Issue link: https://iconnect007.uberflip.com/i/270052
March 2014 • SMT Magazine 21 FEaSIBILITY OF LOW/NO SILvEr aLLOY SOLDEr PaSTE maTErIaLS continues has many different SMD component types such as BGAs (0.8 mm and 1.0 mm pitch), CSP (0.5 mm pitch, 0.4 mm, 0.3 mm), QFN component (0.5 mm pitch and 0.4 mm pitch), leaded com- ponents (SOIC, QFN100, QFN208, etc.), chip components (0201,0402, 0603, 0805), through- hole components, etc. In addition, the test vehicle has different areas designed for print- ability test, slump test, wettability test, solder ball test, pin testability, etc. The test vehicle is shown in Figure 2. Evaluation methodology and Procedure Printability Tests For printability tests, the solder pastes were printed using the optimized printing param- eters at 0-hour and 4-hour stencil life. Solder paste volume and its standard deviation were then recorded and analyzed. Besides the solder paste volume and standard deviation, we also considered other aspects of printability such as printing speed and missing solder. Typically, a slower printing speed tends to provide a bet- ter paste volume and small standard deviation. For volume manufacturing a good solder paste material should perform well not only at slow printing speeds but also at high printing speeds. While the printing speed varies based on the complexity of the product, a good solder paste should be able to print well at a speed of 50–70 mm/s or higher. Different area ratios ranging from 0.3–0.8 were used for the missing solder evaluation (Fig- ure 3). The insufficient or missing prints were analyzed. The missing solder was defined as less than five solder particles on a pad. Slump Test Cold and hot slump tests were performed at 0-hour and 4-hour using the IPC-A-20 sten- cil pattern. The number of solder bridges at different spacings was analyzed. For the cold feaTure Figure 2: Flextronics multi-function test vehicle, rev 1.0. figure 3: Printability area for missing print.