TECHNET Archives

August 1999

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:
Phil Bavaro <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 12 Aug 1999 09:14:25 -0700
Content-Type:
text/plain
Parts/Attachments:
text/plain (46 lines)
Our design group just brought a new technology (to me at least) out
yesterday and I find it hard to believe that this is proven technology in
the industry.

In order to transfer heat away from a part which generates quite a lot of
heat (upwards of 4 watts?), they have placed a matrix of vias below it and
then filled them all with silver filled epoxy, expecting us to then screen
solderpaste on top of this in order to connect the supposedly solid barrel
of the via with the belly of the component.  The assembly consists of
essentially a CCA mounted inside of small chassis and the only cooling
transfer is through the boards which sits on a boss in the chassis.

Is there published reliability data on solder connections made by
interfacing silver filled epoxy and eutectic solder?  If so, please direct
me to it. We do have a very small percentage of silver in our alloy.

The solderability of silver filled epoxy when exposed to solderpaste on top
of a nickel gold substrate does not leave me with a warm and fuzzy feeling.
 I am confused how the intermettalics (I know, I know, which one?) are to
be formed, or even if the silver filled epoxy wets with solderpaste under
normal reflow temperatures.  If there are other concerns I need to focus on
as well, I'm open to all suggestions.  Someone mentioned galvanic
interactions......

My hunch is that we will have large voids in the connections below the part
and this will reduce the heat transfer ability of the assembly when
compared with a solid solder filled via that wets all the way up to the
belly of the component.

But then again I could be wrong..........please enlighten me.
Phil Bavaro

##############################################################
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 Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################

ATOM RSS1 RSS2