DE102011018544A1 - Method for connecting mating face of substrate, electronic portion and mating face of electronic portion for electronic component, involves forming film between mating face(s) and adhering mating face(s) with intermediate film - Google Patents

Abstract

Method for connecting mating face of substrate, electronic portion and mating face of electronic portion involves forming a film containing conductive precious metal, semiprecious metal or precious metal alloy between mating face (a) and mating face (b) and adhering mating face (a,b) with an intermediate film. The film comprises a nanoporous structure. An independent claim is included for electronic component.

Description

The present invention is a method for connecting a first joining surface of a substrate or a first joining surface of a first electronic component and a second joining surface of a second electronic component with the features of claim 1. Furthermore, the invention relates to the use of a film or a film according to the features of claim 15 for joining a substrate or a first electronic component and a second electronic component. Furthermore, an electronic stack is claimed, in which a film is used according to the features of claim 15 between two adjacent joining surfaces.

When mounting semiconductor components on a substrate carrier or on a further semiconductor component, the connection layer lying between the semiconductor component and the substrate carrier has to meet different requirements. Particularly in the case of lossy components, in power electronics and in high-temperature applications, the connecting layer should have low electrical and / or thermal resistance, sufficient mechanical strength and a fatigue-resistant connection at numerous temperature changes. At the same time, when connecting the semiconductor component and the substrate carrier or the further semiconductor component, mechanical stresses should be minimized when connecting by low bond temperature and low bond pressure and the handling and metering of the material of the connection layer should be simple.

In the prior art, different approaches to meet the above requirements. As connecting layers, for example, electrically and thermally conductive adhesives with rather lower conductivity (compared to metals) are used.

Another possibility is the use of soft solders, which allow good thermal conductivity and good topography balance, but often have flux residues or pores in the solder and usually fail early due to solder fatigue.

Another possibility is the use of hard solders, such as AuSn or AuGe, which also allow a good topography balance, but due to the different expansion coefficients lead to mechanical stresses in the device and there is a risk of delamination.

In the context of transient liquid phase bonding, usually thin layers of copper and tin or gold and tin are applied, whereby the forming thin solder layer can only afford a low topography compensation and the different coefficients of expansion between substrate and component can lead to destruction of the component.

Another possibility is the application of sintered layers, which have excellent thermal and electrical conductivity, but can be produced only by means of a paste. This requires complex printing technology and excludes the arrangement in a cavity.

Another possibility of a compound layer is in the DE 10 2007 055 017 A1 described. In this case, first a layer of 20% to 40% gold and 60% to 80% silver is deposited on a substrate or semiconductor component and, by subsequent selective removal of the silver, a nanoporous gold layer is produced from the deposited layer. This is inseparably connected to the substrate or the semiconductor component due to the production method.

By depositing the layer directly on the substrate or semiconductor device, the substrate must have surfaces that are insensitive to the selective removal of the silver. In most cases, this means applying a further layer to the substrate or semiconductor component for protection from the etchant.

The object of the present invention is to provide a method or a stack which, in contrast to the abovementioned possibilities, provides an advantageous alternative to the joining or bonding of two joining surfaces.

The object is achieved by means of a method having the features of claim 1, by the use of a film according to claim 15 and an electronic stack according to the features of claim 16.

Essential to the invention is the use of a film of a conductive noble metal, such as gold, platinum or palladium, a semi-precious metal, such as copper or tin, or a noble metal alloy, wherein the film or film has a nanoporous structure.

The film or the film can be produced in many ways, for example, based on the in SEKER et al. "Nanoporous Gold: Fabrication, Characterization, and Applications", Materials 2009, 2, 2188-2215 , referenced method.

The film or film is placed between the components to be joined, wherein the first component may be a substrate or a first electronic component and the second component may be a second electronic component, and is then pressurized by subjecting the first and second components to pressure and / or or temperature such that a cohesive connection between the film and the first and the second component is formed. For example, for a porous gold foil, the common temperatures and bonding pressures are between 130 ° C. and 380 ° C. or between 10 MPa and 200 MPa. The values for porous silver are comparable to gold, for copper, platinum and palladium, the values are slightly higher. A significant influence on the actual values depends on the pore density and the size of the pores. The bonding time also has a considerable effect on the strength of the connection.

