Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-01-21
2001-05-01
Nguyen, Tuan H. (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S616000
Reexamination Certificate
active
06225205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a plurality of bump electrodes en bloc on a bump electrode formation surface of a wafer from which chips are to be separated, or on a bump electrode formation surface on an upper surface side of a plurality of chips which are separated from a wafer and placed side by side, specifically for use in condenser chips, resistance chips, IC chips, and CPU chips, which are mounted on a surface of electronic parts, and for use in packages semi-conductor-molded ball grid arrays (BGA) and chip size packages (CSP) and connectors.
2. Discussion of Background
In accordance with a recent trend of down-sizing and cost reduction of electronic parts, the above-mentioned chips are mounted on a surface of a substrate via bump electrodes. In particular, there is a tendency that electronic chips such as IC and LSI chips are mounted on the surface of electronic parts via bump electrodes as flip chips without being packaged.
In order to conduct such surface mounting of such electronic parts, it is considered to be preferable that bump electrodes be formed on the side of such electronic parts.
Conventionally, the above-mentioned bump electrodes are formed on the surface of the above-mentioned electronic parts by an electrolytic plating method comprising the steps of forming a predetermined resist pattern on the surface of the electronic parts by photolithography, and having the resist pattern grown to a predetermined thickness, using solder, or a metal such as gold or copper, or by a ball bump method of forming metal balls from a metal wire, and bonding the metal balls to the electronic parts. These conventional methods are used as methods for directly forming bump electrodes on electronic parts. These methods, however, have a shortcoming that many steps to be carried out are involved and accordingly are costly to conduct.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method of forming a plurality of bump electrodes en bloc on a bump electrode formation surface of a wafer from which chips are to be separated, with high precision and at a low cost.
A second object of the present invention is to provide a method of forming a plurality of bump electrodes en bloc on an upper surface of a plurality of chips which are separated from a wafer and placed side by side, the upper surface constituting a bump electrode formation surface.
The first object of the present invention can be achieved by a method of forming a plurality of bump electrodes en bloc on a bump electrode formation surface of a wafer from which chips are to be separated, comprising the steps of:
mounting a stencil mask with through-holes for the formation of the bump electrodes on the bump electrode formation surface of the wafer, and
performing printing with an electroconductive paste through the through-holes of the stencil mask for the formation of the bump electrodes en bloc on the bump electrode formation surface of the wafer.
In the above-mentioned method, when the electroconductive paste is a photo-setting paste, it is preferable that the stencil mask comprise a light-shielding layer at least on such a side of the stencil mask that comes into close contact with the bump electrode formation surface of the wafer, and that the photo-setting paste filled in the through-holes be exposed to light and cured, and that the stencil mask be then separated from the bump electrode formation surface of the wafer so as to fix the cured photo-setting paste to the bump electrode formation surface of the wafer for the formation of the bump electrodes en bloc thereon. When the photo-setting paste is used as the electroconductive paste as mentioned above, micro-bump electrodes can be formed with high accuracy by the provision of the light-shielding layer at least on such a side of the stencil mask that comes into close contact with the bump electrode formation surface of the wafer.
In the above-mentioned method, the stencil mask may comprise a plastic material that can be selectively subjected to ablation working by light irradiation, for instance, visible light irradiation or ultraviolet light irradiation, so as to form the through-holes in the stencil mask. By use of such a plastic material in the stencil mask, through-holes with a smooth inner wall can be formed from which the electroconductive paste can be smoothly released, whereby high quality bump electrodes free of defects can be formed.
In the above-mentioned method, the electroconductive paste may be an elastomer resin paste. When an elastomer resin paste is used as the electroconductive paste, there can be formed such bump electrodes that comprise a highly elastic elastomer resin and are not cracked even when subjected to repeated thermal expansion and contraction.
In the above-mentioned method, each of the bump electrodes may have a thin or conical top edge. By causing the bump electrodes to have a thin or conical top edge, improper connection and crack formation can be prevented.
The first object of the present invention can also be achieved by a method of forming a plurality of bump electrodes en bloc on a bump electrode formation surface of a wafer from which chips are to be separated, comprising the steps of:
filling depressed portions of an intaglio printing mask for the formation of bump electrodes with a liquid metal or an electroconductive paste, and
performing printing with the liquid metal or the electroconductive paste filled in the depressed portions of said intaglio printing mask for the formation of the bump electrodes en bloc on the bump electrode formation surface of the wafer by bringing the intaglio printing mask into close contact with the bump electrode formation surface of the wafer so as to fix the liquid metal or the electroconductive paste thereon from the depressed portions of the intaglio printing mask.
In the above-mentioned method, the electroconductive paste may be a photo-setting paste, and when the electroconductive paste is a photo-setting paste, it is preferable that the intaglio printing mask be transparent so as to allow light to pass at least through the depressed portions of the intaglio printing mask, thereby curing the photo-setting paste in the depressed portions when exposed to light, and comprise a light-shielding layer at least on such a side of the intaglio printing mask that comes into close contact with the bump electrode formation surface of the wafer, and that the photo-setting paste be filled in the depressed portions, exposed to light and cured, and that the intaglio printing mask be then separated from the bump electrode formation surface of the wafer so as to fix the cured photo-setting paste to the bump electrode formation surface of the wafer for the formation of the bump electrodes en bloc thereon.
In the above-mentioned method, the intaglio printing mask may comprise a plastic material that can be selectively subjected to ablation working by light irradiation so as to form the depressed portions in the intaglio printing mask. By use of such a plastic material in the intaglio printing mask, depressed portions with a smooth inner wall and a bottom surface can be formed from which the electroconductive paste can be smoothly released, whereby high quality bump electrodes free of defects can be formed.
In the above-mentioned method, the electroconductive paste may be an elastomer resin paste for the same reasons as in the above-mentioned method using the stencil mask with the through-holes.
In the above-mentioned method, each of the bump electrodes may have a thin or conical top edge for the same reasons as in the above-mentioned method using the stencil mask with the through-holes.
The first object of the present invention can also be achieved by a method of forming a plurality of bump electrodes en bloc on a bump electrode formation surface of a wafer from which chips are to be separated, comprising the steps of:
forming an electroconductive photosensitive layer on the bump electrode format
Nguyen Tuan H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pert Evan
Ricoh Microelectronics Company, Ltd.
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