Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-07-09
2004-05-25
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S426500, C029S843000, C029S426100, C228S006200
Reexamination Certificate
active
06739045
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for removing solder bumps, which form on a semiconductor chip (LSI).
2. Description of the Related Art
There are cases when solder bumps are used to connect an LSI onto a wiring substrate. A connection that uses solder bumps is called a ball grid array (BGA) connection. In this case, for example, approximately 5000 solder bumps will be used to connect a 20 mm LSI. Thus, there are cases when connection defects occur due to misconnections between the connection terminals of a multi-layer wiring substrate and an LSI. When connection defects such as this occur, it becomes necessary to perform repair work, by which the LSI is removed from the wiring substrate and re-connected. Solder is adhering to the connecting surface of the LSI removed from the wiring board at this time. Therefore, this solder is removed using a solder removing device, and solder bumps are once again formed on the connecting surface of the LSI.
As a solder removing device, a device comprising a mechanism for pressing the surface of an LSI to which solder bumps are attached onto a heated copper plate is well known. First, this device attracts the LSI using a suction mechanism. Next, the device uses the suction mechanism to press the surface of the LSI to which the solder bumps are attached against the copper plate. When maintained in this state for a time, the solder bumps are heated and melt. The molten solder adheres to the copper plate. Thereafter, the device raises the suction mechanism with the LSI attracted as-is, pulling the LSI away from the copper plate. In accordance therewith, the solder bumps, which had been adhering to the LSI, are removed. Furthermore, the LSI referred to here is a packaged-type LSI.
As technology related to a solder removing device such as this, there is, for example, the technologies disclosed in Japan Patent Laid-open No. 11-285814 and Japan Patent Laid-open No. 2001-7509.
SUMMARY OF THE INVENTION
In recent years, there have been cases in which bare chip-type LSIs have been connected directly to substrates. Accordingly, in repairing these bare chips, the inventors of the present invention tried removing the solder bumps using the above-described solder removing device. However, when the attracting device pressed the bare chip against the copper plate, there were instances when a mechanical load was applied to the bare chip by the suction mechanism, causing fractures and cracks to be generated in the bare chip. Further, it was also learned that there were cases in which the mechanical load resulting from the suction mechanism gave rise to the problem of damage being caused to the passivation layer and metallization formed on the bare chip. In addition, there were also instance when the solder bumps adhering to the bare chip could not be removed all at once. In these cases, the volume of solder adhering to a bare chip following removal work varies. Thus, it was learned that, when reforming solder bumps on this bare chip, the volumes of the respective solder bumps would also vary, giving rise to the problem that the heights of the solder bumps could not be made uniform to within acceptable levels.
Therefore, the present invention is to provide a method, which does not damage a bare chip when removing solder from a bare chip-type LSI.
Another, the present invention is to provide a method, which enables the heights of solder bumps to be made uniform to within acceptable levels when reforming solder bumps on an LSI.
In the present invention, a first member of a plate shape for causing the adherence of molten solder is mounted on top of a heater. An LSI is placed on top of the first member with the surface on which the solder is attached facing downward. A second member for adding a load to the LSI is placed on top of the LSI. A heater is heated up, the first member and the LSI are heated and the solder is melted. The molten solder is transferred to the first member. A suction mechanism is positioned at a location a predetermined distance away from the top surface of the second member. The second member and LSI are attracted by the suction mechanism, and the LSI is pulled away from the first member. The solder is thereby removed from the LSI.
According to this method, damage is not done to a bare chip-type LSI when solder is removed. Further, the height of the solder remaining on the LSI following solder removal becomes uniform to within acceptable levels.
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patent: 6684494 (2004-02-01), Ambe
patent: 11-285814 (1999-10-01), None
patent: 2001-007509 (2001-01-01), None
Katayama Kaoru
Kimura Motoko
Miitsu Takeshi
Takahashi Takeshi
Yamashita Shiro
Arbes Carl J.
Hitachi , Ltd.
Townsend and Townsend / and Crew LLP
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