[SOLVED] Why thermal pads are used under IC ?

[narainbhosle]

Some power IC's have thermal under them, are they used for heat dissipation?
If so why we need drills in that plane, any how its not exposed to air. What is the use of those drills (thermal pads)?

 

[KlausST]

Hi,

The word "thermal" says it all: Yes, for heat dissipation.

The drills are to spread the heat throuch the PCB to other (copper) layers (No need to be conducted) ... and to the opposite side.
This all reduces the thermal resistance package_to_ambient.

Klaus

 

[FvM]

Heat dissipation and low inductance ground connection for fast logic and RF ICs. The so called "thermal" vias are required to achieve both purposes.

Best way of solder mask generation for thermal vias is a continuous discussion topic, see possible options in a manufacturer application note:
https://www.amkor.com/index.cfm?objectid=42EDA4C7-5056-AA0A-E2A372F025BF8729
or
https://www.amkor.com/go/packaging/document-library Select "Application Notes for Surface Mount Assembly of Amkor’s MicroLeadFrame (MLF) Packages"



Best (and most expensive) option isn't shown in the comparison, plugged and galvanically overplated vias.

 

[marce]

IPC-7093, an IPC spec and guide that covers all aspects of bottom terminated components.