Jim,
	The equations for the equivalent heat transfer coefficient of a composite wall looks like 1/((L1/K1)+(L2/K2)) for a two part wall.  In effect you have the same thing.  The number of layers of different material may be different, but the effect of the solder mask should be the same.  
	If K1 is the thermal conductivity of the solder mask and K2 is the ground lane, it can be easily seen the if L1 is almost zero, the effects on the overall thermal conductivity of the system will be almost be that of the ground plane no matter what the thermal conductivity of the solder mask.

Hope this helps,

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


----------
From: 	JIM ENNIS[SMTP:[log in to unmask]]
Sent: 	Monday, November 18, 1996 7:03 PM
To: 	TechNet
Subject: 	Thermal Conductivity of Soldermask


Looking to find out how much a standard LPI (epoxy) soldermask inhibits the 
transfer of heat from a hot IC to a ground plane under this IC.  Can anyone 
out there tell me whether it would be better to leave this ground unmasked?

Thanks in advance.


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