The white residue is showing up after the PCBA having a cleaning process. The element analysis result of white-residue is C, O, Si and Sn. The Weight% for them are around 27%, 25%, 0.5% and 47.5% from EDS analysis.

The cleaning process that the PCBA after SMT process will put the PCA in the EC7M solvent 5 minutes and brush the board 2 times. Then, put the PCA in the IPA 5 minutes and brush the board 1 time. The last one is using DI water flush the board.

After the above cleaning process, the white residue will show up. Especially on the solder mask clearance.

The solder type is SAC 305.

How do I reduce the amount of the white residue?