US20150306669A1

US20150306669A1 - Method for connecting at least two components using a sintering process

Info

Publication number: US20150306669A1
Application number: US14/650,331
Authority: US
Inventors: Michael Guenther; Andrea Feiock
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-12-06
Filing date: 2013-10-09
Publication date: 2015-10-29
Also published as: DE102012222416A1; EP2928630A1; WO2014086519A1

Abstract

The invention relates to a method for connecting at least two components (18, 20) using a sintering process. The aim of the invention is to improve the sintering process. This is achieved in that the method has the following method steps: a) providing a starting material (10) of a sintering compound (22), comprising particles (12) which can be sintered and have at least one metal or at least one metal compound and comprising at least one polymeric, polymerizable, and/or monomeric organic compound (14), wherein the polymeric, polymerizable, and/or monomeric compound (14) has a flow temperature which is higher than or equal to the room temperature and lower than the sintering temperature, and the polymeric, polymerizable, and/or monomeric organic compound (14) further has a desorption temperature which is higher than the flow temperature and lower than or equal to the sintering temperature; b) arranging the starting material (10) between two components (18, 20) to be connected; c) heating the starting material (10) to a temperature (T1) which is higher than or equal to the flow temperature of the polymeric, polymerizable, and/or monomeric organic compound (14) and lower than the desorption temperature of the polymeric, polymerizable, and/or monomeric organic compound (14) for a period of time (t1); and d) heating the starting material (10) to a temperature (T2) which is higher than or equal to the sintering temperature of the particles (12) which can be sintered, optionally under the influence of a sintering pressure, for a period of time (t2), thereby forming a sintering compound (22).

Description

BACKGROUND OF THE INVENTION

The present invention relates to a method for connecting at least two components using a sintering process.
Power electronics are used in many areas of technology. Especially in electrical or electronic devices, in which great currents flow, the use of power electronics is indispensable. The current intensities that are necessary in power electronics lead to a self-heating of the electrical or electronic components contained. In addition, the components of power electronics can be used at locations that are constantly subjected to an elevated temperature. Control devices in the automotive sector, which are arranged directly in the engine compartment or in the transmission compartment, may be mentioned as examples. In this case, the control device is also exposed to a continual change of temperature, whereby the electrical and/or electronic components contained undergo great thermal loading. Generally, temperature changes in a range up to a temperature of 200° C. are usual. However, operating temperatures that go beyond this are also increasingly being required. As a result, altogether increased requirements are being demanded of the reliability and functional dependability of electrical or electronic devices with power electronics.
Electrical or electronic components are usually joined together—for example on a carrier substrate—by a connecting layer. Soldered connections, for example lead-free soldered connections of tin-silver or tin-silver-copper, are known as such connecting layers. In cases of higher operating temperatures, lead-containing soldered connections can be used. However, for reasons of environmental protection, lead-containing soldered connections are greatly restricted with respect to their permissible technical applications by legal regulations. Alternatively, lead-free hard solders are suitable for use at elevated or high temperatures, in particular over 200° C. Lead-free hard solders generally have a higher melting point than 200° C.
Sintered connections, which can already be processed at low temperatures and are nevertheless suitable for operation at elevated temperatures, are also used. Such sintered connections offer the advantage of an increased selection of electrical or electronic components that come into consideration as parts to be joined on account of the lower processing temperature. Also advantageous in the case of sintered connections is that no creep takes place in the connecting layer, and consequently no crack formation, whereby failure of an assembly having such a connection can be reduced further.
Thus, the patent application DE 10 2007 046 901 A1 shows such sintered connections. To produce a sintered connection, a starting material in paste form comprising readily decomposable silver compounds and silver flakes or nano silver is used. Furthermore, copper for example may be contained in the starting material.
The document EP 2 278 593 A1 discloses a sintered connection which is produced from a paste that contains particles of a silver compound.
The document US 2008/0211095 A1 also discloses a semiconductor component which has a connection between a semiconductor element and an electrode that is formed by an electrically conductive adhesive.
The document U.S. Pat. No. 6,832,915 B2 also discloses a thermally conductive adhesive connection between two components.
The document DE 10 2007 27 999 A1 also discloses a transfer film for the transfer of a silver sintered layer.
The document DE 10 2004 019 567 B3 also describes a method for securing electronic components, in which the components are secured on a substrate by means of pressure sintering using a pasty layer.
The document JP 63258084 A also discloses a carrier film with a sintering paste for joining electronic components.
U.S. Pat. No. 6,951,666 shows the production of different sintered connections. General possibilities for combining different starting elements are thereby described. Included among the elements mentioned as starting elements are molecular metals, numerous metallic particles of nano or micro size, coatings, solvents, additives, reducing agents, crystallization inhibitors, wetting agents and others.

