Modular semiconductor power device

Abstract

A modular semiconductor power device has a conductive member consisting of an alumina plate to which copper layers are soldered on opposite sides. A chip is soldered to one of these layers and the other of these layers is soldered in turn to a metal heat sink. The chip is connected to respective copper strips which, in turn, are soldered to thermal strips originally forming part of a frame so that, after the device is encapsulated in a synthetic resin, the connecting members of the frame can be cut away to leave free ends of the latter strips exposed.

Description

that

SPECIFIC DESCRIPTION

In FIG. 1 the base plate 11 of the device acts as a heat sink as well as a support and fastener for the device itself. It is made of heat-conductive metal with high mechanical strength. The holes A in it serve to secure it, by means of screws, onto the external heat spreader, while the grooves V serve to absorb any possible deformation of the base plate due to the high tightening torque, thereby preventing them from being transmitted to the central portion of the plate.

The S-shaped recesses M, on the sides (see the side and cross-sectional views of the plate shown in FIGS. 2a and 2b) serve to ensure a better adhesion of the subsequently applied resin encapsulation, as is explained more clearly further on with reference to FIG. 8b.

FIG. 1 also shows the components 12 and 13, which are two chip-supporting substrates, which are soldered onto the base plate 11 by means of the layers of solder 14.

As illustrated in FIGS. 3a, 3b and 3c (bottom, top and cross-sectional views of a substrate) each substrate is composed of a quadrangular-shaped thin medial layer 31 of alumina (less than 1 mm thick), with thin copper plates soldered directly onto its two lateral faces. More precisely, soldered onto the face destined to lie facing the upper face of the base plate 11 is a single copper plate 32, which is also quadrangular in shape but with slightly smaller dimensions than those of the layer of alumina, while the other face is provided with rectangular plate 33, for supporting the chips and for the connections with an external electrode, and, on either side of said plate 33, narrower plates (lateral strips) 34, 35 and 36 designed both for soldering the conductor for connection with the chips, and for soldering other external electrodes.

FIG. 4 shows the device 41 as it appears after the two substrates have been soldered onto the base plate, the chips have been soldered onto the larger upper copper plates b and f, and the electrical connections have been carried out between the chips and the lateral strips a, c, d, e, g, similiar similar to those of silicon. This reduces to a minimum the thermomechanical stress which would otherwise be transmitted to the chips due to the differential expansion of silicon and copper (other embodiments envisage the insertion, between the chips and the supporting copper plates, of layers of material, such as for example, molybdenum, having an expansion coefficient lying half way between those of silicon and copper, which however complicate the assembling and lower the thermal performance).

The use of a low-stress type of resin helps to limit the stress transmitted to the chips even in the case of chips of very large dimensions.

It is also clear that numerous modifications, adjustments, variations and substitutions may be made to the embodiments previously described by way of example, always remaining within the spirit of this invention and its scope. For example, the wires connecting the chips to the metal strips of the substrates can be by direct soldering between the inner terminal portions of the one-piece frame and the chips, whenever the latter have wettable metal coatings. These internal portions can then be soldered to points (P) of connection with the chips situated on the aforesaid plates 33 and strips 34, 35, 36 (as in the case illustrated in FIGS. 4 and 5), or situated on the same plates and on wettable coatings on the surface of the chips.

Likewise, the chip-supporting substrates could have a different structure from that previously described and the insulation between the chips and the dissipator could be achieved by means of a layer of encapsulating resin itself--which in this case should be of high thermal conductivity--instead of by a layer of alumina.

Claims

1. A modular semiconductor power device, comprising:

a conductive member comprising:

first conductive-sheet means formed from a plurality of copper strips,

an intermediate layer of alumina to which said first-conductive sheet means is plurality of copper strips are directly soldered attached, and

a further conductive copper sheet directly soldered attached onto a side of said intermediate layer opposite said conductive first conductive-sheet means plurality of copper strips;

a plurality of chips soldered at least one semiconductor chip attached to at least one of said copper strips of said first conductive sheet means ;

a heat-dissipating metal plate for dissipating heat generated by the Joule effect and soldered to which said further conductive sheet is attached; and

a one-piece frame formed with connection strips adapted to form signal and power terminals of said device having temporary connections between outer ends of said connection strips, said connection strips having inner ends selectively soldered attached to points of said first conductive sheet means copper strips connected to said at least one semiconductor chips and to said strips .

2. The device defined in claim 1, further comprising a body of an insulating resin encapsulating at least active parts of said conductive member, said at least one semiconductor chips and said heat dissipating metal plate leaving only said outer ends of said connection strips and an outer surface of said plate uncovered by said resin.

3. A modular semiconductor power device, comprising:

a conductive member comprising:

first conductive-sheet means formed from a plurality of coplanar copper strips,

an intermediate layer of alumina to which said first-conductive sheet means is copper strips are directly soldered attached, and

a further conductive copper sheet directly soldered attached onto a side of said intermediate layer opposite said conductive first conductive-sheet means copper strips;

a plurality of semiconductor chips soldered attached to said copper strips of said first conductive sheet means ;

a heat-dissipating metal plate for dissipating heat generated by the Joule effect and soldered and attached to said further conductive sheet; and

an array of conductor strips selectively soldered connected to points of said first conductive-sheet means copper strips and to said semiconductor chips, said device being encapsulated in an insulating resin so that only outer ends of said conductor strips and an outer surface of said plate remain uncovered by said resin.

4. The modular semiconductor device defined in claim 3 wherein said heat-dissipating metal plate is formed with respective grooves on opposite sides of said conductive member along a surface of said heat-dissipating metal plate soldered attached to said further conductive sheet.

5. The modular semiconductor device defined in claim 3 wherein said heat-dissipating metal plate is formed along a side thereof opposite that at which said further conductive sheet is soldered connected to said heat-dissipating metal plate with S-shaped formations in which said insulating resin is anchored.

6. A modular semiconductor device, comprising:

a conductive member comprising:

a first conductive sheet,

an intermediate layer to which said first conductive sheet is directly attached, and

a second conductive sheet directly attached to said intermediate layer on a side opposite said first conductive sheet;

a semiconductor chip attached to said first conductive sheet;

a heat dissipating plate attached to said second conductive sheet; and

a frame formed with strips to provide signal and power terminals for said device, said strips having inner ends for attachment to contact points for selective connection to said chip.

7. The device defined in claim 6, further comprising a body of an insulating resin encapsulating at least portions of said frame, said semiconductor chip, and said heat dissipating plate.

8. The device defined in claim 6, wherein said first and second conductive sheets are copper and said intermediate layer is alumina.

9. The device defined in claim 6, further comprising a layer between said semiconductor chip and said first conductive sheet.

10. The device defined in claim 6, further comprising a plurality of conductive strips directly attached to said intermediate layer and coplanar with said first conductive sheet, providing connection points for said inner ends of said frame.

11. The device defined in claim 9, wherein said layer comprises molybdenum.