Table 16 in UL 1950 third edition has a temperature rise table that
gives you their view of hot surfaces, I know that many on the list feel is
should be more detailed. With that and your particular construction you can
determine your needs. I wouldn't stop with the safety agencies however. If
the heat sink is getting warm enough to concern you, you should realize that
the heat sink is only an external indicator of your part's internal
temperatures. You can always run a thermal analysis on the part but
obviously, the internal junction temperatures are hotter than the heat sink
and you should investigate whether or not you have a part that is being
overstressed, and maybe the weakest point in your reliability system. As a
minimum it sounds like you want to get some airflow across the heat sink.
Gary
-----Original Message-----
From: Robert Macy [mailto:[email protected]]
Sent: Saturday, May 13, 2000 10:11 AM
To: Grant, Tania (Tania); Benoit Nadeau; [email protected];
[email protected]
Subject: Re: Heat sink temperature rise
Just my two cents worth with regard to temperature:
It is my understanding that for every 10C rise the life of the part is half
what it would have been.
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
619 North First St, San Jose, CA 95112
-----Original Message-----
From: Grant, Tania (Tania) <[email protected]>
To: Benoit Nadeau <[email protected]>; [email protected]
<[email protected]>; '[email protected]'
<[email protected]>
List-Post: [email protected]
Date: Friday, May 12, 2000 7:41 PM
Subject: RE: Heat sink temperature rise
Benoit,
The heatsink is a part;-- whether it is Operator Accessible or only
Serviceman Accessible depends upon the cognizant choice of the manufacturer
and the design of the PC. If that particular area where the IC and heatsink
are located is NOT in an Operator Accessible area, then you shouldn't have
to worry about the heatsink temperature.
If this area IS accessible to any and all, I would highly recommend that you
run some temperature tests of the heatsink to determine just how hot it
gets. Depending upon the results, you may discover that you just
reclassified this area from Accessible to NON-ACCESSIBLE! Either that, or
you are forced with a re-design.
For Serviceman only accessibility, and depending upon the heatsink
temperature, you might be able to get away with a WARNING label near the
heatsink, to protect the Serviceman. However, if he/she have to get their
hands in there and will have to touch the heatsink while performing
servicing activities and the temperature is still hazardous to the skin,
then you will still need to prevent physical access to that heatsink. (Get
a bigger heatsink, if you have the room!)
My personal opinion is that "hot" heatsinks should NOT be accessible to
anyone. If it is too hot to touch, the heatsink is not doing the job, and
the IC will probably have a short life.
Tania Grant, [email protected] <mailto:[email protected]>
Lucent Technologies, Intelligent Network Unit
Messaging Solutions Group
----------
From: [email protected] [SMTP:[email protected]]
Sent: Friday, May 12, 2000 2:54 PM
To: Benoit Nadeau; [email protected]
Subject: Re:Heat sink temperature rise
Forwarding for Benoit Nadeau
____________________Reply Separator____________________
Subject: Heat sink temperature rise
Author: Benoit Nadeau <[email protected]>
List-Post: [email protected]
Date: 5/12/00 12:55 PM
Bonjour de Montréal,
Usually, I am more on the EMC side, but I had a question yesterday
regarding IEC 950 that I would like to get your advices on:
In IEC 60950:, is a metal heat sink, glued on a IC which is soldered on a
PC type add-on card installed into a Personal computer chassis should be
considered as a "PART in OPERATOR ACCESS AREA" or should it be considered
as a component?
In particular I would be interested to know what should be the Maximum
Temperature-rise limits of this heat sink according to 60950 section 5.1
"Heating".
Your comments will be very much appreciated.
Regards,
----------------------------------------------
Benoît Nadeau, ing. M.ing (P.eng., M.eng.)
Conformity Group Manager
Matrox
Tel: (514) 822-6000 (x2475)
Fax: (514) 822-6275
Chairman
2001 IEEE EMC International Symposium on
Electromagnetic Compatibility
Montreal August 13 to 17, 2001
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