SUMMARY OF THE INVENTION

The subject of the present invention is a method for connecting at least two components using a sintering process, having the method steps of:
a) providing a starting material of a sintered connection, comprising sinterable particles, comprising at least one metal or at least one metal compound, and at least one polymeric, polymerizable and/or monomeric organic compound, wherein the polymeric, polymerizable and/or monomeric organic compound has a flow temperature that is greater than or equal to the room temperature and less than the sintering temperature, and wherein the polymeric, polymerizable and/or monomeric organic compound also has a desorption temperature that is greater than the flow temperature and less than or equal to the sintering temperature;
b) arranging the starting material between two components to be connected;
c) heating the starting material to a temperature T1, which is greater than or equal to the flow temperature of the polymeric, polymerizable and/or monomeric organic compound and less than the desorption temperature of the polymeric, polymerizable and/or monomeric organic compound, for a time t1; and

- d) heating the starting material to a temperature T2, which is greater than or equal to the sintering temperature of the sinterable particles, possibly under the effect of a sintering pressure, for a time period t2, thereby forming a sintered connection.

The method described above can make it possible in particular to carry out a sintering process particularly easily and thereby produce a particularly stable and reliable sintered connection.
For this purpose, according to a method step a), the previously described method involves providing a starting material of a sintered connection, comprising sinterable particles, comprising at least one metal or at least one metal compound, and at least one polymeric, polymerizable and/or monomeric organic compound, wherein the polymeric, polymerizable and/or monomeric organic compound has a flow temperature that is greater than or equal to the room temperature and less than the sintering temperature, and wherein the polymeric, polymerizable and/or monomeric organic compound also has a desorption temperature that is greater than the flow temperature and less than or equal to the sintering temperature.
Consequently, according to method step a), first a starting material that is intended in the further course of the method to form the sintered connection is provided. The starting material thereby comprises a sintering base material, which after the sintering can represent the actual sintered connection or at least forms a large proportion of the sintered connection. This sintering base material may be in particular at least one metal or at least one metal compound. Furthermore, the starting material comprises at least one polymeric, polymerizable and/or monomeric organic compound. The polymeric, polymerizable and/or monomeric organic compound may in this case serve the purpose of keeping the sintering base material together, and thus allow the starting material to be provided for example as a compact, for example moldable, for instance thermoplastic, molded body.
A polymeric organic compound may in this case be regarded for example, and not restrictively, as meaning a hydrocarbon-based compound that is polymerized. Consequently, a polymerizable organic compound may for example, and not restrictively, be understood as meaning such a compound, in particular a hydrocarbon-based compound, that can in particular as a result of having specific functional groups be subjected to a polymerization. An organic monomeric compound may furthermore be understood for example, and not restrictively, as meaning such a compound that likewise may be hydrocarbon-based, but need not have any groups suitable for polymerization.
Such provision of a starting material of a sintered connection allows the starting material to be provided as a transportable and storable material, which can be applied at any time and without any special effort. In other words, the starting material is produced in advance and stored and is supplied for use immediately before carrying out the method. This makes possible very dynamic and variable production processes that can be adapted directly to the desired requirements.
In this case, the starting material may for example be provided as a material of a large surface area, from which a material part of a suitable size can be separated, for example punched out or cut out, in each case before use. As a result, just one starting material can be provided for a great range of applications, which can improve the costs for the previously described method still further.
Furthermore, the starting material may be provided for instance by film casting or injection molding, initially for example as a particularly flexible film, which keeps the handling requirements very low. As a result, the starting material can be handled by conventional handling systems, which can allow particularly good incorporation of the starting material in existing process peripherals.
In this case, during or after application of the starting material to a component or during arrangement of the starting material between the components to be connected, it is possible, as described below, to adapt the starting material optimally to potentially existing irregularities of the parts to be joined, such as for example substrate irregularities or component irregularities, so that a particularly intimate contact becomes possible, which can also be accompanied by a particularly stable sintered connection.
In this case, the polymeric, polymerizable and/or monomeric organic compound and the sintering base material or the at least one metal or the at least one metal compound may in particular be made to match one another in such a way that the polymeric, polymerizable and/or monomeric organic compound has a flow temperature that is greater than or equal to the room temperature and less than the sintering temperature of the sintering base material, and wherein the polymeric, polymerizable and/or monomeric organic compound also has a desorption temperature that is greater than the flow temperature and less than or equal to the sintering temperature of the sintering base material.
In the sense of the present invention, a flow temperature may be understood in particular as meaning a specific temperature or a temperature range from which the polymeric, polymerizable and/or monomeric organic compound is flowable, and consequently can flow, that is to say can remove itself from the joining zone of its own accord by a flowing process. In this case, a flow temperature may be understood in particular as meaning a melting temperature or a melting range or a glass transition temperature or a glass transition range.
By such a selection of the sintering base material or the polymeric, polymerizable and/or monomeric organic compound, significant advantages in conducting the process can be made possible.
