Homebrew PCBs

Hi Bertho,

Thanks for the link to your test charts.  I will use these when I have
the Riston film in a few weeks time.  At present I only have a small
piece of already-coated board.

You wrote:

> I 100% agree with you about the limited performance of toner transfer.
> 
> My question is: why exclude positive resist options?

I haven't excluded them.  Are positive photoresists available as film
for lamination at home, or is it necessary to buy already-coated boards?
 If the latter, then I think the result may be higher costs than DIY
lamination of negative photoresist films such as Riston, possibly with
greater difficulty of obtaining whatever FR4 thickness and copper
thickness might be desired.

I don't know about shelf-life of Riston film, shelf-life of FR4 material
which has had this film applied, and likewise shelf-life of positive
film and positive-coated boards.

However, in the message I quoted:

*  http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/29673

Bob Balderstone wrote of pre-coated boards (negative or positive reist?):

>> My experience is they have a shelf-life (older = longer exposure
>> time) which again causes inconsistencies if you don't make many
>> boards at one go.

He mentioned no shelf-life problems with Riston-type (positive
photoresist) film:

>> Very, very good indeed once you've mastered the art
>> of laminating. Definitely worth shelling out the ?10 or so for a
>> cheapo laminator. Very cheap chemistry. No shelf life that I've
>> seen. Very consistent results. Can also be used as a poor man's
>> solder mask. Buy flat sheets (eBay China) not the cheap roll ends
>> which curl up every other whichway when you're trying to apply it.


 - Robin