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SMT electronics assembly manufacturing forum.


dry solder paste

griinder

#32814

dry solder paste | 22 February, 2005

I was curious if anyone else has ever added water soluble flux to water soluble solder paste that is only a few days old, but is too dry to use in production. Also, are there any known bad side effects to this process. I have already searched the archives, with very few results. Thanks

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Austinj

#32819

dry solder paste | 22 February, 2005

Most solder paste has a shelf life of 1 week at room temperature after opened, if resealed at the end of the shift/day. Most shelf lives are 4-6 months at 40F (refridgerated) or 1 month at room temp (unopened/sealed). Recommended stencil life is approximately two hours after being applied to the pcb.

Adding water soluble flux to dry paste does not work. (I know from experience) The original activators and solvents used are usually different than the activators and solvents in the liquidous form and can cause abnormal chemical reactions when heated going through the reflow process.

I do not recommend it.

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#32823

dry solder paste | 23 February, 2005

We've talked about this previously. Search the fine SMTnet Archives. For instance: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=31767

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Zlatan

#32834

dry solder paste | 23 February, 2005

Would you be able to share with me, what specific abnormal chemical reaction could happen?

Thanks

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

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Austinj

#32845

dry solder paste | 23 February, 2005

Solder spattering, solder balls, components "popping" off pads........ Not a serious chemical reaction, however, as replied to by KEN on 12/21/04 in a similar article:

"Are you adding liquid flux? Or paste "Gel" flux?

If liquid flux: This, in my mind, is an unacceptable technique. Why?

1. Can not control metals content. 2. Probably not adding the same chemestry flux...as paste flux has many different additives (that are different from liquid fluxes). 3. Can not control slump factors. 4. If a little is good then a lot is better. Right? I have found this is like giving an Operator or Technician an inch...they think its a ruler! 5. How do you know your cleaning process is qualified for this method. Liquid fluxes don't (normally) see extended durations above 183C. 6. Solder balling or splatter issues? 7. Voiding results on ALL joints. Reliability analysis?

This method is penny wise pound foolish (shakes head)..."

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pmdeuel

#32904

dry solder paste | 27 February, 2005

So true, We had paste flux supplied to us from Alpha metals. It was the same as used in the solder paste. The major problem we noted was the in ability to control the ratio of paste to flux resulting in lots of voids. When we mixed enough to get the paste back to a equivently consistant mix we had it tested. It came out to about 60 %solder and 40 % flux.

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#32905

dry solder paste | 27 February, 2005

pmdeuel: Was that "about 60 %solder and 40 % flux" according to volume or weight?

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