Ask the Experts
October 13, 2010 - Updated
October 11, 2010 - Originally Posted

BGA Rework Clean-up?

After a BGA has been removed for rework, there is an outline of residue on the laminate around the pads. It does not come off easily but has to be carefully scraped away with a knife. Is it necessary to be removing this residue to reinstall a BGA or is it fine to leave it?

J. C.

Expert Panel Responses

A photo could have been helpful to determine if the solder mask is attacked by an aggressive flux or if it is really partially removed flux residues. If it is a flux residue, then it might cause reliability problem. Best way to find out is to run ion chromatography tests, Zestron would be able to do that as a part of service plan for the client. If it is merely an attacked solder mask due to the aggressiveness of the flux. I am not sure if it would still impact the functionality of the board.

Umut Tosun
Application Technology Manager
Zestron America
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".

If its no clean paste that has been used to apply the original BGA then this residue will be fine to leave on and will assist with reapplying the replacement BGA. If you are uncertain, then remove the residue with a proprietary cleaner.

Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

In general, it is NEVER acceptable to leave residues on circuit boards, and this is particularly true with BGA components. BGA components are used to increase the density of circuitry per square centimeter. This means the electrical connections are smaller than the typical SMT component, the chip runs hotter, and each chip can have hundreds if not thousands of electronic connections. To leave an unknown residue adjacent to this fragile environment is to invite corrosion or tin whiskers to form, with potentially catastrophic results. The proper answer is to clean the area thoroughly. Typical dip-and-brush cleaning with alcohol probably will not get it done, due to the flux residues and the high heat of BGA removal systems. Use a modern, nonflammable, high Kb-value solvent, several of which are available from MicroCare and other quality companies. Use a clean brush and rinse thoroughly.

Mike Jones
Vice President
Micro Care
Mr. Jones is an electronics cleaning and stencil printing specialist. Averaging over one hundred days a year on the road, Mike visits SMT production sites and circuit board repair facilities in every corner of the globe, helping engineers and technicians work through the complex trade-offs today's demanding electronics require.
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