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Lead Free BGA Rework Process | Lead Free BGA Repair
Inspection
A “recalibration” of the inspection processes and equipment needs to be included
on the transition checklist for BGA tin-lead to lead free rework. Post
processing inspection includes both visual, XRAY and endoscopic inspection.
While there are density differences between tin lead and lead free solders most
XRAY systems will not need to be recalibrated for inspection of lead free BGA
solder joints. The same types of joint attributes, namely the presence of
bridges and shorts, the presence and uniformity of solder ball dimensions and
uniformity of pad wetting, are inspected using the same acceptance criteria. One
major difference that will be noted by experienced operators, which have seen
many tin lead BGA solder balls after reflow is the more limited wetting of a
lead free solder balls. Figure M and N show the differences between a tin lead
and lead free solder interconnection. X-ray inspection of “lead-free” solder
balls will cause a few minor changes to the X-Ray imaging system setup. Since
“lead-free” solder joints are 5-10% less dense than their tin-lead counterparts,
the gray scale value will be less for these x-ray images. This is indiscernible
to the human eye. This difference in density may cause some slight variations to
the penetration voltage required to get a good image from automatic x-ray
inspection systems. While endoscopic inspection will indicate some differences
in the visual appearance of the lead free solder ball, namely the larger grain
structure and less luster of the solder surface (See Figure O), it is a useful
tool in picking up on the more common lead free BGA defects. Part delamination
can be more easily seen with this inspection tool. In addition surface cracks,
more prevalent in lead free solder joints, can also be more easily with the
endoscope.
Figure M- Typical lead tin lead BGA solder ball interconnection
Figure N- Typical lead free BGA solder ball interconnection
Figure O- Endoscopic image of lead free solder ball interconnect
Lead Free BGA Rework
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