Field of invention

The present invention relates to a molded power module comprising a substrate provided with an upper conductive layer onto which at least one semiconductor is placed. The present invention also relates to a power module assembly.

Prior art

Molded modules such as power modules are widely used. When assembling a power module onto a heat sink with a thermal interface material (TIM) or an adhesive, the thickness of the layer of the TIM or the adhesive most often gets very thick locally because the bottom surface of the power module is not smooth but comprises small indentations. Since the available thermal interface materials and adhesives are not as good at conducting heat as the materials used to make the bottom surface of the power module and/or the heatsink, such local thickenings of the thermal interface material or the adhesive may severely reduce the effectiveness of cooling, and thereby reduce the efficiency of the power module itself.

The TIM or adhesive is a pasty material and during use of a molded module, the TIM or adhesive is repeatedly heated up and cooled down. The volume of the components of the molded module will slightly change in response to the temperature fluctuations. Consequently, the alternating thermal expansion and thermal contraction and forces applied to the module will gradually "pump out" some of the TIM or adhesive. Since the presence of the TIM or adhesive is important for the transfer of heat from the power module to the heat sink, it is a great disadvantage if it is lost during service.

Thus, there is a need for a molded power module which reduces or even eliminates the above-mentioned disadvantages of the prior art.

Summary of the invention

The object of the present invention can be achieved by a molded power module as defined in claim 1 and further by a power module assembly as defined in claim 18. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.

The molded power module according to the invention is a molded power module comprising: a substrate comprising an upper conductive layer; at least one semiconductor placed on the upper conductive layer of the substrate; a molded portion covering the at least one semiconductor, wherein the molded portion comprises at least two domes protruding from the remaining area of the molded portion, wherein the domes are spaced from each other.

Hereby, it is possible to provide a molded power module which reduces or even eliminates the above-mentioned disadvantages of the prior art. It is possible to lower the stiffness of the molded power module and hereby reduce the internal stresses in the molded power module. The invention makes it possible to reduce the thickness of the molded portion of the molded power module and/or only provide a molded portion above the semiconductor(s). The gaps between the domes reduce the overall mechanical stress within the molded power module and provide mechanical flexibility of the module. Accordingly, the force required to provide a sufficient thermal contact to structures below the upper conductive layer (e.g. a heat sink) can be reduced.

The upper conductive layer may be a metal layer. In one embodiment, the upper conductive layer is made of copper. In one embodiment, the upper conductive layer is made of aluminium.

The upper conductive layer may be formed from a lead frame structure.

In one embodiment, a single semiconductor is placed on the upper conductive layer of the substrate.

In one embodiment, two or more semiconductors are placed on the upper conductive layer of the substrate.

The molded power module comprises a molded portion covering the at least one semiconductor. The molded portion is made of an electrically non-conductive material. In one embodiment, the molded portion comprises a mold-compound, polymer, epoxy or cement. In one embodiment, the molded portion is made of a mold-compound, polymer, epoxy or cement.

The molded portion comprises at least two domes protruding from the remaining area of the molded portion, wherein the domes are spaced from each other.

In one embodiment, the molded portion comprises two domes protruding from the remaining area of the molded portion, wherein the domes are spaced from each other.

In one embodiment, the molded portion comprises three domes protruding from the remaining area of the molded portion, wherein the domes are spaced from each other.

In one embodiment, the molded portion comprises four domes protruding from the remaining area of the molded portion, wherein the domes are spaced from each other.

In one embodiment, the molded portion comprises five or more domes protruding from the remaining area of the molded portion, wherein the domes are spaced from each other.

In one embodiment, the domes are arranged above the one or more semiconductor. Hereby, the domes allow significant force to be applied either during manufacture (such as during a sintering or soldering process, in which the substrate is fixed to a heatsink) or during service (such as to compress the module against the heatsink to reduce the TIM layer to an extremely thin layer).

In one embodiment, the width of a dome corresponds to the width of the semiconductor arranged below the dome.

In one embodiment, the width of a dome is equal to or larger than the width of the semiconductor arranged below the dome.