In detail, it can be made possible by the selection in particular of the polymeric, polymerizable and/or monomeric organic compound that the starting material has a good adhesive force, and consequently can adhere well to the components to be joined, such as for instance a substrate and a component, in particular because of the polymeric, polymerizable and/or monomeric organic compound. In other words it is possible for instance as a result of the polymeric, polymerizable and/or monomeric organic compound or a further auxiliary substance, such as for instance a solvent, for the starting material to have a suitable adhesiveness that allows the starting material to adhere to the parts to be joined. This allows particularly good applicability, since the starting material, once arranged, can remain securely in place. For example, such an adhesive force or adhesiveness can be obtained at temperatures below the flow temperature, that is to say purely by way of example at temperatures in the range of less than or equal to 100° C.
In addition, the polymeric, polymerizable and/or monomeric organic compound may serve the purpose of preventing cold fusing of the particles and also of making it possible for the film material to be shaped.
After providing a starting material designed as described above, according to method step b) this starting material is arranged between two components to be connected. This may take place for example in a fully automated manner. In this case, the starting material may for example be arranged between a substrate and an electronic component to be secured on the substrate.
According to method step c), in a further step heating of the starting material takes place to a temperature T1, which is greater than or equal to the flow temperature of the polymeric, polymerizable and/or monomeric organic compound and less than the desorption temperature of the polymeric, polymerizable and/or monomeric organic compound, for a time t1. This method step allows an adhesive attachment of the starting material to the components to be connected to be improved still further. In this case, such a temperature T1 may, depending on the chosen polymeric, polymerizable and/or monomeric organic compound, already lie at temperatures of less than or equal to 100° C., for instance in a range of from greater than or equal to 30° C. to less than or equal to 80° C. In detail, for example, an adhesiveness or an adhesive force of the polymeric, polymerizable and/or monomeric organic compound can be further increased or such an adhesiveness can be formed in the first place by a flowability. Consequently, in this step it can be made possible that the starting material firmly adheres between the components to be connected, and consequently already forms an arrangement that already has good stability for the further sintering operation.
It can consequently be made possible by this method step that the starting material is arranged at a desired position, and furthermore remains there. As a result, particularly defined products can be obtained. In this case, by increasing the temperature beyond the flow temperature of the polymeric, polymerizable and/or monomeric organic compound, the starting material can be held in its position by particularly stable forces. Consequently, an additional fixing medium is not necessary, which allows the previously described method to be made particularly simple and inexpensive.
Furthermore, in particular in the flowable state, the polymeric, polymerizable and/or monomeric organic compound may serve as a dispersing medium, in order to create a homogeneous starting material.
In addition, it can be made possible by a flowability of the polymeric, polymerizable and/or monomeric organic compound that the starting material comes into close contact with the components to be connected, and otherwise, as a result of a softening, in particular reversible softening, of the polymeric, polymerizable and/or monomeric organic compound as a result of the temperature increase beyond the flow temperature, a good adaptation between the layer of the starting material and the parts to be joined is produced. In this way equally an intimate contact of the metallic compound or of the sintering base material with the components to be joined can be allowed. This may contribute to a particularly stable arrangement being produced after a sintering process, as is explained below.
Since, however, only a very small amount of polymeric, polymerizable and/or monomeric organic compound is necessary for an adhesiveness or close contactability and the fixing of the starting material between the parts to be joined, it is possible to achieve the further advantage that the majority of the polymeric, polymerizable and/or monomeric organic compound is removed from the joining zone as a result of flowability. As a result, it can be achieved that a subsequent removal or desorption of the polymeric, polymerizable and/or monomeric organic compound from the joining region does not cause a development or significant development of reaction gases that could possibly expand in the joint, and thereby counteract the formation of a material-bonded connection. Furthermore, for example, and depending on the desorption chosen, no oxygen is required, whereby the sintered connection can also take place with the exclusion of oxygen. This can avoid all the involved parts to be joined undergoing a change or damage during a thermal treatment. In addition, the necessity of supplying gases or the necessity of removing gases can be prevented. It is consequently not disadvantageous in the case of the previously described method that, particularly in the case of connections over a large surface area, the gas transport is limited by the impermeability of the joining material, and consequently for example in the case of production of a sealed connection the material is pressed by mechanical pressure, and consequently specifically inhibits transport of the gas. Consequently, to sum up, the disadvantages of removal of such a matrix according to the prior art can be prevented by a temperature increase above the flow temperature of the polymeric, polymerizable and/or monomeric organic compound.
The time period t1, for which the temperature T1 is maintained, may in this case be chosen in dependence on the starting material that is specifically used. In particular, the time period should be chosen to be long enough for a sufficient flowability of the polymeric, polymerizable and/or monomeric organic compound to be realizable, and consequently for it to be possible for the aforementioned advantages to be achieved in a particularly advantageous way.
In a further method step d), a previously described method involves heating the starting material to a temperature T2, which is greater than or equal to the sintering temperature of the sinterable particles, possibly under the effect of a sintering pressure, for a time period t2, thereby forming a sintered connection. In this method step, consequently, the actual sintered connection is produced.
