"'Jeff Heiss'
jeff.heiss@... [Homebrew_PCBs]"
<
Homebrew_PCBs@yahoogroups.com> writes:
> Your site mentions making four layer boards. How do you make them? Are
> they two two layer boards glued together? How do you handle vias?
>
> “The test board is a four-layer board because it vastly simplifies the
> power system, and I can make them at home as long as they're not too
> complex.”
>
> http://www.delorie.com/electronics/sdram/
Double-sided sticky tape. Really. I got some sheets of 3M double-sided
adhesive film on eBay (the stuff they use to stick front panels on
stoves, etc). IIRC for that project I etched four single-sided 0.005"
or so thick single-sided "boards" (this is the prepreg they use for
many-layer boards, also from eBay). I then pre-drilled the outer layers
for the blind and buried vias (the inner layers were just vcc and gnd,
so I was just exposing them so I could solder to them), taped the layers
together, and drilled the through-holes.
Note: stick the tape to the outer layers FIRST, then drill the clearance
holes in those layers (i.e. you're drilling through the tape).
Otherwise you expose copper that's still covered with tape ;-)
It might be better in the long run to use a standard two-sided board and
tape two prepregs to it, as four taped prepregs gave me a pretty
flimsy/flexible resulting board, which led to some solder breakage over
time.
For the blind vias, no through-hole was drilled. I just shoved some
solder paste in the clearance hole in the top layer, poked in some 30ga
wire, and melted it with a small soldering iron tip, soldering the top
copper to the exposed copper right under it.
For "buried" vias (outer layer to far-side-power), I just drilled a big
hole in the (unused) far layer to expose the vcc/gnd pad, and treated it
like a through-via.