Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Power component thermal via



Power component thermal via | 1 February, 2000

I am to assembly a power SO on the top side of a double side board. My designer has implemented a lot of thermal vias in the heat sink pad of this component. The problem is that i need to prevent the solder cream from polluting the bottom side of the board. Indeed, this bottom surface has to be as flat as possible. I have try to deposit the solder cream on the outside of all thermal vias. But the cream still reflows in some thermal vias, and pollutes the bottom face. Therefore does anybody have a solution or a method to this problem ?

reply »


Re: Power component thermal via | 1 February, 2000

Emmanuel: You have choices to prevent the solder paste from flowing to the second side during reflow:

1 Have your board fabricator plug the vias. 2 Put a temporary solder mask on the secondary side vias. 3 Have your designer relay-out the vias underneath the power SO as blind vias on the secondary side. This has the bonus of improving the secondary side flatness that you mentioned. 4 You may get away with a applying thermal tape, such as Kapton, over the secondary side vias.

God luck

Dave F

reply »

pascal MATHIEU


Re: Power component thermal via | 2 February, 2000

emmanuel : i agree with Dave , it's easy to have blind hole on the bottom side , of course in this case you'll lose some thermal efficiency ;the second solution is to put on the bottom side between the board and your heatsink a soft thermal interface like gap pad or someting like that ; this interface 'll absorbed easily the level difference due to the solder on the bottom side of the board ; main drawback of this solution if you are in a "mass production" configuration ,it's quiet difficult to pick and place automaticaly the thermal interface . see you Pascal

reply »

IPC Training & Certification - Blackfox

Online IPC Training & Certification