<< 1. Our contractor is using WS-609 solder paste from alphametals for double-sided process. The board is cleaned after each side process before going to the next side. My question is: is it necessary to clean after each side process? can it be cleaned only once after the assembly? >> Yuan, If they are doing this operation now, I would not recommend stopping it. Flux residues (of almost any kind) become progressively harder to removed with each successive exposure to reflow temperatures. The WS609 is a pretty good water soluble paste, but don't know what it's cleanability would be if you baked it on. Why subject the board to an additional cleaning challenge? As to whether or not such interim cleaning is "necessary", only a designed test could tell for certain. Doug Pauls CSL [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************