In this case, the particles, for example chemically stabilized particles, are burned out, for instance until the joining temperature or sintering temperature is reached, so that the particles or released metal atoms can come into direct contact with one another and with the material of the parts to be joined. Then, a connection that is stable at high temperatures already forms at low temperatures as a result of solid diffusion processes.
For this purpose, the starting material is heated on its own or together with at least one joining region of the components to be connected to a temperature T2, for instance by a heating source or electromagnetic radiation. In this case, the temperature T2 is greater than or equal to the sintering temperature of the sinterable particles, that is to say the particles comprising at least one metal or at least one metal compound. In this case, the temperature T2 is maintained for a predetermined time period t2, which is sufficient for a stable sintered connection to be able to form.
In this case, the stability of the sintered connection formed can be increased still further by the fact that the polymeric, polymerizable and/or monomeric organic compound also has a desorption temperature, that is to say a specific desorption temperature or a broad desorption temperature, that is to say a desorption range, that is greater than the flow temperature and less than or equal to the sintering temperature. In detail, the polymeric, polymerizable and/or monomeric organic compound is desorbed both by the sinterable particles and by the components to be joined, that is to say in the sense of the present invention is removed. In this way it can be ensured that, after the forming of the sintered connection, it substantially comprises only the sintered particles or sintered products thereof. Therefore, the polymeric, polymerizable and/or monomeric organic compound does not disturb the stability of the sintered connection, as a result of which particularly stable products can be obtained.
To sum up, the previously described method makes possible in particular a particularly simple and defined production of a sintered connection between two components to be connected, with it also being possible for the sintered connection that is formed to be particularly stable.
Within the scope of a refinement, the desorption temperature may be the boiling temperature, decomposition temperature or a reaction temperature of the polymeric, polymerizable and/or monomeric organic compound with the sinterable particles and/or with sintered particles. In particular in this refinement, it can be advantageously ensured that, in the case of method step d), the polymeric, polymerizable and/or monomeric organic compound can be removed completely, or without any residue, and the polymeric, polymerizable and/or monomeric organic compound consequently does not adversely influence the stability of the sintered connection. The fact that at least a certain proportion or advantageously a majority of the polymeric, polymerizable and/or monomeric organic compound is no longer arranged in the direct joining zone during method step d) means that even a vaporization, decomposition or combustion or a reaction, such as for instance an oxidation, by a constituent part of the sintering material, of the polymeric, polymerizable and/or monomeric organic compound arranged in particular outside the joining zone cannot cause the risk of a significant production of gas adversely influencing the sintering process. The proportion of polymeric, polymerizable and/or monomeric organic compound that is still located in the joining zone can in this case be in particular so small that there is no need for the occurrence of any significant gas transport, which adversely influences the sintered connection that is forming or the stability of the sintered connection that has formed. Consequently, here even a removal by the aforementioned processes can be possible without any problem, or else it is possible for the polymeric, polymerizable and/or monomeric organic compound to remain in the joining zone without adversely influencing the sintering process.
Within the scope of a further refinement, the sinterable particles may contain silver, gold, platinum, palladium and/or copper, an organic metal compound, in particular silver carbonate, silver lactate or silver stearate, a metal oxide, in particular silver oxide, or a mixture comprising one or more of the aforementioned substances. Such particles may be particularly advantageously suitable for forming a highly stable and electrically conductive sintered connection. In this case, both the pure metals and corresponding metal compounds may be provided. The metals may in this case allow in particular a material-bonded connection between the parts to be joined to be obtained directly by a heat input or an input of pressure, and thereby make a stable sintered connection possible. With respect to the metal compounds mentioned, they can decompose during a thermal treatment of the starting material, for instance in a range of less than 300° C., to form the elemental metal, and form the sintered connection. When using the starting material described, electrical contacting can already take place with low pressing pressures of the parts to be contacted, which consequently can allow mild reaction conditions, and consequently a simple and inexpensive method.
Within the scope of a further refinement, the polymeric, polymerizable and/or monomeric organic compound may comprise a polyolefin, in particular comprising polyethylene and/or polypropylene, a polyethylene copolymer, a polyketone or a mixture comprising one or more of the aforementioned substances. In particular, such polymeric, polymerizable and/or monomeric organic compounds may have the advantage that, with respect to their flow temperature or with respect to their desorption behavior, they can be integrated well into a sintering process, in particular in combination with the aforementioned sintering base materials, that is to say in particular metals or metal compounds. Consequently, the aforementioned polymeric, polymerizable and/or monomeric organic compounds may be particularly advantageously suitable for taking up the sintering base material and also being removed substantially without any residue from a component to be joined by a desorption process. In addition, the aforementioned polymeric, polymerizable and/or monomeric organic compounds are stable under ambient conditions, that is to say even in an oxidative atmosphere and/or in a moist atmosphere, so that particularly advantageous storability can be made possible for the starting material, even over a long period of time.
