JP4743002B2 - Joining method - Google Patents

Description

  The present invention relates to a joining method, and more particularly, to a joining method in which two metal surfaces are joined with a joining material containing metal as a main component.

As a conventional joining method for joining two metal surfaces with a joining material containing metal as a main component, for example, there is a method described in Patent Document 1 below. This bonding method is obtained by dispersing metal fine particles of several nm, which are known to be fused at around room temperature, with an organic coating film made of an organic material so as not to be fused at room temperature in an organic solvent. A bonding material paste is used. Such a bonding material paste is sandwiched between two metal surfaces to evaporate the solvent and heat it to a relatively low temperature for decomposing the organic coating film, and at the same time pressurize to promote the fusion of the metal particulates. Is applied. In this way, once the bonding layer is formed, the bonding layer retains its strength up to the melting point of the particulate metal, which is much higher than the bonding temperature.
International Publication Number WO 2005/095040 A1

  However, in the above bonding method, when the bonding area is widened, the following problems occur. That is, when the organic coating film is decomposed by the applied heat, the metal fine particles are fused with each other, but since the generation starts at random for each minute region, the organic matter is sufficiently decomposed and scattered outside the bonding region. The path is closed before, and eventually a region in which carbide remains in the bonding layer is generated stochastically, which may adversely affect the bonding strength and conductivity. Therefore, it is important to prevent this from happening.

  An object of the present invention is to solve this problem and to provide a bonding method that realizes good bonding even with a large bonding area.

  In order to achieve the above object, in the present invention, a bonding paste containing metal fine particles and a solvent as a constituent component is applied to one of two metal surfaces to form a striped, checkered or net-like groove. After forming the material uneven film, another metal surface is superimposed on the metal surface, and the pressure within the first pressure range is applied between the two metal surfaces so that the groove does not disappear. The first temperature range is maintained while the pressure in the second pressure range higher than the first pressure range is applied between the two metal surfaces. Holding at a temperature within the second temperature range for a second time completes the bond.

  Form a bonding material uneven film that ensures a path for the decomposition products of organic matter to scatter to the outside of the bonding area, and pressurize and heat the first pressurization and heating so that the scattering path is not closed By performing the process and the second pressurizing / heating process at a higher pressure and higher temperature in two steps, it is possible to provide a bonding method that realizes good bonding even with a large bonding area.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First embodiment]
1-4 is sectional drawing for demonstrating the process of the joining method which is 1st embodiment of this invention. In the figure, 1 and 2 are two metal plates to be joined, 3 is a metal fine particle, 4 is an organic solvent, 5 is a bonding material paste comprising the metal fine particle 3 and the organic solvent 4, and 6 is a mask screen. A screen printing mesh. If the particle size of the metal fine particles 3 is 1 nm or more and 1 μm or less, mutual fusion may occur even at room temperature. In such a case, the surface of the metal fine particles 3 is organically coated with an organic substance such as a higher alcohol. Covering with a membrane (not shown) prevents fusion. In the figure, the upper surface of the metal plate 1 is one of the two metal surfaces described in the claims, and the lower surface of the metal plate 2 is the other of the two metal surfaces.

  In FIG. 1 and FIG. 2, metal fine particles 3 and a solvent (here, an organic solvent 4, but water or an organic / inorganic mixed solvent may be used on one of the metal surfaces (the upper surface of the metal plate 1). FIG. 6 is a cross-sectional view for explaining a concavo-convex film coating step in which a bonding material paste 5 having the above-described components as a constituent component is applied to a bonding material concavo-convex film having striped, checkered or net-like grooves.

  First, as shown in FIG. 1, a mesh 6 is placed on the upper surface of a metal plate 1, a bonding material paste 5 containing metal fine particles 3 is placed thereon, and the surface of the mesh is swept with a squeegee (not shown). Application is performed so that the thickness is uniform.

  Next, as shown in FIG. 2, when the mesh 6 is removed, the organic solvent 4 flows out to the place where the mesh 6 was present (indicated by 6 ′) as in the case of normal printing ink, but the metal fine particles 3 are removed from the organic solvent 4. Since the specific gravity is almost one digit higher, even if the viscosity of the bonding material paste 5 is adjusted, most of it remains in the same position, resulting in a difference in thickness as shown in the figure. In this manner, a bonding material uneven film having striped, checkered or net-like grooves is formed. The place 6 ′ where the mesh is located is the above groove in the bonding material uneven film. If the mesh 6 is, for example, a parallel line, a striped groove is formed, and the mesh 6 may be, for example, an orthogonal lattice. For example, if the mesh 6 is a net-like (honeycomb-like) mesh having a regular hexagonal mesh, for example, a net-like groove is formed.

