Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Rejuvenated solder paste


Rejuvenated solder paste | 16 December, 2004

We use water soluble solder paste. When it gets a little dried out, can we add something to rejuvenate it? Liquid flux?

We do not place components, just print and reflow the solderpaste so solderballs, spattering, and other issues like those are of no concern. We just want to print the paste and reflow it into a meniscus on each smd pad.

When it gets a little dry it is difficult to print on the fine pitch (.4mm) foot prints so we wondered of we could "juice" it up a little to make it print better. Kind of like thinning paint when it drags!!!

Thanks in advance for your input.

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Rejuvenated solder paste | 17 December, 2004

Your solder paste is talking to you, follow its message. Listen to the paste. Be at one with the paste.

If you insist on ignoring the message of the paste, add more paste, if you just need to complete the last board or so, but you really should just dispose of the dry, crusty stuff and restart with fresh paste.

Consider: * If the issue is long cycle time: Determine why your set-up between print cycles takes so long and what you can do about it. * If the issue is short runs, with long setups between runs: Put the paste in a clean paste storage jar between print cycles. * Purchasing one of those closed paste cartridge things [ie, Rheometric Pump, Proflow, etc] that most printer equipment suppliers offer. * Changing from printing to dispensing your paste.

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Rejuvenated solder paste | 17 December, 2004

I agree with dave. However, if you can not afford those expensive cartidges, you start putting enough solder paste on the stencil so to minimize waste. I agree you have to dispose of the excess dried up solder but if your process is not very critical you may experiment on putting some flux. However, it is not recommended.

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Rejuvenated solder paste | 17 December, 2004

Hi Matt,

What printer are you using? you may be able to get an envronmental unit for it to keep the paste cooler & at the right humidity for longer, thus extending it's effective window.



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Rejuvenated solder paste | 17 December, 2004

I have done this several times in order to save my butt: adding liquid flux in a jar of not so fresh paste, stirring it slow for 2-3 minutes, to make it usable. Of course, use no-clean flux for no clean paste, etc.

During one production slow-down, we had 30 or so jars that went more than 6 months without refrigeration, and it was getting stiff. About one teaspoon of flux did the trick, and QC never saw the difference.

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Rejuvenated solder paste | 18 December, 2004

We used to add flux on a "expired" solder paste but we discontinued as there are many problems and customers complaints coming from our American customer. Like unwetted solder pads,dull and cold solder and many others. The profit is really ok but quality wise it suck!

I hope you are not an American manufacturer as I beleived that American product is better than China brand. Quality makes American product stand among the rest.

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Rejuvenated solder paste | 21 December, 2004

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 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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