In one embodiment, the width of a dome is larger than the width of the semiconductor arranged below the dome.

In one embodiment, the smallest width of a dome corresponds to the width of the semiconductor arranged below the dome.

In one embodiment, the smallest width of a dome is equal to or larger than the width of the semiconductor arranged below the dome.

In one embodiment, the smallest width of a dome is larger than the width of the semiconductor arranged below the dome. In one embodiment, at least some of the domes are symmetrical.

In one embodiment, the domes are symmetrical.

In one embodiment, the central portion of the dome is arranged below the central portion of the semiconductor arranged below the dome.

In one embodiment, the molded power module further comprises one or more terminals electrically connected to, and protruding from, the upper conductive layer.

In one embodiment, the molded power module comprises a single terminal electrically connected to and protruding from the upper conductive layer.

In one embodiment, the molded power module comprises two terminals electrically connected to and protruding from the upper conductive layer.

In one embodiment, the molded power module comprises three terminals electrically connected to and protruding from the upper conductive layer.

In one embodiment, the molded power module comprises three or more terminals electrically connected to and protruding from the upper conductive layer.

In one embodiment, the domes extend above the level of the one or more terminals.

Hereby, it is possible to cover the proximal portion of one or more terminals with a dome. Accordingly, force can be applied towards the dome(s) covering the proximal portion of one or more terminals. The force will be transferred to the upper conductive layer via the mold material of the domes and the one or more terminals.

In one embodiment, the substrate comprises an insulator, where the upper conductive layer is placed on the insulator.

In one embodiment, the substrate comprises a lower conductive layer provided below the insulator, wherein the insulator is sandwiched between the upper conductive layer and the lower conductive layer.

In one embodiment, the substrate is a Direct Copper Bonded (DCB) substrate.

In one embodiment, an intermediate area with mold material is provided between adjacent domes.

In one embodiment, an intermediate area with another material than the molded portion is provided between adjacent domes.

In one embodiment, an intermediate area with no material (material free gap) is provided between adjacent domes.

In one embodiment, only the substrate extends all the way between and thus connects adjacent domes. Hereby, it is possible to increase the mechanical flexibility of the molded power module. Accordingly, the overall mechanical stress within the molded power module can be reduced.

In one embodiment, that only the insulator extends all the way between and thus connects adjacent domes.

In one embodiment, the substrate exposed at the surface of the molded power module comprises several separated sections, wherein each separated section is at least partly surrounded by a cavity constituting storage for the thermal conductive material. The surface will normally be the bottom portion of the molded.

In one embodiment, the substrate exposed at the surface of the module is a lower conductive layer.

The lower conductive layer may be a metal layer. In one embodiment, the lower conductive layer is made of copper. In one embodiment, the lower conductive layer is made of aluminium.

In one embodiment, the cavity is in fluid communication with a storage structure that at least partly surrounds the cavity, wherein the storage structure is configured to receive thermally conductive material from the cavity and return thermally conductive material to the cavity. Hereby, the thermally conductive material does not escape to the surroundings like in the prior art.

In one embodiment, each separated section is placed directly beneath a dome.

In one embodiment, only the separated sections are made of metal.

In one embodiment, only the separated sections are made of copper.

In one embodiment, at least some of the cavities are made as cavities in the molded portion.

In one embodiment, all cavities are provided as cavities in the molded portion.

In one embodiment, at least some of the storage structures are made as storage structures in the molded portion.

In one embodiment, all storage structures are made as storage structures in the molded portion.

In one embodiment, the molded portion surrounds the entire substrate except for the separated sections that protrude from the backside of the substrate through the molded portion.

In one embodiment, molded portion covers the top side of the molded power module, wherein the backside of the substrate is not covered by the molded portion.

In one embodiment, grooves forming the cavities are etched into the backside of the substrate.

In one embodiment, grooves forming the storage structures are etched into the backside of the substrate.

In one embodiment, the insulator has a thickness in the range 0.1-0.8 mm.

In one embodiment, the conductive layers have a thickness in the range 0.1-3.0 mm.

