Ask Helena & Leo

Question: We are soldering a cover to a housing and I was not able to find any quality criteria for the amount of solder flowing down the inside of the housing wall. We are hand soldering the lid in place on the cover, filling the seam between the housing and cover with solder. At times we use SN 96 and other times SN 63 solder depending on how the customer will future process the units. Are there any guidelines for this process?

Answer: I would recommend using a smaller diameter solder to reduce the amount of solder protruding away from the shield. As for the flux, the RMA flux is in fact a no clean flux as the activators are bound within the rosin material. The issue is the polymerization of the rosin and the time it takes to fully polymerize and hardened, but in any case the issue to defend your position is IPC-610, Section 10.6.1 on page 10-38.

If the residues can be shown to be no-clean, and that information should be available from the supplier, then this should be sufficient to meet the requirements of the document.