I have a little experience in this area.  
 We have an onsite warehouse that has our ready spares stored within.    We are located on a bluff 85' above the Pacific Ocean.   We have boards stored in the warehouse over 20 years old and some in their 30's and even 40's.     Moisture is an issue, as is the salt air corrosion, one of the storage areas is an "E" room controlled at 68 deg. F and at a 40%RH (sort of)  the air is unfiltered.     The room has 2 large rollup doors to facilitate material handling.        This is for the boards or modules that are graded  "Quality" or "Important to Safety", for all other spares they are stored in an open bay 100000 sq.ft. warehouse.      When we 100% inspect boards prior to use we find, degraded solder, corrosion on traces, rusty component leads.... the list goes on, when repairs are attempted we usually end up with measling around the soldered area.   One of the ways we have minimized damage is baking the boards in a desiccant oven or heating them with a hot air gun at low temperature to bake out the moisture entrained.    Most of these OLD boards are of 68-80 vintage, single sided, fiberglass boards.     Storage may be is in bins or shelves in open ended anti-stat bags, (if they have been looked at in recent times), just in bubble wrap, plastic bags, paper wrap, sometimes in ziploc style anti-stat bags, and sometimes on open shelves in cardboard boxes, depending on when it was last accessed and who did it.    We are not allowed to store them in bags with desiccant bags because the storage facility doesn't have neither  the manpower to deal with maintaining the desiccant nor the "environmental hazards" associated with it,  (My box of soap to stand on).     

We inspect every piece of equipment to 100% prior to installation and under magnification just to be sure, most items are burned-in for 72 hours prior to installation.    

When they get NEW boards/components, they are OPENED by QA to receipt inspect them and remove any foreign material, useful manuals, special tooling, desiccant.... and are put on the shelf without resealing (in most cases) the original packing, if it is retained at all, and no manuals, special tooling, etc., (sorry my box again).     

I think I may site some mentioned IPC standards to our overseers, although it only took 20 years for them to start putting ALL electronic components in anti-stat bags or foam before delivery.
They did store lithium backup batteries in conductive foam though, they looked like chips and they wanted to get them off of the wax-coated cardboard they came in, but that's another story.    

Pat Goodyear
Control Technician 
Pacific Gas and Electric
Diablo Canyon Nuclear Power Plant



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Tuesday, August 14, 2012 5:56 AM
To: [log in to unmask]
Subject: Re: [TN] PCBA shelf life

HI

In storage the bare boards will suffer from ingress of moisture and loss of solderability, the longer you keep them the more they are affected. Baking the boards to dry them can/will degrade solderability. 

Properly packed and stored unopened in original packaging per IPC recommendations, industry wisdom would be something like: expect to see up to a year for most finishes. Exceptions are immersion tin and some OSP which will only go 6 months Probably the longest lasting finish would be Sn/Pb HASL.
NO doubt others will have opinions and probably someone will have stored PCBS for some outrageously long period OK :) What you actually get is an it depends - not just on the quality and type of finish, but on the criticality of your own designs and processes as well as how stored.
IOW, in a perfect world you would work out what you can or can't do. In this world... this topic is a perennial favorite and you will find many references in the TechNet archive. 
Anyway first look at IPC standards, there is one for just about everything you can think of. 1601 for board storage and J-003 for board solderability testing would be good places to start. These will help you Either determine what you should be doing; or confirm that what you are doing is correct.



Regards


Mike Fenner

Bonding Services & Products
M: +44 [0] 7810 526 317
T: +44 [0] 1865 522 663
E: [log in to unmask]

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ivan Feng
Sent: Tuesday, August 14, 2012 2:22 AM
To: [log in to unmask]
Subject: [TN] PCBA shelf life

Folks,

Bare PCB has a shelf life depending on its surface finish, component like electrolytic capacitor and MSD devices also have defined shelf life.
But for PCBA, how to define its shelf life? Is there any applicable standards?

Any suggestions are welcomed.

Regards
Ivan

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