JPH0677980B2 - Bonding method of precious metal foil to substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for crimping a precious metal foil onto a substrate for a printed wiring board.

(Conventional Technology and Problems) Conventionally, a printed wiring board substrate, for example, a substrate made of glass epoxy or ceramic, is provided with a noble metal foil such as Au-A.
To bond the g-Pt alloy foil, it was pressure bonded with an adhesive sheet.

However, this method has a problem in that the adhesiveness between the adhesive sheet and the precious metal foil is poor, the bonding strength is low, there is a risk of peeling, and the reliability is poor.

(Object of the Invention) The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for pressure-bonding a noble metal foil to a substrate, which can improve the adhesion of the noble metal foil and increase the bonding strength. To do.

(Means for Solving Problems) In the method for pressure-bonding a noble metal foil to a substrate according to the present invention for solving the above problems, an upper layer is a noble metal intermediate layer made of tin or tin alloy, and a lower layer is made of copper or copper alloy. A part of the intermediate layer of the foil is thermally diffused into the precious metal of the upper layer to form a diffusion layer, and then the intermediate layer and lower layer other than this diffusion layer are dissolved with acid, and the obtained precious metal foil is bonded on the diffusion layer side. It is characterized in that the sheet is used and pressure-bonded to the substrate.

(Operation) As described above, the method for pressure-bonding the noble metal foil to the substrate of the present invention is
Roughness of the surface of this diffusion layer because a rough surface is obtained by thermally diffusing a part of tin or tin alloy into the precious metal foil and etching the remaining tin or tin alloy to expose the diffusion layer of tin or tin alloy. Becomes compatible with the adhesive sheet and digs into the adhesive sheet, and the adhesive force between the adhesive sheet and the substrate is improved, and the bonding strength between the precious metal foil and the substrate is increased.

When a lower layer is provided, it has the effect of making the rough surface of the diffusion layer uniform when thermally diffusing part of the tin or tin alloy into the noble metal foil. This has the effect of increasing the heat capacity of the material and heating it uniformly.

Although pressure contact was used in the examples as a specific example of thermal diffusion, the present invention is not limited thereto.In addition, seam welding, resistance welding, heat treatment, etc., between the upper layer precious metal foil and the middle layer tin or tin alloy. This is a method of thermal diffusion in which a diffusion layer is generated in a broad sense, and the diffusion layer includes an alloy, a compound, and the like.

Further, the thermal diffusion may be performed twice, such as by heat treatment after pressure contact.

The reason why the lower layer is a metal less base than silver or an alloy of a metal less base than silver is that when a noble metal other than silver is used as the upper layer, nitric acid is the most powerful acid that can dissolve the lower layer without dissolving the upper layer. This is because the limit of the metal that can be dissolved in nitric acid is silver.

When silver is used as the upper layer, the lower layer made of a material less base than silver may be dissolved with an acid other than nitric acid.

The material used for the lower layer is silver, silver alloy, copper, copper alloy,
Some of them are based on Fe or Ni, and those with advantages such as "uniform pressure" and "large heat capacity" are good, and those with good heat conductivity, such as those made of silver or copper, have good tin conductivity. In particular, the one that makes the diffusion layer is particularly good.

(Embodiment) An embodiment of a method for pressure-bonding a noble metal foil to a substrate according to the present invention will be described. First, a width 40 mm, a length 200 mm, and a thickness 35 μm of Au-
Ag-Pt alloy foil with tin coated on one side by 2-3μ, thickness 0.3
mm-width 40 mm-length 200 mm copper plate is pressure-welded on the tin surface and Au-
A diffusion layer of Ag-Pt alloy and tin was formed. HN as a plate with upper layer of precious metal, middle layer of tin, and lower layer of copper
The tin other than the copper foil and the diffusion layer was dissolved and removed with a mixed solution of O ₃ and water at a ratio of 1: 1. After that, the Au-Ag-Pt alloy foil was pressure-bonded to the glass epoxy substrate having a width of 250 mm, a length of 500 mm and a thickness of 1.6 mm on the diffusion layer side with an adhesive sheet.

On the other hand, to describe a specific conventional example, an Au-Ag-Pt alloy foil having the same size as that of the above-mentioned embodiment was directly pressed from the adhesive sheet to a glass epoxy substrate having the same size as that of the above-mentioned embodiment.

In this example and the conventional example, Au-Ag-Pt alloy foil composed of Au70%, Ag10%, Pt5%, Cu14% and Ni1% was used. JIS G-10 material as glass epoxy base material,
A prepreg (trademark) composed of an epoxy resin and a chemical fiber was used as an adhesive sheet.

In this way, the bonding strength of the Au-Ag-Pt alloy foil of the example and the conventional example pressure-bonded to the glass epoxy substrate was measured, whereas the conventional example had an average of only 72 g / cm ² , whereas the example The average of 146 g / cm ² was extremely high, and the bonding strength was extremely high. This is due to the fact that the Au-Ag-Pt alloy foil was pressure-bonded to the substrate by utilizing the rough surface obtained by forming the tin diffusion layer, so that the adhesion with the adhesive sheet was improved.

In the above example, the Au-Ag-Pt foil is pressure bonded to the glass epoxy substrate, but the invention is not limited to this.
All other precious metal foils are applicable, and the substrate may be a ceramic substrate, a resin flexible substrate, or the like.

(Effects of the Invention) As can be seen from the above description, the method of pressure-bonding a noble metal foil to a substrate of the present invention utilizes the rough surface obtained by forming a diffusion layer of tin or tin alloy to form a noble metal foil on the substrate. Since pressure bonding is performed, there is an excellent effect that the adhesiveness with the adhesive sheet is improved and the bonding strength is increased.

Claims (1)

[Claims] 1. A part of an intermediate layer of a plate or foil in which an upper layer is a noble metal, an intermediate layer is tin or a tin alloy, and a lower layer is a metal less base than silver or an alloy less base than silver is thermally diffused to a noble metal above. To form a diffusion layer, and then the intermediate layer and the lower layer other than this diffusion layer are dissolved with an acid, and the obtained precious metal foil is pressure-bonded to the substrate with an adhesive sheet on the diffusion layer side. Pressure bonding method for precious metal foil.