Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

----- Original Message -----
From: twb8899
To: Homebrew_PCBs@yahoogroups.com
Sent: Thursday, January 04, 2007 6:14 AM
Subject: [Homebrew_PCBs] Re: Water soluble photoresist



All of these aqueous materials are negative acting. Coat the blank
copper board and expose with UV light using a negative film. Any area
exposed to the light source will harden and not develop out leaving
traces that can't be attacked by the etchant. Etch the main circuitry
pattern and strip the etch resist in a weak lye solution. Now the
board is ready for soldermask.

After etching the copper image strip the primary etch resist, clean
the copper and dry the board. Now the board can be coated with liquid
photoimageable soldermask and dried. The artwork to expose the
soldermask will be clear with black opaque pads that block the UV
light from exposing any copper pads. Any area not exposed will wash
out during development and that area will now have exposed copper.
Some soldermask materials also need a second UV exposure or thermal
bake cycle after development for proper hardening of the developed
mask. That's the basics of photo imaged soldermask. After you do a few
boards and work out the process it becomes easy to do.

-------------------------

Negative acting photoresist gives better resolution than positive,
apparently, which is why most PCB manufacturers use it. That's one reason
why I'd like to try it. The PCB software I use can generate negative
transparencies.

Leon
--
Leon Heller
Amateur radio call-sign G1HSM
Suzuki SV1000S motorcycle
leon355@...
http://www.geocities.com/leon_heller