Method for low-temperature pressure sintering of two joining partners

Abstract

Method for producing an arrangement with a first (10) and a second joining partner (50) which are materially joined to each other by means of a low-temperature pressure sintering connection, wherein the joining partners (10, 50) each have a contact surface (16, 56) to be joined to the other joining partner, wherein a sintered metal layer (34) is arranged between these contact surfaces (16, 56), comprising these successive steps: a) Providing a first connection partner (10) with a first contact surface (16); b) Applying a layer of sintered metal particles and a solvent-containing sintering paste (30) to the first contact surface (16); c) Temperature treatment (22) of the sintering paste (30) and removal of at least 75% of the solvent, forming the sintered layer (32); d) Applying an adhesive fluid (40) to the sintered layer (32), wherein the adhesive fluid is dimensioned such that it penetrates the sintered layer to at least 20 vol% of its volume; e) Arranging the second joining partner (50) such that its second contact surface (56) lies on a film of the adhesive fluid formed on a part of the surface of the sintered layer (32); f) Applying temperature and pressure (60) to the arrangement to form the material-bonded low-temperature pressure sintering connection between the joining partners (10, 50), whereby the sintered layer (32) is transformed into a sintered metal layer (34).

Description

[0001] The invention describes a manufacturing process for low-temperature pressure sintering of two joining partners with contact surfaces to be joined, and an arrangement produced thereby.

[0002] A pressure-sintered joint is generally known from US 6,823,915 B2. The joint disclosed therein between two workpieces comprises a sintered layer of thermally conductive powder, which is arranged between the two workpieces and makes contact with each workpiece over its entire surface, and an adhesive that fills openings on the surface of the layer and adheres to both workpieces. Preferably, the sintered layer consists of silver powder. First, the sintered layer is produced between the workpieces, then this layer is filled with a curable liquid adhesive, which is then cured.

[0003] From the prior art, specifically disclosed in DE 10 2010 021 764 A1, an arrangement and a method for its production are known. This arrangement comprises a first and a second joining partner, which are metallurgically bonded to one another by means of a sintered metal layer using a low-temperature pressure sintering process. The process steps are: providing a first joining partner with a first contact surface; applying a layer of a sintering paste, consisting of sintered metal particles and a solvent, to the first contact surface; subjecting the sintering paste to heat and driving out the solvent, forming the sintered layer; applying a liquid, preferably glycerin, to the sintered layer; and arranging the second joining partner.An adhesive is placed at the edge of the sintered layer and the second joining partner, in contact with the first joining partner, to fix the joining partners together. The arrangement is then subjected to temperature and pressure to form a metallurgical, low-temperature pressure sintered bond between the joining partners, whereby the sintered layer is transformed into a homogeneous sintered metal layer.

[0004] A disadvantage of this known method is that the adhesive strength of the liquids used is not sufficient in all applications. An advantage of this method is that the liquids used do not affect the time required for the manufacturing process.

[0005] In light of the aforementioned circumstances, the invention is based on the objective of presenting a manufacturing process and an arrangement produced thereby with a materially bonded connection in the form of a low-temperature pressure sintering connection of two connecting partners, whereby the process reliability is increased and whereby the formation of voids in the sintered metal layer of the low-temperature pressure sintering connection is prevented and their typical size is significantly reduced.

[0006] This problem is solved according to the invention by a manufacturing process having the features of claim 1,

[0007] The inventive method for producing an arrangement with a first and a second connecting partner which are materially bonded to each other by means of a low-temperature pressure sintering connection, wherein the connecting partners each have a contact surface to be bonded to the other connecting partner, wherein a sintered metal layer is arranged between these contact surfaces, is described by these successive steps: a) Providing an initial connection partner with an initial contact surface; b) Applying a layer of sintered metal particles and a solvent-containing sintering paste to the first contact surface; c) Applying heat to the sintering paste and driving out at least 75% of the solvent, forming the sintered layer; d) Applying an adhesive liquid to the sintered layer, wherein the adhesive liquid is dimensioned such that it penetrates the sintered layer to at least 20 vol% of its volume; e) Arranging the second joining partner such that its second contact surface lies on a film of the adhesive fluid formed on part of the surface of the sintered layer; f) Applying temperature and pressure to the arrangement to form the material-bonded low-temperature pressure sintering connection between the joining partners, whereby the sintered layer is transformed into a sintered metal layer.

[0008] Advantageously, the adhesive fluid is in the form of an aromatic alcohol, such as preferably benzyl alcohol or terpineol.

[0009] It is preferred that the adhesive fluid has a viscosity of 5 mPas to 250 mPas. It is also preferred that the adhesive fluid has a refractive index of 1.41 to 1.55.

