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May 1997

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Thu, 29 May 1997 08:17:42 -0500
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Steve,
	There is no way to determine the internal temperature of the component from the outside temperature of the component alone.  This is because the temperatures you are measuring on the component lead are transient (changing with time).  The internal temperatures of the component are related to the external temperatures as a function of time, temperature, thermal conductivity all the materials involved and the physical configuration of the system you are trying to predict.  As you can see, there is no quick answer to your problem, but there are a few ways that you can go about solving it.
	The first is to measure it.  This can be done by placing a thermocouple inside the component in the area that you are interested in.  Needless to say, you want to use the smallest thermocouple you can lay your hands on and getting it mounted in the component will be a real challenge.
	The second is to use a finite element model that accurately represents your component.  Once you have the model you can determine if you reflow profile is the problem.  This solution involves getting the software to run the model, if you don't have it already, and learning how to use it.  This doesn't mention the problems with finding good material properties.
	Either way you go, you have some challenges ahead of you.  If you would like to discuss this further, feel free to contact me off line and either the phone number or e-mail address below.  Good luck and remember, this is the stuff tat makes kind of work fun to work on.

Hope this helps,

John Guy
American Competitiveness Institute (EMPF)
317-655-3673 x130
[log in to unmask]

----------
From: 	Steve Quinn[SMTP:[log in to unmask]]
Sent: 	Wednesday, May 28, 1997 5:14 AM
To: 	[log in to unmask]
Subject: 	ASSY:  Profiling parts.

We have profiled an IC, which we are now seeing failures on.  The max temp
on the leg of the part was 217 C.  We have been told by our supplier that
the max temp for the part is 221 C.  They are saying we are reflowing solder
internally, which causes a short, and the failure.  
        My question is, does anyone have a good idea of what the correlation
is from external temps on the leg of a part, to the internal temps of an IC.

Thanks for any ideas or data to prove us right or wrong.


Steve Quinn
Heurikon Corp
Madison, Wi

608/831-5500

[log in to unmask]

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