WO2009068010A1 - Laminated power electronics subassembly - Google Patents

Abstract

Disclosed is a semiconductor subassembly for power electronics, comprising an at least partly metallized substrate (10) with at least one semiconductor component (30) that is arranged thereon and is electrically contacted on the bottom face. Said semiconductor subassembly further comprises an electrically insulating polymer film (50) which tightly surrounds the semiconductor component by applying pressure and is made of a polymer that can flow under pressure. The film has slots at predetermined points. At least one metal band (40) is guided through said slots at least once from one side of the film to the other as a contact element and electrically contacts the top face of the semiconductor component.

Description

 P 5684t> va7045

University of Applied Sciences Kiel Sokratesplatz 1

D-24149 Kiel

Laminated power electronic bauble

The invention relates to a semiconductor module for the power electronics, which is assembled in a one-step pressure contact method and at the same time laminated at the same time.

From DE 10 2004 057 494 A1, a semiconductor component is known, in which the upper side makes electrical contact with a metallization by means of an electrically insulating polymer film which tightly encloses the element. DE 101 21 970 Al describes a similar device whose metallizations are part of a flexible printed circuit board. DE 10 2006 014 582 A1 and DE 10 2005 031 836 A1 relate to semiconductor components which are provided with a metal strip serving as a contact element.

Semiconductor modules for power electronics typically comprise a plurality of semiconductor components on a circuit-wise prestructured substrate and an arrangement of connecting elements on the upper sides of the components. The connection or the contact elements usually consist of a plurality of parallel bonding wires, which are rubbed by a suitable Verbmdungstechnik, for example, micro-O-welding or ultrasonic bonding in the semiconductor surfaces. This goes with a considerable deformation the wires and is with respect to the cycle load of the assembly with currents of the order of 100 A proved to be disadvantageous for the durability of the bonds.

The semiconductor devices themselves are according to the teaching of DE 34 14 065 Al preferably via pressure sintering technology (in particular with silver) connected flat to the substrate. Common substrates are industrial ceramics with double-sided metallization layers, of which at least the side facing the semiconductor components is prestructured. The pre-structuring implements a circuit-compatible arrangement of mutually insulated interconnects via which the interconnection of the semiconductor components sintered onto the interconnects takes place from the underside. The metal cushion between the component and the substrate, which is produced by the pressure of the beads, serves, in addition to the attachment, also to realize a low electrical contact resistance as well as a small heat transfer resistance. The assembly of the assembly with the side of the substrate facing away from the components onto a heat sink (for example water cooling) is also state of the art.

The problem of bonding the contact elements is examined in detail in the work of Amro et al., "Double-Sided Low-Temperature Joining Technique for Power Cycling Capability at High Temperature" (Proc. EPE2005, Dresden 11-14 Sept.2005) Work comes to the realization that the service life of power assemblies can be significantly increased, even if the contact elements are attached to the tops of the semiconductor devices via a sintering technique instead of the adverse deformation of the contact elements themselves, the sintered mass (eg silver powder-containing paste) under pressure and heat formed and causes the fixed embedding of the contact elements.

Since the pressure sintered connection is to be preferred to a planar fastening in relation to the punctiform one of the wire bonding, Amro et al. Instead of a plurality of parallel bonding wires, individual metal ribbons ("ribbon"), for example made of silver, are also used, which, due to their large cross-sectional area, are well suited for the transport of large currents.

Due to the considerable differences in the coefficients of thermal expansion of the metal of the contact elements and of the semiconductor components, during operation of the module Set shear forces along the assembly plane, which in particular act on the contact bonds and solve them over time. As a remedy, it is state of the art to arrange the contact elements in the form of lifting off from the module level loops, so that the thermal expansion of the metal contacts leads primarily to shear force components perpendicular to the module level, which remains harmless for the bonds. Such loops are common in wire and ribbon bonds.

To achieve sufficient impact resistance of the finished power assemblies, it is common to shroud the assembly with an insulating material (e.g., silicone rubber) above the contact elements. Also known is the use of a potting compound with a high dielectric constant for improved internal electrical insulation.

From DE 196 17 055 Cl a power assembly in multi-layer construction is known, in the production of the same time the electrical contact between the substrate and semiconductor devices and between components and connecting elements circuit in a single step, such as by isostatic pressurization with heating (sintering step) can take place. The potting compound is hereby replaced by prefabricated, in particular provided with local recesses Isoliermaterialfolien, so-called PrePregs (PRE inPREGnated sheet material). These are flexible insulator sheets (e.g., a polymer) with double-sided resin coating, whereby the resin can be brought into its final solid form by hot pressing. On the semiconductor devices and the PrePreg, a flexible printed circuit board (e.g., polyimide with incorporated copper traces) is laid for circuit-wise contacting the device tops in the region of the recesses of the PrePregs.

