Issue link: https://iconnect007.uberflip.com/i/1284035
SEPTEMBER 2020 I SMT007 MAGAZINE 131 pened. We built these boards, and every one of the reds failed reflow testing. Three of them passed. Therefore, as seen in Figure 15, we had a void in the microvia at the cap plating. The one on the bottom right passed. When you build them right, they pass; but if you have problems, they will fail. This is a real case study (Figure 16). I had a new CAM planner that planned for a 5-mil microvia; because of the price at five, it is a five-mil laser via, and the aspect ratio was high. I highly recommend 0.75:1.0. Figure 17 shows the test cycle at 245°C. The black line is the actual temperature on the cou- pon. Here is what happened during the rou- tine first reflow. It looked like it was okay, but then we started having failures at the second reflow, and it happened more and more as we got down to the sixth reflow cycle (Figure 18). Figure 15: Example of WMI failure caught by OM testing. Figure 16: A microvia at 0.005" with an aspect ratio of 1:1 and a dielectric target of 0.0045". Figure 17: OM thermal cycling on the actual D-Coupons.