|Ask the Experts|
June 22, 2018
BGA Rework Residue Concern
Sometimes after removing a BGA for rework we see an outline of residue on the laminate around the pads. This residue is not easily washed off so we carefully scrape off the residue with a knife. Is it necessary to remove this residue before we install the new BGA?
|Expert Panel Responses|
The residue is most likely flux residue, if this is the case the question is best addressed to your paste supplier as they will have the relevant reliability data (it is a no clean product that you are using then most flux systems will withstand multiple reflow cycles without adverse impact on the reliability of the residues). One further point if your rework flux is different to the original you should consider possible flux interactions it is not common but can happen. If the residue is not flux then you will need to identify it before its impact on reliability, and consequently the need to remove it, can be determined.
Senior Applications Chemist
This sounds like flux residue from either the original process or flux being added during the rework operation. Contact the manufacturer of your solder paste or flux and find out the correct cleaner to use to remove this residue. "Careful" scraping may lead to PCB damage.
Regional Sales Manager
OK International Inc.
It's hard to be sure if the contamination will cause problems or not, since you are not sure of the nature of the contamination. If it's flux residues -- the most likely candidate -- they there is a high probability the residues will react with the solder balls on the BGA and over time cause problems. (The most common problems are tin whiskers and corrosion, both of which are bad news on today's tightly-spaced BGA components.) So, for reliability's sake, I would urge you to clean the substrate with a modern, high-purity cleaning fluid. Many companies make such products; from my own company I would recommend PowerClean lead-free defluxer, because it's strong, fast-drying and nonflammable. As a general rule, stay away from the flammable cleaners in this application because they usually will not have the cleaning muscle to remove temperature-hardened residues.
My guess is that this polymerized flux residue. If you clean after initial soldering, thisresidue was there after cleaning and was hidden. When you replace the BGA the new flux should redissolvethe residue which would then be cleanable, if you clean after rework, orencapsulate the residue if you do not clean. In any case, I believe you risk more harm byscraping it off so I would leave it alone.
Austin American Technology
The residue is most likely flux. Do you use any bonding agents or under-fill on the component? Those can also be causes for this residue. The good manufacturing practice is to clean the pads solder) and the adjacent areas for any residue. Usually this cleaning process is relatively simple and the outcome is good. If you have so much trouble with it try to use some chemicals - you have some recommendations already. I will have another question - are you sure that this is not from the flux on your initial reflow process? Is your cleaning process efficient for low profile components?
Engineering and Operations Management
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