Dave,

Thanks. I was comparing the via copper walls to the area of the via center. I was assuming vias would be solder filled. Solder has a conductivity value of about 50. 

For a 12mil via with a 1 mil wall the ratio of wall cross section to open via is about 3. If the epoxy fill is 10% of the thermal conductivity of copper then the wall is the major contributor of heat transfer. The smaller and denser the placement of the vias the copper wall get even more important. I recall figuring that a 40mil via had equal heat conducted by wall and solder. Below 40 mils the wall transfer more heat. So I am wondering if filling the vias (small vias) really does much to transfer heat..

Please check my math!

When I measured 1C/W for my DPAK I called it mission accomplished and I moved on. I am just curious if anyone actually measured things.

Thanks,
Bob K.

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Dave Schaefer
Sent: Friday, August 30, 2019 10:15 AM
To: [log in to unmask]
Subject: Re: [TN] [External] Re: [TN] TYPE III vs TYPE V vias

Robert,

From Amitron website:

" Non-Conductive fill has a thermal conductivity of 0.25 W/mK whereas Conductive pastes have a thermal conductivity anywhere from 3.5-15 W/mK. In contrast, electroplated copper has a thermal conductivity of more than 250W/mK.

So while Conductive via fill can offer needed conductivity in some applications more often than not it is possible to use non-conductive paste and add additional vias. Often this results in superior thermal and electrical conductivity with minimal cost impact. "

Recall reading a more complete paper on this somewhere but can't locate it right now.

More ammunition for the idea of using many smaller VII non-conductively filled vias and calling out increased minimum hole plating (Class 3 hole plating).