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What has been your experience with low-temperature solder?

baldengineer

Recently I found Chip Quik Sn Bi Ag Solder PasteChip Quik Sn Bi Ag Solder Paste. It is a low-temp alloy with Bismuth (and Silver.) When using hot air to solder parts, or during re-work, it makes the process go so much faster. It melts around 140C. It also does not appear to need refrigeration and has a long shelf-life. With all of those positives, I'm wondering what the downsides to using it are compared to more "traditional" solder alloys.

 

So whether positive or negative, what has been your experience when using "low temp" solder?

Parents

  • One has to be very careful when using low-temp solder on existing leaded solder joints. Apparently, if there’s any lead involved, such as with pre-tinned wires or leads, the combination of Bi58Sn42 and the lead can lower the melting point to 95 C and create very weak and brittle joints that can be pried apart with a toothpick.

     

    I use low-temp solder for all tricky to solder ICs on prototype boards only. It can never leave the lab bench! As shabaz said, it is perfect to solder QFNs, I also did BGA with hot air and low temp solder successfully.

    - W.

  • in reply to wolfgangfriedrich

    Yes, that's an important point.

     

    Solder - Wikipedia

    Different elements serve different roles in the solder alloy:

    • Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn
      16Pb
      32      Bi
      52       with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability.

     

     

    Eutectic system - Wikipedia

     

    Gerald

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Reply
  • in reply to wolfgangfriedrich

    Yes, that's an important point.

     

    Solder - Wikipedia

    Different elements serve different roles in the solder alloy:

    • Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn
      16Pb
      32      Bi
      52       with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability.

     

     

    Eutectic system - Wikipedia

     

    Gerald

    ---

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