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flux compositions

genesmelik

#6334

flux compositions | 22 August, 2000

Good morning Dr. Lee. I was wondering how flux chemistries have changed, or will change, with the transiton to Pb-Free, given the higher reflow temperatures required for SMT assembly?

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Dr. Ning-Cheng Lee

#6335

Re: flux compositions | 22 August, 2000

Excellent question. Alloy development is relatively easy compared to flux formulation.

New fluxes for Pb-Free alloys need upgrades in 2 critical areas: 1) thermal stability 2) oxygen barrier efficiency

Since the Pb-Free alloys require reflow processing at ~240C (higher than conventional SnPb), the new fluxes must be able to endure this new condition.

And, since these higher temperatures increase the oxidation potential of the alloys and the fluxes, the new fluxes must be able to handle this.

For both solvent and water-wash systems, flux residue cleanability is becoming a challenge.

Finally, the new Pb-Free alloys generally exhibit poorer wetting than SnPb alloys, the flux must compensate for this, as well.

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davewsnyder

#6336

Re: flux compositions | 22 August, 2000

Hello Dr. Lee, Will no-clean fluxes be more of a challenge to develop?

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Dr. Ning-Cheng Lee

#6337

Re: flux compositions | 22 August, 2000

Yes, no-clean is more of a challenge, particularly for halide-free no-clean. Requirement on probe testability will make it more difficult.

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