JP2600669B2 - Metal bump for transfer bump - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer bump interposed between an electrode of a semiconductor element and a film hard when a metal bump for a transfer bump is used to connect the electrode to a film lead. The configuration of the metal projection for use.

2. Description of the Related Art There is a film carrier mounting method as a method for mounting a thin or small semiconductor device of IC.LSI. In this technology, semiconductor elements are formed on a wafer in the form of Cr.Cu, Ti-Pd, T
After depositing a multi-layer metal film such as i-Cu, Cr-Cu, a pattern in which the electrodes of the semiconductor element are opened is formed by a photolithography process, and Au, Cu, solder, etc. are formed in the opening. The metal projection is formed to a thickness of 10 to 30 μm. Then, the unnecessary photoresist layer and the multilayer metal film are removed by etching to form metal projections on the electrodes of the semiconductor element. Then, a film lead formed by etching a Cu foil formed on an insulating tape and the metal protrusion are pressed,
Heat and bond by thermocompression bonding or eutectic alloy.

However, in this technique, a metal projection must be formed on an electrode of a semiconductor element. Therefore, a step of applying a multilayer metal film, a photolithography step of forming a mask for plating or forming a mask for selectively removing the multilayer metal film, and a method of forming metal projections by electrolytic plating. Plating process and etching process, etc.
Not only do a lot of complicated processes and expensive equipment for this process be required, but also all the processes are performed on a wafer basis, so that expensive metal projections are also provided on defective chips, which leads to manufacturing costs. Rise and yield decrease.

As a new method to solve this, a transfer bump mounting method has been invented. In this technology, metal protrusions are formed on a substrate that can be repeatedly played back in advance, and the metal protrusions are transferred and bonded to the film lead side, and the transferred and bonded metal protrusions are pressed and applied to the electrodes of the semiconductor element. The film lead and the electrode of the semiconductor element are joined by heating and thermocompression bonding. More specifically, an easily peelable metal film is applied to an Au plating such as Pt, ITO, or Pd on an insulating substrate such as a ceramic or a glass, and is opened at a position corresponding to an electrode of a semiconductor element. A mask pattern for plating having holes is formed. The material of the mask pattern is SiO ₂ , Si ₃ N ₄ or a heat-resistant photoresist film, and the size of the opening is 5 μm to 30 μm
^□ .

Next, the metal film is used as one electrode, and a metal projection made of Au, Cu, or the like is formed in the opening at a height of 20 to 30 μm by electrolytic plating. Au or Sn plating is formed on the film lead formed by etching the Cu foil to a thickness of 0.3 to 0.6 μm, and the film lead and the metal protrusion are aligned, and pressed and heated with a bonding tool. If the temperature is 5 to 20 g per lead at 300 ° C.), the metal projection on the substrate is transferred and bonded to the film lead side. For example, if the metal projection is formed of Au and the lead is plated with Sn, the lead is joined with an alloy of Au and Sn. Thereafter, the aluminum electrode of the semiconductor element is aligned with the metal projection transferred and bonded to the film lead, and heated and pressed (for example, at 450 ° C., 60 ° per lead).
−100 g), the film lead and the aluminum electrode are joined by an alloy of Au and Al. This technology allows repeated use of a substrate on which metal projections are formed, and unlike conventional methods, does not require complicated processes and expensive equipment, and also handles only good chips, resulting in high yield and low cost. Can be implemented.

Problems to be Solved by the Invention However, in this technique, in the step of transferring and joining the metal projections from the substrate to the film lead side, 100% of the metal projections may not be transferred and joined to the film lead side. For this reason, the temperature of the plating solution,
Efforts have been made to change the current density, change the crystal structure of the metal, and improve transfer and bonding properties, but it has been difficult to reliably increase the yield.

An object of the present invention is to enhance transfer and bonding of metal protrusions selectively formed on a metal film on a substrate to a film lead.

Means for Solving the Problems In the present invention, the composition of metal projections formed on a substrate is formed by a layer having a plurality of hardnesses.

Effect Although the conventional metal projection has a single hardness, when formed from a layer having a plurality of hardnesses as in the present invention, a layer having a stress proportional to the hardness due to a difference in hardness appears on the metal projection. The generation of this stress layer weakens the adhesive force between the substrate and the metal projection, and makes the metal projection easier to peel off than the substrate.