[0010] Preferably, in step c) the solvent is driven off to at least 90% and preferably to at least 95%.

[0011] Preferably, in step d) the amount of adhesive liquid is at least 40 vol% and preferably at least 60 vol% of the volume of the sintered layer.

[0012] It is advantageous if, in step e), the portion of the surface is at least 20%, in particular at least 40% and preferably at least 60% of the total surface.

[0013] It is particularly advantageous if the waiting time between step d) and e) does not exceed 5 minutes, in particular 2 minutes, and most preferably 1 minute.

[0014] It is also advantageous if, after step e), an additional temperature exposure to a temperature between 50°C and 200°C is carried out without pressure.

[0015] This process deliberately accepts the inclusion of a previously unknown, time-critical step. A specific time window must be maintained, allowing the adhesive fluid to penetrate the sintered layer only to the extent necessary to preserve the adhesive properties on the surface for a sufficient duration and strength. This is fundamentally dependent on the type and design of the two bonding partners, as well as the thickness of the sintered layer, and can only be determined empirically.

[0016] According to the invention, the arrangement produced by the above-mentioned method is designed with a first and a second connecting partner which are materially bonded to each other by means of a low-temperature pressure sintering connection, wherein the connecting partners each have a contact surface to be connected to the other connecting partner, wherein a sintered metal layer is arranged between these contact surfaces.

[0017] It follows that the sintered metal layer is homogeneous with respect to the distribution of voids. Likewise, it follows that the sintered metal layer contains only voids with a diameter of no more than 10 µm.

[0018] Of course, unless explicitly excluded, the features mentioned in the singular, in particular the second joining partner, the contact surfaces, the sintering paste, the sintered layer, and the sintered metal layer, can be present multiple times in the respective process steps or in the resulting arrangement. In other words, arrangements can also be produced in which several second joining partners are simultaneously and metallurgically bonded to the first joining partner using the described process.

[0019] Further explanation of the invention, advantageous details and features, will become apparent from the following description of the invention contained in the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6 illustrated embodiment. Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. Figure 5 shows different stages of the process according to the invention. Fig. Figure 6 shows an arrangement produced using this method according to the invention.

[0020] Fig. Figure 1 shows a section of a typical substrate 10, which is widely used in power electronics, as the first connection partner. This substrate has an insulating body 12, preferably an industrial ceramic such as aluminum nitride, and a metallic conductor 14 on one of the main surfaces of this insulating body 12. This conductor 14 is preferably made of copper. The conductor has a typical thickness in the range of 200 µm to 400 µm, although the invention is not limited to the configuration of the first connection partner in this form. The first connection partner is generally and preferably a commonly used substrate.

[0021] The first contact surface, that of the substrate's conductor track with which the second connection partner is to be brought into electrically conductive contact, has a surface suitable for low-temperature pressure sintering. It is preferred that the first contact surface 16 has a precious metal surface 18, in particular with a silver content of more than 90%. Also shown is a sintering paste 30 arranged on this first contact surface 16, which in turn consists of sintered metal particles, here precious metal particles, preferably silver particles, and a solvent, and has a thickness between 30 µm and 50 µm. This is only an exemplary value within the scope of this embodiment.

[0022] Fig. Figure 2 schematically shows the subsequent process step of temperature-induced solvent removal from the sintering paste. The temperature application 22 can be configured in any way, particularly in accordance with industry standards; for example, it can be carried out by directly acting on the sintering paste 30 or by heating the substrate 10. The key advantage of removing the solvent at this stage is that this level of removal cannot be achieved as effectively if the second bonding partner is added later. Residual solvent leads to undesirable voids in the resulting sintered metal layer. In this embodiment of the process, between 80% and 90% of the solvent is removed from the sintering paste.

[0023] After this process step, 30 of the sintered paste are present, according to Fig. 1 almost exclusively the precious metal particles remain, which will be referred to below as sintered layer 32. In contrast to the adhesive effect on a second bonding partner arranged on the surface of a sintered paste due to the solvent content, the sintered layer 32 exhibits no or only very weak adhesive forces from its free surface to second bonding partners.

[0024] In order to nevertheless achieve a fixation of a second connection partner, as shown in Fig. 3, an adhesive liquid 40 is applied to the free surface of the sintered layer 32. This adhesive liquid, which here is present as terpineol or as benzyl alcohol, spreads out on the surface of the sintered layer 32, see Fig. 4, and covers approximately 50% of this surface. The amount of adhesive fluid is limited and here amounts to approximately 55% by volume of the sintered layer. In contrast to the prior art, the adhesive fluid has the special property that it is able to penetrate the sintered layer 32 easily and, with sufficient waiting time, almost completely.