Compared to the direct application of a nanoporous layer to a first or second joining surface of a first or second component, galvanic deposition, sputtering or vapor deposition of a master alloy from a noble metal and a further, less noble metal to be removed in the course of a leaching process are avoided. Thus, the method presented here in cases of full-surface or at least a large area connection between two components on a significant simplification in the handling and the requirements of the components to be joined.

The film or the film with the nanoporous structure still has a high porosity even after the joining or bonding of the first and second component. For example, the porosity may be between 20% and 70% of the total volume, i. that is, compared to the volume of the compressed film (due to the bonding process), the pores occupy between 20% and 70% of the volume. The open-pore structure of the film or the film has a branched network of branches. This network of branches, which surround the largely convex pores, is characteristic of the de-alloyed metal sponge. In bonding itself and the concomitant progressive compression, this branch structure is retained.

In contrast, in a film or film produced by a sintering process, sintered contact necks are formed on the powder balls which enclose concave pores which initially form a network via channels. As compression progresses, the pore channels are closed and the pore network breaks up into isolated pores.

The film or the film have the property that they have a higher density on topographies than outside the topographies. Topographies are, for example, elevations and edges which can occur via vias, passivation openings and buried interconnects. Unintentional topographies are caused by particles from sputtering sources, saw dust, burrs, micro-scratches from handling and small dust particles. The method is thus suitable for full or large area connections with requirements for good electrical and / or thermal conductivity and / or for an increased yield. In addition, the reduced stiffness of the sponge is capable of absorbing deformations at significantly lower forces, increasing the reliability of the connection and reducing the load on the component. Applications include high performance LED to light module assembly, mounting of sensitive laser diodes and laser diode bars, assembly of power amplifiers and switches, based in particular on silicon carbide and gallium nitride, assembly of sensitive microelectromechanical systems (MEMS), especially for high temperature applications, the assembly of components in cavities, for example of a substrate, so that the components produced in this way are used in lighting technology in the automotive sector in power electronics, in industrial electronics, in communications technology, such as transmission modules and radars, and in photonics for optical communication can.

As a precaution, it should be noted that all aspects mentioned in the proceedings are also based on the present claims, ie. H. the protection of the use of the film or the film with the nanoporous structure and on the electric stack are applicable. For this reason, all features named for the method can also be used in concrete form for the present claims.

In particular, this refers to the degree of porosity of 15% to 75%, a pore size between 20 nm and 10 microns, or between 100 nm and 10 microns, between 20 nm and 3 microns, or between 100 nm 3 microns, or between 70 nm and 700 nm for films of high reactivity and between 1 μm and 5 μm for soft films. Preferably, the pores are predominantly convex in shape and the nanoporous structure is formed by branched branches of the noble metal, semiprecious metal or the noble metal alloy. Furthermore, the pores are preferably filled with a polymer. Further features of the stack will become apparent from the following process variants.

Further embodiments of the invention are described in the subordinate claims.

In a first embodiment, the nanoporous structure of the film or film is prepared by dissolving out a metal that is less noble than the noble metal, semi-precious metal or the components of the noble metal alloy. For such a film, an alloy of a nobler and a less noble metal is first processed into a film, and then the less noble metal is dissolved out of the nobler metal, so that a nanoporous structure is formed. In this case, it is preferable if the less noble metal is dissolved out by an etching process. The less noble metal may, for example, be silver, tin or zinc, the more noble metals, for example gold or platinum or palladium. Although copper has high reactivity and oxidation susceptibility, the nobler metal may also be copper. Furthermore, noble metal alloys, for example of platinum or gold are possible.

In the case of the film or film, which is initially produced from an alloy of a nobler metal and a less noble metal, the volume fraction of the less noble metal is 60% by volume to the total volume of the film or film prior to leaching out of the less noble metal 90 vol .-%, so that the film or the film may have a porosity of 40% to 90%. The volume fraction of the noble metal, semiprecious metal or the noble metal alloy is consequently between 10% by volume and 40% by volume. The weight proportions or atomic proportions of the individual components can be calculated taking into account the density, and the mass number.

