Hi, Earl,

We're not into all this teeny-weeny stuff yet, as it's reckoned to be too
fragile for military use, or something. If we did, we would have a slight
problem using your great tricks with the boards currently on the go. Our
second layer and second last layer are thermal planes, not electrically
connected to anything so we'ld have to go down another layer. No problem
with that particularly, but all that complexity and all those holes ... and
cost! Also, the 10:1 aspect ratio would give our Technical Director
sleepless nights, dreaming of hole plating stretching and cracking while
the boards are pushing up the
ZZZzzz in their cozy thermal cycles instead of him. He won't consider
anything longer and thinner than 5:1 and prefers 4:1. Do you have any
thoughts on that?

Peter





                    Earl Moon
                    <[log in to unmask]        To:     [log in to unmask], DUNCAN
                    M.COM>               Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain
                                         cc:
                    04/08/02             Subject:     Re: Vias in pads
                    06:28 PM






Peter,

I just use micro vias to get the dogbones on the second layer then use a
bottum up blind via to that layer, when the aspect ratio is below 10:1.
This
provides the test pads on the bottom side. When the aspect ratio gets
absurd, I do the double micro via trick with buried vias connecting both
sides. You already knew that but I needed to say it for some strange
reason.

I've been filling, sequentially laminating and plating over the top for
many
years. Still have some dimples but minor stuff. Works well and have you all
noticed how prices have come down significantly? Why do you suppose that
is?

Earl




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