Electronics Assembly Knowledge, Vision & Wisdom
Solder Paste  Beyond The Shelf Life?
Solder Paste Beyond The Shelf Life?
We have some solder paste that has been in a sealed box at 4 degree Celsius for 8 months. The shelf life is 6 months. Can it be used?
Board Talk
Board Talk is presented by ITM Consulting

Phil Zarrow
Phil Zarrow, ITM Consulting
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.

Jim Hall
Jim Hall, ITM Consulting
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

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Welcome to Board Talk with Phil Zarrow and Jim Hall of ITM Consulting, the Assembly Brothers.  I think today we have a material question, is that correct Jim?

It comes from G.H. We have some solder paste that has been in a sealed box at 4 degree Celsius for more than 8 months. The shelf life is 6 months. Can it be used? 

What adverse effect might we expect, if any, using solder paste slightly over the shelf life? Well my brother Phil has very intimate knowledge of the answer to this question.  Don't you brother Phil?

No, don't use it! There's a limit, they have expiration dates for crying out loud!  And that means it doesn't keep up anymore!

If you want to do that with your medications, I know I do with mine go beyond the expiration date, go ahead, take your chances and suffer the consequences.

There's a reason there's an expiration date. Having been involved in a lot of solder paste evaluations, I've seen paste that even in a short time, go beyond it's expiration date and just turn to crap - for lack of a better word.

So it might look like it's working but you're really rolling the dice as far as additional defects.

We recommend actually going the other way. We try to look at putting almost a half life onto solder paste. The manufacturer recommends an expiration date of 6 months, we try to make sure we're going through our inventory within 3 months.

People wave their finger at you and say, "Well you should buy it in smaller quantities." What a lot of solder paste companies will allow you to do is to make a blanket purchase order, spread out the actual deliveries of the paste so that you're getting the price of the quantity, but yet you're basically getting fairly fresh solder paste in whatever quarterly, monthly basis.

I think most solder paste companies accommodate you. I think they want it because it's a very, very, very competitive industry.

Just to re-emphasize, it's the most critical material that you've got in your assembly. It's doing a lot for you.

It's going to stencil print well, it's going to be tacky to hold your parts in place, it's going to solder well when you go for the reflow, it's either going to have a safe no-clean residue or you're going to be able to clean it - it's a lot that you're asking from that paste and there's a lot that goes into that formulation.

As Phil said, there's a reason they put a shelf life on it because there's a very delicate chemical formulation and you don't want to take any risks. Because it could affect virtually every joint on the board.

We like to equate solder paste as being what blood is to your body what your solder paste is to your circuit board and as Jim has said, it's pretty important stuff.

On that note I'll also add, don't solder like my brother.

Don't solder like my brother either. 

Don't try to use expired water-soluble solder paste, results will be very ugly. But with no-clean leaded and leaf-free solder paste even after 4 years from date of expiry I had acceptable results. Color of residues was little bit more yellow, but it was soldered and devices works more than 2 years.
Vitalii Gladkyi, Biakom LTD
Solder paste doesn't turn to dust the day the label shows for expiration, but the user bears any risks inherent with using paste beyond its published shelf life. Some pastes are very robust and can perform adequately well beyond their stated shelf life, but other pastes may not be so forgiving and can result in unanticipated costs that far exceed the replacement cost of the expired paste.

With our pastes, we can recertify users' material for shelf life extension by performing some testing on a sample from that storage lot. Assuming the paste is recertified, users can continue to use the paste for the extension period and comply with all material control audit requirements.
Jason Fullerton, Alpha Assembly Solutions
Some years ago when I was a PCBA manufacturing industry employee we used solder paste beyond shelf life with great results. The assembly was a quite simple class 2 application with big SMD components and no fine pitch ones. There was also a hot air application which sample of flat cables soldered by hot air were submitted to pull test force.

Not a single sample produced with this out of date solder paste was reproved. Also we had a failures lab internally in site and the FA lab guys, by doing cross section, did not find a single reason to reprove the assemblies. At the end, our final customer approved to receive all the batch assembled under this circumstances. For me the answer depends type of assembly to be soldered with solder paste.
Glayson Figueiredo, Philips Medical Systems, Brazil
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