Absolutely, look for smallest delta T on the thermocouples, and be aware
that although most current recirculated ovens will be less sensitive to
thermal mass than older designs, it is still important not to exceed their
capacity to deliver heat. This means that you may need to space the boards
in production, (This is sometimes overlooked when setting a profile as only
one is done at a time)
Regards
Mike Fenner
Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Leadfree: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Graham Collins
Sent: Wednesday, January 15, 2003 5:25 PM
To: [log in to unmask]
Subject: Re: [TN] Thermal Mass
Bonjour Yannick!
Thermal mass is not an accurate term, but is widely used as it seems to be
something people can easily understand. If I say to you that this heavy
part will absorb more heat it sounds reasonable. The profile results are a
result of many factors including how heavy / dense components are, how thick
the PWB is, what oven you are using, surface finishes on components... much
more than just the weight.
There is no easy calculation, the only way I know of to be sure you have the
right profile is to hook thermocouples to the board and run some trials.
You must use thermocouples on both the smallest and most exposed parts, as
well as the heaviest and most shadowed parts.
Good luck!
regards,
Graham Collins
Process Engineer,
Northrop Grumman Canada Corporation
Halifax
(902) 873-2000 ext 6215
>>> [log in to unmask] 01/15/03 01:09PM >>>
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
============================
Technicien SMT
Technician SMT
M2S Électronique
2855, Rue de Celles
Québec, Québec
G2C 1K7
Téléphone: (418) 842-1312 Ext: 264
Télécopie: (418) 842-0123
[log in to unmask]
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