Mostly the thermal mass of a board is not calculated - it's judged on a
relative basis against what you already know for boards done in the past.
If you judge a number of different assemblies as being similar to each
other in terms of board material, size, thickness, copper content, size,
weight, density and distribution of components, then you can judge that one
thermal profile will suffice for them all.
If, however, you find you have some boards with a few light-weight
components, you will probably need a profile that's different from one that
has a lot of large, heavy components.
You would be seriously wasting your time to minutely calculate and work out
a profile for evey board, as the profiles you get would be so similar to
one another as to not have been worth the effort.
If you've never profiles any boards in the past, you may want to profile si
ilar boards individually just to prove to yourself that the resultant
profiles are very similar, and that minor differences have no detectable
effect.
Have fun.
Peter
Yannick Brisson <[log in to unmask]> 16/01/2003 01:09 AM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Yannick
Brisson
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Thermal Mass
Hi,
For quiet long I've heard people said that the reflow profile must be
change for each board depending of the thermal mass of the board. My
question is how do you calculate this Thermal mass? Or to have a good
profile do you take all the datasheet of the component on the board and
take
an average of that?
Hope you can help me with this issue.
Thanks You
Yannick Brisson
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