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NC Flux Splattering

#6302

NC Flux Splattering | 23 August, 2000

Dr. Lee: We had a discussion on the forum recently and I wanted to get your input.

What is the best method(s) for elimating (reducing) no-clean solder paste flux from splattering on gold interconnect fingers on a PCA?

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Dr. Ning-Cheng Lee

#6303

Re: NC Flux Splattering | 23 August, 2000

From solder material point of view, a solder paste with slow coalescence rate, or slow wetting rate, will be most desirable. Processwise, allowing the paste to stay at soaking zone for longer time will dry out the volatiles, and reduce the chance of flux spattering upon coalescence. However, it should be noted that too long a soaking period may also produce excessive oxide and result in poor wetting. The optimal reflow profile is a strong function of flux properties, and usually is developed experimentally.

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#6304

Re: NC Flux Splattering | 24 August, 2000

How does flux selection fit into the mix of factors affecting splattering? Do various flux formulations splatter more than others?

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Dr. Ning-Cheng Lee

#6305

Re: NC Flux Splattering | 24 August, 2000

Yes, a flux with a fast wetting rate will be more prone to have spattering. Fluxes with high boiling point solvents are also more prone to have spattering, if the same flux is fast in wetting rate.

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#6306

Re: NC Flux Splattering | 24 August, 2000

What factors in the manufacturers' description of a paste properties give clues to the wetting rate and boiling point of solvents of fluxes?

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Dr. Ning-Cheng Lee

#6307

Re: NC Flux Splattering | 24 August, 2000

Regarding the boiling point, MSDS may have some infomation reflecting that. Other description such as long stencil life and long tack time may also reflect.

Wetting rate typically is not stated in product data sheet. You will need to determine it yourself.

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