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56 SMT007 MAGAZINE I AUGUST 2024 sis by micro-sectioning. 3D X-ray virtual cross-sections were compared to opti- cal images of the physically destructive micro-sections. In addition, a compari- son of the 3D X-ray "images" before and aer 3,000 cycles was performed for the CTBGA 228 component. Test Results and Discussion Thermal Cycle Results: As received/burn-in SnPb BGA228 assemblies ree FPBGA assemblies completed 3,000 cold-biased thermal cycles (-105°C and +40°C). Each assembly had four BGA196, four BGA208, two BGA228, two BGA360, two LGA97, two MLF100, two MLF72, and SMRs. Figure 5 shows resistance continuous monitoring for CABGA208 and CTBGA228 assemblies up to 3,000 biased thermal cycles. As apparent, there were no failures of CABGA208 to 3,000 cycles; therefore, the biased hot/cold failure cycles could not be compared to previous CTF result presented for CAB208 12 . However, as shown in the monitoring plots, there were two failures for CTBGA228, one at 2,128 and the other at 2,372 cycles. is allowed us to generate a qualitative compari- son with the hot-biased thermal cycle (-45°C and +105°C) results. Resistance monitoring test results clearly indicate that once fail- ure initiated, within less than 10% CTFs and with 10 consecutive cycles, resistance increases more than 20% as required by IPC 9701. Figures 6 shows the qualitative com- parison of Weibull data plots for cycles- to-failure for the CTBGA228 under hot/ cold-biased conditions, each a separate test (-40°C/+105°C and –105°C/+40°C), respectively. Testing to the extreme low temperature showed higher CTFs. With limited sample size, especially for the cold- bised case, it is difficult to draw a conclu- sion, but it could be stated that possibly resistance values were also taken before test- ing and at key points between sets of thermal cycles for each channel. In addition, sample FPBGAs were sectioned from the test vehicles pre- and post-thermal cycling. ese components were used for a combination of non-destructive 3D X-ray and destructive micro-sectional analyses. Non- destructive 3D X-ray was first performed to determine if cracking conditions could be identified for subsequent destructive analy- Figure 3: A photo of thermal shock cycle chamber for cold-biased TC with hot/cold zones and monitoring equipment. Figure 4: A representative profile of cold-biased thermal shock cycle (–105°C to 40°C ).