Topsides and bottoms of the semiconductor devices are already provided with sintering paste during assembly. By adding, for example, a drop of alcohol, the components are held in place by adhesion to the pressure sintering on the substrate. The entire "sandwich" of substrate, pre-mounted components, prepreg and flexible circuit board can then be pressed into a finished laminated assembly with a single pressurization. - A -

The currently used pressure range for the pressure sintering step is 10 MPa to 60 MPa. In the production according to the teaching of DE 196 17 055 Cl there is therefore the risk of mechanical destruction, in particular of the edge regions of the semiconductor components. DE 10 2005 047 567 B3 therefore teaches to replace the PrePreg with an insulating molded body which initially projects beyond the height of the semiconductor components and has recesses for the components which are longer and wider than the component dimensions. By pressing the height of the insulating molding is reduced, at the same time it expands laterally and the components then surrounds flush from all sides. In this way, a more even pressure distribution during the pressure sintering is achieved.

The insulating moldings of DE 10 2005 047 567 B3 have, in addition to the electrical insulation and the pressure distribution, the advantage of a relatively flush leveling of the upper sides of components and moldings during the pressing process. The applied flexible printed circuit board is thereby exposed under the high pressure only minor differences in level. In particular, it is not bent over the edges of the components away by pressing, which can damage the conductor tracks in the circuit board.

Nevertheless, according to the teaching of DE 10 2005 047 567 B3, the laminated assembly still consists of the four structured construction levels mentioned above, which must all be accurately fitted together prior to pressure sintering.

It is therefore an object of the invention to propose a laminated power assembly, which consists of only three structured building levels and in particular dispenses with a pre-punched insulation molding.

The object is achieved by a power module having the features of claim 1. The subclaims indicate advantageous embodiments.

The starting point of the invention is a structured substrate with prefabricated, circuitally positioned semiconductor devices according to the prior art. Preferably, between components and substrate already in the automatic Bestü- a sintered metal paste arranged, which is solidified by pressure sintering only in the final, at the same laminating pressing process.

It is now provided according to the invention to completely dispense with the insulating molding, and to replace the flexible printed circuit board by a structured polymer film. Preferably, the film should consist of PTFE or a silicone polymer, since these materials are good electrical insulators and at the same time flowable under pressure. The latter is not the case, in particular for polyimide, from which conventional flexible circuit boards are made.

The inventive, flowable under pressure film has a structuring, with the aid of which metallic contact elements can be fixed in a circuit-oriented arrangement therein. According to the invention, the contact elements are relatively thick (300 μm-500 μm) metal strips, preferably of copper, with lengths in the centimeter range. The film thickness is also preferably selected to be 300 μm - 500 μm, but thicker films may also be used.

In a preferred embodiment of the film, it has slits through which the metal strips are guided. Portions of the contact bands then each run on one of the two sides of the film. In particular, tapes can be electrically isolated from each other cross over, if they are arranged in the region of the intersection on different sides of the film. The specific arrangement of the slits and contact strips results in the individual case from the intended interconnection of the upper sides of the semiconductor components. In the following, the side of the film which is facing the semiconductor components during assembly should be referred to as the inside of the film.

The outside of the invention slotted and equipped with metal strips polymer film initially has blank metal contact surfaces. These could in principle be used to bring about a further interconnection of these areas with each other or with external contacts. However, any such desired interconnection can also be achieved via the film inside, so that preferably on the outside Another, unstructured polymer film - preferably the same material - is adhered to completely isolate said metal contact surfaces.

Sint-metal paste is applied to the exposed metal contact surfaces of the film inside or alternatively to the surfaces to be contacted with these on the upper side of the semiconductor components, and the polymer film according to the invention, which is flowable under pressure and equipped with metal strips, becomes in a single pressure sintering step Pressed prepared substrate with components arranged thereon pressed to produce a laminated power assembly. The thick polymer film acts both electrically insulating and distributing pressure. On a height leveling of the assembly, as achieved with the known insulating moldings is, however, omitted. Consequently, the metal bands are bent over the edges of the components during pressure sintering and then run following the profile. A sharp bending of the bands in the region of the edges is avoided by the cushion effect of the polymer film, which is arranged there between the metal strip and the component. The thickness of the bands also ensures that the contact bands are not interrupted even in the area of severe deformation.

As emphasized in the prior art, the effects of force due to different thermal expansion of metal strips and components can impair the durability of the module contacts. Of course, in the proposed laminated construction, despite the use of thick metal bands can not realize lifted loops for force reduction, a closer design of the metal bands is recommended according to the invention.