In an alternative embodiment, the film having the porous structure is prepared by sintering a powder of the noble metal, semiprecious metal or the components of the noble metal alloy. Here, the individual, for example, spherical or flaky particles of the powder combine at small contact points and thus form a porous structure.

The size of the pores can be chosen differently depending on the application. Here are pores of an average diameter of 20 nm to 10 microns in question. Here, the average diameter means that the extent of a pore between two adjacent surfaces of the noble metal, semi-precious metal or the components of the noble metal alloy has an average length of the above-mentioned mean diameter. In this case, in a further embodiment, the porous structure of the film or of the film can be further varied by subsequent tempering. The porosity, d. H. this compared to the total volume relative pore volume of the film or of the film, thereby essentially retained. Fine-pored or nanoporous metal foils have the advantage that they are very reactive, but because of the increased surface diffusion they have the disadvantage that they have a higher yield stress. Coarsely porous films are mechanically softer but reduced in reactivity.

In a further embodiment, after the film has been produced, the film or film is joined to one another first with either the first or second joining surface before joining the first and second joining surfaces. This is advantageous, for example, if one of the two components used forms a bond with the film or the film under different conditions with respect to the other component, and the conditions for joining the one component with the film could possibly lead to destruction of the second component , In this case, on the not provided with the component surface of the film nichtbondfähiges material, eg. As a PTFE or graphite foil, are applied in order to build up a corresponding pressure on both sides of the film for bonding.

In the previous embodiments, the nanoporous structure is produced prior to joining the film or film with both the first joining surface and the second joining surface. In this case, therefore, the film is first produced and only then connected to the first and / or second component. This is compared to the embodiment that the film is first connected as an alloy (alloy foil) with a component and only then the less noble component is removed (de-alloyed) to distinguish.

In another embodiment, prior to the joining of the first and second joining surfaces, an adhesive or an adhesive is applied to the first and / or second joining surface in order to connect the first and second joining surfaces of the first and second component with the aid of the film to simplify. During assembly of the component onto the substrate or in general during connection of the thus prepared joining surfaces, an adhesive connection to the connecting surfaces is produced. The shrinkage of the adhesive during curing as well as the shrinkage on cooling lead to a pressure contact in which the porous film is pressed against the joining surfaces.

Furthermore, the nanoporous structure can also be post-annealed after joining the first and second joining surfaces or the first and second components.

In one embodiment, the film has a thickness between 10 μm and 150 μm. The thickness is chosen here based on the intended use of the film.

In order to enable large-area processing, has an edge of the film and / or the film perpendicular to the thickness of an edge length between 200 microns and 25 cm. As a result, both very small components and very large components can be mounted in a single process step by means of the film on another component or a substrate.

The invention will be explained in more detail with reference to some embodiments. Show it:

1A to 1E first embodiment of a method according to the invention;

2A to 2F second embodiment of a method according to the invention;

3A to 3F third embodiment of a method according to the invention;

4A to 4E fourth embodiment of a method according to the invention.

Based on 1A to 1E is intended a first variant of a method according to the invention 10 be explained in more detail. In the 1A is an alloy foil 11 shown, which has a thickness of 100 microns and an edge length of 4 cm. The alloy foil 11 consists of a gold / silver alloy of 20% by volume of gold and 80% by volume of silver. The size of the alloy foil 11 is already pre-cut to the size of the components to be joined later. This blank can also only after the de-alloying of the alloy foil 11 be made.

With the help of dilute nitric acid at temperatures around 60 ° C, the silver is removed from the alloy as part of an etching process, as this represents the less noble metal compared to the gold. A film remains behind 12 with nanoporous structure, where the nanoporous structure is formed due to large ramifications. A mean pore size is 200 nm. Smaller pores can be achieved by etching in cold etching solution or larger pore sizes by means of a post-annealing.

After completely de-alloying the film 12 this will be on a substrate 13 hung up. Subsequently, on the not lying on the substrate surface of the deflated foil 12 an electronic component 14 applied, leaving a full-surface connection between the electronic component 14 and the de-alloyed film 12 and the underlying substrate 13 is present. To the surfaces of the substrate 13 and the electrical component 14 To bond and to facilitate the bonding, the film can be fixed with the help of alcohol. Subsequently, as in the 1D illustrates, by applying a bond pressure of 100 MPa a temperature of 200 ° C, a material bond between the substrate 13 and the de-alloyed film 12 and between the deflated foil 12 and the electronic component 14 causes. The pressure 15 is first applied to the electronic component, but can also be done by pressing on the substrate.

