TECHNET Archives

April 2000

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Kelly M. Schriver" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 10 Apr 2000 07:10:58 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (98 lines)
Morning Craig and All -

Most of the major PCB chemistry suppliers offer via fill compounds, ie.,
Enthone, MacDermid, Lackwerke/Peters, etc.  All of these materials are fully
curable adhesive formulations, tailored to improve their flow into plated
thru holes and vias.  These materials are generally economical, and don't
greatly increase the difficulty of the board fabrication processes.  Most
importantly, they are somewhat better thermal conductors than just plain old
air.

Thermally conductive via fill compounds are also available - two sources I
have worked with in the past are Able-Stick Adhesives and DuPont.  These
materials are generally metal filled and more expensive than those noted
above.  My personal experience has been that these are somewhat more
difficult for the PC Fabricator to work with than the more conventional
compounds.

Most of these suppliers can provide a good bit of engineering data on the
performance of their products, as well as advising you on which fab houses
are using them.

Which approach you select is highly dependent on your specific design.  A
good thermal analysis is in order, perhaps followed with some instrumented
testing.  In the case of BGA's and the like, I have often found that the
copper load in the board structure immediately beneath the devices functions
quite nicely with conventional via fill compounds, particularly when I use a
reasonable heat tranfer adhesive to dissipate the heat to the thermal core.
With DIP's, QFP's, etc., the problem is often getting the heat from part
body to the board surface.

Three criteria which I have imposed on via fill applications are:
1] SMOBC - so we have no bare metal exposure under component bodies;
2] No protrusions greater than 0.002" above copper surfaces, to prevent
interferance with solder paste stencils;
3] No surface voids allowed, which may ingest fab or assembly process fluids
and later produce contamination problems.

Regards - Kelly





-----Original Message-----
From: Craig Mcglinchy <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Sunday, April 09, 2000 4:16 PM
Subject: [TN] Thermally enhanced via's


>I have an application where I wish to dissispate heat from one side of
>the PCB through
>to a heat sink on the other side.. Someone has mentioned filled via's..
>ie vias that
>are filled with some sort of thermal paste by the PCB fabricator. Has
>anyone had any
>experience with this, or know where I can find more information? Any
>other suggestions
>would also be welcome.
>
>Thanks in advance.
>--
>Craig McGlinchy
>PCB Designer
>Tait Electronics Ltd
>Ph. (64) 3 357-0779
>Fax (64) 3 358-0432
>
>##############################################################
>TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
>##############################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with following
text in
>the body:
>To subscribe:   SUBSCRIBE TECHNET <your full name>
>To unsubscribe:   SIGNOFF TECHNET
>##############################################################
>Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
>information.
>If you need assistance - contact Keach Sasamori at [log in to unmask] or
>847-509-9700 ext.5315
>##############################################################

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################

ATOM RSS1 RSS2