Issue link: https://iconnect007.uberflip.com/i/1524755
AUGUST 2024 I SMT007 MAGAZINE 55 is an enlarged image showing the lands, daisy- chain pattern, and probing pads in one of the CTBGA228 zones. Environmental Testing In previous testing, eight 12 test vehicles with two different burn-in conditions were sub- jected to accelerated hot-biased thermal cycle (-40°C and 105°C, with 15-minute dwells) test- ing in order to evaluate the solder-joint reli- ability. During thermal cycling, an event detec- tor was used to detect resistance spikes that exceeded 500 ohms and 200 nanoseconds, per IPC 9701 8 , thus capturing solder joint failures. For the current test, three identical SnPb test vehicles were subjected to cold-biased air-to-air thermal shock testing with hot and cold zone, which TVs shuttle between the two zones as shown in Figure 3. Figure 4 shows cold-biased thermal shock profile that was performed over the tempera- ture range of -105°C to +40°C with seven-minute dwells and >100°C/min ramp rates. is temperature range has the same overall ΔT of 145°C, while revers- ing the high and low temperature limits with respect to the hot-biased version. ree thou- sand cycles were performed on FPBGA assem- blies before failure analyses. e resistance of each channel (i.e. zone) was measured every 10 seconds using a data acquisition unit dur- ing testing. In-situ resistance measurements were taken during thermal cycling to detect any component experiencing a change in resis- tance +/-20% from the nominal reading, which was considered a failure. Also, hand-probed Figure 1: Reflow for SnPb assembly: direct ramp to 206˚C at 0.75˚C/s and -1.4˚C/s cooling rate. Figure 2: CTBGA228 land pattern and daisy-chain (left) and top-down view of an assembly (right).