Some years ago I created a software tool, StencilCoach™, to calculate the stencil parameters to provide for an adequate amount of solder paste for the pin-in-paste process. Since solder paste is typically 50% by volume flux, it is often the case that the solder paste cannot supply enough solder to form a proper fillet for the through-hole solder joint. Solder preforms in the shape of passives have often been used to supplement the required solder volume.
The Input Page for Donut-Shaped Preforms in StencilCoach™
Some assemblers might want to use donut-shaped solder preforms. So, I upgraded StencilCoach™ to be able to perform the calculations for these preforms. Check it out here. Let me know what you think—email@example.com.