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Solder Paste/Preform Bond Line Thickness

When helping customers with the optimization of their soldering process, the question often comes up;

What will my solder bond line thickness be when utilizing this material?” 

The amount of volume lost to flux content while utilizing a solder paste, in comparison to a flux-coated preform, is much greater.  Whereas a flux-coated preform only contains about 1-2% flux by weight, a stencil printing solder paste is approximately 10% flux by weight.   This may not sound like much, but when you consider the density of the powdered alloy in the solder paste (7.40 g/cm3 for SAC305) versus the density of the flux (~1 g/cm3), you end up with a material that is almost 50% flux by volume! 

Therefore, if you were to print a 0.5” x 0.25” deposit utilizing a 0.005” thick stencil (0.001in3 of printed solder paste volume), you would only end up with approximately 0.0005in3 of actual metal solder.  In short, your final bond line thickness will be half of the thickness of the solder paste printed.

For help determining your bond line thickness, or for help determining the appropriate solder material for your application, please contact AskUs@indium.com.