White residue on back of motherboard after cleaning with 91% IPA

[Dragnerok X]

Photo:

All I did was brush on a light coat of 91% isopropyl alcohol to remove any caked-on dust, and this residue appeared after it dried. How do I remove it?

 

[Calvin7]

Alcohol is a very weak cleaner. It absorbs water from the air, which dilutes the alcohol and weakens its ability to clean. 91% alcohol also is diluted with 9% water.

This dramatically reduces its cleaning strength. Using weak, water-filled alcohol is a bad process that can lead to labor-intensive cleaning. Make sure you specify the purest, most water-free alcohol you can find.

Cleaning using a "dip-and-brush" process actually can make boards dirtier and more prone to premature failure.

Most people using alcohol develop problems with white residues, especially when cleaning lead-free materials. If these residues are streaky lines across the board, you are not rinsing thoroughly. Re-clean the board. If the residues are an even, smooth layer of white film across a large area this usually indicates you have the wrong solvent for that flux. You will need to upgrade to a stronger solvent and the problem will go away.

 

[Dragnerok X]

Alcohol is a very weak cleaner. It absorbs water from the air, which dilutes the alcohol and weakens its ability to clean. 91% alcohol also is diluted with 9% water.

This dramatically reduces its cleaning strength. Using weak, water-filled alcohol is a bad process that can lead to labor-intensive cleaning. Make sure you specify the purest, most water-free alcohol you can find.

Cleaning using a "dip-and-brush" process actually can make boards dirtier and more prone to premature failure.

Most people using alcohol develop problems with white residues, especially when cleaning lead-free materials. If these residues are streaky lines across the board, you are not rinsing thoroughly. Re-clean the board. If the residues are an even, smooth layer of white film across a large area this usually indicates you have the wrong solvent for that flux. You will need to upgrade to a stronger solvent and the problem will go away.

Thanks for the detailed explanation. I tried re-cleaning the board, this time with a harder-bristled brush and it just spread the residue (flux?) around without removing any of it. Would electronics contact cleaner be a better solvent?