Seth and other fine folks,
I do a lot of work in the R/F MLB world. Who doesn't. In this regard, I
asked Steve if he'd kindly post two x-section images. Both show blind vias
not of the micro type. One is shown from a bucket shop not knowing what they
had done really was pretty good but for obvious plating problems.
The first image shows a "normal" blind via that has been plated over. The
fill resin was formed in the sequential lamination process. I try to ignore
all the 7628 material but for its ability to fill the hole to the top with
resin. Then, the hole/resin fill was plated over. The hole diameter, as I
recal, was about ten mils. Therefore, it was producible through "norman"
drilling processes and should have shown no ill effects as the poor plating
shown. What's really important is the plating over the top. It is robust and
shows little depression, though exagerated by the micro section, at about a
mil or so. I rather like it as it is a near perfect depression and suits
BGA's very well though they need little help self aligning.
The second (color) image shows a "normal" drilled blind via. I think Proto
Engineering provided this section (how are my latest boards coming?). What's
interesting here is the possible plating over capability. If filled
properly, like Sanmina's tech center process and others, it would be plated
over without much notice.
I tried to find a surface photo but could not. The example is somewhere in
my endless collection of PCB stuff. When I find it, I'll photograph it and
post it as well. I do remember the old Praegitzer, in Fremont, CA, did it a
few years back. Trust me, the image is one looking down and shows minor
depressioning from the surface.
Anyway, that's my story and I'm sticking to it with photos to back it up,
MoonMan
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