  Next, FIG. 3 shows a state in which the metal plate 2 is superimposed on the upper surface of the metal plate 1 in the state shown in FIG. This state is a state in which another metal surface is in close contact with the metal surface to which the bonding material uneven film is applied. Here, a state where the organic solvent 4 has already evaporated and scattered is shown.

  When the evaporation and scattering of the organic solvent 4 is performed in the state shown in FIG. 2, the time for which the organic solvent disappears may be shortened, which may be convenient. That is, in the state shown in FIG. 2, a preheating step of maintaining at a temperature within a third temperature range in which at least one component (for example, organic solvent 4) contained in the bonding material uneven film can be scattered for a third time. You may implement.

  In FIG. 3, the tunnel formed between the two metal plates 1 and 2 is designated as 7. The tunnel 7 is constituted by the groove. Since the groove is striped, checkered or net-like, it always leads to the periphery of the bonding material uneven film. Accordingly, the evaporation and scattering of the organic solvent 4 proceeds smoothly via the tunnel 7.

  Next, in the prior art, pressurization and heating are performed in a single step to complete the joint formation. In the joining method according to the present invention, the first pressurization / heating step and the second step are performed. Carry out in two steps, the pressurization and heating process.

  First, as a first pressurizing / heating step, a pressure within the first pressure range is applied between the two metal surfaces so that the tunnel 7 constituted by the grooves does not disappear. Hold at the temperature for a first time. That is, a pressure is applied so that the groove remains without being crushed, leaving the tunnel 7, and maintaining the temperature at which the organic matter (eg, the organic coating film of the metal fine particles 3) in the bonding material uneven film is decomposed. Encourage disassembly. In the first pressurizing / heating step, the decomposition product of the organic substance that is almost a gas can easily reach the outside of the film via the tunnel 7 leading to the periphery of the bonding material uneven film.

  And even if organic matter remains, it is higher than the first pressure range as the second pressurizing / heating step when it is reduced to an amount that does not affect the properties of the completed bonding layer. While a pressure within the second pressure range is applied between the two metal surfaces, the temperature is maintained at a temperature within a second temperature range higher than the first temperature range for a second time. As a result, a high pressure and a high temperature are applied to complete the bonding layer 9 as shown in FIG.

  In this way, the second pressurization / heating process following the first pressurization / heating process can form the bonding layer 9 without being disturbed by residual organic matter and carbides, which is higher than the conventional technique. A strong bond can be obtained.

  Here, as described above, if the particle size of the metal fine particles 3 is 1 nm or more and 1 μm or less, they may be fused together at room temperature. In such a case, fusion is prevented by covering the surface of the metal fine particles 3 with an organic coating film (not shown) made of an organic substance such as higher alcohol. When the metal fine particles 3 are larger than 1 μm, there is no fear of mutual fusion at room temperature, so an organic coating film is not necessarily required. However, in order to form a bond on the metal plate surface, Preferably, the organic matter is oxidized by the metal oxide film on the surface of the metal plate, and the metal oxide film is reduced to metal. In this case as well, the tunnel 7 is used to improve the bonding strength. It works effectively.

  As the organic solvent 4, one having a boiling point relatively higher than room temperature is selected so that the metal fine particles 3 can be easily dispersed and handled. As a suitable solvent, for example, cyclohexane and the like are known.

  However, when the mass of the metal fine particles 3 on the metal plate 1 and the metal plate 2 are brought into contact with each other without the organic solvent 4, there is a possibility that an area that does not touch the metal fine particles 3 is formed on the surface of the metal plate 2. There is. Especially when metal fine particles covered with an organic coating film are used, when this organic coating film decomposes, there is an action that reduces the metal oxide film on the surface of the metal plate, but there is a region that cannot receive it. In this case, as a countermeasure, a predetermined amount of the bonding material paste 5 is applied to the surface of the metal plate 2 in advance. That is, a step of applying the bonding material paste 5 to the surface of the metal plate 2 is provided before the first pressurizing / heating step.

  Here, the metal fine particles are, for example, Ag having an average particle diameter of about 10 nm. Ag decomposes at a temperature of about 180 ° C. to become oxygen and Ag even if an oxide has been formed on the surface, so there is no need to worry about oxidation of the metal surface due to high temperature heating. In addition, Au, which is not oxidized, and Cu, Pt, Pd, Ni, Ru, Rh, etc., in which a metal oxide is reduced to a metal when an organic substance is oxidized, are known as suitable metals. That is, the constituent metal element of the metal fine particles is preferably any one of Au, Ag, Cu, Pt, Pd, Ni, Ru, and Rh.

  Further, as a constituent metal element on at least the surface of the metal plates 1 and 2, Cu, Ag, Au, Pt, or the like is preferable.

