Hi, Daan,
Sorry if this is a late reply, but I've just returned from a week's well
earned holiday and am now catching up with everything that's arrived during
my absence.
As one who uses both HASL boards and ENIG boards in the same
conduction-cooled box, I can safely say that there is an insignificant
difference between the two finishes as far as thermal transfer/conductivity
properties are concerned. There are other, more significant factors at play
- one of them being the flatness of finish delta between HASL and ENIG -
ENIG, being the flatter finish, has better point-to-point contact than HASL
does, and its generally a thinner finish as well so thermal resistivity is
lower than for HASL. The biggest factor of all, though, that grossly
outweighs which finish is the better conductor, is the interface thermal
resistance between the board and the casing. Unless you have perfect face
to face contact, which is impossible, or a very good gap filler (which is
impractical between boards and casing) you will have a high thermal
resistivity between the two surfaces anyway. Merely changing the finish
from HASL to ENIG will still not cause the board finish to become the
weakest point on the thermal path, and I cannot believe that the thermal
path is so critically designed that a few decimal points of a degree
difference in thermal conductivity will cause the board to overheat
I think your designer should get out more often and learn to be more
practical.
Peter
"d. terstegge" <[log in to unmask]> 17/03/2003 06:32 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to "d. terstegge"
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Heat transfer from ENIG board to aluminium casing
Hi Technet,
We are in the process of converting some of our boarddesigns from HASL
to ENIG conductor finishing. Now one of our designers is worried about
the effect that this change may have on heat transfer from the plated
board-edges to the aluminium casing on which the board is mounted. He
feels that the heattransfer from leadtin to aluminium is better that for
nickel/gold to aluminium, possibly resulting in heat problems in the end
product.
Any ideas on this ?
Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net
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