Spraying photoresist

[HerbertMunch]

mvs sarma,
I have perfected my technique now, and the washing thoroughly has helped
Also it wasnt that the developer was too strong, it was because my drying regime wasnt sufficient.

If you spray with the board vertical the coating will sag or at least be heavier on the bottom.

This is true, as i mentioned in my post above. However if you allow a cm at the bottom of the board, the surpless resist will build up in this cm, but will leave a perfect coating on the rest of the board. I have tried this a few times now, and the results are almost as good as the commerical stuff.

Most spray processes have an optimal distance for applying the coating. If you move in closer to save on the spray you may get bad results too. Follow the directions for distance

I disagree! Maybe if you are spraying horizontally, but vertically, gravity does a fine job no matter how close you spray.

Even though you waste a cm of board and spray, you actually use less spray, becuase you can spray almost a few mm away from your target. It doesnt matter about consistancy, gravity will pull the stuff down the board and leave a lovely coating instead of spraying loads on the box, becuase you have to spray 10-15 cm away.

the vertical method also ensures that only the thinnest of coating is left. Its also consistent all the way down the board (appart from that cm). This way, when you develop the board, its like using a commercially sprayed product, The resist gets eaten away consistantly.

Why perfect ones spraying technique, when you can be a lazy sod and let gravity perfect the coating?

 

[jpanhalt]

This is true, as i mentioned in my post above. However if you allow a cm at the bottom of the board, the surplus resist will build up in this cm, but will leave a perfect coating on the rest of the board. I have tried this a few times now, and the results are almost as good as the commerical stuff.

A few years ago I called a manufacturer (Injectorall) and he made a comment about having just dipped some plates. If you can get resist in bulk (not a spray can), you may want to give dipping a try. I have used dipping with regular paint, and the only tricky part was to get it thin enough (about usual spraying consistency), but not so thin as to cause the film properties to break down.

I used a re-sealable plastic food storage bag for the painting -- put the paint and object in the bag, seal it, mix everything around gently, let it drain and the few bubbles settle, then remove. The bag gives you a saturated atmosphere so the paint doesn't start to evaporate during the process and allows use of very little paint. I was using primer and wanted to get the inside of some hollow steel doors primed. It was a non-sandable primer, and the finish coat looked fine. Of course, there is no over-spray and the paint in the bag can be saved and re-used. John

 

[3v0]

Chris,

It is good to hear you have developed a process that works. After you have perfected it, it would be a good thing to write it up in detail for others to use.

I am surprised the only the bottom cm of the board is bad. It sounds like a certain amount of spray will stick to a vertical board and any excess slips down and collects at the bottom, neat stuff. I agree regarding spray distance not mattering in this case.

 

[HerbertMunch]

Chris,

It is good to hear you have developed a process that works. After you have perfected it, it would be a good thing to write it up in detail for others to use.

I am surprised the only the bottom cm of the board is bad. It sounds like a certain amount of spray will stick to a vertical board and any excess slips down and collects at the bottom, neat stuff. I agree regarding spray distance not mattering in this case.

Thanks for your encouragement.

As soon as I get my hands on a digital camera, i will write a tutorial for the method, and post it here.

Im suprised that no one else seems to use this method, i havent seen any websites.

With regards to the bad cm, im sure that there is a solution to this minor problem. Perhaps I will have sorted this when I get round to posting the tut.
Maybe use a fan? The only problem with this is that you would have to make extremely sure that all dust was removed from the spraying box, and possible even the entire workshop. At the moment i seem to be able to get away with just vacuuming the box.

The real beauty of this method though, is that anyone of a non artistic disposition (like me) can end up with an almost premium quality coating, at a fraction of the cost.
Paying over £2 (more than twice the cost of the board itself!) just for the privelledge of a machine spraying the board, leaves a bad taste in my mouth .

 

[HerbertMunch]

...If you can get resist in bulk (not a spray can), you may want to give dipping a try....

I like the sound of that, though I bet it would cost a lot of money!

200ml spray = £10 (**broken link removed**)

Even though it seems expensive, its nothing compared to the cost of the commericially sprayed boards. You can buy the cannister for the cost of about 3 160x100 SS pre-sprayed boards! 200ml would easily do many more than 3 boards, boards that cost less than a £ each.

 

[HerbertMunch]

Also, on the dipping front, I bet the liquid stuff wouldn’t reek as badly as the spray, or at least it wouldn’t be airborne.

The problem with the spray is that you need to do it under tungsten lighting, with the door shut to stop the daylight.

I really need to get a respirator, or maybe take up late night spraying

 

[3v0]

You can eliminate the bad cm by giving the liquid some place to go. Tape/glue/connect/butt a bit of scrap PCB to the bottom of the board you are spraying and the excess should run down onto it. Providing the joint between the boards is not too loose.

Interest in photo resist has been reduced by the use of toner transfer.

