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Shelf life of PCBs

O'Connor

#23872

Shelf life of PCBs | 21 March, 2003

Hi, Is there a standard that covers the shelf life of PCB's? I need to know, how long after manufacture a PCB can be stored in an uncontrolled envoirnment exposed to the atmosphere before being built on, currently we say 1 year, but nobody really knows where this came from, the PCB Fab dumps any boards over 6 months old, with the downturn we have PCBs as old as 3 years so I don't know if there is a problem using them, we do build on them if they pass a solderability test however I'm not sure if they will exhibit any problem in the field after being around for such a long time befor deing built on. Any Advice appreciated.

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#23874

Shelf life of PCBs | 21 March, 2003

There is no standard.

If your boards solder well, they're good. Well soldered boards that have been stored a long time will have field life similar to well soldered boards that have not been stored a long time.

The solderability of boards depends on: * Fabrication methods and controls * Board design, materials, and selection * Storage methods and control * Soldering methods, materials, and controls

Given that proper inventory and building environment control would be preferred, consider baking these boards and packing them in sealed barrier bags.

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MA/NY DDave

#23889

Shelf life of PCBs | 23 March, 2003

Hi

I have no idea where your company exists yet for some places with certain finishes 1 year or even 6 months would be too long to meet certain products' long or high reliability goals and may make assembly more difficult or costly.

When you solder make sure that you really inspect the boards well, at least for some scattered samples to be sure they pass all their specifications and are yielding comparable familiar results. Maybe you might want to take some cross sections at high magnification. I say this only because you note that you have this historical 1 year requirement that may have been from a good engineer or maybe just a bad experience. I do know about limits and these usually are based on experience of too much rework and component loss.

1>Know the specs your assembly is supposed to meet 2>Runs some lot soldering samples to minimize cost if you do decide to scrap or bake or ?? 3>Do at least a little post soldering analysis to assure yourself that the results are similar to experience or acceptable to the specifications. 3>Know your customer 4>Some accelerate stress testing might be needed to give a full thumbs up, yet that is hard for me to judge.

YiEng, MA/NY DDave

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MA/NY DDave

#23891

Shelf life of PCBs | 23 March, 2003

Hi,

From re reading, I think I did OK with my previous message yet I wanted to hit some other items, maybe differently.

Without checking all the sources I don't believe there are any industry wide standards. I am sure and know there are industry wide reports that look at things from different perspectives. In my experience with some rather huge companies, storage standards existed and were based on their specifications and experience. 6 months and 1 year were common yet sometimes the 1 year had to do with Financial Inventory Write-Offs(sorry an aside)

As I hope I wrote, this is variable based on "your uncontrolled environment", the PCB surface finish, your soldering process, the product's specifications, and the reliability you need or want to achieve.

You should check on why your PCB Fab dumps at 6 months. If they are dumping at 6 months I BETCHA they have a good reason. Yet you might be a customer for which 6 months is too agressive.

If the soldering at a micro joint level, and the PCB's post soldering condition is equivalent to what it should be or is usually, than there isn't any affect.

One final winding set of thought questions If you had wanted to store PCB's for 3 years what surface finish should you have chosen? Bare Copper, OSP?? By-the-Way Back so Long Ago it is (well you know), this was one of the ways we decided what surface finish to use as the best Cost Trade Off. If you had wanted to store PCB's for 3 years what storage conditions should you have chosen? -Would you move the parts several times and scrape the soldering surfaces, Would you have back up generators. Forget the desicants and the bags unless your really really know what you are doing.

YiEng, MA/NY DDave

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O' Connor

#23908

Shelf life of PCBs | 25 March, 2003

Thank you for your feedback, I've also looked at the archives on this issue & found useful information there as well.

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MA/NY DDave

#23916

Shelf life of PCBs | 25 March, 2003

Hi O'Conner,

You are more than welcome.

If you found anything really great in the Archives Please give the info so that I can also read and continuously learn.

YiEng, MA/NY DDave

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PCB contract manufacturer