In one embodiment, the thermal conductive material has a thickness in the range 0.005-1.0 mm

In one embodiment, the thermal conductive material is sinter having a thickness below 500 pm, preferably below 100 pm.

In one embodiment, the thermal conductive material is a thermal interface material having a thickness below 50 pm, preferably in the range 5-50 pm.

In one embodiment, the domes comprise a flat top portion and inclined portions extending therefrom.

In one embodiment, the angle a between the top portion and the inclined portions is in the range 30-89 degrees.

In one embodiment, the angle a between the top portion and the inclined portions is in the range 40-88 degrees.

In one embodiment, the angle a between the top portion and the inclined portions is in the range 45-88 degrees.

The molded power module may with advantage be combined with a heat sink or a baseplate to form a power module assembly.

In one embodiment of such a power module assembly, a heat sink or baseplate is arranged below, and thermally connected to, the substrate. Hereby, the heat sink or baseplate can be used to provide an efficient cooling of the heat generated by the molded power module.

In one embodiment, a thermally conductive material is provided between the heat sink or baseplate and the substrate.

In one embodiment, the power module assembly comprises structures arranged and configured to press the molded power module against the heat sink or baseplate by applying pressure onto the domes. Hereby, the overall force can be reduced compared to prior art because in the invention only applies pressure in the areas (above the semiconductor(s)) where it is required to provide pressure. In one embodiment, the power module assembly comprises a fixing device configured to provide a force on top of the domes downwards towards the substrate.

In one embodiment, fixing device is attached to the heat sink or baseplate by means of screws.

In one embodiment, the fixing device comprises one or more spring washers.

In one embodiment, the fixing device comprises one or more screws.

In one embodiment, the fixing device is a lid of a housing.

In one embodiment, the fixing device is a lid of an inverter housing.

In one embodiment, the fixing device comprises a plate that is arranged and configured to provide a force towards the top surface of the domes.

In one embodiment, the fixing device comprises clamping structures arranged and configured to provide a force of at least 1 N towards each dome.

In one embodiment, at least some of the cavities described above are made as cavities in the in the upper face of the heat sink.

In one embodiment, all cavities are made as cavities in the in the upper face of the heat sink.

In one embodiment, at least some of the storage structures described above are made as storage structures in the in the upper face of the heat sink.

In one embodiment, all storage structures are made as storage structures in the in the upper face of the heat sink.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1A shows a side elevation view of a molded power module according to the invention;

Fig. IB shows a side elevation view of a power module assembly comprising the molded power module shown in Fig. 1A;

Fig. 1C shows a side elevation view of the power module assembly shown in Fig. IB, wherein the power module assembly comprises a fixing device arranged and configured to provide a force towards the top surface of the molded power module portion;

Fig. 2A shows a cross-sectional view of a molded power module according to the invention;

Fig. 2B shows a cross-sectional view of another molded power module according to the invention;

Fig. 2C shows a cross-sectional view of a power module assembly according to the invention;

Fig. 3A shows an exploded view of a power module assembly according to the invention comprising a molded power module;

Fig. 3B shows a cross-sectional view of the power module assembly shown in Fig. 3A in a configuration in which the molded power module is attached to the heat sink; Fig. 4A shows a cross-sectional view of a molded power module according to the invention;

Fig. 4B shows a cross-sectional view of another molded power module according to the invention;

Fig. 5A shows a perspective top view of a molded power module according to the invention;

Fig. 5B shows a perspective bottom view of the molded power module shown in Fig. 5A;

Fig. 5C shows a cross-sectional view of the molded power module shown in Fig. 5A and Fig. 5B;

Fig. 6A shows a cross-sectional view of a power module assembly according to the invention;

Fig. 6B shows a close-up view of a portion of the power module assembly shown in Fig. 6A;

Fig. 6C shows a prior art molded power module.

Fig. 7 shows a side elevation view of a power module assembly similar to that shown in Fig. 1C;

Fig. 8 shows a side elevation view of a particular embodiment of a power module assembly comprising the invention;

Fig. 9 shows a cross-sectional view in detail of the cavities and the storage structures which are used to control the motion and distribution of the thermally conductive material;

Fig. 10 shows a partial cross-sectional view of an embodiment of the molded power module according to the invention, and

Fig.11 shows a partial cross section of a further embodiment of the inventive power module.

Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a molded power module 2 of the present invention is illustrated in Fig. 1A. Fig. 1A illustrates a side elevation view of a molded power module 2 according to the invention. The molded power module 2 comprises a lower box-shaped part onto which two spaced apart domes 18, 18' are placed.

The height (thickness) of the lower box-shaped part basically corresponds to the height (thickness) of the domes 18, 18'.

The lower box-shaped part comprises a first base structure 26 and a second base structure 26'. The first base structure 26 constitutes a first end portion, while the second base structure 26' constitutes a second opposite end portion. An intermediate area 24 is provided between the domes 18, 18'. The space between the domes 18, 18' basically corresponds to the width of the second dome 18'. Each dome 18, 18' is shaped as an isosceles trapezoid.

Fig. IB illustrates a side elevation view of a power module assembly 3 comprising the molded power module 2 shown in Fig. 1A. The molded power module 2 is placed on an interface 13 that is placed on a heat sink 20. The interface 13 comprises a material which is thermally conducting to enable heat generated within the molded power module 2 to be conducted into the heat sink 20. The interface may comprise a material suitable for enhancing the thermal contact between the molded power module 2 and the heat sink 20. Such a material may comprise a thermal interface material, grease, fluid. The interface may alternatively or additionally comprise a material that holds the molded power module 2 in fixed contact with the heat sink 20. Such a material may comprise a sinter layer, solder layer or glue layer.

Fig. 1C illustrates a side elevation view of the power module assembly 3 shown in Fig. IB, wherein the power module assembly 3 comprises a fixing device 28 arranged and configured to provide a force towards the top surface of the molded power module 2. The fixing device 28 is shaped as a plate provided with through-going bores. Screws 31, 31' extend through these through-going bores. The screws 31, 31' are attached to the heat sink 20. Hereby, the fixing device 28 presses the molded power module 2 towards the heat sink 20. In one embodiment, the screws 31, 31' are screwed into corresponding threaded bores in the heat sink 20.

Fig. 2A illustrates a cross-sectional view of a molded power module 2 according to the invention. The molded power module 2 comprises a lead frame structure 11 provided with three separated upper conductive layers 5, 5', 5". A first semiconductor 10 is placed on the first upper conductive layer 5. A second semiconductor 10' is placed on the third upper conductive layer 5". A wire bond 22 electrically connects the first semiconductor 10 and the second upper conductive layers 5'.

The molded power module 2 comprises a molded portion 30 that basically corresponds to the one shown in and explained with reference to Fig. 1A. The molded portion 30 comprises a lower box-shaped part and two spaced apart domes 18, 18' that protrude from the box-shaped part.

The height of the box-shaped part corresponds to the height of the domes 18, 18'. The lower box-shaped part comprises a first base structure 26 and a second base structure 26' and an intermediate area 24 provided between the domes 18, 18'. The domes 18, 18' protrude from the remaining area of the molded portion 30.

Fig. 2B illustrates a cross-sectional view of another molded power module 2 according to the invention. The molded power module 2 comprises a molded portion 30 that comprises the same structures as the one shown in and explained with reference to Fig. 2A. The molded power module 2 comprises a substrate 12 provided with three separated upper conductive layers 6, 6', 6" that are placed on an insulator 4. The insulator 4 is placed on a first lower conductive layer 8 and a second lower conductive layer 8'. The lower conductive layers 8, 8' are arranged below the first semiconductor 10 and the second semiconductor 10', respectively. The substrate 12 may be a DCB substrate.

The first semiconductor 10 is placed on the first upper conductive layer 6, while the second semiconductor 10' is placed on the third upper conductive layer 6". A wire bond 22 electrically connects the first semiconductor 10 and the second upper conductive layers 6'.

