Photoresist exposure via sun rather than UV box - Page 1
Forum section: electronics / projects

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 10:06:53 am
content: I haven't got a UV box at the moment and want to knock out a PCB quickly for something today (before I have to go back to normal slavery tomorrow). I do have some photoresist board in the junk box and it's pretty sunny here.Simple question: yes or no and how long should I consider throwing it outside for?

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 10:24:22 am
content: By all means give it a go but there's no way to know the exposure time, unless you have a UV meter.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 10:31:15 am
content: I'll take a guess and give it a couple of hours of direct sun and see what happens

author: kurt
author_rank: Contributor
timestamp: April 20, 2015, 10:43:27 am
content: Do a regular calibration run. When I calibrate my UV box I setup a small PCB with a regular artwork mask and then mask off most of it with tinfoil.I then move the tinfoil back ~5mm every 15 second of exposure. You can of course use larger intervals if you expect the exposure time to be much larger than the ~2min. I have ended up at.After the whole PCB has been exposed, you develop it and calculate the time based on were you get the best result.

author: madires
author_rank: Super Contributor
timestamp: April 20, 2015, 10:52:17 am
content: The sun has no constant UV power mode and that will ruin any reliable exposure process.

author: sleemanj
author_rank: Super Contributor
timestamp: April 20, 2015, 10:57:23 am
content: Quote from: smjcuk on April 20, 2015, 10:31:15 amWhen I do a sunlight exposure, it's never more than 10 minutes, and that's with dry film and exposing pretty heavily. ABout 2m to 5m is workable.But of course, it varies.But whatever the case, a couple of hours will be WAY too much unless you're like in Antarctica or something I imagine.

author: wraper
author_rank: Unknown
timestamp: April 20, 2015, 11:04:08 am
content: You will need transparencies of very good contrast. Otherwise dark areas will be overexposed or transparent areas underexposed as you have no way to calibrate the Sun. Therefore will need to expose for longer time under Sun to be sure.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 11:06:48 am
content: that's what I thought. Fingers crossed. Might turn out to be a turd yet and I'll ship it off to OSHpark and wait patiently

author: SaabFAN
author_rank: Frequent Contributor
timestamp: April 20, 2015, 11:23:56 am
content: Did you check with other PCB-Factories? I've found out that there are cheaper and faster manufacturers than OSHPark, which produce basically the same quality, except for the ENIG-Finish. But HASL is enough for me.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 12:05:02 pm
content: But they're not purple and gold!

author: Refrigerator
author_rank: Super Contributor
timestamp: April 20, 2015, 12:24:02 pm
content: UV exposure box shouldn't be too hard to make considering how cheap UV LEDs are on ebay.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 12:39:16 pm
content: That's the next project but I'm on holiday today so wanted a PCB done today as I'm impatientThe other option for UV LEDs is to go down the road to my RS trade counter, bend over and take the shaftingAnyway, the answer to this is: no it doesn't work very well. It appears that after hitting it with the developer it has big holes in the traces. Straight to the bin!

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 20, 2015, 01:00:43 pm
content: Quote from: smjcuk on April 20, 2015, 12:39:16 pmUsing ordinary paper works better in this case, that increases the exposure time and gives you a broader error margin.I even use normal paper with my UV tubes, way, way cheaper and works just as good. Works even better if you brush a bit of acetone on the paper from the backside, that makes the toner clump together and will produce better contrast.

author: sleemanj
author_rank: Super Contributor
timestamp: April 20, 2015, 01:15:50 pm
content: Quote from: smjcuk on April 20, 2015, 12:39:16 pmDon't throw away good copper clad if it's not been etched badly, just clean itnoff and put it in your scraps drawer for future use with toner transfer, dry film, resist pen, manhatten construction, and any of the other methods for pcb making!

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 01:22:59 pm
content: It's only a 2" by 1" bit. Hardly worth it.PeterF: good idea with the paper. Works as a diffuser as well

author: Fred27
author_rank: Unknown
timestamp: April 20, 2015, 01:38:45 pm
content: Why would you want a diffuser? Sunlight may be of an unpredictable strength, but the excellent collimation is one thing it does have going for it.

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 01:47:08 pm
content: Have you tried toner transfer?Insect killer tubes are a good source of UV for the photographic process and are cheap too.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 01:53:38 pm
content: Quote from: Hero999 on April 20, 2015, 01:47:08 pmI don't have a laser printer unfortunately otherwise that would have been first call.

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 02:06:11 pm
content: Quote from: smjcuk on April 20, 2015, 01:53:38 pmCan't you go to a library and photocopy it?

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 02:37:23 pm
content: My local library now has a Starbucks logo on it unfortunately.No copiers for about 10 miles each direction. I went looking for one ages ago and ended up buying a cheap all in one inkjet thing that does copying.

author: zapta
author_rank: Super Contributor
timestamp: April 20, 2015, 02:41:46 pm
content: Quote from: smjcuk on April 20, 2015, 10:06:53 amThis is how I used to do my boards. Never used an UV lamp. It was sometime ago, don't remember the exposure time but IIRC it was not in the hours.

author: Refrigerator
author_rank: Super Contributor
timestamp: April 20, 2015, 03:52:55 pm
content: My brother did some UV boards with just a desk lamp.

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 20, 2015, 04:47:38 pm
content: Quote from: Refrigerator on April 20, 2015, 03:52:55 pmSunshine, incendecent lamps, tanning lights, grow lamps... they all work.You just have to do a exposure test board first, depending on the source in 15 second to 2 minute intervals and everything is good.Much better process control then toner transfer, way simpler, pain free and quicker.If you want to use toner transfer, go ahead, but it is not the best solution.Photo resist is much, much better and i can not understand how someone wants to stick to toner transfer.And PLASE do not try to tell my why, i do NOT CARE why someone would want to use toner transfer.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 20, 2015, 04:59:20 pm
content: Starting to think my developer was knackered. Its about 15 years old

author: Canobi
author_rank: Regular Contributor
timestamp: April 20, 2015, 09:27:21 pm
content: Just made this for £45 and it works a treat, even has a 2 min timer thanks to the £10 nail gel curing unit.I use 200gsm tracing paper for etch exposures, and heat stable clear film for solder resist (only cuz it's easier to line things up).

author: alanb
author_rank: Frequent Contributor
timestamp: April 21, 2015, 01:01:49 pm
content: Before purchasing a second hand UV exposure box I used a normal 11W CFL bulb at a distance of about 10 cm. I used laser printed tracing paper with some glass from a photo frame to hold the paper in contact with the PCB. The exposure time was around 20 Minutes.