twb8899 wrote:
>
[deleted other interesting paragraphs]
> When drilling multilayers we always used new bits and never resharps.
> Our bits were used first for multilayers, resharpened and then used
> on two layer panels for a couple of cycles and then junked. Many
> shops now days are only doing multilayer work so they put out tons of
> bits that have drilled 2500 or less holes. These are the bits to get.
> For single sided and hobby boards you can just about drill until they
> break although the dull bits will make a larger burr.
>
Thanks Tom for sharing your knowledge with the group, although I have couple of
questions.
What is different about the holes drilled in multilayer boards that make it you
cannot use re-sharpened bits ? Is it because the bore is left smoother with a
new drill bit and sometimes that makes a more reliable copper connection
(electroless plated) to the inner layers ?
I read that they etch back the epoxy to make sure "drill smear" does not cover
the exposed copper foil of inneralyers inside the holes. The process is called
"desmear" and consists of three steps. An epoxy swell (a water miscible organic
solvent), epoxy etch (hot potassium permaganate/hydroxide), followed by
neutralize (sulfuric acid/ammonium persuflate). Is this what you used to do ?
I would imagine that after epoxy desmearing that it wont matter what mess is
left behind after drilling with old & blunt bits.
Adam