In the 1E is the electronic stack 16 shown which on the deflated film 12 a cohesive connection between the electronic component 14 and the substrate 13 taught. It should be noted that the thickness of the film was reduced as part of the compression process, so that the initial porosity of 80% was reduced to a porosity of 40%.

Remaining high porosity reduces the rigidity of the connection and is therefore favorable for low mechanical stresses and higher reliability. Here, in the present case, a high porosity is understood to mean that the pores and, in particular, the pore framework surrounding the pores (which is formed by so-called branches) determine the mechanical properties of the deflated foil. If the pores only appear at longer intervals (low porosity), the pores are isolated and the mechanical properties of the film are dominated by the solid. In order to prevent the penetration of liquids into the open-pore connection zone of the film, the pore seam circulating at the edge of the component can be filled with a low-viscosity polymer by applying a small drop of the polymer to the edge of the film and pulling the polymer into the gap. On the other hand, the bond parameters can also be increased so much that the film is largely compressed and the open pores are closed. For larger joint gaps, multiple foils may be used instead of a single porous metal foil. With thicker films higher non-planar surfaces z. B. minor levels are over-bonded. Small particle contamination can also be tolerated because the films simply trap the particles by local compression.

In the 2 is a shadowy alternative method 20 shown. When in the 2A The film shown is a de-alloyed film 12 , which in contrast to in the 1A produced film was produced by a sintering process. This has a thickness of 15 microns and an edge length of 10 cm. As in 2A Illustrated, the film becomes 12 with nanoporous structure on an electronic component 21 placed. On the unit of foil 12 and electronic component 21 becomes a non-bondable platelet 24 which in the present case consists of oxidised silicon ( 2 B ). Like in the 2C shown, pressure and temperature 23 applied, leaving a stack of the non-bondable plate 24 as well as the electronic component 21 and the film is made. This results in a cohesive connection between the electronic component 21 and the foil 12 , Subsequently, the non-bondable platelets 24 removed and the pile 22 with the surface of the film 12 on a substrate 13 placed so that the joining surface of the substrate 13 is covered with the foil. Subsequently, as in the 2E illustrated, pressure 25 applied, which leads to a cohesive connection between the film 12 and the joining surface of the substrate 13 leads. In the 2F is the finished electronic stack 26 shown. As in the previous procedure 10 is the porosity due to the pressure 25 greatly reduced and is in the present case at 30%.

In the 3 is another alternative method 30 illustrated. The alloy foil 11 made of gold and silver will be on an electronic component 14 hung up and - as in the 3B illustrated - by means of pressure and temperature 31 bonded with this. Subsequently, the alloy foil 11 by means of an etching process ( 3C ), such as in the context of the procedure 10 described, de-alloyed, leaving the pile 32 is formed. The stack 32 includes the electronic component 14 and the de-alloyed film 12 , Then this stack, as in the 3D shown with the joining surface of the substrate 13 connected and by means of pressure and temperature 33 together. In this way, the one in the 3F illustrated electronic stack 34 educated.

In contrast to the previous method, the film is thus de-alloyed after bonding with the electronic component.

At this point it should be mentioned that the alloy foil 11 also first with the substrate 13 can be connected, then de-alloyed and subsequently with a joining surface of the electronic component 14 is connected.

In the 4 is another procedure 40 illustrated.

Like in the 4A is shown, a de-alloyed film 12 , as described in the preceding embodiments, with a substrate 13 connected. In addition, however, is adhesive 41 on the joining surface of the substrate 13 applied before the deflated foil 12 placed on the joining surface ( 4B ). After connecting 42 the adhesive spreads through the film so that the deflated film 12 impregnated with adhesive. This is in the 4C due to the different hatching of the film 12 clear. Subsequently, a joining surface of the electronic component 14 on the surface of the de-alloyed film 12 , which is impregnated with adhesive, placed.

In the 4D it can be seen that the glue 41 when applying pressure 43 also emerges from the lateral edges of the film and an encapsulation of the electronic component 14 with the substrate 13 causes. In this way comes the encapsulated electronic stack 44 of the 4E conditions.