Within the scope of a further refinement, the polymeric, polymerizable and/or monomeric organic compound may form a matrix, in which the sinterable particles are embedded, or the polymeric, polymerizable and/or monomeric organic compound may take the form of a coating on the sinterable particles. These are particularly advantageous refinements for surrounding the sinterable particles by the polymeric, polymerizable and/or monomeric organic compound.
With respect to a matrix in which the sinterable particles are embedded, it is thus possible to produce a molded body that can be adapted in all dimensions to the desired application area. In detail, such a body can be adapted in its length, width and height to the components to be joined. As a result, the method can be made even more simple and inexpensive. For example, in this way a moldable composition that can adhere to itself, and in particular can be handled well, can be produced. In this case, such a starting material may for instance be producible by melting the polymeric, polymerizable and/or monomeric organic compound followed by mixing with the sintering base material and final cooling.
With respect to a coating, the proportion of the polymeric, polymerizable and/or monomeric organic compound can be kept particularly low, so that the composition leaving the joining region when there is an increase in temperature beyond the flow temperature of the polymeric, polymerizable and/or monomeric organic compound can be kept particularly small. Consequently, the method can be carried out in a particularly time-saving manner. In this case, the coating of the particles may already be applied during the production of the particles, in particular in order to prevent a reaction of the sinterable particles with one another, for instance cold fusing. For example, the metal particles, which are produced for example as silver particles by a gas-phase deposition or precipitation in a solvent, are coated by the solvent comprising a corresponding coating material, for example as a surface-active material. After removal of the solvent, for example, the starting materials comprising the sinterable particles, which for instance as a powder are in a form that can be handled, can be obtained with the coating, in particular chemically or physically bonded coating.
In these refinements, the starting material can thus be applied, or brought into contact with the components to be joined, as a powder or as a pressed body of the powder or else as a paste with a solvent by means of methods that are known in principle, such as for instance placement of the green body. Also in these refinements, the viscosity of the polymeric, polymerizable and/or monomeric organic compound can be set by means of a temperature control, so that the viscosity is controllable by a temperature setting and in that case a temperature increase can have the effect that the compound can be removed from the joint, in particular by capillary forces, and in a further method step can be completely removed or desorbed.
Within the scope of a further refinement, the starting material may be applied to at least one component to be connected by printing, doctor blading or dispensing. These are particularly simple and well-established processes for applying the starting material to at least one of the components to be connected. In these refinements, a particularly precise and highly accurate arrangement of the starting material is possible, which can make highly stable sintered connections possible even in components of small dimensions. In this case, the starting material may be applied both to only one of the components to be connected or to both starting components to be used.
Within the scope of a further refinement, the starting material may have a transfer layer, which is arranged between at least two protective layers, in particular comprising a polymeric, polymerizable and/or monomeric organic compound. For example, the transfer layer may comprise the sintering base material or the sinterable particles and possibly the polymeric, polymerizable and/or monomeric organic compound. In this case, the polymeric, polymerizable and/or monomeric organic compound of the transfer layer may be the same compound as the compound of the protective layers. Alternatively, it is possible to dispense with the polymeric, polymerizable and/or monomeric organic compound in the transfer layer, which may enclose the sinterable particles directly, for instance as a coating or as a matrix, so that the sinterable particles are only surrounded by the protective layers comprising a polymeric, polymerizable and/or monomeric organic compound. In this refinement, the starting material can be handled particularly easily and nevertheless be arranged very precisely at the desired location. In this case, the transfer layer is protected particularly well from external influences, and as a result is particularly storable.
In this case, arranging the starting material on one of the components to be joined can be realized by way of example, and not restrictively, by the protective layers being removed before or during method step b). In this case, as an example, it may be that first a protective layer is removed and the exposed side of the transfer layer arranged on the component, and then the further protective layer is removed. In this way, the starting material may have in particular a transfer layer that is surrounded on two opposite sides by the protective layer. In this case, the protective layers may also be formed in such a way that substantially the entire transfer layer is surrounded by protective layers. It may be that this can be realized by providing more than two protective layers and also by a corresponding form of the at least two protective layers.
In this case it is possible in this refinement in particular to dispense with applying the sintering base material by printing, dispensing or doctor blading with a subsequent thermal treatment for drying the applied layer. Therefore, in this refinement in particular, the previously described method can do without some steps in the process, which can save production costs of the components to be produced and also time for producing such components.
Within the scope of a further refinement, the protective layers may comprise polyethylene terephthalate. In particular, polyethylene terephthalate may serve as a stable protective layer, in order to protect the transfer layer reliably from external influences, such as for example mechanical influences. In addition, it is inert with respect to the materials occurring in the transfer layer, so that no adverse influencing of the transfer layer is to be expected, even over a prolonged period of time. Furthermore, polyethylene terephthalate can be obtained inexpensively, so that also in this refinement the method can be realized particularly inexpensively.
Within the scope of a further refinement, the starting material may be provided in the form of a paste, a powder, granules or a film. Such forms of the starting material can be handled easily, inexpensively and by known methods, so that in these refinements in particular the method can be possible particularly simply and inexpensively. In addition, storage is unquestionably possible, so that the advantages with respect to production in advance and use or provision immediately before the method are possible without any problem.