  Further, when a bonding material containing silver oxide or silver carbonate particles in addition to these metal fine particles is used, these also become Ag at 180 to 190 ° C. and generate oxygen, so that organic substances (for example, organic coating films) are oxidized. Then, it is gasified and becomes support for scattering through the tunnel 7. Thus, it is effective for promoting the oxidation of organic matter that the bonding material paste 5 contains a substance that releases oxygen in the first temperature range to become a metal.

  Alternatively, the first pressurizing / heating step is performed in the atmosphere or in a gas containing more oxygen than the atmosphere, and the pressure of the atmosphere or the gas is, for example, between atmospheric pressure and a fraction of the pressure. It may be carried out while reciprocating, and oxygen necessary for the oxidation of the organic substance may be supplied through the tunnel 7 to support the scattering of the gasified carbon oxide.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS.

  The main point of the present embodiment is that the organic decomposition gas can be scattered to the outside in the film of the bonding material between the two metal plates 1 and 2 by a method different from that of the first embodiment. The tunnel 7 as shown in FIG.

  In the present embodiment, as shown in FIG. 5, the bonding material paste 5 is applied flatly on the upper surface of the metal plate 1, and while the bonding material paste 5 maintains fluidity, as shown in FIG. The pressing die 8 is pressed against the coating film of the bonding material paste 5 to give a difference in thickness to the coating film. If the surface of the pressing die 8 has irregularities opposite to the striped, checkered, or net-like grooves, the bonding material uneven film formed in this way has the striped, checkered or net-like shape. It has a groove.

  The subsequent steps are the same as those in the first embodiment.

  After such a process, that is, after the bonding material paste 5 is applied flat on one of the metal surfaces, the film of the bonding material paste 5 has an uneven surface opposite to the striped, checkered or net-like grooves. The process of pressing the pressing mold may be more efficient.

  The bonding method according to the present invention is effectively used in a semiconductor mounting process. In this case, the back metal electrode of the semiconductor chip corresponds to the metal plate 1 or 2.

It is sectional drawing explaining the process of 1st embodiment. It is sectional drawing explaining the process of 1st embodiment. It is sectional drawing explaining the process of 1st embodiment. It is sectional drawing explaining the process of 1st embodiment. It is sectional drawing explaining the process of 2nd embodiment. It is sectional drawing explaining the process of 2nd embodiment.

Explanation of symbols

  1, 2: metal plate, 3: metal fine particles, 4: organic solvent, 5: bonding material paste, 6: mesh, 6 ': place where the mesh was present, 7: tunnel, 8: pressing mold, 9: bonding layer.

Claims (10)

In a bonding method in which metal fine particles are interposed between two metal surfaces, pressurized and heated to complete the bonding between the two metal surfaces,
An uneven film coating step of applying a bonding material paste comprising the metal fine particles and a solvent as constituent components to one of the metal surfaces to form a bonding material uneven film having a striped, checkered or net-like groove;
The other metal surface is overlapped with the metal surface on which the bonding material uneven film is formed, and the first pressure range is applied between the two metal surfaces so that the groove does not disappear. A first pressurizing / heating step for maintaining the temperature within the temperature range for a first time;
After the first pressurizing / heating step, a second pressure higher than the first temperature range while applying a pressure within a second pressure range higher than the first pressure range between the two metal surfaces. And a second pressurizing / heating step of maintaining the temperature within the temperature range for a second time.   Between the uneven film coating step and the first pressurizing / heating step, the bonding material uneven film has a temperature within a third temperature range in which at least one component contained in the bonding material uneven film can scatter. The bonding method according to claim 1, further comprising a preheating step for holding for a third time.   The bonding method according to claim 1, wherein a particle diameter of the metal fine particles is 1 nm or more and 1 μm or less.   The joining method according to claim 1, wherein a constituent metal element of the metal fine particle is any one of Au, Ag, Cu, Pt, Pd, Ni, Ru, and Rh.   The bonding method according to claim 1, wherein the metal fine particles are covered with an organic coating film.   The bonding method according to claim 1, wherein the bonding material paste contains a substance that releases oxygen in the first temperature range to become a metal.   2. The bonding according to claim 1, wherein the first pressurizing / heating step is performed in the atmosphere or in a gas containing more oxygen than the atmosphere while changing the pressure of the atmosphere or the gas. Method.   The bonding method according to claim 1, wherein the uneven film application step includes a step of applying the bonding material paste to one of the metal surfaces through a mask screen.   After the uneven film coating step applies the bonding material paste flatly to one of the metal surfaces, the uneven film surface opposite to the striped, checkered, or net-like grooves is applied to the bonding material paste coating film. The bonding method according to claim 1, further comprising a step of pressing a pressing die having a shape.   The bonding method according to claim 1, further comprising a step of applying the bonding material paste to the other of the metal surfaces before the first pressurizing / heating step.

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