It should also be noted that the adhesive can be applied both in liquid form, for example by means of a cannula and as a pre-cut plate in the solid state. It is thus also possible to form a stack consisting of a substrate, a de-alloyed film, an adhesive wafer and a component or a substrate, an adhesive wafer, a de-alloyed film and a component. When applying pressure and temperature, the adhesive melts, saturates the porous film and wets the joining surfaces of the component and the substrate.

It should be noted that the steps illustrated in the various embodiments may be combined with steps of other embodiments or other embodiments as described in the specification, or that individual steps of the methods according to various embodiments of the invention may be omitted.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102007055017 A1 [0008]

Cited non-patent literature

• SEKER et al "Nanoporous Gold: Fabrication, Characterization, and Applications", Materials 2009, 2, 2188-2215 [0013]

Claims (16)

Procedure ( 10 ; 20 ; 30 ; 40 ) for joining a first joining surface of a substrate ( 13 ) or a first electronic component and a second joint surface of a second electronic component ( 14 ), the method comprising the following steps: a) arrangement of a film ( 12 ) or a film of a conductive noble metal, semi-precious metal or a noble metal alloy between the first joining surface and the second joining surface, wherein the film or the film has a nanoporous structure; b) joining the first and second joining surfaces and the intermediate film ( 12 ) or the intermediate film with each other by applying pressure and / or temperature ( 15 ; 23 . 25 ; 31 . 33 ; 43 ). Method according to one of the preceding claims, characterized in that the noble metal is gold, palladium or platinum, that the semi-precious metal is copper and the precious metal alloy has platinum and gold. Method according to one of the preceding claims, characterized in that the nanoporous structure of the film ( 12 ) or the film is prepared by dissolving a metal which is less noble than the noble metal, semi-precious metal or the components of the noble metal alloy. A method according to claim 3, characterized in that the leached out less noble metal is silver and is preferably dissolved by an etching process. Method according to one of claims 3 or 4, characterized in that the less noble metal prior to dissolution of the film or of the film, a volume fraction of 40 vol .-% to 90 vol .-% and the noble metal, semi-precious metal or noble metal alloy has a volume fraction of 10 wt .-% to 60 wt .-% has. Method according to one of claims 1 or 2, characterized in that the nanoporous structure is prepared by sintering a powder of the noble metal, semi-precious metal or the components of the noble metal alloy. Method according to one of the preceding claims, characterized in that the nanoporous structure is formed like a sponge and / or having pores with an average diameter of 20 nm to 10 microns. Method according to one of the preceding claims, characterized in that the film ( 12 ) or the film has a porosity of 10% to 90%. Method according to one of the preceding claims, characterized in that the film or the film is joined together before joining the first and second joining surface, first with either the first or second joining surface. Method according to one of the preceding claims, characterized in that the nanoporous structure is produced before the joining of the film or of the film both with the first joining surface and with the second joining surface. Method according to one of the preceding claims, characterized in that before the joining of the first and second joining surface an adhesive or adhesive ( 41 ) is applied to the first and / or second joining surface. Method according to one of the preceding claims, characterized in that the film ( 12 ) or the film is post-annealed after joining with the first and second joining surfaces. Method according to one of the preceding claims, that the nanoporous structure by subsequent annealing of the film ( 12 ) or the movie is edited. Method according to one of the preceding claims, characterized in that the film ( 12 ) or the film has a thickness of between 10 μm and 150 μm and / or an edge with an edge length of between 200 μm and 25 cm. Use of a film or a film made of a conductive noble metal, semi-precious metal or a noble metal alloy for connecting a first joining surface of a substrate or a first electronic component and a second joining surface of a second electronic component, wherein the film or the film has a nanoporous structure. Electronic stack ( 16 ; 26 ; 34 ; 44 ) with a substrate ( 13 ) or a first electronic component and a second electronic component ( 14 ), the substrate ( 13 ) or first component, a first joining surface and the second component ( 14 ) comprises a second joining surface and between the first and second joining surfaces a nanoporous structure of a noble metal, semi-precious metal or a noble metal alloy is present, characterized in that the nanoporous structure in a film ( 12 ) or a movie lies.

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