Within the scope of a further refinement, the polymeric, polymerizable and/or monomeric organic compound may be discharged or removed during or after method step c). In this refinement, the effect occurring in principle as a result of flowability of the polymeric, polymerizable and/or monomeric organic compound, whereby the compound already leaves the joining zone by flowing away, can be further enhanced or assisted.
With respect to discharging of the polymeric, polymerizable and/or monomeric organic compound, one or a plurality of collecting containers may be provided for example, such as for instance cavities, into which the flowable compound can be discharged, that is to say guided. For this purpose, channels may be provided for example, arranged in such a way that the compound flows in a flowable state, or the collecting containers may themselves be directly arranged in such a way that the flowable compound flows in there. In this case, the collecting containers may for instance be arranged directly alongside the components to be joined and the channels may for instance reach into the joining region.
With respect to removal of the polymeric, polymerizable and/or monomeric organic compound, the flowable compound may for example be taken up and carried away by means of a suitable device.
Sponge-like devices or capillary bundles, which can take up or suck in the compound by means of capillary forces, may for example be used for this purpose. This can bring about particularly low-stress removal of the compound, and as such not adversely influence the sintering process.
Within the scope of a further refinement, the polymeric, polymerizable and/or monomeric organic compound may contain at least one additive that reacts with the sinterable particles, in particular with the organic metal compound, while reducing the sintering temperature. In this refinement in particular, a particularly low-stress method can be made possible, since low temperatures may already be sufficient for a sintering process. As a result, even such components that should not be exposed to temperatures that are all that high can be connected to one another. In addition, polymeric, polymerizable and/or monomeric organic compounds that have a relatively low desorption temperature can also be used, which can for example increase the selection of such compounds, including with respect to conventional polymers. Oxidizable organic compounds, such as for instance fatty acids, for example stearic acid or lauric acid, in particular in combination with the aforementioned sintering base materials, such as for instance silver, may be mentioned as exemplary and nonrestrictive examples of such additives.
Within the scope of a further refinement, it is possible to produce a sintered connection that has an electrical conductivity of from greater than or equal to 30 MS/m to in particular less than or equal to 45 MS/m, in particular from greater than or equal to 36 MS/m to in particular less than or equal to 44 MS/m, and/or to produce a sintered connection that has a thermal conductivity of from greater than or equal to 200 W/mK to less than or equal to 300 W/mK, in particular from greater than or equal to 220 W/mK to less than or equal to 275 W/mK. Such sintered connections in particular may be customary for a large number of electronic components that are possibly used in power electronics. Such conductivities may for example be achievable by the use of the previously described sintering base materials.
Within the scope of a further refinement, an electronic component may be used as one of the components to be connected and a substrate, for instance comprising a copper compound, may be used as another of the components to be connected. In this refinement, electronic components in particular may be applied to the corresponding substrates. In the case of such applications in particular, a very stable connection, which is additionally electrically conductive, is beneficial. Therefore, in this refinement in particular it is of advantage that the sintered connection can be positioned highly accurately, and furthermore no gas transporting processes have a significant adverse influence on the forming of a stable connecting layer. For example, in this refinement in particular an electronic component of power electronics can be produced.
With regard to further technical features and advantages of the method according to the invention, reference is hereby made explicitly to the explanations in connection with the use according to the invention, the figures and the description of the figures.
The subject of the present invention is also a use of a method refined in the way described above for producing an electronic component, in particular an electronic circuit. In the case of this use, an electronic component or an electronic circuit can consequently be produced by a component, in particular an electronic component, being secured on a substrate by a sintering process. In this case, power semiconductors or integrated circuits may for example be secured as electronic components on the substrate by the sintered connection. In particular, the previously described method can be used in the case of components to be joined that should only be exposed to low thermal loading, since the temperatures that are necessary for flowability or desorption of the polymeric, polymerizable and/or monomeric organic compound and are necessary for sintering the sintering base material can likewise be kept low in the case of a previously described method on account of the selection of the starting material. For example, in this refinement silicon chips or silicon carbide components, which can withstand temperatures of for example 250° C. or 350° C., respectively, can be joined without any problem, such as for example in the so-called “die attach” process.
In principle, this refinement consequently comprises a use of the previously described method in the region of electronic construction technology or connection technology, in particular as a low-temperature sintering technique. For example, diffusion soldering or active soldering can be replaced by the previously described method.
With regard to further technical features and advantages of the use according to the invention, reference is hereby made explicitly to the explanations in connection with the method according to the invention, the figures and the description of the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and advantageous refinements of the subjects according to the invention are illustrated by the examples and drawings and are explained in the description that follows. It should be noted here that the examples and drawings only have a descriptive character and are not intended to restrict the invention in any form. In them:

