Issue link: https://iconnect007.uberflip.com/i/699765
July 2016 • SMT Magazine 19 DIVERGENCE IN TEST RESULTS USING IPC STANDARD SIR AND IONIC CONTAMINATION MEASUREMENTS Methodology Two different SAC305 solder pastes were printed and reflowed on IPC B-52 test coupons (Figure 1). The assembled coupons were broken into two separate test vehicles after the solder pastes were printed, populated and reflowed. The section of the board on the center right was used to measure ionic contamination. The left portion of the test vehicle was used to measure SIR. The four smaller panels on the far right were discarded. A schematic diagram of the Ionograph that was used is depicted in Figure 2. The Ionograph is considered a "dynamic" ROSE measurement in which the extraction solution is continuously passed through ion exchange columns that remove the ionic material in the solution. A conductivity bridge detects ions in solution, and a flow meter measures the volume of solution passing by the conductivity bridge, allowing ionic contamination to be integrated with extraction solution volume. A second measurement using three IPC-B-24 coupons (usually used for single material SIR measurements) for each of the two pastes was made. Experimental Procedure 1. IPC-B-52 Coupon Preparation Ten IPC-B-52 coupons were processed for each of the two selected solder pastes. These coupons were used as delivered from the board fabricator; no further cleaning was done. The pastes were printed using a 0.125 mm (5 mil) stencil. Positions 2, 3, 5, 7, 8 and 10, as shown in Figure 1, were populated with dummy com- ponents. The coupons were then reflowed us- ing an OmniFlo 7 oven with a 1.1 °C/s straight ramp to a peak temperature of 243°C with a time above liquidus of 53 s using a nitrogen atmosphere (600–800ppm O 2 ), as shown in Figure 3. 2. SIR Measurements The SIR portion of twenty coupons and two unprocessed control coupons were mounted in a temperature-humidity chamber. Teflon-insu- lated leads were hand soldered to the coupons. The chamber was programmed to run at 40°C +-1°C and 90–93% RH, and a GEN3 AutoSIR was programmed to apply 12V bias and to measure Figure 2: Schematic diagram of the "Ionograph."