How resistant is photo resist?

[alparent]

I've been etching stuff using the toner transfer method. Then rubbing Ferric Acid with a sponge. Very fast!

But Toner Transfer limits me in the size of trace and space I can use when designing a board.

I was thinking of trying the photoresist method but was wondering if the resist is resistant enough for my rubbing ferric acid with sponge method.

I know my Sharpie pen touch-ups don't resist well the rubbing down technique.

[DavenPaget]

Sponge ? 
Isn't ferric chloride very corrosive ?

[Perrow]

Sponge ? 
Isn't ferric chloride very corrosive ?

http://www.pcbfx.com/main_site/pages/tech_support/no_etching_tank.html

The page looks like they're trying to sell you something, they're not.

[deadastronaut]

@alain:  you can get very fine traces with toner transfer resist...as long as your image is sharp (svg) vector graphics etc..and you tape down the image

so it doesn't move/smudge while ironing...ive had some real good results with fine stuff...toner is quite tough really, as long as the surface your doing is clean and keyed properly

you should be ok to go really detailed...

[Keppy]

I've had excellent results with the presensitized boards from Small Bear. I never get great results from toner. The photoresist is precise and doesn't come off while etching. It is definitely tougher than sharpie. I've never tried rubbing it, though.

I recommend trying it if no one else here has. Worst case scenario, you're out the cost of one board and some lye. $10, tops.

[G. Hoffman]

It doesn't really hold up to much rubbing, but I've never found that to be a problem.  Make sure you fill as many empty spaces on your board as you can with filled planes, and your etchant will last a long time.  Also, you will be able to get much better results with photo resist systems, much easier than with toner transfer.  The first time I used it, I got better results than I ever got with toner transfer, and that was after I put the mask on upside down!  (remember, the matte ink side goes towards the copper!)

Warm your etchant, and let it eat out most of the copper away.  I usually end up using some long q-tips to rub the last bits.  The photo resist will put up with a little bit of rubbing, but it will not hold up to doing the whole board that way.  I do frequently spend 10-15 seconds rubbing the center of the board, since that usually takes longer than the edges, which I think helps to minimize the amount of undercutting.

If you need a cheap and excellent way to expose your boards, I really like the light box I made for this;




You can read more about it IN THIS THREAD[/i], but it is really easy, and works great!  I've never tried the florescent tubes they sell for this purpose, but I have this feeling mine is more forgiving because the light is coming in from a more nearly vertical angle, so the light is less likely to get under the mask.  I may well be wrong on that, though!


Gabriel

[davent]

I've always just used any old regular  flourescent tube i can rest the exposure package  to within an inch of. Nine minute exposure and we're good to go. With the presensitized board you can get incredibly fine detail. The resist does seem pretty delicate and i wouldn't want to chance rubbing it.

Fresh acid/peroxide etchant will finish the board in a couple minutes. From printing out the transparency to having the etched board easily in a half hour.



Exposure shelf.



dave

[G. Hoffman]

How the heck did you get that picture?  Even in Macro mode I can't get my camera to focus that close!

But yeah, I've never found a level of detail I can't get with the photo resist.


Gabriel

[davent]

Just my wifes Canon Powershot A630 in Macro mode. When i was shopping for the camera i had a PCB with me as i wanted to be sure i could get decent close-ups when i borrowed it and this camera won out in my price range.

Toner transfer would be  a sado-maschistic journey after the ease and speed of using photoresist.


Take care
dave

[Tacoboy]

Hmm, I always have good results with the good old iron/toner method. I never need to rework the etch mask. Pictures below: some pcb's done in 15 minutes...
I think the result is fine, no rework was needed. The main advantage is you can wipe off a bad design and start all over again (I was surprised how firm the toner sticks to the copper).

Etch bowl, kept warm (50°C) au bain marie. Etching done in 2.5 minutes.


Etch result:

[G. Hoffman]

I've done them both, and I would never go back to toner transfer if I can help it.  There are guys who make it work for them, but with the photo method, I've NEVER had to start over - not even the first time I tried it.  With toner transfer, I usually had to do two or three passes, and I had to keep my traces much bigger, which is a problem with some of the boards I've been doing lately.  Also, with the photo-method, I can print it out once, and make as many copies as I need.  Seldom a big deal, but nice none the less.

Of course, in an ideal world, I'd order them all from a PCB house.  I try to do that for anything that actually matters.  Plated through holes are nice.


Gabriel

[alparent]

With toner transfer, I usually had to do two or three passes, and I had to keep my traces much bigger, which is a problem with some of the boards I've been doing lately.

Exactly why I'm looking into photo resist. Most of the layouts you find on the web are suited for toner transfer. But when I do my own thing, It would be nice to have smaller traces. I like 125b boxes and the biggest board I can fit is 3" by 2.3". You can fit a lot of things on on board this size.......but with the size of the traces and space between then you need for a good toner transfer can be a pain to layout. And I've also started designing things using SMD and the pitch on some of those chips........I can't imagine doing the board using toner transfer!

And after rereading articles on the sponge technique....I think I don't really need to scrub as much as I do.....the goal is to brake the surface tension.....I'll try a litter touch next time.

But I will try photo resist...........I the repeatability without reprinting is also a plus.

[Perrow]

And after rereading articles on the sponge technique....I think I don't really need to scrub as much as I do.....the goal is to brake the surface tension.....I'll try a litter touch next time. 

Google "Edinburgh Etch", adding citric acid to the ferric chloride, keeps the board from "clogging" (they say).

[markeebee]

And after rereading articles on the sponge technique....I think I don't really need to scrub as much as I do.....the goal is to brake the surface tension.....I'll try a litter touch next time. 

Yeah, I don't think you need to rub at all.  I just let the sponge soak up the acid and then squeeze it out again. Seems to work ok.....

[alparent]

Yes I did read up on the Edinburgh Etch. I make my own wine so I just happen t o have citric acid (it helps to prevent oxidation of the wine).
Will try it next time I etch.

They talk about 40% ferric acid.............is the stuff you get at radio shack 40%
When Radio Shack switched to The Source here in Canada they had a HUGE liquidation sale. I purchased ALL the ferric acid bottles my local stores had in stock.