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No-clean in RF assemblies



No-clean in RF assemblies | 6 September, 2001

I am trying to convert a customer from a water wash process to no-clean but am receiving much resistance. They suspect that no-clean residue played a part in field failures they experienced several years ago. They are quoting an AT&T study that stated that no-clean and RF does not mix.

Any leads on research or studies on no-clean in RF circuits would be greatly appreciated.

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Michael Parker


No-clean in RF assemblies | 6 September, 2001

The main criteria is at what frequency is the RF operating?

If it's in the microwave region, forget no-clean.

Low frequencies - 0 to 100 MHz, probably ok.

Beyond that, it's application specific. Depends on components used and circuit design. The problem is mostly caused by current surface creep, where the residual flux acts as a conduit for conductivity. If isolated within a grounding ring on the board, only the local parts may be affected. Talk to their design engineer and find out where the critical circuits are, then determine if your process can be done safely with no-clean. Long term field failures can have more causes than just no-clean. Maybe they have a point, maybe they are pointing a finger without sufficient cause. Todays no-cleans are better formulated than in the past. Get references from the various paste suppliers where they know for sure where no-clean is working OK in an RF application.

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