Homebrew PCBs

Phil wrote:
> I've often wondered why not use a cnc machine to cut a paste stencil?
>  Bascially, its just a couple mil thick piece of plastic sheeting that
> you squeegee (sp?) the solder paste over.  A stencil is pretty easy to
> use - I watched a guy prep a board for reflow in about 5 minutes with one.

Stencils are really a production assembly tool used
where volumes of boards are being produced.  The
amount of solder paste waste/contamination otherwise
is excessively high.

For contemporary solder paste formulations, once the
paste is brought to room temperature and handled in a
stencil screening process the shelf life is drastically
reduced.  With the cost of solder paste in prototype
quantities somewhere between $25-40 per 250gm a more
conservative approach is quite attractive.

-- 
uhmgawa@...        www.gnu.org