problem in exposing solder mask - Page 1
Forum section: electronics / general

author: mov-jump
author_rank: Contributor
timestamp: March 25, 2016, 05:27:22 pm
content: helloI am in the way of exposing pads for the final step of creating PCB at home.I tried too many time :fix glass sheet on the pcb which is etched and turn light on>>> after 45 min put the pcb into sodium carbonate for 5-7 min with brushing pcb but every I follow this way I couldn't catch the goal of exposing solder mask to make pad copper visible.please help me from this mind blowing thing.Notice that:I try the step of lightning for 5 times:1- 10 min (LED lamp position)2- 30 min (LED position)3- 30 min (Lamp position)4- 45 min (LED lamp position)5- 1 and a half (sun and lamp position)

author: mov-jump
author_rank: Contributor
timestamp: March 29, 2016, 07:51:32 am
content: Nobody can help ??

author: Psi
author_rank: Super Contributor
timestamp: March 29, 2016, 08:02:08 am
content: You need to use a PCB which is designed for this purpose. It needs to be Photosensitive.Regular copper clad pcb isn't photosensitive

author: mov-jump
author_rank: Contributor
timestamp: March 29, 2016, 04:07:00 pm
content: Quote from: Psi on March 29, 2016, 08:02:08 amI see . And of course I am using a photosensitive sheet to cover my copper clad pcb

author: jpanhalt
author_rank: Super Contributor
timestamp: March 29, 2016, 04:20:37 pm
content: @mov-jumpMy first post, so apologies for technical problems.I have used a photoresist method for making PCB's for many years. I start with a blank PCB that is coated with the resist. One can also start with a plain PCB and laminate a photosensitive resist to it. Your post cannot be answered, because it is not really clear what you are doing.1) Are you laminating a photoresist onto a blank PCB?2) Or, is your PCB precoated with the photoresist?For either answer, what brand of product are you using? The methods can be quite different depending on the brand. If you are familiar with the terms "positive -resist" and "negative-resist," which are you using?Regards, John

author: sleemanj
author_rank: Super Contributor
timestamp: March 29, 2016, 09:02:58 pm
content: Quote from: mov-jump on March 29, 2016, 04:07:00 pmIf you *are* sensitizing using dry-film or other, then sounds to me like you are over exposing. 1 to 3 minutes is a normal exposure time, 10 minutes is likely over exposed.for dry film, see my tipshttp://sparks.gogo.co.nz/dry-film-tips.pdf

author: mov-jump
author_rank: Contributor
timestamp: March 30, 2016, 10:39:05 pm
content: Quote from: jpanhalt on March 29, 2016, 04:20:37 pmIs there difference between laminating photoresist onto a blank PCB & PCB precoated with the photoresist?If there is so I am using the first one.And I don't know any thing about positive resist and Negative resist >> could you attach a link for me to know about it?Regards, Mostafa

author: sleemanj
author_rank: Super Contributor
timestamp: March 30, 2016, 11:40:09 pm
content: Quote from: mov-jump on March 30, 2016, 10:39:05 pmDry film is negative ("copper is transparent" on artwork), pre-sensitised is usually positive ("copper is opaque" on artwork).You are almost certainly exposing for far too long.See the PDF I already posted.

author: mov-jump
author_rank: Contributor
timestamp: March 31, 2016, 01:07:56 am
content: Quote from: sleemanj on March 30, 2016, 11:40:09 pmAt the first thanks you for short but complete answer to my question.I am using fluorescent lamp and found that by these lamps and the dry film which I am using, it takes about 20 min to expose .1-3 min is good for UV lamps.Now I am confused that although pads are exposed but in the sodium carbonate step I can't expose pads complete to see copper, places of pads got thin film but not complete expose.

author: sleemanj
author_rank: Super Contributor
timestamp: March 31, 2016, 10:18:55 am
content: You should develop it longer, or expose it shorter, or both.Note that:It sounds like you are using Dynamask or similar to create a soldermask on an already etched PCB, rather than an etch resist to do the etching in the first place.Your PADS should be black and the rest (every where you want there to be soldermask remaining) should be transparentPictures of what you are doing may help.

author: mov-jump
author_rank: Contributor
timestamp: March 31, 2016, 12:52:48 pm
content: Quote from: sleemanj on March 31, 2016, 10:18:55 amI am now in the step of developing pads:http://s7.picofile.com/file/8245350242/IMG_%DB%B2%DB%B0%DB%B1%DB%B6%DB%B0%DB%B3%DB%B3%DB%B1_%DB%B1%DB%B5%DB%B2%DB%B7%DB%B2%DB%B0.jpgAnd the final step is having something like below picture:http://s6.picofile.com/file/8245349950/Untitled111111.jpgAnd the picture below is my glass sheet (I draw pads onto it by permanent marker):http://s7.picofile.com/file/8245347884/IMG_20160331_135643.jpgAlthough I tried the developing pads step almost 20 times but I could catch goal of having this final result:http://s6.picofile.com/file/8245349950/Untitled111111.jpg

author: ruffy91
author_rank: Regular Contributor
timestamp: March 31, 2016, 02:51:51 pm
content: Your marker is too transparent. The pads are exposed through the marker. Try exposing it shorter. Also use nail lacquer if you really want to draw them by hand.

author: sleemanj
author_rank: Super Contributor
timestamp: March 31, 2016, 11:00:54 pm
content: Quote from: mov-jump on March 31, 2016, 12:52:48 pmThe marker is probably too transparent to UV as ruffy91 says.Also be sure that the artwork (the ink in your case) is against the board.WRONG: PCB GLASS|INK LIGHTCORRECT: PCB INK|GLASS LIGHT

author: mov-jump
author_rank: Contributor
timestamp: April 01, 2016, 08:23:18 pm
content: Quote from: sleemanj on March 31, 2016, 11:00:54 pmyes it's too transparent but I used double glass sheet to have darker pads.

author: sleemanj
author_rank: Super Contributor
timestamp: April 01, 2016, 08:56:23 pm
content: Quote from: mov-jump on April 01, 2016, 08:23:18 pmUnless glass is a mis-translation, that would never work, light will just go in between the glass layers. print the artwork same as you do for etching.

author: Fred27
author_rank: Unknown
timestamp: April 01, 2016, 09:14:44 pm
content: I had great results with Dynamask dry film solder mask. I used a Canon MG5250 ink jet printer in T-shirt mode onto transparencies. It left a nice thick opaque layer of ink. Printed straight from Eagle.