No luck with dry film photoresist - Page 1
Forum section: electronics / general

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 25, 2018, 10:16:29 am
content: I've been making PCBs using the toner transfer method, which involved a lot of work before getting a decent PCB. I've been told that I should try the dry film photoresist method. So I got everything I needed and tried it out.The problem it that the whole thing just peels off when I dip it in the developer. Nothing really remains on the PCB after that.I'm guessing that the film simply does not adhere properly to the copper, but raising the temperature simply melts it.I've tried pressing it using a laminator (118 degrees), iron, hot air. Before exopsing, the film seems to have been stuck well to the board, but after... well see the picture.The developer is made from sodium hydroxide, water glass and distilled water.

author: wraper
author_rank: Unknown
timestamp: August 25, 2018, 10:29:43 am
content: Quote from: bogdan2014 on August 25, 2018, 10:16:29 amsodium hydroxide is used for stripping negative photoresist after etching, not developing. You need sodium carbonate.

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 25, 2018, 10:41:12 am
content: Thanks to Robin Moorshead for the following procedure to make silicate developer solution:Take 200cc of "water glass", add 800cc of distilled water and stir. To this add 400g of sodium hydroxide (caustic soda).Source:www.electricstuff.co.uk/pcbs.html

author: BradC
author_rank: Super Contributor
timestamp: August 25, 2018, 10:45:13 am
content: Quote from: bogdan2014 on August 25, 2018, 10:41:12 amYou must have missed the first paragraph under Developing : "The main thing to say here is DO NOT USE SODIUM HYDROXIDE for developing photoresist laminates. Use of Sodium hydroxide is the primary reason people complain about poor results when trying to photo-etch PCBs.It is completely and utterly dreadful stuff for developing PCBs - apart from it's causticity, it's very sensitive to both temperature and concentration, and made-up solution doesn't last long. Too weak and it doesn't develop at all, too strong and it strips all the resist off. It's almost impossible to get reliable and consistent results, especially so if making PCBs in an environment with large temperature variations (garage, shed etc), as is often the case for such messy activities as PCB making. "

author: wraper
author_rank: Unknown
timestamp: August 25, 2018, 10:45:47 am
content: Quote from: bogdan2014 on August 25, 2018, 10:41:12 amAnd on what basis did you assume it's fornegativedry film photoresist? Sodium hydroxide can be used forpositive photeresist onlyand even then it sucks a big time and silicate developer should be used if you care about consistency of the results.

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 25, 2018, 10:49:55 am
content: Well I thought he meant not using sodium hydroxide ALONE, but mixed with the other two.I tried looking for sodium carbonate, but could not find anything here.

author: wraper
author_rank: Unknown
timestamp: August 25, 2018, 10:57:25 am
content: Sodium carbonate or potassium carbonate (works as well) is a very cheap stuff. You can buy it on ebay if cannot find locally. It's also called "washing soda" or "soda ash". You can also make your own. Take baking soda and heat it, done.

author: sleemanj
author_rank: Super Contributor
timestamp: August 25, 2018, 11:14:01 am
content: I am willing to wager that sodium carbonate is available in every simple supermarket in the entire developed world, probably the undeveloped world too.Look in your laundry aisle, in fact, look in your laundry you may well already have some.Sodium carbonate is also called Washing Soda, you can also use Sodium Percarbonate, also known as Sodium Peroxyhydrate, which is the primary ingredient in "whitening" laundry powders.I currently use "Sard Wonder OxyPlus".With that said, your problem looks to be adhesion more than developer strength.I always sand the PCB, if I don't, I get adhesion issues, I use a fine grade sandpaper, 400 or higher.Also, read my tips:http://sparks.gogo.co.nz/dry-film-tips.pdfAnd bigclive has done a number of videos also now.I use a clothes iron.

author: wraper
author_rank: Unknown
timestamp: August 25, 2018, 11:18:39 am
content: Quote from: sleemanj on August 25, 2018, 11:14:01 amNah, it's sodium hydroxide. It makes negative photoresist to come off without dissolving it. Therefore it's good as a stripper.

