Electronics > Beginners

photosensitized boards have a "use by" date ???

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But if someone sells you old stuff better get a deep discount. ;)

I have recently used a presensitized board that was forgotten in a dryer FOR MORE THAN 20 YEARS. It worked like new.

from what I know we are talking photographic chemicals, these last years if kept cool, I've never heardof film or photographic paper having a use by date, well paper maybe but still it's years (dark room paper I mean not inkjet)

The difference with photographic paper and film is it is expected to produce very predictable and consistent greyscales and colour balance - decades old film will still work but will look different to brand new stock.
PCB coatings are essentially a binary process, and any variation in processing time due to age etc. isn't a problem as the develop process is closed-loop, i.e. you pull it out when it's done. 
The worst I've ever seen is on one particular piece of cheap material that was maybe 20yrs old, where the cover film adhesive had dried out so it took patches of the resist off with it. 


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