Qualification of the Assembly Process of Flip-Chip BGA Packages ...

6.1 Results
Texas Tech University, Nivetha Shivan, May 2012
CHAPTER 6
DATA AND ANALYSIS
6.1.1 Pre-engineering Qualification Phase I
6.1.1.1 Stress Test Results
44 units were subjected to MSL3 pre-conditioning. These units were then divided into 2
lots and each of these lots were subjected to temperature cycling and pressure cooker test
respectively. The full qual and FYI read points were taken. Since the quality level chosen
for this project is LTPD=10, 22 devices were considered from each DOE for the stress
tests with an acceptance number of 0. Table 6.1 shows the stress test results from Phase I.
Table 6.1: Stress Test Results from Phase I
CSAM analysis post MSL3 soak and TCT showed no abnormality. All four DOEs
showed suspected failure locations in the CSAM image after PCT 288 Hours which is the
robustness readpoint. This tells us the part may not be robust after 288 hours of applying
the pressure cooker conditions. Further analysis during electrical verification in Phase II
was required. The three major anomalies seen in these CSAM images were:
� A white area in the underfill region
This was suspected to be a delamination in the underfill region. Cross-section was
performed to validate the suspected failure. Figure 6.1 shows CSAM image of the
suspected failure location. Figure 6.2 shows the SEM image of the bump after cross
section.
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