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This technique makes possible the salvaging of semiconductor wafers which have either low solder compositions or an insufficient volume of solder.
English (United States)
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Semiconductor Solder Pad Rework Technique
This technique makes possible the salvaging of semiconductor wafers which
have either low solder compositions or an insufficient volume of solder.
For a variety of reasons one component of a solder alloy which has been
deposited on the solder pad of a semiconductor device may be too low, or the
overall volume of the solder on the pad may be insufficient to form an effective
solder bond. These semiconductor devices or wafers can be reworked by this
technique and salvaged.
As shown in Fig. 2, a semiconductor device 10 is depicted
having a plurality of solder pads 12 having either a solder
composition that is low in one component, or a low volume solder pad.
In this process a quartz chip 14, as shown in Fig. 2 has on its
surface a mirror image of the solder pads shown in Fig. 1 formed of
the component lacking in the solder pads 12. For example, if the
solder pads 12 contain less than the desired amount of indium, the
pads 16 can be formed of indium in a mirror image of the pad pattern
on device 10.
The chip 14 with its pads 16 is used as a decal by positioning the chip 14
over pad 12, as shown in Fig. 3, with appropriate flux and subsequently heating
the assembled unit. Chip 14 is preferably transparent to insure perfect alignment
of the pads 12 and 14. Upon heating the material of pad 16 is transferred to the
pads 12 since the chip 14 does not contain solder-limiting metallurgy, e.g., Cr-
Cu-Au, and the solder will therefor...