ECU7 EFI project plans

[Tony Bryant]

> > I've had good luck using photo etching, from laser prints onto
> > transparency. Just did a double-sided board with a .65mm spacing
> > QFP on it. Turned out pretty good. Takes a fair bit of practice and
> > experimentation to get it right.
> 
> never tried photo etching myself... paid others to do it, but my work has always been
> simpler in nature therefore the "radio shack" or equivilent kits have been good enough,
> using three trays (acid, base, and water wash), sorta like photography :)
> 

You need a spray can of positive photoresist. Radio shack 
probably has it. You spray it on the clean board (two light coats). 
Cure it for 20 mins at about 140F (oven set as low as possible is 
good). Align your laser printed transparency on the board. Make 
sure the toner side is down or you loose the details. Sheet of 
picture frame glass over the top to press it down flat. Expose 4 
inches under a flourescent tube for 30-60mins per side.  UV lights 
or sunlight would be quicker. Develop in _very_ weak NaOH 
solution (1 tblsp per quart), until shiny copper shows through. 
Takes about 2-4 mins. Rinse and Etch using FeCl or amonnium 
persulfate. Rinse and clean resist off with alcohol or elbow grease.

Not quick, but it works with practice. Getting to know how much 
light, developer strength and duration takes some experience.