SAC is relatively strong under compression, but underlying Cu cct  
might not be under pressure (consider each Ball as  point contact).  
you might need to do FEM to find out.. for example, if you have via  
in pad, you might damage the via before compressed SAC ball (same  
apply for the BT-substrate on component side).  IMHO.
On Mar 14, 2018, at 12:49 PM, Dave Schaefer wrote:

> Does anyone have any references to good information regarding the  
> amount of compression that can be applied to an SAC BGA component  
> for heat sinking purposes? We want to maximize our thermal  
> performance without sacrificing solder joint & component reliability.