Power module elements and their function

[Semicon Enthusiast]

Hello Guys,

I am currently digging deeper into the world of power modules and I have a couple of questions that I hope you can help me with:

Please see the picture below:

The substrate consists of a stack of Cu-Ceramic-Cu.

1) Has the substrate the same function for power modules as the leadframe has in discrete devices (connect the "die" to the "outside world")?
2) Why is there Cu on the bottom of the substrate aswell? There is no electrical conductivity necessary (or even wanted). Does it only have to do with the CTE of the materials?
3) What is the main purpose of the baseplate? I guess it is to have a "solid foundation" for everything above but is it not possible to make the substrate "strong" enough to remove the baseplate and connect the substrate directly with the heatsink via the TIM?

Thanks for your help as always.

Regards,
Tobias

 

[Paul2]

1) Has the substrate the same function for power modules as the leadframe has in discrete devices (connect the "die" to the "outside world")?

No, it has no conductors. It has to beryllia ceramics is there only as a heat conducting insulator.

2) Why is there Cu on the bottom of the substrate aswell? There is no electrical conductivity necessary (or even wanted). Does it only have to do with the CTE of the materials?

It prevents BeO2 plate from cracking by equalising the bending force from top copper plate from below.

3) What is the main purpose of the baseplate? I guess it is to have a "solid foundation" for everything above but is it not possible to make the substrate "strong" enough to remove the baseplate and connect the substrate directly with the heatsink via the TIM?

Yes, more stiffness. I think the module image is rather outdated in comparison to the leading edge now. Wire bonds on high power modules these days are usually replaced by solid copper plates.