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Solder Paste

Doug

#7297

Solder Paste | 19 July, 2001

I have a sealed and refridgerated 350g jar of solder paste (water soluable flux). According to the label it expired July 1st. 2001 after the 6 month shelf life. Can this be used? Why or why not? What is the relevance of the expiration date? Can I re-test and justify it is acceptable for use?

Doug

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#7306

Solder Paste | 19 July, 2001

Most paste manufacturers talk about a 12 month shelf life for paste. They give the user half of that time. The remainder is used-up in processing and distribution.

We'd give it a shot. You paste supplier should be able to give you a much clearer idea of how much shelf-life is left in your jar.

So what are we talkin' about? How long is it gunna take for you to bust the jar?

As a secondary issue, we'd be concered about the paste seperating after sitting around for that long. Of course if you "rotate" your jars periodically, while in storage, that's no BIG whoop.

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CPI

#7381

Solder Paste | 25 July, 2001

As Dave said you should be concerned about separation. If you open the jar and see that the flux has separated from the paste ditch it. I guess I am a little more hesitant than others, I would discard the material and use fresh. You have to way the costs a jar of paste vrs the possible cost to touch up or rework the brds if you don�t get good wetting or a poor joint.

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mugen

#7389

Solder Paste | 26 July, 2001

We gave standing order, if its past the expiry date, ditch the can/jar, get a new can/jar....

Visual confirmation, for previously open & recycle can/jar, if you see seperation, of yellowish flux floating above, goolie grey much beneath, then ditch it....period.....

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Hussman

#7408

Solder Paste | 26 July, 2001

Most solder paste manufacturers will take a reasonable amount of paste back, just so they won't loose your business due to bad paste. But if you're asking to ask to ask - separated paste from flux is not a bad thing if the jar was never opened. Paste will not "go bad" like the banana's you have on your counter top at home. Just be sure to THOUROUGHLY mix it back together. That's why paste makers want you to refrigerate your paste - to slow the separating cycle down (I'm sure I'll get an argument here).

If the jar was opened and the flux and metal have separated, then I'd be more worried about how much flux has evaporated. Most fluxes are alcohol based and evaporation can be pretty quick. I've seen paste dry up on my shoe in about 6 hours time! Hey, it happens to the best of us. Scary part is - it's still on my shoe 10 days later! Now I wouldn't recommend everyone to perform this high precision test as results vary from loafers to sneakers - but a quick spin in your viscosity testing machine (notice no name brands) should tell you a lot.

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mugen

#7452

Solder Paste | 30 July, 2001

Hey....sneaky smartie here.... my finance manager, would love to have you on the MRB team....

Anyway, most technical paste specs, do highlight the possibility, should the paste become "dry" or "sticky", we MAY recondition the paste, by "place it from stencil into empty jar", and "add in 2-3 drops of so-so-brand Thinner", and "mix for 2-3 mins with spatula" and Volia!!! it *paste* is ready for use....

Only problem I sense with this, actual guidelines from the supplier, is who the hell is gonna confirm, that use of such paste, isn't gonna messup my PCBA solder fillets?

and should the nicky-picky customer, use a fine-tooth comb, to seperate my processes, into segment audit items, how do we assure the customer, that such paste has no potential reliability issue? *shhessshhhh.....where's that legal lawyer???*

Been there, done that, am still opinionated, to declare, until some industrial guideline, is published by recognized eggbrain(s), still rather propose, any yellowish liquid layer, floating above squishy/harden grey matter (no...that stuff ain't your brain....) its all unproven *unstable* techniques, of saving costs of expired paste.....

Of coz, I could be wrong, so for the skeptical, just go ahead and publish your data & proof, and then we can have industrial leadership evidence, to show that nicky-picky customer, who needs such proof, before reaching general consensus, to permit questionable solder paste, on a PCBA that the customer, paid good money, to have assemblied....

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