My apologies to Dan, Susan and all... I PRESUMED to know that Susan was
referring to sequentially laminated blind via's. The "filling" with resin occurs
in this type of blind via. As Dan mentions, we also have done the controlled
depth drill variety, which do not fill with resin.
The removal of resin I mentioned previously, is in regard to thermal via's with
a large area of metallization used to absorb and displace heat from a device. In
the case of TAB devices, they are glued to this "heatsink". In the use of seq.
lam'ed blind via's, the resin in these holes has been known to swell during
thermal cycles. In this case. the resin interferes with a device mounted or
glued directly to the metallization.
Regards,
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Re[2]: Blind Via's in MLB's
Author: [log in to unmask] at internet_gateway
Date: 2/19/96 3:19 PM
I don't understand the need to 'depth drill after lamination to remove
some of the resin'.
However, nearly all of the blind-via work that we do is
controlled-depth drilled at the same time through holes are drilled
and processed, essentially, the same as non-blind-via product.
Regards,
Daniel Buxton
Mfg. Engineer
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Subject: Re: Blind Via's in MLB's
Author: [log in to unmask] at INTERNET
Date: 02/19/96 2:27
Susan
Here's my opinions:
1) REAL ESTATE. When holes only go halfway or part way through a
board, the hole and associated pads don't take up space on all layers.
This gives more routing room to designers to run traces, where a
normal through via would not allow.
2) & 3) Blind and buried via's "typically" get filled with resin
during the lamination step(s). I can't imagine a case where you
prevent the holes from becoming filled.
4) I wouldn't say they are required to be capped with plating and or
soldermask. As part of the natural process after lamination, boards
see an e'less deposition (direct platers, no offense) and electroplate
of coppers. This tends to "cap" the blind via's. I have seen cases of
"thermal via's" actually being depth drilled after lamination to
remove some of the resin. During thermal cycling, the resin will
soften and "move" and can cause the plating on the surface to break
away or lift.
I would offer some pictures of the above conditions, but I'm not very
skilled in ASCII art, as are some of our fellow `netters. Please feel free to
call me to discuss or perhaps I could FAX you something!
Regards,
Tom Bresnan
Product Eng'g Mgr
MULTEK
16 Hammond
Irvine, CA 92718
714.951.3388
714.951.8794 FAX
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Unidentified subject!
Author: [log in to unmask] at internet_gateway
Date: 2/18/96 12:09 PM
ding Blind Vias in multilayer
printed boards.
1) Why would someone want to use them?
2) If used are they always filled?
3) When does the filling operation take place?
4) Are they required to be capped by plating
or solder mask?
I am looking at a lot of multilayers with blind vias and
need some help in understanding the manuf process.
Thanks,
Susan Mansilla
Robisan Laboratory
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