screen printing emulsions on PCB's?

[Brian Marshall]

any one ever have any luck trying to use emulsion on PCB's

It seems like it could almost work, and just when i almost have all the unexposed emulsion off the traces start to peel off.

I'm using the stuff that comes with the speed ball kit.  is there something better.

I really want to make my pcb's this way.

I am using a 250 watt light that is meant meant for outdoor lighting.  one of those ones they sell at home depot, i'm thinking maybe it is getting the board too hot.

[Paul Perry (Frostwave)]

There is a huge amount about this if you search google groups. A problem with emulsions straight on the PCB, according to some, is that the etchant softens the remaining emulsion & might attack the board thru it.
Of course, if you made a screen & then screened a resist onto the board, you wouldn't have that problem. But it might not be easy to get enough resolution.

[Brian Marshall]

Yeah.  that is going to be my next thing to try.  I think that may actually be faster anyway.

Brian

[sfr]

my first circuit boards (before I found out about P'n'P) I made by screening.  I was doing a lot of band t-shirts at the time, so I used some of the room left on a tshirt screen to put a PCB design.  I just printed it with acrylic paint, and as long as I got a thick coat and let it dry all the way, it worked fairly well.  Board needs to be pretty clean, like with anything else.  YMMV.  

(and yeah, I forgot to mask the PCB artwork once, so somewhere there's one of my band's tshirts with a Distortion+ layout underneath the band design.  oops!)

[axr]

i use epoxy paint to silkscreen pcbs.

[Brian Marshall]

Thought id'd update on this.  Last night i pulled out my last board that i had coated with emulsion.  This was my 5th try, and i told my self that this was it.  if it didnt work i wouldnt even try it anymore.  

I realized that my light was actually 500 watts, so i moved it further away, about 20 inches total.  I was having problems with the board getting too hot, so i put a fan on it, and set the board on a wet sponge.  

Before i had been waiting about 10 minutes for the emulsion to expose before.  when i went to remove the emulsion it there would be a lot that would not come off.  My hunch was that this was due to the heat, and not over exposure to light, so i decided to increase the exposure time to 20 minutes.

Now my previous boards were prety hot after 10 minutes.  this one was just a little warm.  About 1 minute of luke warm water and a sponge later it came out almost perfet.

i put it in etchant for 25 minutes, and pulled it out rinsed it off, and here is the really wierd part.  the exposed emulsion came off really easilly.

Anyways, I'm happy with this process, although it is a little involved

Brian