trouble making PCB - evil ink?

[Nasse]

Here is my few pennies for the subject

I´m not happy about your troubles with pcb making, though it is nice to hear that many other people and not just me have had similar problems

I can not make perfect black images with my cheepo inkjet, when I look against light it is not totally opaque. I have used laser printer or photocopier to overhead polyester foil method (I use the machines at my work ). Over the years when people are discussing about the subject on line or in some magazine article, few times I remember people mention they use two or three foil patterns layered on top of each other to make it more "black" (sorry my english)

Few times I have used this kind of method for laser/photocopy image: I was once fixing or modifying a laser/photocopy film with a pen I use for technical drawing, it was Rotring capillary tube ink pen, and I spilled the ink over the image. Because the ink is water soluble, I could easily fix my accident by wiping off the ink and make a new start. But I noticed the laser/photocopy toner looked better and more black, the ink had soaked small holes. After that I have on purpose soaked some drawing ink on the pattern. Maybe not so useful tip but worked for me. The ink was "Higgins Black Magig", amazing stuff, it is best stuff. Blacker than a black man eating licorice in a dark cellar (I am not a racist).

I have used old 250 watt UV lamp from old 60´s Philips sunbath device (I think those lamps are available maybe). But last time I used it I had no success, maybe the lamp is too old and does not have enough UV output.

I spoiled about a half dozen boards when fuzzing with bad developer. It was painful for me to find it, I bought sodium hydroxide solution at where they sell medicine and stuff here, and it was not easy and cheap. So I re-used that stuff, which was a mistake. Later I read somewhere that it is better to use fresh stuff every time. I found this true, it makes big difference. I use "Plumber´s helper" pipe opener stuff mixed with water...

 

[PRR]

> exposure times are 30 minutes.

> I expose for 30sec, ....with Positiv 20 spray, exposure is 4 min.

Very different operation, but probably same chemistry: when we "burned" printing plates we used about 10-15 seconds over a blinding arc-lamp. And the master printer could be very fussy: after seeing the developed plate, even though it was costly, he sometimes threw it out and ordered another burn at a different time. (But he was pretty good at looking at the negatives and guessing exposure times).

The flaw does look some like snapshot film that has been grossly overexposed. Light turns emulsion black (or hard), but WAY too much light breaks it down and it goes clear (or soft?).

Still can't explain the way the edges are so well preserved. It is possible to get edge effects if the developer is VERY stagnant, not only zero agitation but hasn't been disturbed by slipping the film in. The developer in the big areas gets exhausted, but the developer at the edge has inactive developer next to it. It is rarely seen in photographic work, and I would not expect it on high-contrast work like this.

 

[Emperor-TK]

I still consider myself a DIY newbie (I'm still struggling with my SSL build). However, by day I am a Chem E/research scientist specializing in electronic materials. Hopefully I can help out whenever chemistry questions come up :grin: .

I would bet money that your problem is in your photomask. It is unlikely that you are getting 100% opacity with either a conventional ink-jet or laser printer (with a single pass). There are high resolution, high density laser-printers out there that make film masks for printing screens, stencils, flexo plates, etc, but that isn't typical. The fact that your edges are still present isn't very surprising either. If you printed with an ink-jet printer, your pigment will collect at the edges of your traces during the drying process (like a coffee cup stain). If you printed with a laser printer, the effective charge density on the optical photo-conductor plate will be greatest at the trace edges, leading to denser prints there as well. Granted, diffraction is working against you here, but I still think its possible that greater ink build-up at the edges could overcome this effect. Also, I wouldn't expect any chemical reaction between either laser toner or ink-jet pigment and a photo-resist.

The acid-test for this is to hold your mask up to a bright light. If you see any light coming through your mask, that's your problem. As others have mentioned, 30 minutes is a very long exposure time and almost certainly more than you need.

This is what I suggest:
1) Print two copies of your mask. Line them up (registration) with their ink sides down and tape them together at their edges.
2) Cut your exposure time down.

