Werner,
Given the broad array of assemblies being constructed today, both in terms
of size and in terms of types/density of components, how can you ever know
how inaccurate your measurements are unless you use a fully populated
board. For some designs, a bare board with few components may be
completely acceptable. But for others, it may lead to significant errors.
Jeff Perkins
-----Original Message-----
From: Werner Engelmaier [SMTP:[log in to unmask]]
Sent: Thursday, November 12, 1998 8:29 AM
To: [log in to unmask]
Subject: Re: [TN] Temp Profiling
Hi Tom,
In a message dated 11/11/98 18:14:10, you wrote:
>Werner,
>Perhaps I should clarify my question. My question is if temp
>measurements using bare fab and few components on it including the
>biggest thermal mass and few passives are inaccurate, should I use the
>first loaded board prior to reflow?(just out of the PnP) and if so,
>should I place the thermalcouples in the solder paste or on the lead?
>Tom Han
>Ardent Systems
You make an assumption, that "temp measurements using bare fab and few
components on it including the biggest thermal mass and few passives are
inaccurate." I do not agree with this premise, unless you have an old reflow
machine. Modern so-called 'Convection'-machines, and even the late generation
so-called 'IR'-machines (I put the emphasis 'so-called' on them, because these
nomers are conventions and do not describe the complete heat transfer
situation), have sufficient heat transfer from both IR and covection, that
neighboring components have no significant impact on each other.
Since the leads are the slowest heating parts of the solder joints, it is best
to place the thermocouples on the leads. Make sure, that the thermocouples are
placed so not to interfere with the heat transfer to that solder joint; and
use the thinnest thermocouple wire you can handle to avoid errors from the
thermocouple wire.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]
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