Sintering tool for the lower die of a sintering device

Abstract

Tool (10) for the lower die of a sintering device, the tool (10) having a rest (20) for an electronic subassembly (30) comprising a circuit carrier, to be sintered, where the rest (20) is formed from a material with a coefficient of linear expansion that is close to the coefficient of expansion of the circuit carrier of the electronic subassembly (30).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of International Patent Application No. PCT/EP2015/070621, filed on Sep. 9, 2015, which claims priority to German Patent Application No. 102014114096.6, filed on Sep. 29, 2014, each of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to a tool for the lower die of a sintering device, the tool having a rest for an electronic subassembly to be sintered.

BACKGROUND

Sintering devices for carrying out the low-temperature pressure sintering of electronic subassemblies are already known. These have, for example, a sintering chamber which can be filled with a gas that is particularly conducive to the sintering operation or a corresponding gas mixture, and have an upper die and a lower die arranged in the sintering chamber, it being possible for the upper die and the lower die to be moved towards one another and preferably to have in each case a heating device of their own.

The lower die and/or the upper die often have to be specially shaped for carrying out specific processes or for adaptation to the products to be sintered, and so tools that can be fastened to the lower die or the upper die and allow easy modification of the device as a whole are usually provided.

For example, a sintering device for sintering an electronic subassembly comprising a circuit carrier is formed in such a way that a lower die is provided with a massive tool which carries and heats the planar circuit carrier. A temperature-resistant elastic medium of the upper die tool, in the form of a pressure pad, produces an increasing pressure on the surface of the circuit carrier, whereby the latter is pressed onto the planar support of the lower die tool. The flexible medium of the pressure pad provides a quasi-hydrostatic pressure not only on the components to be joined of the electronic subassembly but also on all of the surfaces of the lower die tool. A massive lower tool therefore forms a counter bearing in the quasi-hydrostatic sintering process, onto which the circuit carrier is pressed with compressive engagement by the elastic medium. The thermal energy is also supplied to the circuit carrier by way of this metallic compressive engagement.

However, a disadvantage of this design is that, at the temperature prevailing during the sintering operation of up to 350° C., stress cracks occur in ceramic materials which form part of the electronic subassembly, on account of the different coefficients of expansion of the ceramic material of the electronic subassembly and the lower die, which may, for example, comprise high-grade steel.

SUMMARY

The object of the invention is therefore to provide a tool for a sintering device with which cracks and fractures of the ceramic material that occur during the sintering operation are avoided.

This object is achieved according to the invention by the tool for a sintering device comprising a tool for the lower die of a sintering device, the tool having a rest for an electronic subassembly comprising a circuit carrier, to be sintered, where the rest is formed from a material with a coefficient of linear expansion that is close to the coefficient of expansion of the circuit carrier of the electronic subassembly. The subclaims provide advantageous designs of the invention.

The basic concept of the invention is to provide a rest for the electronic subassembly, which rest has a low coefficient of linear expansion, and one that is similar to that of the electronic subassembly as a whole or the circuit carrier thereof. Such a coefficient of linear expansion may be approximately 11·10⁻⁶K⁻¹. This results in no displacements, or only very minor displacements, between the electronic subassembly and the rest during temperature changes.

Since such low-expansion materials, that is to say materials having a low coefficient of thermal expansion, such as molybdenum or Kovar, are very cost-intensive to procure and are very difficult to machine, on account of the properties of the material, recourse is made to the designs claimed, which makes easy and work-friendly production of the tool possible.

According to the invention, therefore, a tool for the lower die of a sintering device is provided, the tool having or forming a rest for an electronic component to be sintered and the rest being formed from a material with a coefficient of linear expansion (measured at 20° C.) of less than or equal to 11·10⁻⁶K⁻¹.

The material preferably has a coefficient of linear expansion (measured at 20° C.) of less than or equal to 6·10⁻⁶K⁻¹.

In particular, the rest may be formed by coating at least a partial region of the tool by means of a thermal spraying method, in particular by cold gas spraying.

Alternatively, the rest may be formed as a plate, the tool having a depression receiving the rest formed as a plate. In this case, the depression has a channel in the wall or on the bottom of the depression leading to outside the tool, in order that no air or gas is trapped in the depression when the sintering operation is being carried out and a pressure equalization can take place between the depression and the atmosphere surrounding the die tools.

In order to ensure an effective heat transfer with the electronic subassembly to be sintered, the plates serving as a rest should be designed to be as thin as possible.