The metal bands may have approximately longitudinal slots along which thin metal strips have been removed. For example, these strips are already punched out during production at regular intervals. This weakens on the one hand the internal mechanical structure of the metal bands, so that they have an increased mobility, for example against compressive forces, and on the other hand creates a "within the metal strip itself provided space" for receiving a temperature-induced increase in volume. It is particularly advantageous that metal strips in the form of a braid of metal wires also aurweisen the desired mobility and the internal space for receiving material expansions, and that these are already available, for example as Entlötlitzen on the market. Therefore, it is proposed as a particularly preferred embodiment of the invention to equip the polymer film of the invention from the outset with Metallflechtbändern as contact elements.

The invention will be described in more detail with reference to the following figures. It shows

Figure 1 is a cross-section through a laminated power assembly made in accordance with the present invention just prior to assembly and pressure sintering.

2 shows a plan view of the substrate, the polymer film according to the invention with threaded metal strips and the superposition of the two as in FIG. 1.

In the following description, it is always assumed that the outside of the slotted polymer film is covered with an additional, unstructured polymer film in order to isolate the contact elements to the outside. In the figures, this film is not shown and it will not be discussed further below.

In Fig. 1, a common substrate (10) is shown consisting of an industrial ceramic with metal coating on both sides, wherein the metal layer of the top has a structuring in mutually insulated conductor tracks. On the substrate pressure sintered material (20), in particular silver sintering paste, is arranged at suitable locations, which serves for the formation of solid, flat contact connections with the semiconductor components (30) and the metal strips (40) according to the invention. The metal strip is liier Kupferflechtband (or strand), which preferably still with a precious metal (eg gold, silver, palladium) coated (eg galvanized) is. The film (50) according to the invention consists of a polymer which is flowable under pressure (for example polytetrafluoroethylene, PTFE) and, in this example, has slots and recesses. The illustrated left metal band (40) runs, for example, first on the inside of the film (50), passes through a slot on the outside and covered there an area with a recess. A contacting should take place in the regions of the recess and the inner foil course, for which purpose a further arrangement of pressure sintering paste (60) on the upper side of the semiconductor component (30) is provided in addition to the pressure sintering paste (20). It should be noted separately that instead of the recess and a simple slotting of the film (50) on the left edge of the recess for achieving the same interconnection is sufficient when the metal strip (40) is guided by this again on the film inside. The metal strip (40) is then reliably fixed in position by being passed through at least two slots in the film (50).

The design of the film (50) as one having only slots for passing the metal strips (40) is therefore proposed as a preferred embodiment of the invention.

Fig. 2 illustrates this by omitting the representation of the pressure sintering paste (20, 60). The left picture shows the substrate (10) with the semiconductor components (30) on the structured metal layer (coarsely hatched). In the middle, the polymer film (50) is shown, which is provided with a total of four slots for the passage of two rectangular metal bands (40). In this case, each metal band extends partially below (41) and above (42) the image plane, i. the polymer film. By placing the film (50) over the substrate (10), the metal strip portions (41) can be contacted with the components (30) and the external terminals.

Claims

P 5684pya7045patents claims 1. A semiconductor module for power electronics comprising an at least partially metallized substrate having at least one arranged thereon, electrically contacted on the bottom semiconductor device marked by an electrically insulating polymer film of a pressure-flowable polymer which tightly encloses the semiconductor component under pressure, wherein the film has slits at predetermined locations, through which at least one metal strip is guided as a contact element at least once from one side of the film to the other side of the film and electrically contacts the upper side of the semiconductor device. 2. A semiconductor device according to claim 1, characterized by a second polymer film without slits, which is arranged on the side facing away from the substrate of the first polymer film. 3. The semiconductor device according to claim 2, characterized in that the first and second polymer films consist of the same polymer which is flowable under pressure. 4. The semiconductor device according to any one of the preceding claims, characterized in that at least provided with the slotted polymer film made of polytetrafluoroethylene (PTFE) or a silicone polymer. 5. A semiconductor device according to any one of the preceding claims, characterized in that at least the slotted polymer film has a thickness of more than 300 microns. 6. The semiconductor device according to one of the preceding claims, characterized in that the at least one metal band has internal space for receiving a thermal increase in volume. 7. The semiconductor device according to claim 6, characterized in that the at least one metal strip is a metal braiding tape. 8. A semiconductor device according to any one of claims 6 or 7, characterized in that the metal strip consists of copper or silver. 9. The semiconductor device according to any one of claims 6 to 8, characterized in that the metal strip is an Entlötlitze. 10. A semiconductor device according to any one of claims 6 to 9, characterized in that the metal strip has a gold or silver or palladium coating. 11. A semiconductor device according to any one of claims 6 to 10, characterized in that the metal strip has a thickness between 300 and 500 microns. 12. The semiconductor device according to any one of the preceding claims, characterized in that all electrical contacts are formed as a surface connection by means of pressure sintering technology.