I am using Flow simulation to determine heat transfer inside a box with a PCB in it.  I do not have the electronics module, so I am trying to figure out the best way to model the chip on the PCB.  Currently, I separated the chip into three separate bodies and assigned the top layer as Acrylic, the middle layer as Silicon, and the bottom layer as Tin-Bearing Bronze.  I then used the middle Silicon layer as my heat source.  Fortunately, we have real world testing of this part (we are trying to modify it to make it better but want to know our results are accurate first) so we have something to compare it against, unfortunately the temperatures are about 15 degrees Celsius too high.  Does anyone have any suggestions for materials that could make my study more accurate?  It seems to me that not enough of the heat is being tranferred to the circuit board so if I had a material with a higher thermal conductivity that would help.  I don't, however, just want to start guessing at materials so I was hoping someone that had more experience modeling chips could help me out.

Thanks for any help,

Jason