Re: Thermal Relief Design

Farrokh Mottahedin (fmottahe@qntm.com)
Mon, 16 Jun 1997 10:19:54 -0700

Chris,

I did a similar backplane design for a mainframe class RAID storage
subsystem. We also used Positronics connectors with 15A carrying
capacity pins in a distributed power system environment. However, we
were concerned with the same problem that you are facing now and chose
to use multiple pins on the connector but limited the number of power
planes to TWO 2 oz planes. Please note that the thermal relief area
of contact to the pin should be taken into account in calculating the
total current carrying capacity. AT&T Bell Labs published some good
application notes on the subject of "Forced Load Sharing in Redundant
Power Systems" a few years ago. You may also be interested in an
article on "Powering DC-DC Converters in a Distributed System" in
Electronics Design supplement, May 16, 1994.

Regards,

Farrokh Mottahedin
Quantum Corporation

fmottahe@qntm.com

______________________________ Reply Separator _________________________________
Subject: Thermal Relief Design
Author: Chris_Heard@3com.com at SMTP
Date: 6/16/97 10:50 AM

I am designing a backplane that uses Positronics power connectors as its
interface to the the power supply. The pin in the backplane solders into a
0.070" diameter hole. Each pin can carry up to 15A and there are up to five 2
oz. planes in the stackup that connect to the hole.

My dilemma is heat vs. dc resistance. I need to use a thermal relief on all 5
planes that will allow me to heat the hole enough for solder to flow. However,
the thermal releif connection cannot be resistive enough to cause a problem with
IR drop.

The male/female mated total resistance is 1.7 milliohms.

Anybody have any experience with this problem?

Chris Heard
3Com Corporation
118 Turnpike Rd.
Southboro, M.A. 01772
508-490-5616