photosensitized boards have a "use by" date ??? - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: December 28, 2010, 05:09:25 pm
content: I bought some presensitized double sided board from Farnell and it actually has a use by date on itWhat ? we are talking photographic chemical right ? it is supposed to last years. I have a 2' square sheet that I bought off RS a year ago and I'm still using lumps off it as and when required yes the farnell stuff has 3 month date on it.Ideas anyone ?

author: Zyvek
author_rank: Regular Contributor
timestamp: December 28, 2010, 06:23:10 pm
content: Quote from: Simon on December 28, 2010, 05:09:25 pmSimon, if they are anything like the darkroom chemicals I used to use, just keep them in an airtight container and you can usually exceed the use by date with any major problems. Throw a silica gel pack in to reduce moisture.Cheers.

author: Simon
author_rank: Unknown
timestamp: December 28, 2010, 06:45:07 pm
content: well having a protective plastic sheet over the board pretty much makes them airtight to my mind. it is the first time I hear of a use by date, to be honest I call "bull shit" on it

author: Zero999
author_rank: Super Contributor
timestamp: December 28, 2010, 06:50:35 pm
content: They're just being cautious.It makes sense that the photo-resist will degrade over time. I think the temperature and background radiation will be the most significant factors: I think ionising radiation will cause the photo-resist to become exposed and it's likely to be more sensitive at higher temperatures.I'd say the date is more for them than the consumer - I don't think you'd like it if they sold you some 10 year old board which gave poor results.

author: Zyvek
author_rank: Regular Contributor
timestamp: December 28, 2010, 06:52:47 pm
content: Quote from: Simon on December 28, 2010, 06:45:07 pmAgreed. Just a way to ensure more business! It's not like were talking about food! If it's the photo sensitivity, keeping them in dark storage will also help. As they age it might need a longer exposure, but unless you pull the plastic off and leave them direct in sunlight I'd imagine they are still usable.

author: Chasm
author_rank: Regular Contributor
timestamp: December 28, 2010, 08:04:58 pm
content: They will desensitize over time and thus fall out of spec. That is usually not to tragic for home use.Just store them cold and dry - and of course dark.

author: Simon
author_rank: Unknown
timestamp: December 28, 2010, 08:38:49 pm
content: well it should be used up in six months

author: Zero999
author_rank: Super Contributor
timestamp: December 28, 2010, 09:03:46 pm
content: Quote from: Zyvek on December 28, 2010, 06:52:47 pmI'm not sure if that's true.Don't forget it's an inconvenience for them not being able to store it for longer than 2 years: they have to sell it or throw it away before the use by date.

author: Simon
author_rank: Unknown
timestamp: December 28, 2010, 09:12:20 pm
content: although the date is on a label in the bag so easily printed and inserted as they sell it although it would be the board manufacturer doing not farnell so still rings odd

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 28, 2010, 11:22:54 pm
content: Don't worry about use-by dates - I have stuff over 10 years old that's still fine. .

author: Chasm
author_rank: Regular Contributor
timestamp: December 29, 2010, 01:18:09 am
content: But if someone sells you old stuff better get a deep discount.

author: ElektroQuark
author_rank: Unknown
timestamp: December 29, 2010, 08:03:31 am
content: I have recently used a presensitized board that was forgotten in a dryer FOR MORE THAN 20 YEARS. It worked like new.

author: Simon
author_rank: Unknown
timestamp: December 29, 2010, 11:56:41 am
content: 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)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 29, 2010, 12:34:59 pm
content: 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.