Good-day Dave,
Conductive epoxy is "sort of conductive"; it is really quite resistive. What I have noticed is that manufacturers tend to believe that it can be used instead of good plating control. The conductive epoxy contacts may be OK in a digital circuit, but they are usually unacceptable in the analog realm. I use only non-conductive epoxy and plate over the ends of the cylinders and keep a close eye on the plating of the via holes. You should only need to do this if you are designing a "via in pad" structure. If you design a dog-bone (interstitial) structure, the holes should not need to be filled if the hole to pad size ration is correct. Reference the application note at the following link for a fair discussion of PCB concerns and design reliability on fine pitch packages.
http://focus.ti.com/general/docs/techdocsabstract.tsp?abstractName=spraa99
Good designs to you,
Kim Haynes
Interface and Clock Products
High-Speed Serial Link Applications
Texas Instruments, Inc.
214-567-2057 Telephone
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Connitt
Sent: Tuesday, December 02, 2008 9:01 AM
To: [log in to unmask]
Subject: Re: [TN] Conductive Epoxy filled Vias
Joyce,
Our board house is concerned about meeting the 0.003" annular ring
requirement with a drill and hole size that small. Remember they have to
use a larger drill size to get our finished hole size. The conductive
epoxy sounds like it will "relieve us" of that issue..
Dave Connitt
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, December 02, 2008 9:16 AM
To: [log in to unmask]
Subject: Re: [TN] Conductive Epoxy filled Vias
Why not plated via?
--------------------------
Sent using BlackBerry
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Dec 02 09:07:27 2008
Subject: [TN] Conductive Epoxy filled Vias
Hello List,
We are considering implementing a 0.80 mm pitch BGA on a development
project and I have question about escape vias.
The part manufacturer recommends that we use a 0.019" pad with a 0.010"
drill. The board has to be a IPC-6012 class 3 PWB and I would like to
have a 0.003 annular ring on the escape vias.
One of our board vendors suggested we use a epoxy filled via which would
relieve us of the annular ring issue but I am not sure about still being
a class 3 board. Does anybody know where I can confirm that epoxy filled
vias are acceptable in a class 3 board?
Thanks,
Dave Connitt CID+
Printed Circuit Designer
KDI Precision Products, Inc.
A Wholly Owned Subsidiary of:
L3 Communications
3975 McMann Road
Cincinnati, Ohio 45245
Ph. 513- 943-2010 Fax 513-943-2288
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