 

[Svart]

i use a laser printer with the toner turned all the way up, 1200dpi resolution. never had a problem except for trying to print more than one thing on a piece of transparenecy at different times.. the rollers leave some kind of residue on the plastic that makes the toner splotchy...

 

[peterc]

I use a Lexmark inkjet for my masks, but I HAVE to print the pattern twice & stick them together to get a dark enough mask, no matter what the print resolution. Probably better with a Laser printer.

If my etchant is slightly old & I use a single layer mask, my PCB's look like these faulty ones from the previous page.

Regards
Peter

 

[mnats]

I use "Plumber´s helper" pipe opener stuff mixed with water...

Exactly. Bought as PCB Developer it costs a fortune. Bought as drain cleaner it costs about $2.50 for 500 grams. Mix with a good scale - I think I use 3.5 grams to 500ml water.

I used to double up transparencies too when I used transparent film. Again, the edges start getting fuzzy when you use a multiple tube light box like I do. Now that I use tracing paper it's one pass through the laser printer and bingo! Works every time. Sharp as a tack.

Practice , practice
once you get the hang of it
... it all just works.

It's true! But for me it was more like TORTURE, TORTURE.

Holding your transparency up to the light...I think the contrast is too great to be able to see any detail in the dark areas. Since he's using a positive there's a good chance the light areas will take up a greater percentage than the dark. Kinda like trying to recognize someone while they're standing with their back to the sun and you're sitting on the ground looking up at them.

 

[olafmatt]

Thanks for all the input!

Today I tried again, this time with a 1000 Watt film lamp in 20 cm distance from the PCB and exposure time was.... guess?... 1 minute! So it seems I was a) overexposing the boards with the 150 Watt lamps or b) the lamps didn't have enough UV output. With the new technique I managed to make several PCDs with very similar results which wasn't possible before. Now I have to order new boards from Reichelt...

The strange thing is that development times are shorter now, too. Before it was about 2 - 5 Minutes, now its about 30 sec - 1 minute.

A word on the inket foils: I usually print twice to the same foil! After the first print I let it dry for at least two days and then put it through the printer again to get blacker blacks. But not all printers work that exactly that the two prints fit exactly. Mine does (most of the time).

Olaf

 

[Mbira]

It seems like that problem worked out. Good. I really would suggest trying vellum paper and seeing the results. I was skeptical at first thinking that a transparency would develop better, but that was not the case. The vellum holds the ink a lot sharper. Much better results.

Joel

 

[PRR]

> The strange thing is that development times are shorter now, too.

Any old-time photographer knows: if you under-exposed, you have to over-develop.

> the lamps didn't have enough UV output

Incandescent lamps have roughly ZERO output in the UV band. What they really are is IR lamps that bleed a little into the red and green range, with a whisper of blue and even less violet.

Basic photo-film is mostly UV sensitive, so much that sky over-exposes and red lips come out black. For most eye-candy photography, this is a big problem (solved by Panchromatic film which has dyes that filter far-UV and catch red better). For process work, UV film is easier to use because you can handle it in incandescent light without fogging. So you really need a UV source.

a 1000 Watt film lamp

What is that?

There are photographer's lamps that are incandescent but worked VERY hot to increase light (and blue-violet light) at the cost of short life (maybe 5 hours). Sometimes they even have a blue coating to reduce the excess red in an incandescent. And modern halogen lamps can work much hotter (and bluer) than the old vacuum lamps.

A proper UV lamp would be best. These will give more photo-effect and less heat-cooking. In the home shop, this would be fluorescent, not "warm white" but "cool bluish" and preferably "black light", preferably for this purpose not a 1960s party-light. In industry, 30 years ago, we used an arc-lamp.

But if you are getting great results with what you have, stick with it.

 

[Kev]

yep
I call it tracing paper
currently I'm getting better performance out of an ink jet than my old laser

as I said before
once you get the hang of it, you just make adjustments as you go
printer, ink, PCB board, the light box and developer ... it all seems to change over time and you just go with the flow.

:thumb: