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

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5.2 Pre-engineering Qualification Phase II Texas Tech University, Nivetha Shivan, May 2012 The difference between Phase I and Phase II being the electrical characteristics, the devices are also checked for their electrical functionality at time-zero, after MSL3 pre- conditioning, after 300 cycles of temperature, 500 cycles of temperature and 1000 cycles of temperature. These read points after temperature cycling called as conditional qualification, full qualification and robustness check (FYI) respectively, are important in that they help us determine when the failures occurred. The conditional qual, full qual and FYI read points for Pressure Cooker test are 96 hours, 168 hours and 288 hours respectively. 51
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. 52
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Qualification of the Assembly Process of Flip-Chip BGA Packages ...

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