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Component-level gap height between LSC and collapsed
BGA solder ball
As a continuation to the aforementioned SMT process
corner investigation, quantifying the LSC process capability
to the collapsed BGA solder ball gap height after the FCBGA
assembly process was studied. High LSC process control to
the collapsed BGA solder ball clearance is a prerequisite to a
robust SMT assembly process to ensure no defects manifest
associated with LSC clearance with the PCB after mounting
(to the PCB). As such, gap height measurements between
the LSC and BGA solder ball were evaluated across multiple
assembly lots to determine if Cpk values meet automotive
requirements, i.e., ≥1.67.
Figure 8 is a simplified illustration of the gap height
measurement between the LSC and the collapsed BGA solder
ball being investigated on the flip-chip substrate after the
FCBGA assembly process. The target minimum gap height
is greater or equal to 130µm. To prove a high assembly
process margin, gap height measurements between the
LSC and the BGA solder ball were performed on 100% of
the units across three assembly lots using standard ball
Figure 7: Color map showing a moderate positive correlation between the gap
height between a LSC and a PCB and between the BGA standoff height.
Figure 8: Dead-bug illustration of a LSC to a collapsed BGA solder ball gap height
measurement.
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