As a final check, at 300 and 500 temperature cycles, sample boards were removed from the oven for cross sectional analysis. While more commonplace on multiple layer boards, delamination can occur on 2-layer boards, as well as compounding solder issues as the device leads and board expand and contract over the temperature cycles. Figure 2-14 shows worst case cross sections for a device at 300 cycles, and Figure 2-15 shows the same for 500 cycles.

Figure 2-14 Cross Section - 300 Temperature Cycles

Figure 2-15 Cross Section - 500 Temperature Cycles

As expected from the observations made during x-ray, there is evidence of solder voiding (highlighted by red arrows in the images), but even in the presence of these artifacts, none of the boards failed by abnormal heat signatures or open circuit. The cross sections show no evidence of delamination, solder adherence to the frame and PCB is still nominal, and there is no evidence of damage.