Popcorning

I am looking for some details about the failure modes in popcorned components. Does the component usually fail to operate. Is the damage likely to extend to the gold bond, wires, or substrate. We have experienced a high failure rate on a subset of our PLCCs and some of the investigators are proposing the theory that the failures are due to inadequate storage and consequent moisture absorbtion. A sample was sent to the manufacturer and they determined that the failure were due to "Pull_out of the silicon beneath the bond pads". Is this a typical failure mode for popcorned parts. They also noted that "External examination of each device did not reveal any evidence of physical damage that may be suggestive of popcorning". Since this is the first time we have had any suggestion of moisture absorbtion as a cause of failure, I find myself ignorant and seeking help. Thanks in advance for any insights.

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