How do you make SMT pc boards at home?

Question

I cannot find "dry transfers" for a 20 pin SMT PIC chip. I need URL's to places that I can find the necessary materials. Right now for other through hole projects I am using resist ink/ ferric chloride process, and I dont think that it is precise enough for this SMT chip. What about the UV process? Is it more precise?

I already know about places like www.pcb123.com, I just cant afford a new board design everytime my application changes

Like I said URL's Please, www.digikeys.com gets me a 404 screen

ALGRANT,

I want to use the SMT's for two reasons,
PCB real estate, and in bulk they are at least a whole dollar cheaper each.

Answer 1

You may have to suck it up and do a through-hole mount board. If you're worried about changing your application that often, you might consider socketing your chips. Or not, the PICs are cheap enough if you can get a few of them on hand.

Answer 2

I make homemade circuit boards using the photo silkscreen method. A silkscreen consists of a wooden or metal frame with a polyester or stainless steel mesh stretched tightly across it. It is first coated with a photo sensitive emulsion and kept in dim light until dry. After drying, a film positive of the desired artwork is attached to the screen with clear tape and exposed to U.V. light. The exposure can come from a dedicated exposure unit or from simply being in direct sunlight. Just be sure the emulsion side of the artwork is in tight contact with the screen so light doesn't leak under the image undercutting the image. After exposure the emulsion is hardened where it was exposed to light and where the artwork was opaque the emulsion stays uncured and water soluble. Then when sprayed with water the uncured emulsion washes away leaving an exact stencil of your artwork. The resolution of the stencil is a function of how fine the mesh of your screen is. A 600 strand per inch fabric is a good starting point. After the stencil is made you put resist ink in the screen and force it through the stencil onto a clean pcb blank with a squeegee. While resist ink is specially made for this application just about any lacquer based printing ink works. Now the ink must be dried. While leaving the board to dry for a few hours works I like to speed things along with a heatgun. Now you're ready to etch your board as usual although you might try using amonium persulfate instead of ferric chloride. After etching you can use the slik screen process to selectively apply solder mask (that green(usually) coating that repels solder) and print component legends. I have been able to make pcb's this way that were nearly indistinguishable from board house boards. I have even made double sided boards. The only thing I haven't been able to do yet is create plated through holes. I just design my boards to have as few vias as possible and give them a dedicated pad on each side so I can connect both sides as needed with a small bare jumper wire. While this method can cost a few hundred to get set up the beauty of the process is that once you are set up you can make as many copies as you want for only the cost of the pcb blanks. Also the screens can be stripped and reused. As far as electronic component transfers find a company that carries the complete Datak product line. They should have what you need.

Answer 3

I have had some success etching my own circuit boards by using a graphical layout editor on my computer, printing out the pattern using a laser printer on photo paper, and transferring the pattern to the PCB using a hot clothes iron.

See this article:
http://max8888.orcon.net.nz/pcbs.htm

The technique requires some practice, but you can get very professional looking boards if you do it carefully.

Answer 4

Anytime you're trying to etch features much less than 30 or 40 thou' it's a real crap shoot ☺
You might try going to DigiKeys website and looking through their collection of 'do it at home' and 'do it yourself' PC board materials.
One of the bigger tricks is to get pre-sensitized boards. If you try to coat boards yourself, yo get so many variations in thickness that trying to develop it is impossible.
UV really isn't the answer. Plus you can get a pretty bad burn from it if you aren't careful.
Good luck ☺

Doug