Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-08-11
2001-10-30
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C441S040000, C441S040000, C441S040000, C441S040000, C441S040000
Reexamination Certificate
active
06309280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of grinding a semiconductor wafer having bumps formed on one surface, particularly grinding the bump-free surface of the semiconductor wafer so that the wafer may be reduced to a predetermined thickness.
2. Related Arts
Referring to
FIG. 8
, a plurality of chips or pellets each having an integrated circuit pattern formed thereon can be provided by cutting a semiconductor wafer W along crosswise streets S to separate it into small squares. Prior to dicing the rear surface of the semiconductor wafer is ground a predetermined thickness to reduce its heat storage capacity. Also, this meets the downsizing requirement.
Referring to
FIG. 9
, the front surface
61
of the semiconductor wafer W is laid and sucked onto the chuck table
62
of a grinder, and a rotary whetstone
63
is applied to the rear surface
60
of the semiconductor wafer W under a predetermined pressure.
The grinding can be equally effected no matter which type of semiconductor pellets may be, pellets to be packaged for surface-mounting such as chip size packages (CSPs) or ball grid arrays (BGAs) or bare chips to be mounted on printed-wiring boards.
Such pellets P, however, have bumps formed thereon for making required connections to selected electrodes in printed-wiring boards. The semiconductor wafer W is ground while being laid on the chuck table
62
with its rear, bump-free surface up. As the semiconductor wafer W is pushed against the chuck table
62
, it is liable to be broken by the stress, which will be caused by the bumps as a counter force to the push given to the semiconductor wafer W by the rotary whetstone
63
.
In an attempt to prevent the semiconductor wafer from being broken an adhesive tape
64
is applied to the front surface of the semiconductor wafer W, thereby allowing the bumps to be buried in the thickness of adhesive layer, as seen from FIG.
10
. The adverse effect, however, cannot be reduced completely with recourse to this remedy, and what is worse is that: adhesive agent is apt to remain more or less on the semiconductor wafer W after removal of the tape
64
from the semiconductor wafer, thus lowering the quality of pellets significantly.
After bonding the bumps of a pellet to selected electrodes of a printed-wiring board the space between the printed board and the pellet is usually filled with resin, thereby solidifying the pellet-and-printed board combination. To assure that a good electric connection be established between each bump and the counter electrode it is necessary that the bump is 0.09 mm tall, but to reduce substantially the possibility of the semiconductor wafer being broken it is necessary that the bump is 0.05 or less tall. Disadvantageously this necessity is a cause for incomplete bonding between bumps and electrodes, leading to disconnection between the printed circuit and pellets.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a method. of grinding semiconductor articles without causing any breakage on the semiconductor wafer or contamination with adhesive agent in spite of using bumps tall enough to assure good bonding between, bumps and electrodes.
To attain this object a method of grinding semiconductor articles according to the present invention comprises the steps, of: dicing a semiconductor wafer having bumps formed on one surface to separate individual pellets; putting the pellets on a, printed-wiring board with their flat, bump-less surface up; bonding each pellet to a selected area of the printed-wiring board via its bumps, thus providing a pellet-and-board combination; and holding fixedly the pellet-and-board combination on the chuck table of a grinder to grind the flat, bump-less surfaces of the pellets until they have a predetermined reduced thickness.
The printed-wiring board may be a board whose surface is alloted for mounting electronic parts and devices.
After the pellets are bonded to the printed-wiring board, their flat, bump-less surfaces are subjected to grinding, and therefore, the force applied to each pellet by the rotary whetstone is distributed over the whole surface of the printed-wiring board, thus preventing any breakage of pellet which, otherwise, would be caused by allowing the force to be localized to the bumps of the pellet. No source for contamination such as adhesive agent exists, and the height of bumps need not be reduced to prevent the semiconductor wafer from being broken.
All pellets of the semiconductor wafer can be ground simultaneously to one and same thickness, and therefore, it is assured that all pellets have equal thickness as required for the final products.
The grinding of pellets follows the dicing, and therefore, minute chippings which were produced in dicing can be removed from the pellets while being ground.
Other objects and advantages of the present invention will be understood from the following description of a semiconductor article grinding method according to the present invention, which is illustrated in accompanying drawings.
REFERENCES:
patent: 3811183 (1974-05-01), Celling
patent: 4749120 (1988-06-01), Hatada
patent: 5299091 (1994-03-01), Hoshi et al.
patent: 5843251 (1998-12-01), Tsukagoshi et al.
patent: 5920769 (1999-06-01), Ball et al.
patent: 5977641 (1999-11-01), Takahashi et al.
Kaneda Yukihiro
Takizawa Shuichi
Arent Fox Kintner Plotkin & Kahn
Disco Corporation
Hail III Joseph J.
McDonald Shantese
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