and the circuit carrier 30. Depending on the individual position and thickness of the semiconductor module, the contact pins 71, 81 are thereby pulled out of the contact openings 31, 32 to a greater or lesser extent within the scope of the maximum compensation capacity h.

[0051] In the example according to Figure 1, the second semiconductor module 80 is somewhat thicker than the first semiconductor module 70. Particularly if this difference in thickness is due to manufacturing and cannot be foreseen, structural compensation is difficult and a sufficient amount of thermal paste 60 must be present between the semiconductor modules 70, 80 and the heat sink 50 in order to compensate for any possible differences in thickness. The same applies to tilting due to construction or caused by thermal stresses. As shown in Figure 1, the spring elements 72, 82 ensure that the difference in thickness d between the semiconductor modules 70, 80 that exists here is compensated. This utilizes the fact that the contact pins 71, 81 are movable in the contact openings 31, 32 and thus the first semiconductor assembly 70 can be slightly raised relative to the second semiconductor assembly 80.This can be seen in Figure 1 in that the contact pins 72 of the second semiconductor assembly 80 are pushed further into the contact openings 32.

[0052] Because the spring elements 72, 82 are independent of one another, each of the semiconductor assemblies 70, 80 can also be tilted within the scope of the compensation capacity h. In this case, the contact pins 71, 81 of one of the semiconductor assemblies 70, 80 are pressed out of the contact openings 31, 32 to different extents, so that the respective semiconductor assembly 70, 80 is inclined relative to the circuit carrier 30. This can also compensate for bending or twisting of the circuit carrier 30 and / or heat sink 50. This can occur, for example, due to thermal stresses caused by different manufacturing temperatures, storage temperatures and operating temperatures.

[0053] In other embodiments, the material 100 is a low-melting solder with a melting point of, for example, 100°C or 120°C, and the operating temperature is normally 80°C. In such an embodiment, the material 100 is not yet liquid at the operating temperature, but is already liquid at a slightly elevated temperature. This enables compensation by displacement of the contact pins 71, 81 when an excessive temperature occurs and the material 100 liquefies. The material thus acts as a protective device that, at excessive temperatures, allows improved connection of the semiconductor module 70, 80 to the heat sink 50 in order to counteract the causes of a momentarily excessive temperature.

[0054] Reference sign

[0055] 1 Circuit arrangement

[0056] 30 Circuit carrier 31, 32 Contact openings

[0057] 50 heat sinks

[0058] 51 Fluid channel

[0059] 60 thermal paste

[0060] 70, 80 Semiconductor assembly 71, 81 Contact pins

[0061] 72, 82 spring elements

[0062] 100 Material h maximum compensation capacity d thickness difference

Claims

Patent claims 1. Circuit arrangement (1) with - a semiconductor assembly (70, 80) with a plurality of contact pins (71, 81) arranged parallel to one another, - a circuit carrier (30) with a plurality of internally metallized contact openings (31, 32) assigned to the contact pins (71, 81), wherein the contact pins (71, 81) are inserted into the contact openings (31, 32), - a cover element (50) which is arranged on the side of the semiconductor assembly (70, 80) facing away from the circuit carrier (30), - means for generating a first force which presses the circuit carrier (30) and the cover element (50) towards each other, wherein - the contact openings (31, 32) have on their inside a material (100) which has a melting point of at most 150 °C, - a plurality of spring elements (72, 82) are arranged between the semiconductor assembly (70, 80) and the circuit carrier (30), which spring elements cause second forces between the circuit carrier (30) and the semiconductor assembly (70, 80) which press the semiconductor assembly (70, 80) against the cover element (50).

2. Circuit arrangement (1) according to claim 1, wherein the spring elements (72, 82) are arranged such that the second forces can cause a tilting of the semiconductor assembly (70, 80).

3. Circuit arrangement (1) according to claim 1 or 2, wherein the spring elements (72, 82) are arranged at the edge of the semiconductor assembly (70, 80).

4. Circuit arrangement (1) according to one of the preceding claims with a paste (60) for heat conduction and / or electrical conduction between the cover element (50) and the side of the semiconductor module (70, 80) facing the cover element (50).

5. Circuit arrangement (1) according to one of the preceding claims, wherein the cover element (50) is a heat sink (50), in particular a heat sink (50) made of copper.

6. Circuit arrangement (1) according to one of claims 1 to 4, wherein the cover element (50) is a second circuit carrier (30).

7. Circuit arrangement (1) according to one of the preceding claims, wherein the material (100) is liquid at room temperature.

8. Circuit arrangement (1) according to one of claims 1 to 6, wherein the material (100) is solid at room temperature.

9. Circuit arrangement (1) according to one of the preceding claims, in which the material (100) has a gallium content.

10. Circuit arrangement (1) according to claim 9, wherein the material (100) is a eutectic alloy with gallium, indium and tin.

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