Acceptance Testing Of Low-Ag Reflow Solder Alloys (Part 2)

Estimated reading time: 7 minutes

Solder joints of the leaded DoE test board (SMTA Saber) assemblies using the respective low-Ag paste alloys were evaluated to the IPC-A-610E criteria. A range of lead and joint types such as J-leads, gull-wing leads and passive components were inspected. However, BGA joints were not inspected due to lack of access for visual inspection.

Solder defects such as cold solder and lack of fully reflowed paste were found across all low-Ag alloys and all process conditions of 230°C and 240°C. Cold solder is defined per IPC-A-610 as ‘‘a solder connection that exhibits poor wetting, and that is characterized by a grayish, porous appearance. (This is due to excessive impurities in the solder, inadequate cleaning prior to soldering, and/or the insufficient application of heat during the soldering process.) Defects (see Figures 3-8) appeared randomly distributed across the PCAs. Acceptable solder joints were observed on boards processed at 250°Cand times above liquidus of at least 60 seconds (see Table 3).

Table 3: Visual inspection summary of soldering acceptability criteria per IPC-A-610E

Examples of the observed defects:

Figure 3: Low-Ag Alloy A - Peak 240°C at 60 sec TAL (Uncoalesced/Unreflowed solder paste)

Figure 4: Alloy A - Peak of 230°C at 120 sec TAL (Uncoalesced/Unreflowed solder paste)

Figure 5: Alloy A – Peak of 240°C at 60 sec TAL (Uncoalesced/Unreflowed solder paste)

Figure 6: Alloy A – Peak of 240°C at 60 sec TAL (Cold Solder)

Figure 7: Alloy B – Peak of 240°C at 60 TAL (Cold Solder)

Figure 8: Alloy B – Peak of 240°C at 30 sec TAL (Cold Solder)

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