FIGS. 1 a, 1 b and 1 c show a schematic representation of production of one embodiment of a starting material for a method according to the invention;

FIGS. 2 a, 2 b and 2 c show a schematic representation of a method according to the invention using a starting material according to FIG. 1; and

FIGS. 3 a, 3 b and 3 c show a schematic representation of a method according to the invention using a further refinement of a starting material.

DETAILED DESCRIPTION

In FIG. 1 c, a starting material 10 for a method according to the invention for connecting at least two components using a sintering process is shown. In the refinement according to FIG. 1 c, the starting material 10 of a sintered connection comprises sinterable particles 12, comprising at least one metal or at least one metal compound. Furthermore, the starting material 10 comprises at least one polymeric, polymerizable and/or monomeric organic compound 14, which according to FIG. 1 is arranged as a coating on the sinterable particles 12. In this case, the sinterable particles 12 and/or the polymeric, polymerizable and/or monomeric organic compound 14 are chosen in such a way that the polymeric, polymerizable and/or monomeric organic compound 14 has a flow temperature that is greater than or equal to the room temperature, that is to say according to the invention is greater than or equal to 22° C., and less than the sintering temperature of the sinterable particles, and the polymeric, polymerizable and/or monomeric organic compound 14 also having a desorption temperature that is greater than the flow temperature and less than or equal to the sintering temperature.
In this case, an exemplary production process for the starting material 10 is shown in FIG. 1. In FIG. 1 a, a sinterable particle 12 that has been produced in a solvent 16 is shown. The sinterable particle 12 may for example be a silver particle. In FIG. 1 b, it is also shown that a coating of a polymeric, polymerizable and/or monomeric organic compound 14 is arranged on the sinterable particle 12. This coating may be produced by the polymeric, polymerizable and/or monomeric organic compound 14 being added to the solvent 16, for example dissolved or dispersed. By way of example, a colophony resin, which can serve as a fluxing agent, may be used as the polymeric, polymerizable and/or monomeric organic compound 14. This has the advantage with respect to the method according to the invention that it is soft and adhesive at slightly elevated temperatures of well below 100° C., but in the further course of conducting the process evaporates virtually without any residue by decomposing and can be produced as a preform at 25° C. The completed starting material 10, obtained as described above by evaporating the solvent, is shown in FIG. 1 c.
Such a starting material 10 may be arranged directly between two components 18, 20 to be connected, as is shown in FIG. 2 a. In this case, the starting material 10 may be applied to at least one component 20 to be connected by printing, doctor blading or dispensing. For example, the component 20 may be a substrate, whereas the component 18 may be an electronic component, such as for instance a power semiconductor component.
In FIG. 2 b, a first thermal treatment step is shown. In detail, a state after a method step comprising heating of the starting material 10 to a temperature T1, which is greater than or equal to the flow temperature of the polymeric, polymerizable and/or monomeric organic compound 14 and less than the desorption temperature of the polymeric, polymerizable and/or monomeric organic compound 14, for a time t1 is shown in FIG. 2. This results in part of the polymeric, polymerizable and/or monomeric organic compound 14 being removed from the joining zone and arranging itself on the component 20 or wetting the surface of the component 20. In this case, the polymeric, polymerizable and/or monomeric organic compound 14 can be discharged or removed during or after this method step of the first heat treatment.
In FIG. 2 c, furthermore, a formed sintered connection 22 of the two components 18, 20 is shown. Such a sintered connection 22 is formed by sintered sinterable particles 12, by a further method step involving heating the starting material 10 to a temperature T2, which is greater than or equal to the sintering temperature of the sinterable particles 10, possibly under the effect of a sintering pressure, for a time period t2, thereby forming a sintered connection 22. For example when using silver as sinterable particles 12, the sintered connection 22 may have an electrical conductivity of from greater than or equal to 30 MS/m to in particular less than or equal to 45 MS/m, in particular from greater than or equal to 36 MS/m to in particular less than or equal to 44 MS/m, and/or may have a thermal conductivity of from greater than or equal to 200 W/mK to less than or equal to 300 W/mK, in particular from greater than or equal to 220 W/mK to less than or equal to 225 W/mK. Furthermore, sintering may by way of example take place at a sintering pressure of less than or equal to 10 MPa, for example of less than or equal to 1 MPa and/or at a sintering temperature in a range of less than or equal to 300° C., for example less than or equal to 250° C.
In FIGS. 3 a to 3 c, a further refinement of a starting material 10 and a method performed with it is shown. In the refinement according to FIG. 3 a, the polymeric, polymerizable and/or monomeric organic compound 14 forms a matrix, in which the sinterable particles 12 are embedded. In this case, the polymeric, polymerizable and/or monomeric organic compound 14 is arranged together with the sinterable particles 12 in a transfer layer 24, for instance as an adhesive film. The transfer layer 24 is in this case arranged between at least two protective layers 26, 28, in particular comprising a polymeric, polymerizable and/or monomeric organic compound 30.
In order to form a sintered connection 22, it may be the case that first a protective layer 28 is removed and the starting material 10 is transferred to the first component 20. After the removal of the second protective layer 26 or of all the protective layers still present, the second component 18 is correspondingly positioned on the starting material 10 or on the transfer layer 14. In this case, reference is made here, and possibly also in respect of further method steps, to the starting material 10, even though sometimes only part of the starting material is present, which however can be included in the sense of the invention by referring to starting material 10. This state is shown in FIG. 3 b.
This may be followed by a first thermal treatment, in which the polymeric, polymerizable and/or monomeric organic compound 14 melts, and for example may become adhesive. In the sintering process, the polymeric, polymerizable and/or monomeric organic compound 14 can be removed and, furthermore, as a result of the elevated temperature, the sintered sinterable particles can form a sintered connection 22, as is shown in FIG. 3 c.

