Work lights for photo resist PCB fab - Page 1
Forum section: electronics / projects

author: JimmyM
author_rank: Regular Contributor
timestamp: March 11, 2014, 12:08:21 pm
content: I tried just working in very dim light but found it difficult to properly register the artwork to the PCB. I have one of those RGB remote control flood lights from eBay. If you search for this "LED Underwater Light 10W 12V IP65" it's one of the top items. Small, round, some have convex lenses, others don't. I used the red setting and things were way easier. So I'm putting together some proper red work lights. Using lights similar to the ones above.I bought 2 flat lens flood lights and 2 convex lens spot lights. The floods are just a verry broad beam. The spots throw a 2-3' (.6-1m) spot onto my bench when mounted at the ceiling. Of course the LEDs are white. Those have to go. However, the white lights like these...http://www.ebay.com/itm/LED-IP65-Underwater-Spot-Light-10W-12V-800-900LM-Pure-White-Light-Black-/310531930569?pt=LH_DefaultDomain_0&hash=item484d2539c9are AC/DC input and have a current regulator built in. I've bought these before and have torn them down and done measurements. It typically runs the LED at 700mA. So I also bought some red 10W LEDs to swap.Round ones to replace the the LEDs in the flood lights...http://www.ebay.com/itm/10W-High-Power-LED-Deep-Red-660nm-For-Plant-Grow-Light-/121056357998?pt=LH_DefaultDomain_0&hash=item1c2f856e6eand square ones for the convex lens lights...http://www.ebay.com/itm/10W-Watt-RED-HIGH-POWER-LED-Plant-Grow-Growth-Light-lamp-655-660nm-500LM-6V-DIY-/270856487031?pt=LH_DefaultDomain_0&hash=item3f104e0077I should be able to drive them with 12V. The White ones I can drive with my Ryobi 18V flashlight. No problems at all.I'll let you know how it goes.

author: philpem
author_rank: Frequent Contributor
timestamp: March 11, 2014, 01:03:26 pm
content: Interesting!I've been using low-pressure sodium (SOX) lights -- specifically, streetlights. They emit enough light to see what you're doing, but they're completely monochromatic (~589nm yellow). The great thing is, the eye is quite sensitive to that wavelength (not as much as green, but much better than red) and the PCB resists are completely insensitive to it.And they're cheap, especially if you know a streetlight collector who's downsizing their collection :-D

author: sleemanj
author_rank: Super Contributor
timestamp: March 11, 2014, 01:06:38 pm
content: Quote from: JimmyM on March 11, 2014, 12:08:21 pmWhat sort of resist are you using, positive, negative, pre-sensitized, dry film.... have you actually tried working under normal lighting?I use dry film (negative acting) and have no trouble working under normal household lighting conditions, naturally close the curtains in daytime.

author: Circuitous
author_rank: Unknown
timestamp: March 11, 2014, 01:12:03 pm
content: I use normal incandescent lighting without any problems on my UV pre-sensitized boards from MG Chemical. But, I make sure to turn off the fluorescent lights, monitors, and cover the windows.

author: JimmyM
author_rank: Regular Contributor
timestamp: March 12, 2014, 01:47:14 am
content: I use positive pre-sensitized boards from MG Chemicals. I only have fluorecents in the basement, so I worked in near darkness. After the exposure the board was way overexposed. I walked them up to the kitchen in daylight and developed them in the sink. Trying to shade them. It was a mess. So I read about "safe lights", etc. Then settled on red LEDs. Ordered the parts. I was thinking of Yellow, but, what the hell. I can always buy yellow LEDs if I need to. Then figured out that my boards that were exposed from 1-3 minutes only needed 15 seconds.I don't think brightness will an issue with 40 Watts of LEDs. Didn't even think of sodium vapor.

author: Circuitous
author_rank: Unknown
timestamp: March 12, 2014, 01:54:55 am
content: Hmm... I think the 40 watts of LED illumination might be the problem.I am using the same MG boards with a Kinsten UV box, it took me a few tries to get the time down. I run about a 230 second exposure with the circuit printed on Vellum paper (Helix brand from OfficeMax... it's probably crap). The process is reliable and repeatable. If you print on transparencies, then it would probably be a lot faster exposure.I don't think you need to go out of your way for sodium vapor lamps, just get an incandescent lamp or two... maybe just a couple of clamp-on lamps. I use two 75 watt bulbs to light my work area, and I have no problems.

author: JimmyM
author_rank: Regular Contributor
timestamp: March 12, 2014, 02:24:45 am
content: Good to know. But the stuff is on its way. So at least I'll have some fun swapping emitters. Wow 230 seconds. What kind of light source?The 40W of LEDs are for the work lights. The UV LEDs are about 12W.

author: Circuitous
author_rank: Unknown
timestamp: March 12, 2014, 02:36:40 am
content: It's a Kinsten unit, made in Australia, available in the U.S. at:http://www.circuitspecialists.com/kvb-30d.htmlI like it, not cheap, but I got tired of messing around.A big part of the exposure time is probably the vellum paper that I am using... if I switched to transparencies or a thinner tracing paper then I would probably have to re-calibrate the timing.Good luck getting the timing right... it's just trial and error. I'm sure the LEDs will work fine, but for repeatability, I'd cut the power and go for longer times for exposure and developing.BTW, I'm not an expert, just an extreme enthusiast!

author: Harvs
author_rank: Super Contributor
timestamp: March 12, 2014, 02:55:11 am
content: Quote from: Circuitous on March 12, 2014, 02:36:40 amThey have once been, but certainly now made in Taiwan. Mine arrived two days ago

author: philpem
author_rank: Frequent Contributor
timestamp: March 12, 2014, 08:09:49 am
content: Quote from: Circuitous on March 12, 2014, 01:54:55 amTrue, they are a bit special. I only have mine because -- like I said -- a friend was downsizing their streetlight collection.Thorn Lighting "Beta" (I think mine is a Beta 5) series units are (from what I've been told) sold quite cheaply if you want to go down that route. One of those lights my fairly large garage quite well.

author: JimmyM
author_rank: Regular Contributor
timestamp: March 12, 2014, 08:10:42 pm
content: Quote from: Circuitous on March 12, 2014, 02:36:40 amI'm sure the vellum is attenuating the UV. I may turn down the UV power so exposure time is 30-45 seconds. With a single layer of transparency I might be looking at 5-10 seconds with the full ~12W power. I'll be doing more testing with the test grid I'll be making.I'll be doing strips (~1 x 4") of PCB, 1/2 will be single layer transparency, 1/2 will be double layer. Then I'll dial the power back and run tests at 15, 30, & 45 seconds. Ideally I'd like to get to a single layer at ~30-45 seconds. Perhaps I'll build a new UV panel using 5mm LEDs in a tight grid for evenness since I know how much power is enough.

author: JimmyM
author_rank: Regular Contributor
timestamp: March 12, 2014, 08:31:02 pm
content: If I can reliably get 10mils without undercutting I'll call it good.However, if 10 mils is not doable I might try using a 10W/30W UV LED and a collimating lens.Of course the light would have to mounted above the PCB in a hood of some sort. They make 10W & 30W UV LEDs with reflectors that accommodate an aspherical lens. I've read that glass attenuates UV energy to some degree. We'll see. Could be another project. I do love a good project.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 12, 2014, 11:02:10 pm
content: Photoresist PCB has minimal sensitivity to normal light - just avoid sunlight and minimise any unncecessary exposure.If in doubt about your lighting, try a small test piece. I've never taken any precautions other than avoiding direct sunlight & never had a problem

author: Circuitous
author_rank: Unknown
timestamp: March 13, 2014, 12:26:22 am
content: Mike, Do you use transparencies or vellum/tracing paper? If so, what brand or weight seems to work the best?

author: mamalala
author_rank: Unknown
timestamp: March 13, 2014, 12:34:43 am
content: Use yellow light, that will solve your problems. Take a yellow bucket, for example, place a CFL in it, close the lid, and be done with it. The light that comes out is yellos and won't hurt your photosensitive boards, while at the same time you can work in yellow light rather well.Greetings,Chris

author: JimmyM
author_rank: Regular Contributor
timestamp: March 16, 2014, 04:55:07 am
content: I get that i have over estimated the pcb sensitivity. However, I have already ordered and received the LED lights and am awaiting the replacement red emitters. If I find that the red light is difficult to work with, I'll switch to yellow.Most of that over-estimation came from using an unexpectedly powerful UV exposer. But as long as I get consistently sharp results, I'll be happy. But since I have already ordered, paid for, received the LED "solution", I'm not going to spend more money on a CFL and yellow bucket or anything else until i test what I've already paid for.But if others are looking for a solution, they can try the ones suggested here.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 16, 2014, 09:48:22 am
content: Quote from: Circuitous on March 13, 2014, 12:26:22 amTracing paper, 90gsm or heavier - thinner stuff crinkles in the fuser.Cheap, and much better blackness and toner retention than shiny transparency film.