Example Originally, in electroplating, the composition of the plating solution and the plating conditions are set so as to increase the adhesive force depending on the metal body. However, plated metal protrusions in the transfer bump mounting technique must be easily peeled from the plated metal film. The present invention is based on the principle that a layer having a different hardness is provided inside the metal projection to peel off the metal film and the plated metal projection, thereby generating internal stress and reducing the adhesive force at the interface between the substrate and the metal projection. It is a suggestion.

As shown in FIG. 1, a transfer bump substrate 1 is formed by forming a metal film 3 such as Pt, Pd, or ITO on an insulating substrate 2 such as glass or ceramic, and forming a metal film 3 on the insulating film 2 at a position corresponding to an electrode of a semiconductor element. An insulating film 5 having an opening 4 is provided. The insulating film 5 is formed of SiO ₂ , Si ₃ N ₄ , heat-resistant resin or the like.

Next, the opening 4 on the substrate 1 is formed by electrolytic plating.
The method for forming the metal projection of the present invention will be described below. In FIG. 2, the plating layer 10 is filled with an Au plating solution (product name: Neutronex 210) 11, and in the heating tank 12 surrounding the plating tank 10, the plating solution 11 may be any temperature between 40 and 70 ° C. Kept at temperature. When an electric current 14 flows between the substrate 1 and the anode plate 13, a projection of Au is formed in the opening 4 of the substrate 1. When the specified current density of the plating solution is, for example, 0.04 mA / mm ² and the height of the metal projections is 30 μm,
If the current density is 0.04 mA / mm ² , the remaining two layers 16 are formed at a current density of 0.08 to 0.2 mA / mm ^2, which is 2 to 5 times the specified current density. As shown in FIG. 3, two layers having different current densities are formed (third layer).
Figure). That is, the hardness of the layer 15 formed at the specified current density is
The stress inside the layer is small at 50 to 70 Hv. However, the layer 16 formed at a specified current density or higher has a hardness of about 100 Hv and a large internal stress. When layers of different hardness or stress are present in the same protrusion, mutual stress acts,
The metal projection is easily separated from the substrate 1 by a very small external force in a bimetallic manner. Double layer 1 in Fig. 3
The thickness of the layers 5 and 16 is not limited to 10 μm, but may be in the range of 2 to 20 μm, which is determined from the ease of peeling. Similarly, the current density at the time of plating the second layer 16 is determined in the same manner.

As another embodiment, in the configuration of FIG.
The second layer 16 may be formed at a specified current density by plating the layer 15 at a current value higher than the specified current density. Also in this case, the ratio of the thickness of the first layer to the thickness of the second layer is determined by the ease of detachment of the metal projection from the substrate.

FIG. 4 shows another embodiment. FIG. 4 shows a state in which the metal projections 20 have been formed by plating.
The metal protrusions 2 are formed by changing the current density in three stages and sequentially forming three layers having different hardnesses. The first layer 17 and the third layer 19 are formed with a specified current density, and the second layer 18 is formed sequentially with a higher specified current density. Alternatively, the first layer 17 and the third layer 19 are plated at a higher current density than the specified current density.
A configuration in which the layer 18 is formed at a specified current density may be employed.
Alternatively, the first, second, and third layers may be formed with different hardnesses.

Effect of the Invention As described above, according to the present invention, since the metal projections on the substrate are formed of a plurality of layers of the same material and different hardness, the metal projections can be easily removed from the substrate by the stress generated inside the metal projections. Can be peeled off, and a metal bump for a transfer bump having a high transfer and bonding ratio can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a transfer bump substrate used to form a transfer bump metal projection in one embodiment of the present invention, FIG. 2 is a cross-sectional view showing the structure of the plating tank, and FIGS. FIG. 3 is a cross-sectional view illustrating a configuration of a metal protrusion according to one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Transfer bump board, 2 ... Insulating substrate, 3 ... Metal film, 4 ... Opening, 5 ... Insulating film, 15-19 ... Plating tanks with different hardness.

Claims (2)

(57) [Claims] A metal bump for a transfer bump selectively formed on a conductive layer and formed of a layer having the same material and a plurality of hardnesses. 2. The metal bump for a transfer bump according to claim 1, wherein the hardness of at least one of the layer on the conductive layer surface side and the outermost layer is higher than that of the other layers.