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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