Metal fusion bonding – Process – Preplacing solid filler
Reexamination Certificate
1999-04-09
2001-08-21
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Preplacing solid filler
C228S253000, C228S123100, C228S180220
Reexamination Certificate
active
06276599
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of forming solder bumps on a substrate, a semiconductor chip, etc. and an apparatus for carrying out the method.
2. Description of the Prior Art
Solder bumps are recently formed by depositing fine solder balls onto a number of metal pads formed on a semiconductor package, for example. The solder bumps are used in a mounting technique for fixing and electrically connecting the semiconductor package. Japanese unexamined patent publication No.
10-64947
(1998) discloses such a method of forming solder bumps as described above. The disclosed method will be described with reference to
FIGS. 16A
to
16
D. A metal plate
2
formed with a number of through holes
1
is placed on a horizontal base
3
. A predetermined amount of solder paste is applied to the metal plate
2
using a squeegee
4
so that the through holes
1
are filled with the solder paste. A substrate
6
on which solder bumps are to be formed is attached to the metal plate
2
. The substrate
6
and the metal plate
2
are then placed on a heating plate
7
to be heated such that molten solder
8
is transferred to the substrate
6
side.
In the above-described method, however, transfer of the molten solder
8
to the substrate
6
is carried out merely using adhesion to a metal portion of the substrate
6
resulting from surface tension of the molten solder
8
. Accordingly, since the molten solder
8
is not positively extruded, the transfer of the molten solder
8
lacks reliability and accordingly, the amount of molten solder
8
transferred is not constant. As a result, the size of the solder bump is not uniform.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a method of forming solder bumps on a substrate etc. which can provide a uniform the size of the solder bumps and provide a good productivity and in which the solder bumps can be formed on the pads even when the pads are formed at small pitches on the substrate etc., and an apparatus for carrying out the method.
The present invention provides a method and an apparatus for forming solder-bumps on pads formed on a surface of a base material such as a semiconductor package etc. The method comprises the steps of supplying solder to a template having a number of through holes formed to correspond to the pads of the base material respectively so that the through holes are filled with the solder, the template having an upper side and an underside, scraping the sides of the template by doctors to remove an excessive amount of solder, and opposing the template to the base material so that the pads are aligned with the through holes respectively, covering the side of the template opposite to the base material with a pressure housing and increasing pressure in an interior of the pressure housing so that a difference in pressure between an exterior and the interior of the pressure housing extrudes the molten solder from the template to the pad side of the base material.
According to the above-described method, both sides of the template are rubbed by the doctors after the through holes of the template have been filled with the solder. As a result, the excessive solder on both sides of the template is removed such that each through hole is usually filled with a proper amount of solder. In the solder transferring step, the molten solder is reliably extruded from the through holes of the template to the base material side by the pressure difference between the interior and the exterior of the pressure housing. Consequently, since an amount of molten solder transferred onto the pads of the base material becomes fixed, the size of each solder ball can be uniformed.
Either molten solder or solder paste may be used to fill the through holes in the solder filling step. In the case of molten solder, a pressure-reducing housing is applied to the upper side of the template so that a pressure-reducing chamber is defined therein, and the molten solder is sucked into the through holes by reducing pressure in the pressure-reducing chamber.
When an inert gas is supplied into the pressure housing in the solder transferring step, the solder with which the through holes are filled is melted in an atmosphere of the inert gas. Consequently, since the solder is prevented from oxidation, solder balls of high quality can be formed.
The invention also provides a solder bump forming apparatus for attaching solder bumps to pads formed in a surface of a base material. The apparatus comprises a support sheet disposed horizontally and having an opening, a template provided to close the opening of the support sheet and having a number of through holes formed to correspond to the pads of the base material respectively, the template having an upper side and an underside, means for filling the through holes of the template with solder, a pair of doctors for scraping the sides of the template to remove an excessive amount of solder having overflowed the through holes, base material support means for supporting the base material so that the template with the through holes filled with the solder is opposed to the base material so that the pads are aligned with the through holes respectively, heating means for heating the solder in a state where the base material is supported by the base material support means, and a pressure housing covering the side of the template confronting the base material, which side is opposite to the base material. The solder is extruded from the through holes of the template to the pad side of the base material by increasing pressure in an interior of the pressure housing.
REFERENCES:
patent: 5238176 (1993-08-01), Nishimura
patent: 5261593 (1993-11-01), Casson et al.
patent: 5788143 (1998-08-01), Boyd et al.
patent: 5834062 (1998-11-01), Johnson et al.
patent: 5855323 (1999-01-01), Yost et al.
patent: 5880017 (1999-03-01), Schwiebert et al.
patent: 0 259 102 (1988-03-01), None
patent: 565 908 A3 (1993-10-01), None
patent: 565 908 A2 (1993-10-01), None
patent: 10-65055 (1998-03-01), None
patent: 10-71695 (1998-03-01), None
patent: 10-64947 (1998-03-01), None
A.C. Andreasen et al., “Solder Washer Pneumatic Applicator”, IBM Technical Disclosure Bulletin, vol. 23, No. 8, Jan. 1981, pp. 3625-3627.
Johnson Jonathan
Noda Screen Co., Ltd.
Ryan Patrick
Wenderoth , Lind & Ponack, L.L.P.
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