Basic FA Flows (Page 4) - Package Cracking FA Flow

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Basic Package Cracking FA Flow

1) Failure Information/Device and Lot History Review. Understand the customer's description of the package crack failure. Check the FA history of the device to determine if it has exhibited package cracking occurrences before, whether in the field or in the manufacturing line.  Check the assembly and test history of the lot to determine if the lot has exhibited any yield or process issues potentially related to package cracking. 

2) Failure Verification. Perform external visual inspection on the sample to confirm the package cracks reported by the customer.  Note the similarities and differences between the customer's description of the package crack and the actual package crack.

3) External Visual Inspection. Perform a more thorough external visual inspection on the sample to completely characterize the package crack.  Check how many distinct crack lines there are, where they originate and where they end, and how they propagated from these end points.  Note also all other package anomalies that may indicate the unit having been subjected to thermo-mechanical stresses, i.e., package chip-outs, tool marks, bent/non-coplanar leads, discolored/burned package, etc.

4) Look for Origin/Propagation Patterns. Check how many distinct crack lines there are, where they originate and where they end, and how they propagated from these end points. If there are several units affected, check for specific patterns with regard to how the cracks are localized. Are they on one side of the package only? Do they affect certain pins only? Do they always occur at certain features of the package only, e.g., at the top-bottom package interface, at the tie bar, at the leads, etc.?

5) CSAM.  Perform CSAM on the samples to check for any internal delaminations that are indicative of the unit having been subjected to extremely high temperatures. Check also for localized delaminations that correlate with the locations of the package cracks.

6) Stress Analysis.  Analyze the package crack characteristics and internal delaminations to formulate your best hypothesis (or hypotheses) on how the unit was stressed. A good guideline to follow for this is that fractures always occur under tensile stresses.  List down as many possible scenarios or conditions that can result in these cracks. Pay particular attention to the possibility that these have been caused in the manufacturing line.  Be sure to enlist the help of the Back-end Assembly experts in generating the list of hypotheses.

7) Simulations.  Perform simulations on good units to verify each of your hypothetical root causes. For example, if you think that debris under the package during DTF caused the problem, then perform DTF on units with debris underneath them. You know you've pinned down the actual cause if you've duplicated the exact package crack pattern.