Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "frankwinter1"
<frankwinter1@...> wrote:
>
> I have been using "the" toner transfer method for about 2 years and 
> produced some very good PCBs.
> Until a week ago!
> I had problems making the toner sticking to the copper.
> 
> After a lot of frustration I tracked the problem to the kind of 
> liquid soap I used with Scotchbright pads to clean the copper.
> 
> It turned out that my wife changed the brand of liquid soap to 
> one "that is kind to your skin". So it may be - but it leaves an 
> invisible (oily?) film on the copper which is virtually undetectable.
> 
> Using my old liquid soap brand cured the problem.
> 
> I feel pretty silly now, but then again 20:20 hind sight always leads 
> to highly accurate observations.
> 
> The moral of the story is of course - check the cleaning agent and 
> don't let your wife decide the brand.
> 
> Frank
>



A mild etching of the copper before lamination will always help
adhesion of the etch resist. This process is known as micro etching. I
use a Dupont hot roll laminator to apply dry film photoresist for my
boards but always microetch the blank panels first. One method that
works good is a vinegar and peroxide mixture. This makes a very weak
etchant that leaves a matte surface on the copper. Here is my process:

Wet sand copper with 220 grit sandpaper using a bit of dish detergent

Water rinse

Soak in the microetch mixture for five minutes

Rinse and dry

Laminate dry film photoresist with hot roll laminator

Wait thirty minutes for photoresist to bond 

Expose panels using film negative and UV light

Wait twenty minutes for photoresist to polymerize 

Develop in 1% sodium carbonate (soda ash) solution

Rinse

Etch copper panels

Rinse and dry

This is the process I use and I make a lot of boards with almost zero
rejects. Sanding and microetching the copper panels first is the most
important step. Proper adhesion of the etching resist is critical as
this prevents the etchant from lifting the edge of the resist. Micro
etching should be used no matter what type of etch resist system you
plan to use. 

Tom