[0025] Therefore, the second bonding partner 50, here a power semiconductor device, must be positioned within approximately 2 minutes on this adhesive fluid 40, which in the meantime forms only a very thin layer, a film, on the surface of the sintered layer 32. The adhesive force, mediated by the adhesive fluid 40, between the sintered layer 32 and the second bonding partner 50, cf. Fig. 5, fixes this at the desired location on the first connection partner. The power semiconductor device 50 has a second contact surface 56 accessible for low-temperature pressure sintering, which is to be brought into electrically conductive contact with the first contact surface of the substrate. For this purpose, it is preferred if the second contact surface 56 has a precious metal surface 58, in particular with a silver content of more than 90%.

[0026] Fig. Figure 5 shows the power semiconductor device 50 arranged and fixed on the sintered layer 32 with an adhesive liquid arranged between it and parts of this adhesive liquid that have already penetrated the sintered layer. In the further process, this arrangement is subjected to pressure 60 and temperature in a manner customary in the industry, whereby the sintered layer is transformed into a sintered metal layer 34. This sintered metal layer 34 is characterized in that the sintered metal particles of the sintered layer are bonded together to form a solid layer, which thus, as in Fig. Figure 6 shows a material-bonded low-temperature pressure sintering connection formed between the first and second connection partners 10, 50.

[0027] Due to the aforementioned process according to the invention, the resulting metallurgically bonded low-temperature pressure sintered joint exhibits a particularly high quality, which is especially evident in the small number of voids in the produced sintered metal layer 34 and in the small size of these voids, which is less than 10 µm. The process according to the invention also has the further advantage that process reliability, particularly during the transport of the arrangement consisting of the first bonding partner 10, the sintered layer 32, and the second bonding partner 50 to the pressure sintering device, which applies pressure and temperature to this arrangement, effectively prevents any change in the position of the second bonding partner relative to the first bonding partner.Thus, a very high quality is achieved with regard to the electrical parameters as well as the durability of the connection between the connecting partners as such, and also with regard to the position of the connecting partners relative to each other.

Claims

[1] Method for producing an arrangement with a first (10) and a second joining partner (50) which are joined together by means of a low-temperature pressure sintering connection, wherein the joining partners (10, 50) each have a contact surface (16, 56) to be joined to the other joining partner, wherein a sintered metal layer (34) is arranged between these contact surfaces (16, 56), comprising these successive steps: a) Providing a first connection partner (10) with a first contact surface (16); b) Applying a layer of sintered metal particles and a solvent-containing sintering paste (30) to the first contact surface (16); c) Temperature treatment (22) of the sintering paste (30) and removal of at least 75% of the solvent, forming the sintered layer (32); d) Applying an adhesive fluid (40) to the sintered layer (32), wherein the adhesive fluid is dimensioned such that it penetrates the sintered layer to at least 20 vol% of its volume; e) Arranging the second joining partner (50) such that its second contact surface (56) lies on a film of the adhesive fluid formed on a part of the surface of the sintered layer (32); f) Applying temperature and pressure (60) to the arrangement to form the material-bonded low-temperature pressure sintering connection between the joining partners (10, 50), whereby the sintered layer (32) is transformed into a sintered metal layer (34). [2] Method according to claim 1, wherein the adhesive liquid (40) is an aromatic alcohol, preferably benzyl alcohol or terpineol. [3] Method according to any of the preceding claims, wherein the adhesive fluid (40) has a viscosity of 5 mPas to 250 mPas. [4] Method according to any of the preceding claims, wherein the adhesive liquid (40) has a refractive index of 1.41 to 1.

55. [5] Method according to any of the preceding claims, wherein in step c) the solvent is driven off to at least 90% and preferably to at least 95%. [6] Method according to one of the preceding claims, wherein in step d) the amount of adhesive liquid is at least 40 vol% and preferably at least 60 vol% of the volume of the sintered layer. [7] Method according to one of the preceding claims, wherein in step e) the part of the surface is at least 20%, in particular at least 40% and preferably at least 60% of the surface. [8] Method according to any of the preceding claims, wherein the waiting time between step d) and e) does not exceed 5 minutes, in particular 2 minutes, particularly preferably 1 minute. [9] Method according to one of the preceding claims, wherein after step e) an additional temperature exposure to a temperature between 50°C and 200°C is carried out without pressure. [10] Method according to one of the preceding claims, wherein the first and / or second contact surface (16, 56) has a precious metal-containing, preferably silver-containing, surface (18, 58).

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