The domes 18, 18' comprise inclined side portions 32, 32'. The angle a of the left side portion of the first dome 18 is indicated. The angle a (between the top portion 50 and the inclined side portion 32) is approximately 45 degrees. The angle a can, however, be smaller e.g. in the range 5-40 degrees.

Fig. 2C illustrates a cross-sectional view of a power module assembly 3 according to the invention. The power module assembly 3 comprises a molded power module 2 with the same features as the one shown in and explained with reference to Fig. 2B. The power module assembly 3, however, comprises a heat sink 20. The first lower conductive layer 8 and the second lower conductive layer 8' of the substrate 12 are placed on and attached to the heat sink 20. Hereby, a thermal connection is established between the lower conductive layers 8, 8' and the heat sink 20. Accordingly, heat produced by the first semiconductor 10 and the second semiconductor 10' can be transferred to the heat sink 20. The heat sink 20 can release the generated heat to the surroundings through heat exchange.

Fig. 3A illustrates an exploded view of a power module assembly 3 according to the invention comprising a molded power module 2. The molded power module 2 basically corresponds to the one shown in and explained with reference to Fig. 2A. The molded power module 2 is arranged above an insulator 4. The insulator 4 is arranged above a heat sink 20.

Fig. 3B illustrates a cross-sectional view of the power module assembly 3 shown in Fig. 3A in a configuration in which the molded power module 2 is attached to the heat sink 20. Force F is applied to the domes 18, 18' in such a manner that the molded power module 2 is pressed towards the heat sink 20.

Fig. 4A illustrates a cross-sectional view of a molded power module 2 according to the invention. The molded power module 2 comprises a DCB substrate 12 having an insulator 4 that is sandwiched between upper conductive layers 6, 6', 6" and lower conductive layer 8, 8'. A first semiconductor 10 is attached to the first upper conductive layer 6. A second semiconductor 10' is attached to the third upper conductive layer 6". A wire bond 22 electrically connects the first semiconductor 10 and the second upper conductive layers 6'.

The molded power module 2 comprises a molded portion 30 that comprises two spaced apart domes 18, 18'.

The first dome 18 protrudes from a first base structure 26 of the molded portion 30. Likewise, the second dome 18' protrudes from a second base structure 26'. An intermediate area 24 is provided between the domes 18, 18'. It can be seen that the intermediate area 24 is empty and thus contains no mold compound. An empty space is also provided under the insulator 4 below the intermediate area 24.

Fig. 4B illustrates an exploded view of another molded power module 2 according to the invention. The molded power module 2 basically corresponds to the one shown in and explained with reference to Fig. 4A. A material 34, however, is provide in the intermediate area 24. Accordingly, the intermediate area 24 is not empty like in Fig. 4A. Likewise, the material 34 is also provided under the insulator 4 below the intermediate area 24.

Fig. 5A illustrates a perspective top view of a molded power module 2 according to the invention. Fig. 5B illustrates a perspective bottom view of the molded power module 2 shown in Fig. 5A. Fig. 5C illustrates a cross-sectional view of the molded power module 2 shown in Fig. 5A and Fig. 5B.

The molded power module 2 comprises a molded portion having a plurality of domes 18, 18' protruding from the remaining part of the molded portion. The domes 18, 18' are provided at the top side 36 of the module 2. The domes 18, 18' are equally shaped and spaced apart. The domes 18, 18' are arranged in two sections separated by a space provided above the central portion of the molded power module 2.

The molded power module 2 comprises a plurality of terminals 14, 15, 16, 17. Three terminals 14, 15, 16 protrude from a first end portion of the molded power module 2. A single terminal 17 protrudes from the opposite end of the molded power module 2. The terminals 14, 15, 16, 17 extend parallel to each other.

The terminals 14, 15, 16, 17 extend through base structures 26 of the molded portion.

Fig. 5B illustrates that a plurality of substrate sections 40, 40' are provided at the bottom side 38 of the molded power module 2. Each section 40, 40' is arranged below a dome 18, 18'. A gap 41 may at least partly surround each section 40, 40'. The gaps 41 in this embodiment are formed as a trench that completely surrounds the respective substrate section. These gaps 41 may, with advantage, act as the cavities 44 and/or the storage structures 48 described below.

