Dry film photoresist developing - Page 1
Forum section: electronics / beginners

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 07:55:11 am
content: Photoresist newbie hereSo I purchase some dry film photoresist its unbranded and the website I bought it from doesn't have any specific instructions of developing.However I found a instructable at this linkhttps://www.instructables.com/id/Dry-Film-Photopolymer-for-making-circuit-boards/So I went thu the usual steps of first printing a negative of my artwork on tracing paper with a laser printer. One sheet was not providing me high contrast So I printed on 2 tracing paper sheets and overlapped them.The I stuck the photoresist film on the copper side of the pcb and laminated it with a hot ironThen I kept my tracing paper over this with the printed side closest to the photoresist film.I exposed it in bright sunlight for 10min.The I tried developing it in 1% sodium carbonate solution. (5gm of soda ash in 500ml of distilled water) but after 3 min I washed the pcb in water and say than only a few small spots had exposed copper. I did developing for another 3min and just a little most copper got uncovered.I have attached the picture of the pcb.What did I do wrong here1. Did I overexpose the film, so its difficult to develop now.2. Is my developing solution too mild and do I need to do 3% concentration of sodium carbonate. Because I used distilled water at around 30 deg.

author: JackJones
author_rank: Regular Contributor
timestamp: March 31, 2019, 08:04:11 am
content: How did you place the tracing paper on it while developing? Because it really needs to be flat, I use a piece of glass and some clamps to keep it nice and firm on top of the pcb.I don't know how well developing it in sunlight works, but I'd wager it's not the optimal method and probably the source of your problems. You can buy a nail polish curer for about €10 and they work quite well. That's how I expose my photoresist.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 08:13:30 am
content: Quote from: JackJones on March 31, 2019, 08:04:11 amAfter appling the photoresist film and laminating it. I stuck the pcb on a piiece an wood and then stuck the tracing paper an top of this with tape taking care that it was streched tightly over the pcb.The I kept this whole contraption in the sun.I don't understand how you expose with nail poilsh curer? Does it have uv or fluorescent lights inside them?

author: JackJones
author_rank: Regular Contributor
timestamp: March 31, 2019, 08:20:16 am
content: Nail polish curers use UV lamps to harden the polish. Luckily that is also what cures photoresist so you can use them for exposing photoresist.It only takes about a minute to expose photoresist through a piece of glass. You can get very fine details too, I regularly do 0.5mm pitch stuff.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 08:23:06 am
content: Quote from: JackJones on March 31, 2019, 08:20:16 amOk I guess is a sure shot way to get it to work unfortunately I will have to wait for it because I don't have one handy at the momont.Would fluorescent bulbs work. I can buy a few as they are readily available.

author: JackJones
author_rank: Regular Contributor
timestamp: March 31, 2019, 08:28:42 am
content: I don't think regular fluorescent bulbs work, it should really be UV to develop properly.Looking at the picture you posted, leaving it in sunlight did have some sort of effect. It looks to me a bit overexposed, you could try leaving it outside for a little less time.

author: ogden
author_rank: Super Contributor
timestamp: March 31, 2019, 09:20:25 am
content: Quote from: JackJones on March 31, 2019, 08:28:42 amNail polish lamp works and what's even more important - gives consistent results.QuoteDefinitely overexposed. It is necessary to find correct exposure time, every UV resist beginner shall start with step wedge exposure test. Info from silksreen guys, but it's the same for PCB as well:https://medium.com/@spotprintsonline/step-wedge-test-a-high-quality-print-requires-a-good-stencils-cb1fbaa11998 I find this guide well-written:https://sparks.gogo.co.nz/dry-film-tips.pdf. Pay attention to PCB "before/after" pictures in page 13 that shows how unexposed areas shall look like after expo - they look the same (color) as before expo.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 09:39:29 am
content: Quote from: JackJones on March 31, 2019, 08:28:42 amSo this time I took a smaller part of the pcb and exposed in sunlight for lesser time to 2 to 3 min.Then I dipped it in sodium carbonate soln. for 5 min.Wash with water but still looks like the sodium carbonate is not developing the resist.

