Homebrew PCBs

Simao Cardoso wrote:
>  
> 
> On Thu, 2009-09-03 at 09:44 +1000, Adam Seychell wrote:
>  >
>  > The link below is of a board I did recently. I know its quite ugly,
>  > but
>  > I'm only just learning about this solder mask stuff.
>  > http://members. optusnet. com.au/eseychell /revH_photo. jpg 
> <http://members.optusnet.com.au/eseychell/revH_photo.jpg>
>  >
>  > I'd like to know what experience people have with dry film
>  > soldermasks.
>  > Might be lot more practical for hobbyist.
>  >
> 
. It can seem a good option for the homebrew but the
> LPI options out there seem even better and also easier to get.

Thanks very much for sharing your experiences with dry film solder 
masks. After trying out the LPI I think with some experimenting the 
process can be made cheap and reliable in a hobbyist setup. I was going 
to get prices for dry film solder mask, but if I'm faced with the 
problems you describe then I won't bother. The LPI soldermask is 
available in much lower minimum order cost. I paid AU$70 for 1kg, and 
split that with a someone else. 500g will last me a life time. I'd agree 
that dry film would be far far more expensive.

With some simple home made jigs , the LPI solder mask should be a fairly 
painless process.

All solder mask data sheets (liquid or dry film) I have read mention 
pre-drying the PCB before applying solder mask . This suggest to me 
that unlike photoresist, wet laminating dry film solder mask will simply 
not work.



> 
> BTW, you should rename your method to 'Painless Dry film lamination
> method for the homebrew (with water)' , wet lamination is spraying hot
> water between the hot rubber roll and dry film to replace microscopic
> air bubbles by water which will disappear in some hours because the
> dryfilm is water soluble.
> 

Ok, thanks for the suggestion. I need to update the article a little, It 
can be simplified.
When I was experimenting various manual lamination methods, I found if 
the film is applied cold then it traps too much water and *sometimes* 
causes adhesion problems. It would appear initially that no water is 
trapped , but after heating to complete the bond, I often saw pail marks 
appearing through the dry film.  I found fine traces often lift off the 
copper where these marks were located. It had me puzzled for a while. I 
tried copper micro etching, various post heating times and temperatures 
to try improve adhesion. It was only when applying hot water when I 
discovered it was trapped water causing the problem. This is the main 
reason why a squeegee board is necessary for my method.
I'm not sure what the minimum temperature is, but its likely over 35C.

Adam