Fig. 5C illustrates that the molded power module 2 comprises a substrate provided with an upper conductive layer, wherein a plurality of semiconductors 10, 10', 10" are placed on the upper conductive layer 6. It can be seen that the molded power module 2 comprises several terminals 14, 17 that are electrically connected to and protruding from the upper conductive layer 6. The molded power module 2 comprises a molded portion that covers the semiconductors 10, 10', 10". The domes 18, 18' comprise inclined portions 32, 32' and flat top portions. The domes 18, 18' are spaced from each other as an Intermediate area 24 extends between them.

Fig. 6A illustrates a cross-sectional view of a power module assembly 3 according to the invention. The power module assembly 3 comprises a substrate 12 having an insulator 4 that is sandwiched between upper layers 6 and lower layers 8. Semiconductors 10, 10' are placed on the upper layers 6. Wire bonds 22 are used to electrically connect semiconductors 10, 10' with upper layers.

The power module assembly 3 comprises a terminal 17 electrically connected to and protruding from the upper conductive layer 6. The power module assembly 3 comprises a molded portion that covers the semiconductors 10, 10'.

The molded portion comprises a plurality of domes 18, 18', 18" protruding from the remaining area of the molded portion. The domes 18, 18', 18" are spaced from each other. Intermediate areas 24 are provided between adjacent domes 18, 18', 18". The lower layers 8 are attached to heat sink 20. A thermal conductive material 42 (e.g. thermal interface material, grease, fluid or sinter material) is provided between the lower layers 8 and the heat sink 20 to improve the thermal connection. Force F is applied to the domes 18, 18', 18" from above.

Fig. 6B illustrates a close-up view of a portion of the power module assembly 3 shown in Fig. 6A. It can be seen that the cavities 44 are provided next to the sections 40, 40' of the lower layer 8. Each cavity 44 is used as storage for the thermal conductive material 42. In this embodiment, the cavities 44 surround each "metal island" section 40, 40' of the lower layer 8. Each section 40, 40' is surrounded by one larger cavity 44 which in turn is further surrounded by two smaller storage structures 48, here are formed as grooves. The storage structures 48 act as reservoirs whereto surplus TIM (or adhesive) can flow when the module is pressed into a heat sink 20 with a force F. This enables the thinnest TIM layer possible (constrained only by the surface roughness of the module and the heat sink) without local thickening that would otherwise increase the thermal resistance significantly.

The substrate 12 exposed at the surface of the power module assembly 3 comprises several separated sections 40, 40', wherein each separated section is at least partly surrounded by a cavity 44 constituting storage for the thermal conductive material. Accordingly, during alternating thermal expansion and thermal contraction and when forces applied to the power module assembly 3 the thermal conductive material 42 can enter and leave the cavities 44.

It can be seen that a fill material 46 is provided in the space between the adjacent lower layers 8. Moreover, a storage structure 48 is provided next to the cavities 44. The storage structure 48 may constitute a guide structure or barrier.

Fig. 6C illustrates a prior art power module assembly 102. The power module assembly 102 comprises a DCB substrate 112 having an insulator 104 sandwiched between upper layers 106 and a lower layer 108. Semiconductors 110, 110' are placed on the upper layer 106. The DCB substrate 112 is attached to a heat sink 20. The power module assembly 102 comprises a molded portion having a basically box-shaped geometry. A wire bond 122 is used to electrically connect a semiconductor 110 and an upper layer.

Fig. 7 shows a side elevation view of a power module assembly similar to that shown in Fig. 1C. Here the power module assembly 3 comprises a fixing device 28 arranged and configured to provide a force towards the top surface of the molded power module 2. The fixing device 28 is shaped as a plate provided with through-going bores. Screws 31, 31' extend through these through-going bores. The screws 31, 31' are attached to the heat sink 20. Hereby, the fixing device 28 presses the molded power module 2 towards the heat sink 20. In one embodiment, the screws 31, 31' are screwed into corresponding threaded bores in the heat sink 20. In contrast to the embodiment shown in Fig. 1C, springs 62, 62' are inserted between the plate and the module in order to further stabilise the application of a downward force to the module on top of the dome structures 18, 18'.

