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Expiration date of PWB

Vincent_F

#18751

Expiration date of PWB | 30 January, 2002

Hello everybody,

I would like to use PCB which have expired. I have already planned to bake them in order to avoid pop corn effect but I wonder about some few items : 1) How can I identify the optimal baking parameters ? 2) Even after baking, is there any risks in term of reliability of the PWB ? Thank you. Best regards.

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#18766

Expiration date of PWB | 30 January, 2002

PCB never expire, they just become more difficult to solder. [Many shops impose �shelf life� periods for their boards, but they aren�t going to discard the boards if the exceed the limits, unlike they would with some other process materials.]

IDENTIFYING THE OPTIMAL BAKING PARAMETERS. The optimal baking parameters are dependant on: * Type of materials from which the board is fabricated. <= FR-4 is baked differently / has different baking requirements than flex. * Amount of moisture that your boards have absorbed. * Loss of solderability on the pads. * Thickness of PTH / via plating [and maybe other board construction issues].

In determining these parameters, try this: * Weigh your boards. * Search the fine SMTnet Archives for guidelines and opinions on baking boards. * Bake the boards for maybe half the expected time. * Weigh your boards, partially toasted. * Solder the [unloaded] board. * Assess the solder connections on the board. * Plot data. * Repeat until bored.

RELIABILITY ISSUES. If you don�t get �crazy�, there are no reliability issues with baking. A wild a crazy board baker would do things like: * Running the oven too hot. * Ramping the temperature to quickly. * Allowing BIG temperature swings.

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Gregers

#18780

Expiration date of PWB | 1 February, 2002

PWB shelf life: HASL---3mth ENTEK-- 2mth

Before using expired PWB, it is suggested to go thru HASL or ENTEK angain. Ask your VDR to serve this.

Re immersion Au, mostly when the thickness under 3u"(micro pores present), the surface gold will serve as cathode to oxide underlying Ni. This is often beyond help. FYI.

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