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 25, 2018, 11:24:33 am
content: I did find some washing salts but they don't say it's sodium carbonate on the labels. I guess I'll just try something.Sent from my Mi A1 using Tapatalk

author: bsfeechannel
author_rank: Super Contributor
timestamp: August 25, 2018, 12:03:37 pm
content: In Romania, Na2CO3is variously known as soda, soda de rufe, soda calcinata or carbonat de sodiu.Try these links:https://www.okazii.ro/soda-de-rufe-soda-calcinata-1kg-a173369415http://promoplus.ro/product/soda-calcinata/https://ro.wikipedia.org/wiki/Carbonat_de_sodiuThere are others, of course. But you surely know your country better than I.

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 25, 2018, 12:11:07 pm
content: Quote from: bsfeechannel on August 25, 2018, 12:03:37 pmThanks! It was hidden under those names.Sent from my Mi A1 using Tapatalk

author: bsfeechannel
author_rank: Super Contributor
timestamp: August 25, 2018, 12:39:15 pm
content: Quote from: bogdan2014 on August 25, 2018, 12:11:07 pmYou're lucky. In my country it is commercially sold under an absolute cryptic name that in no way resembles soda and it is used to raise the pH of swimming pools.

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 25, 2018, 07:13:03 pm
content: I managed to make some sodium carbonate from bicarbonate. It seems to work, but I get some areas where the solution doesn't really penetrate. Those areas appear cloudy (such as the thick trace on the bottom of the picture).Is this overexposure?Sent from my Mi A1 using Tapatalk

author: wraper
author_rank: Unknown
timestamp: August 25, 2018, 08:09:43 pm
content: Quote from: bogdan2014 on August 25, 2018, 07:13:03 pmMost likely. If your print is not very opaque, try exposing less.

author: ruffy91
author_rank: Regular Contributor
timestamp: August 25, 2018, 08:11:45 pm
content: Most probably.The resist should mechanically be very stable. You should be able to scrub it off with a toothbrush or your fingers.I always gently scrub it with my fingers to develop faster. (Do not use bare hands with sodium hydroxide)

author: sleemanj
author_rank: Super Contributor
timestamp: August 25, 2018, 09:28:25 pm
content: Typically the exposure time required is surprisingly short, but the exposure time tolerated is surprisingly long.It is best to expose for as short as possible in my experience, but it's easy to do some calibration tests and find out what works best for you, make one pcb with a repeated test pattern (https://github.com/sleemanj/pcb-test-pattern) and remove a cardboard shield progressively during exposure so that the patterns are exposed for progressively shorter times, now find the one that develops best.With my UV box, 22 seconds is my initial exposure before developing. After developing I expose again to UV (without mask) for at least double that which will further harden the resist we want and make any remaining residue we didn't want more obvious, if there is any another dip in the developer for 30 seconds and some rubbing will usually clean it up.I use single layer tracing paper artwork

author: eliocor
author_rank: Unknown
timestamp: August 25, 2018, 09:54:35 pm
content: Much better to use a Stouffer scale:https://www.google.com/search?q=stouffer+scalehttp://www.stouffer.net/using21step.htmIt is rather cheap (7.50USD) and it is very easy to use it.Just as an example, the photoresist I use (Ordyl Alpha 900) require a range of exposition between 6 and 9 which means (with my bromographer) about 2:45 of exposure.This is an example of the precision which can be reached using photoresist methods: much better than toner transfer.

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 26, 2018, 06:33:35 am
content: The unit is a typical one used for nails, 4x9W UV CFL bulbs. I'll try exposing to the sun and see if I can get better results, maybe the unit is just too strong.Sent from my Mi A1 using Tapatalk

author: bogdan2014
author_rank: Regular Contributor
timestamp: August 27, 2018, 06:03:50 am
content: After more experimenting, I found that my laser printer does not print dark enough (even at max settings). Doubling the layer does improve things, but it's very easy to overexpose the film. I removed two of the bulbs from the unit and exposed the film for under a minute (about 30-40s). I've used the test pattern as suggested by sleemanj, and it worked out ok, but for larger boards the exposure is sometimes uneven.Also, the sun is surprisingly strong this time of year.

author: wraper
author_rank: Unknown
timestamp: August 27, 2018, 12:27:19 pm
content: Quote from: bogdan2014 on August 27, 2018, 06:03:50 amIncrease the distance to the board. Also making stronger developer and rubbing with brush may help. Negative photoresist in much more forgiving than positive.