The surface of the plates serving as a rest may preferably be coated with the material. Alternatively, however, the plate is formed solidly from the material.

The material used is preferably molybdenum or an alloy comprising molybdenum. Other substances with a likewise low coefficient of expansion, for example the material known by the trade name Kovar, are likewise conceivable.

Furthermore, for carrying out batch processing, it is preferably provided that the tool has a plurality of rests, each for receiving an electronic subassembly to be sintered.

Finally, a sintering device in which the lower die as a whole is formed as the tool described above is also provided according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail on the basis of an exemplary embodiment that is represented in the appended figures. In these figures:

FIG. 1 shows a sectional view through a first exemplary embodiment according to the invention of a particularly preferable design.

FIG. 2 shows a sectional view through a second exemplary embodiment according to the invention of a particularly preferable design.

FIG. 3 shows a perspective view of a third exemplary embodiment according to the invention of a particularly preferable design.

DETAILED DESCRIPTION

FIG. 1 shows a tool 10, which has a depression, in which a rest 20 formed as a plate and an electronic subassembly 30 to be sintered arranged thereupon are represented. The depression in the tool 10 is designed such that the rest 20 and the subassembly 30 are received completely by the depression and the surface of the subassembly 30 finishes flush with the surface of the tool 10. It may be provided in this case that the rest 20 is stocked in various thicknesses, in order to compensate for differing heights of the subassembly 30.

FIG. 2 shows a tool 10, which has a depression, in which a partial coating 20a formed as a layer at the bottom of the depression and an electronic subassembly 30 to be sintered arranged thereupon are represented. The depression in the tool 10 is designed such that the partial coating 20a and the subassembly 30 are received completely by the depression and the surface of the subassembly 30 finishes flush with the surface of the tool 10. It may be provided in this case that the partial coating 20a is varied in thickness, in order to compensate for differing heights of the subassembly 30.

FIG. 3 shows a tool 10, which has a number of depressions, in which a plurality of rests 20 formed either as a plate or a layer at the bottom of the depression. The depressions in the tool 10 are designed such that there are channels leading to the periphery of the tool 10.

In all of the embodiments illustrated, if the tool 10 is at the same time the die of a sintering device, it preferably comprises a heating element (not shown).

While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.

Claims

1. A lower die of a sintering device, the lower die comprising a tool, the tool having a rest for an electronic subassembly comprising a circuit carrier, to be sintered, where the rest is formed from a material with a coefficient of linear expansion measured at 20° C. of less than or equal to 15·10−6K−1, wherein the tool has a depression and the rest is located within the depression, wherein the rest is configured to receive the electronic subassembly to be sintered thereupon, wherein the rest is not a component of the electronic subassembly to be sintered, and wherein a top surface of the rest is located below a top surface of the tool.

2. The lower die according to claim 1, wherein the rest is formed from a material with a coefficient of linear expansion measured at 20° C. of less than or equal to 11·10−6K−1.

3. The lower die according to claim 1, wherein the rest is formed by coating at least a partial region of the tool.

4. The lower die according to claim 1, wherein the rest is formed as a plate.

5. The lower die according to claim 4, wherein a surface of the plate serving as a rest is coated with the material.

6. The lower die according to claim 4, wherein the plate is formed solidly from the material.

7. The lower die according to claim 1, wherein the depression has a channel in the wall or on the bottom of the depression leading to outside the tool.

8. The lower die according to claim 1, wherein the material is molybdenum or an alloy comprising molybdenum.

9. The lower die according to claim 1, wherein the tool comprises a plurality of rests.

10. A sintering device comprising the lower die according to claim 1.

11. The lower die according to claim 2, wherein the material is molybdenum or an alloy comprising molybdenum.

12. The lower die according to claim 3, wherein the material is molybdenum or an alloy comprising molybdenum.

13. The lower die according to claim 4, wherein the material is molybdenum or an alloy comprising molybdenum.

14. The lower die according to claim 5, wherein the material is molybdenum or an alloy comprising molybdenum.

15. The lower die according to claim 6, wherein the material is molybdenum or an alloy comprising molybdenum.

16. The lower die according to claim 7, wherein the material is molybdenum or an alloy comprising molybdenum.

17. The lower die according to claim 1, wherein the rest of the tool has a surface configured to removably receive the electronic subassembly.

18. The lower die according to claim 1, wherein the tool comprises a plurality of depressions and a plurality of rests, each of the plurality of rests located within one of the plurality of depressions.