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safetyman 15th April 2006 05:26 PM

Problem with etching PCB!!! Please help!
 
I am trying to produce a PCB using a film developed from a redrawn pdf file, then PCB goes thru an exposure and developing process and finally the etching. Problem is that the results are far from good. I have posted a pic of how it looks like with holes on the tracks where they should not be. Anyone encountered this using whichever method and would like to share the solution to this problem? :confused:

http://i49.photobucket.com/albums/f2...io/small04.jpg

Thanks.....

acenovelty 15th April 2006 10:45 PM

Howdy safetyman,
Ooops, several things can be happening.
If you are using a black and white film to UV expose the presensitized board, the time/intensity can be wrong. The film can be not in good physical contact with the board causing bubbles or bits of dust between the two. Or the film may have small holes in the traces not easily seen without a light table. The exposed board can be overdeveloped causing small holes that etch larger. The etching solution can be too strong, temperature high or longer than needed. The presensitized board can have problems of its own. Date of make can be a factor.
If you use a magnifyer over the developed board before etching, you may see the problems first. Then it can be fixed using an oil based ink pen or model airplane enamel paint and a small brush. Neither is much fun, but better than holes in the traces.
You can of course just ignore the holes. Get some good silver solder and completely "tin" the entire board with enough solder to fill the holes.
Try again and standardise every step. Making quality pcb's is a learned craft with a bit of voodoo involved. My first boards were a much bigger disaster.

rephil 16th April 2006 06:29 AM

Hi Safetyman,

The tiny horizontal trace at the right of your pic seems to me a problem of too high an exposition time or your redrawn original is not black enough where it has to be. Maybe both...

I hope this helps.

Best regards

rephil

safetyman 16th April 2006 03:46 PM

Guys, thanks the help.

The exposure was done with a unfiltered 2000watt UV lamp for 120 secs. This is actually one of those exposure machines that printers use to make their printing blocks with. My friend is a printer and this is the first for him in making a copper board. I believe their printing blocks are not made out of copper.

That could well be the main culprit.

Elso Kwak 16th April 2006 04:06 PM

hi safetyman,
What PCB material are you using? Did you apply the UV sensitive layer yourself? The holes seem like splashes of chemical burning photo layer away. Never experienced that.
It is not over-etching as the fine tracks disappear 1st.

safetyman 17th April 2006 04:22 PM

Hi Elso,

I am using a photosensitive board from Farnell. A friend is having a go at etching the second board using the same procedures. I'll probably know soon how it will turn out and I'll know if it's due to the exposure process or the etching process. Will report back.

rephil 17th April 2006 07:14 PM

2 Attachment(s)
Hi safetyman,

we all make errors and correct them. In order to get better boards, find in the pic a sample containing tracks, numbers and pads. The number above are 1mm height. At the left and at the right of the tracks you see their width (left : mm, right : thou). I have put a ruler in order to let you appreciate the dimensions of the board (in cm).

This pic is difficult to get on the board. The zero may come pqartially or fully filled, the 9 and 0 may not be separate, the tracks may come not evenly etched (variable width), the tiny hole in pads may not appear ... You have so a way to get errors to correct without throwing away precious $ in etching full boards...

I use always this pic and calibeate my process in order to correct the exposition time when I get new boards. When it is calibrated ok, it is ok for all the otyher boards I have got.

Don't overlook the 3 last sentences of acenovelty's reply : they are truth and the way to go. My first boards were awfull too. Yours is much better.

Regards

rephil

safetyman 19th April 2006 03:10 PM

Thank you, thank you for the guidance.

rephil, thanks though I do not understand what I am supposed to do with the pic? :D Am I supposed to do a board with that and get the method right till everything shows up and that means that would be the way to go?

Anyway, I did another board exposing it to the same source for 95 secs this time round instead of the 120 secs. After etching, the result us much better, except that some of the "pads" (I think that's what they are called) on the finer tracks were etched off but generally, no holes this time. Another problem that showed up though, is that some of the tracks seem to be scratched. Is this normal? Is there anything that I can do to fix this?

Beside the above circuit, on the same board, I had a preamp circuit with much finer tracks and when that was etched, some of the tracks went missing. Could this be an indication of the solution being too strong?

Thanks again.

acenovelty 20th April 2006 01:46 AM

Sounds like underexposure/underdevelopment. But then under exposure and over development causes similar problems at the etch.
What are you using for the etch solution? You can also over etch as in too strong solution, temperature too high or too long in the etch solution. This is where the voodoo comes in as everything must be in balance for a good board.
Keep on trying. You've only made a couple attempts.
Some folks claim better success with a laser printer and Press-N-Peel Blue. http://www.techniks.com/
No developing, but ironing down big boards is a different problem.

safetyman 20th April 2006 04:39 PM

ace, I am expreimenting but it's getting pretty expensive with ruined boards. :D I think the Press-N-Peel Blue is not available where I am and I am trying to master this process as I need to produce about 10 or so boards for my friends and myself to do. :D The solution used is ferric chlorite.

I'll defnitely update this page as I go along till I find the right process. This way, the page may be useful for some poor soul in the future who faces the same problem as I do.


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