Issue link: https://iconnect007.uberflip.com/i/1137649
JULY 2019 I SMT007 MAGAZINE 67 Manufacturability: Wetting Test 1 In this test, we printed a circle of paste on an oversized copper pad and measured the diam- eter after reflow (Figures 12 and 13). There is no specific pass-fail criteria for this test in terms of diameter. It is used, as with Wetting Test 2, to gauge the wetting properties of the material. The lower-temperature solders do not wet as well as the control material. This can be an advantage in paste-in-hole (PIH) applications. Manufacturability: Wetting Test 2 In this test, we deposited the paste on rect- angular pads at 5% intervals from 90–120% of the pad length. We then looked for the smallest percentage to completely cover the pad (Fig- ures 14 and 15). As expected in Figure 15, the low-tem- perature materials do not wet as well as the Sn3Ag0.5Cu control paste material. Manufacturability: Cold Slump In this test, we printed multiple lines spaced from 0.075 mm (3 mils) to 0.300 mm (12 mils) and counted the bridged lines at each spacing (Figures 16 and 17). The paste all performed similarly, but the low-temperature materials did slump a little more. The overall ranking is as follows: • Rank 1: Material D (120 avg. bridges 3 boards) • Rank 2: Material A (125 avg. bridges 3 boards) • Rank 3: Material B (185 avg. bridges 3 boards) • Rank 4: Material C (196 avg. bridges 3 boards) Manufacturability: BGA Voids We observed approximately between 1% and 10% voiding on the BGA balls across all solder pastes tested with no significant perfor- mance difference between materials. Since we are not fully melting the BGA ball, we are not Figure 11: Missing print test data and rank. All materials passed. Figure 14: Wetting Test 2 sample. In this sample case, the result is 105%. Figure 15: Results of Wetting Test 2. Figure 12: Wetting Test 1 sample. Figure 13: Wetting Test 1 results.