Claims

1. A method for connecting at least two components (18, 20) using a sintering process, comprising:

a) providing a starting material (10) of a sintered connection (22), comprising sinterable particles (12), comprising at least one metal or at least one metal compound, and at least one polymeric, polymerizable and/or monomeric organic compound (14), wherein the polymeric, polymerizable and/or monomeric organic compound (14) has a flow temperature that is greater than or equal to room temperature and less than a sintering temperature of the sinterable particles, and wherein the polymeric, polymerizable and/or monomeric organic compound (14) also has a desorption temperature that is greater than the flow temperature and less than or equal to the sintering temperature;

b) arranging the starting material (10) between two components (18, 20) to be connected;

c) heating the starting material (10) to a temperature T1, which is greater than or equal to the flow temperature of the polymeric, polymerizable and/or monomeric organic compound (14) and less than the desorption temperature of the polymeric, polymerizable and/or monomeric organic compound (14), for a time t1; and

d) heating the starting material (10) to a temperature T2, which is greater than or equal to the sintering temperature of the sinterable particles (12), for a time period t2, thereby forming a sintered connection (22).

2. The method as claimed in claim 1, wherein the desorption temperature is a boiling temperature, a decomposition temperature or a reaction temperature of the polymeric, polymerizable and/or monomeric organic compound (14) with the sinterable particles and/or with sintered particles (12).

3. The method as claimed in claim 1, wherein the sinterable particles (12) contain silver, gold, platinum, palladium and/or copper, an organic metal compound, a metal oxide, or a mixture comprising one or more of the aforementioned substances.

4. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) comprises a polyolefin, a polyethylene copolymer, a polyketone or a mixture comprising one or more of the aforementioned substances.

5. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) forms a matrix, in which the sinterable particles (12) are embedded, or wherein the polymeric, polymerizable and/or monomeric organic compound (14) takes the form of a coating on the sinterable particles (12).

6. The method as claimed in claim 1, wherein the starting material (10) is applied to at least one component to be connected by printing, doctor blading or dispensing.

7. The method as claimed in claim 1, wherein the starting material (10) has a transfer layer (24), which is arranged between at least two protective layers (26, 28).

8. The method as claimed in claim 7, wherein the protective layers (26, 28) are removed before or during method step b).

9. The method as claimed in claim 7, wherein the protective layers (26, 28) comprise polyethylene terephthalate.

10. The method as claimed in claim 1, wherein the starting material (10) is provided in the form of a paste, a powder, granules or a film.

11. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) is discharged or removed during or after method step c).

12. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) contains at least one additive that reacts with the sinterable particles (12), while reducing the sintering temperature.

13. The method as claimed in claim 1, wherein a sintered connection (22) that has an electrical conductivity of from greater than or equal to 30 MS/m is produced, and/or wherein a sintered connection (22) that has a thermal conductivity of from greater than or equal to 200 W/mK to less than or equal to 300 W/mK is produced.

14. The method as claimed in claim 1, wherein an electronic component is used as one of the components to be connected and a substrate is used as another of the components (20) to be connected.

15. The use of a method as claimed in claim 1 for producing an electronic component.

16. The method as claimed in claim 1, wherein method step d) includes heating the starting material (10) to a temperature T2 under the effect of a sintering pressure.

17. The method as claimed in claim 1, wherein the sinterable particles (12) contain silver, gold, platinum, palladium and/or copper, an organic metal compound, comprising silver carbonate, silver lactate or silver stearate, a metal oxide, comprising silver oxide, or a mixture comprising one or more of the aforementioned substances.

18. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) comprises a polyolefin, comprising polyethylene and/or polypropylene, a polyethylene copolymer, a polyketone or a mixture comprising one or more of the aforementioned substances.

19. The method as claimed in claim 1, wherein the starting material (10) has a transfer layer (24), which is arranged between at least two protective layers (26, 28), comprising a polymeric, polymerizable and/or monomeric organic compound.

20. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) contains at least one additive that reacts with the organic metal compound, while reducing the sintering temperature.

21. The method as claimed in claim 1, wherein a sintered connection (22) that has an electrical conductivity of from greater than or equal to 30 MS/m to less than or equal to 45 MS/m is produced, and/or wherein a sintered connection (22) that has a thermal conductivity of from greater than or equal to 200 W/mK to less than or equal to 300 W/mK is produced.

22. The method as claimed in claim 1, wherein a sintered connection (22) that has an electrical conductivity of from greater than or equal to 36 MS/m to less than or equal to 44 MS/m is produced, and/or wherein a sintered connection (22) that has a thermal conductivity of from greater than or equal to 220 W/mK to less than or equal to 275 W/mK is produced.

23. The method as claimed in claim 1, wherein an electronic component is used as one of the components to be connected and a substrate, comprising a copper compound, is used as another of the components (20) to be connected.