In the embodiment shown in Fig. 7, a thermally conductive material 42 is shown placed between the base of the power module 2 and the heat sink 20. In this case, the thermally conductive material comprises a fluid (such as a thermal grease) or other material which can flow under the application of pressure on top of the module. This application of pressure to the top of the module via the dome structures 18, 18'results in higher pressure directly beneath the domes 18, 18', and thus a thinner film of thermally conductive material. Thus in the areas marked by the reference 64, the thermally conductive material is significantly thinner than in other areas. This thinning of the thermally conductive material will preferentially happen in areas directly under the dome structures, and thus directly under the heat producing components within the power module.

Fig. 8 shows a side elevation view of a particular embodiment of a power module assembly 3 comprising the invention. Here, a film 61, such as an organic film, is placed between the power module 2 and the heat sink 20 and pressure has is applied, together with heat, so that the power module 2 and the heat sink 20 become permanently laminated together to form a single power module assembly structure 3. As has been described above, the combination of pressure applied to the tops of the dome structures 18, 18' and the fluidity of the material 43 during the lamination process results in areas 64 of significantly thinner thermally conductive material at critical points in the structure.

Fig. 9 shows a cross-sectional view in detail of the cavities 44 and the storage structures 48 which are used to control the motion and distribution of the thermally conductive material 42. The cavities 44 and storage structures 48 are here formed within the encapsulation mold material 30 at the same level as the lower conductive layer 8 of the substrate 12. Portions of the thermally conductive material 42 are shown partially filling the cavities 44 and the storage structures 48.

Fig. 10 shows a partial cross-sectional view of an embodiment of the molded power module 2 according to the invention. The structure of the molded power module 2 in this embodiment is similar to that shown in Fig. 2C, and comprises a molded portion 30 that comprises the same structure as the one shown in and explained with reference to Fig. 2A. The power module 2 is shown in combination with a heat sink 20 to form a power module assembly 3. Hereby, a thermal connection is established between the lower conductive layer 8, and the heat sink 20. Accordingly, heat produced by the semiconductor 10 can be transferred to the heat sink 20. The heat sink 20 can release the generated heat to the surroundings through heat exchange. Cavities 44 and storage structures 48 are again used in this embodiment to control the motion and distribution of the thermally conductive material 42. The cavities 44 and storage structures 48 are here formed within the upper surface of the heat sink 20. Portions of the thermally conductive material 42 are shown partially filling the cavities 44 and the storage structures 48.

Fig. 11 shows a partial cross section of a further embodiment of the inventive power module 2. Here the cavity 44 used for storage of the thermally conductive material 42 (not shown here) is formed from etched structures in the lower conductive layer 8. Material has been removed from the lower conductive layer 8 to form gaps which form the cavities 44 used for storage of the thermally conductive material.

List of reference numerals

2 Molded power module

3 Power module assembly

4 Insulator

5, 5', 5" Upper conductive layer of a lead frame

6, 6', 6" Upper conductive layer

8, 8' Lower conductive layer

10 Semiconductor Lead frame structure

12 Substrate

13 Interface

14, 15 Terminal

16, 17 Terminal

18, 18', 18" Dome

20 Heat sink or baseplate

22 Wire bond

24 Intermediate area

26, 26' Base structure

28 Fixing device

30 Molded portion (mold compound)

31, 31' Screw

32, 32 Inclined portion

34 Material

36 Top side

38 Bottom side

40, 40' Section of substrate

41 Gap

42 Thermally conductive material (e.g. thermal interface material, grease, fluid or sinter material) 44 Cavity (storage for the thermally conductive material)

46 Fill material

48 Storage structure

50 Top portion

61 Laminate film

62, 62' Spring

63 Force applied during lamination

64 Area of thin thermally conductive material

F Force a Angle

102 Power module assembly

104 Insulator

106 Upper layer

108 Lower layer

110 Semiconductor

110' Semiconductor

112 Substrate

122 Wire bond