Spraying photoresist

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Nigel Goodwin said:
Your mains connections are really badly (and dangerously) designed, why on earth have you got copper filling in between the mains pins?.

But the actual PCB looks really great!.
Click to expand...
My exact thoughts.

If I dont leave at least a couple of miles between any high and low voltage stuff on the PCBs I design (even 12v and 5v) then I don't feel comfortable with them.

Having traces that close for 220v is asking for trouble though.
 
I've got a complete silk screening setup here in the workshop (with 50kgs of fabric ink rather than the solvent based stuff unfortunately).

I'll probably try using it for screening PCBs when I go into quantity production of some stuff I'm working on to see how it goes.

I'll be looking at making up around 50-100 double sided boards a week so the silkscreen and etch method could be quite handy.

The only problem I can see is removing the ink from the solder pads but with a small cnc machine this could be achievable.
 
picbits said:
The only problem I can see is removing the ink from the solder pads but with a small cnc machine this could be achievable.
Click to expand...

Here are two other options:
1) Use something like conformal coating (acrylic lacquer) as your "ink" and solder though it. Of course, you need the right lacquer/coating for that.

2) Remove all of the ink/paint, then re-silkscreen the areas that won't be soldered.
John
 
Sexy PCB!
As mentioned by Hero999, adding an AC ground termination to the fill pad around the 220V input would be prudent. It appears that the fill area is already connected to the DC negative supply so this should not be too much of a problem to retrofit. You could almost bodge a 3 pin screw terminal block in place of the 2 terminal one, though it would hang off the edge of the board a bit and would detract from the sexiness a bit.
 
pitronix said:
I have been doing small quantities PCB manifacturing for some time and again I have to advice people to try using silk screening with PVC colors. It is easy enough and pays out in a long run much more then all other methods...
Click to expand...

If you are going to suggest people try a process you need to specify what you are talking about.
 
Would it be safe to say i can follow this tutorial:
**broken link removed**

From Step 9 and up using
**broken link removed**

?
 
while the positve20 is also costly process, for those who prefer to use, I suggest that they try spin the copper clad immediately after spay. This would make uniform distribution and even drying of the material sprayed. This was what a friend was doing when he made few PCBs way back in 1985.
 
Hi Chris,


If you (or your board) have speckles when spraying that's because there
is a residual layer of dirt and/or grease on you(r board). It is absolutely
necessary to degrease the surface of the board before spraying.
About the spraying itself, you have to start spraying beside the board
and then gradually and evenly move the can over the board from left to
right and back. So start and stop spraying when you are beside the board.

on1aag.
 
Explanation

3v0 said:
If you are going to suggest people try a process you need to specify what you are talking about.
Click to expand...
OK!
For silk screening first thing you need is Silkscreen. Use some intended for textile (fabric) printing because it has biger holes which we need because we want to use thicker PVC based color. Prepare print of your PCB on film for use on laser printers or (worse) kinde of paper used for drawing plans and technical drawings (white, yellow or greenish, semitransparent paper), sorry I don't know name for it in english. You first spreed thin coat of photo sensitive emulsion (commercial one) on bothe sides of silkscreen (done in dark). Then you dry it with hair dryer. When dry it's ready for next step. You take your positiv printed on foil and put it over silk and expose it to light something like 500/1000 W. at 40 cm distance. You acctualy need to know how much of light and for wath time which deppends of kinde of emulsion. After it is developed you just remove undeveloped thing (your PCB traces) with water under presure (I use car washing compressor). You dry it again with hair dryer and voila, it's ready. Then you print it with PVC color and after it drys it's ready for etching. As I said I use H2O2 30% and 12/15% HCl. For more infos see sites about silc screening on T-shirts and similar. I hope this helps!!!
 
P.S. you need first to clean copper and to be sure your boards are clean and dry. PVC layer can fall of if not clean and/or dry.
 
on1aag said:
Hi Chris,
....If you (or your board) have speckles when spraying that's because there
is a residual layer of dirt and/or grease on you(r board).
on1aag.
Click to expand...

thanks, ill make sure i clean them properly in future.

The spinning idea sounds good.

I have been experimenting and have found out the following things:


SPRAYING

Vacuum out your spraying box as suggested on the website (.

Instead of fighting gravity, it seems that spraying the stuff on verically works nicely.
Stick the board to one of the walls of your box, and then spray.
Graivty pulls the laquer downwards, and ensures an even coating (appart from the bottom cm, which is too thick, but just make your pcb 1cm longer than it needs).

Spraying vertically you can use less spray as you can spray closer to the board, and waste less on the surrounding paint box.



CURING
80C for 40 minutes seems to work very nicely. Any hotter and the stuff gets cooked onto the board and refuses to devlop.

DEVELOPING

2.5 Teaspoons of caustic soda into 1 litre of water.
 
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AtomSoft said:
Would it be safe to say i can follow this tutorial:
**broken link removed**

From Step 9 and up using
**broken link removed**

?
Click to expand...


Sounds about right.

That commercial board is the stuff i bought. Its really good, and so much better than spraying your own (if you can afford it!).
If i was rich, i woudnt bother spraying, i would just use the precoated stuff.
 
Most of my boards are small in size even if it was large around 8x10in i would still use just 2 4x5 boards. Saying that i would recommend buy this in bulk like :

PHOTOETCH PCB SS 100 X 160 (RC) - 1.99 x 50 = $100 (add shipping = tax)

but you get a nice large supply and save money at the same time? I guess just having a safe place to keep them all would worry me
 
pitronix said:
OK!
For silk screening first thing you need is Silkscreen. Use some intended for textile (fabric) printing because it has biger holes which we ..... I hope this helps!!!
Click to expand...

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.
 
AtomSoft said:
but you get a nice large supply and save money at the same time? I guess just having a safe place to keep them all would worry me
Click to expand...

No reason to worry! Keep the PCBs in a fairly dark and dry place, e.g. clothes locker, and use a black plastic bag for additional light protection. The boards are well usable even after two years of storage. Stored a longer period than that they are still usable; they just require a slightly longer exposure time (from 240 seconds to 270 seconds with UVA incandescent lamps)
 


From Rapid online that would be £100 or ~$200! I could not warrant spending £100 just on boards.

I think that using the method i described above and spraying your own is likely to be the most cost effective solution.
 
HerbertMunch said:
From Rapid online that would be £100 or ~$200! I could not warrant spending £100 just on boards.

I think that using the method i described above and spraying your own is likely to be the most cost effective solution.
Click to expand...

Let me trace your 1st post back,. You already have the spray with you. Did you try little more diluted solution of the developer to prevent the stripping effect by trial and error by using few 1" size layout. this will confirm at what concentration it works for the spray used by you.

Already you have received suggestions that you might need to clean the board to prevent speckling. Hope to see the results of a fresh trial.
 
Some thoughts.

It has been a long time since I used the spray resist but I want to make a few comments regrading some of what has been mentioned.

I am thinking that when you spray the board you create a wet film on the board the must be dried.

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

If you spin the board the coating will be thicker on the edges.

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.

The things that have been mentioned that should help are:
A super clean board and spray chamber.
Perhaps better longer drying.
Work on your spray technique.

There is also the possibility that the spray is old and will not work regardless of what you do. Check with the maker to see if that can happen.
 
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