Hi ,
I have seen the following statement for the maximum pressure that has to be applied on top of TDA4VMideco SOC lid. What does 6x-10x margin means does this mean we need to apply within this range only 40.83N-24.5N? or can we apply more? Please confirm
The detailed answer is related to at what point will the solder balls start to collapse. This is related to the solder ball size and temperature of the system. There are tables in some of the threads that give max pressure estimates for different solder ball configurations vs 5, 10, 15, 20 years and temp 70, 90, 100C.
If we take the worst case scenario, 33g is the max pressure that can be applied over 20 years at 100C to a 0.65mm ball pitch. 0.8mm, lower time, or lower temp can support more pressure.
If we use 33g as the limit, scaled by 760 pins (different SoCs have different number of pins, but this is at the low end of the AM57/TDA/DRA product portfolio, that results in a maximum of 25 kgf of *uniform* force, which is equivalent to 55 lbf or 245 Newtons.
That number should be margined to account for non-uniform force. The amount of margin that is desired can be end user specific. I usually recommend 6x-10x margin, and a max pressure between 6 to 10 lbf, which seems like a reasonable “common sense” answer to how much pressure would give reasonable compression of thermal interface material and stay far away from the theoretical limit. The customer should confirm their final target based on their own tolerances and thermal interface material's optimal pressure.
