clean pyralux foil in water
wet copper side of pcb with water
this helps applying the resistive film
preper resistive dry film
we use carpenter tape to seperate the dry film protective backing
it will come off eventually
discard the clear side, and apply the blue film onto the copper
push the air bubbels. from the center out
lift gentley, with sharp object
we will now preper the flexPCB to go into the laminator.
cut the resistive foil edges
as this is a big PCB we dont want it to overtake the paper.
note we leave 1-2cm of foil at the edges you will see why later
place flexpcb between 2 folded A4 paper.
into the laminator, twice
after the lamination, we remove one of the two A4 pages
the other paper is attached to the foil, we cut it along the flexPCB edges
note we leave a piece of paper/foil. it will help removal later
we are using an ultraviolet (UV) exposure unit sun can also work as well as an halogan lamp.
but first we place our design ontop of the laminated resistive foil. this is not a mirror image. as is.
the design is printed twice on a "laser printer transparency" sheet
then glued to each other using a few drops of super glue on edges.
twice so no light will "bleed" through
secure the mask to the prepared PCB with tape. keeping rough alignment
place the PCB face down on your UV light source.
we found 90 seconds of exposure time is good for our exposure unit your might vary
carefully remove the resistive foil using that piece of overhang you left before
we will now remove the areas not exposed to the UV light so place the PCB in your sodium carbonate solution ( 1 gr of sodiumCarbonate for 100 ml of water )
scrubing it genttly with a tooth brush. for 2-3 minutes until all the non UV exposed resistive foil detach
remove all the unxposed foil as it will interfere with the etching.
take your time