 

[HerbertMunch]

But wouldnt taping something to the board not produce similar undesirable effects or at least end up with part of the board not being covered?

Also,
Something that really sets the commercial stuff apart from the diy, the black film that they stick to the sprayed boards, to prevent unwanted exposure.
It allows you to work with the board before you expose it. i.e cutting etc, thus making it possible to mass produce diy-ed boards and store them for later use.

I was thinking maybe experimenting with different black plastics (i.e. bin bags, etc) and possibly sticking it to the dried diy boards with spray mount adhesive. I.e. sprayed to the plastic and then sticking the plastic to the board.

I’m going to cut out some small pieces of board and coat them, and then see what it takes to expose them through different black materials. Also do a few control tests with boards exposed through a mask by tungsten, fluorescent and daylight.

I cant really do a tutorial justice until i have a camera ( and another can of resist).
Interest in photo resist has probably gone down hill, due to the expense of the pre-coated boards, and the difficulties associated with spraying your own.

No matter how well toner transfer can work out, it will never be able to recreate the same level of detail and repeatability that the resist can. I just couldnt see an institute such as a university ironing on bits of magazine paper!

Its off putting, having no information to work with. But i suppose once ive finished my experiments, i will be able to publish the findings for others here at the forums, and hopefully convert a few of you from the dark side

 

[pitronix]

Thanks. We uses a similar process back in the Z80 days. The ink was a special PCB ink. It is a good process for production runs. But it is more difficult then either photo resist or toner transfer. Unless a person has previous silk screen experience the chance of success is very very low. And it is a lot of work for one board.

The only reason I asked twice was because the people having trouble with either toner or photo are looking for another process when they fail with the current one. Suggesting that silkscreen could be used does not help them.

Sharing is a good thing. But it needs to be in context.

I just tried to help. I found it easy to do. On the other hand I do have a lot of experience in silk screening as well as other printing techniques since I worked in that field for a couple years. And it is worth learning in any case since you can do so much more things. But I agree that it could be hard to start.

 

[jpanhalt]

If the commercial boards you get come with a plastic protective coating, there is a chance they are made by laminating the photoresist, not spraying it. See:

**broken link removed**

Here are some additional links to laminated photoresists. Note the low temperatures used. Once laminated, processing with the positive-resist version is identical. These links also include some good technical information on making developing solutions, etc. Laminating the resist avoids all odor and most of the chemical risks.

I have put an asterisk on the two links I found best. John

**broken link removed**
** **broken link removed**
** **broken link removed**
**broken link removed**

 

[HerbertMunch]

ok thanks.

 

[HerbertMunch]

I bought some of the spray that didnt recommend (PRP green spray) just to see why he didnt recommend it.

excuse my french but its absolutely ****. Its has the consistancy of water, and it pisses out all over the place when you use it.
The positive 20 spray(purple) is thick and syrupy, and when you spray it vertically it will leave a nice coating. This PRP crap just runs right off onto the box below, leaving a rubbish coating.

I CANNOT STRESS THIS ENOUGH, STAY AWAY FROM PRP!

I bet this stuff is responsible for quite a few people being scared away from spraying their own.

 

[Sputnik]

Sorry to dig up a seemingly dead thread but does anybody know where to get spray resist in the US?

Or perhaps small quantities of resist film?

Think and Tinker sells film but its expensive, $85 for 12inx50ft roll. I guess thats not that expensive for what it is, but an $85 whack in the wallet is crude. Oh, and its negative acting. Which would be fine I guess.


For all of you wondering about the Photographic method using pre-coated boards, THERE IS NO OTHER WAY TO GO. I have gotten 100% sucess using this method.

And guess what, despite all of the info saying it isnt possible I do it all with an inkjet printer, always have and never had a bad board due to the transparency.

If ive had a bad board it wasnt due to the methodology, just me not paying attention to the clock, or forgetting the board was in the developer.

Here is a small board I just made using this method. I have made even smaller boards with tiny QFN package ICs etc. with even better results.

 

[3v0]

"THERE IS NO OTHER WAY TO GO."

.......... Ouch ! ..............​

 

[jpanhalt]

And guess what, despite all of the info saying it isnt possible I do it all with an inkjet printer, always have and never had a bad board due to the transparency.

My impression is that inkjet was the preferred method, particularly in the early days when lasers were 300 dpi. It is not so much the opacity of the ink, but the lack of defects that benefits inkjet method. The ink flows just a little to fill defects. With laser, that does not happen.

People are using newer laser printers the photo-resist methods and report good results. A few are adding the green toner transfer from Pulsar or the equivalent to the laser transparency to correct the defect problem. I plan to try that in a few days.

As for obtaining the laminate film is smaller amounts, I agree. I think it would be fantastic if one could get just a foot or two to experiment with.

John

 

[Sputnik]

Mega in the UK sells a kit that contains 5 8.5x11 sheets of resist film, however I cannot find these sheets on their site, just the rolls.