author: ogden
author_rank: Super Contributor
timestamp: March 31, 2019, 09:48:06 am
content: Quote from: ZeroResistance on March 31, 2019, 09:39:29 amUse pure "washing soda", not those fancy overpriced "oxy-blablabla". Also 1% seems like on the low end of concentration. Try to increase concentration to 3%, 15g/500mL. Development means gentle soothing of resist using soft painbrush or toothbrush. Resist shall dissolve in the developer. You wash not to remove resist but to rinse developer off PCB.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 09:51:20 am
content: Quote from: ogden on March 31, 2019, 09:48:06 amYes I used soda ash power 5g in 500ml of distilled water. And then gently agitated it in the solution for 5min.I will increase concentration as you say and try again.After washing I should see exposed areas of copper correct ? I don't see any.

author: ogden
author_rank: Super Contributor
timestamp: March 31, 2019, 09:57:03 am
content: Quote from: ZeroResistance on March 31, 2019, 09:51:20 am*During* development unexposed areas (light blue) shall dissolve in developer. When done, you see either copper or exposed (dark) resist. You wash using water only when you see that you are done with development and unexposed resist is removed completely.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 10:00:35 am
content: Quote from: ogden on March 31, 2019, 09:57:03 amOk, currently the unexposed resist is not getting removed. I will try with 3% concentration of sodium carbonate.

author: ogden
author_rank: Super Contributor
timestamp: March 31, 2019, 10:06:05 am
content: Quote from: ZeroResistance on March 31, 2019, 10:00:35 amAlso make sure solution is not cold, bring it into 30..40 oC range.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 10:34:57 am
content: Quote from: ogden on March 31, 2019, 10:06:05 am3% concentraton of sodium carbonate slight difference. Its not dissolving the unexposed photoresist.Looks like its still an issue of overexposure @ 2 to 3 min of sunlight.Next I will try 30 sec of sunlight.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: March 31, 2019, 11:02:41 am
content: Quote from: ogden on March 31, 2019, 09:20:25 amThis is some pretty amazing info. Many Thanks!I guess I'll try to calibrate the dry film with a bunch of fluorescent bulbs to get more control over the exposure.

author: beanflying
author_rank: Super Contributor
timestamp: March 31, 2019, 11:36:05 am
content: Have a good scan through some of Big Clives Videos from this search toohttps://www.youtube.com/user/bigclivedotcom/search?query=pcblots to be learned with a few different exposure devices including the nail curing lamps.

author: Jwillis
author_rank: Super Contributor
timestamp: March 31, 2019, 11:09:24 pm
content: Its over exposed.Higher intensity UV at shorter periods works best.5 minutes in the box I madehttps://www.eevblog.com/forum/projects/diy-dry-film-uv-exposure-box/msg2036233/#msg2036233Even considering trying shorter exposure time. Theirs also a period of holding time between laminating ,between exposing and between developing. Approximately 30 min between each stage.Each holding to be done with board covered from light and at room temperature.This PDF explains it well and when followed the process works much better.https://ir.nctu.edu.tw/bitstream/11536/74691/7/851507.pdfThey mention DI water which is de ionized water but not really necessary.Just good clean low mineral water is fine.I have high sodium tap water but the difference is minimal to bottled distilled.Hope this helps

author: jmelson
author_rank: Super Contributor
timestamp: April 01, 2019, 12:33:06 am
content: Quote from: ZeroResistance on March 31, 2019, 07:55:11 amThe stuff I use is exposed by a bank of fluorescent black light bulbs (405 nm) for one minute. I use high-contrast silver film, but still have problems if the exposure is much longer than 1 minute.My developer is 35 g per US gallon, so your solution sounds about right.Jon

author: jmelson
author_rank: Super Contributor
timestamp: April 01, 2019, 12:39:01 am
content: OK my method is to heat the developer solution to about 35 - 40 C, and then drop the board in. I wipe the board continuously with my fingertips which removes the softened layer, allowing the devloper to attack the layer underneath. I generally have full development in under 2 minutes. If your skin is sensitive to the devloper, then you can try using the softest brushes. After development is complete, wash the board for at least a minute in flowing water, and again wipe the entire surface very gently to remove any remaining resist "slime" so it doesn't dry back onto the copper.Jon

author: beanflying
author_rank: Super Contributor
timestamp: April 01, 2019, 01:04:35 am
content: This Just in. Talking about issues with applying the film. From about 4.30 for the PCB part.https://youtu.be/ZE5JASv3XyY

author: sleemanj
author_rank: Super Contributor
timestamp: April 01, 2019, 03:38:46 am
content: Still overexposed in your second attempt.Don't overestimate how exposed you need it, you really only need it "just visible" when you develop it. You probably only need like 40 seconds, perhaps a minute going by your images (of course sunlight exposure is rather imprecise, but there's plenty of margin).See page 13 of my tipshttps://sparks.gogo.co.nz/dry-film-tips.pdfLook how the exposed areas are only a little darker.In short, expose just-long-enough to develop cleanly, it will be a bit soft and fragile but hard enough to withstand light rubbing or vibration from an electric toothbrush (gently, not scrubbing!), after developing put it in the sun for a few minutes and the resist will get much darker and harder to withstand the etching and handling better.

author: Jwillis
author_rank: Super Contributor
timestamp: April 01, 2019, 05:54:23 am
content: One thing I forgot to mention is the laminating temperature.Don't get to high or that can caused premature polymerization of the film.This can cause difficulty at the development stage.This happened to me when I got started and had similar problems.I had also received film that looked darker than normal and didn't work very well. Wonder if X-rays may have been the problem passing customs.Noway of really knowing.

author: rcbuck
author_rank: Frequent Contributor
timestamp: April 01, 2019, 06:41:34 am
content: When you laminate the dry film to the copper clad board are you working in a yellow light environment? That is recommended, or at least a very dimly lit room. Taping the tracing paper to the board material will not create a close enough contact with the dry film. You need to use a piece of glass as JackJones suggested to hold the tracing paper against the board.Also, tracing paper is not the best material to use for your negative. Clear mylar laser jet film is best. I mirror the image when I print mine so I can press the printed side of the mylar against the board. This ensures the tightest fit.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: April 02, 2019, 05:43:39 am
content: Quote from: rcbuck on April 01, 2019, 06:41:34 amWhile working on the film I tried to keep light at a minimum. But not yellow light.By yellow light would you mean a low wattage incandescent bulb?I had to go for tracing paper because the transparencies that I had were not laser compatible and there were lot of holes in it. So I printed on tracing paper because the toner tends to bind better on these.

author: beanflying
author_rank: Super Contributor
timestamp: April 02, 2019, 05:49:46 am
content: Quote from: ZeroResistance on April 02, 2019, 05:43:39 amIt is getting fairly difficult to get hold of Photographic Incandescent bulbs so I roilled my own LED one.https://www.eevblog.com/forum/projects/homemade-pcb-exposure-units/msg1477465/#msg1477465Also that thread is my Scanner hack for an Exposure unit. Works well and reminded I should go add a few more posts to it sometime

author: Jwillis
author_rank: Super Contributor
timestamp: April 02, 2019, 06:12:59 am
content: I just have warm led lamps lighting were I work and the stuff won't expose in a week.I left some out to see what happens .You don't need to go to great expense on special lighting.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: April 02, 2019, 06:41:37 am
content: Quote from: beanflying on April 02, 2019, 05:49:46 amBTW I was referring to lighting to work with the dry film photoresist, I meant which light is best to work on the photoresist without exposing it.

author: beanflying
author_rank: Super Contributor
timestamp: April 02, 2019, 06:45:53 am
content: Quote from: ZeroResistance on April 02, 2019, 06:41:37 amI use that light I linked to to work with un developed film generally. Short bursts of mixed spectrum LED lights are generally OK but less is better. Best practice is reduce light that has an effect on the media bearing in mind that the PCB film is more tolerant than Photographic Paper.