Thermal Interface Material

Versal ACAP Packaging and Pinouts Architecture Manual (AM013)

Document ID
AM013
Release Date
2020-07-16
Revision
1.0 English

When installing heat sinks for Versal devices, a suitable thermal interface material (TIM) must be used. This thermal material significantly aids the transfer of heat from the component to the heat sink.

For lidless and bare-die flip-chip BGAs, the surface of the silicon contacts the heat sink. For lidded flip-chip BGAs, the lid contacts the heat sink. The surface size of the lidless or bare-die flip-chip BGA and lidded flip-chip BGAs are different. Xilinx recommends a different type of thermal material for long-term use with each type of flip-chip BGAs package.

Thermal interface material is needed because even the largest heat sink and fan cannot effectively cool an Versal device unless there is good physical contact between the base of the heat sink and the top of the Versal device. The surfaces of both the heat sink and the Versal device silicon are not absolutely smooth. This surface roughness is observed when examined at a microscopic level. Because surface roughness reduces the effective contact area, attaching a heat sink without a thermal interface material is not sufficient due to inadequate surface contact.

A thermal interface material such as phase-change material, thermal grease, or thermal pads fills these gaps and allows effective transference of heat between the Versal device die and the heat sink.

The selection of the thermal interface material (TIM) between the package and the thermal management solution is critical to ensure the lowest thermal contact resistance. Therefore, the following parameters must be considered.

  1. The flatness of the lid and the flatness of the contact surface of the thermal solution.
  2. The applied pressure of the thermal solution on the package, which must be within the allowable maximum pressure that can be applied on the package. The use of a smart-torque tool is suggested when applying a thermal solution to control the rate of short-term transient pressure as the TIM material relaxes. Specifications from the TIM supplier should be taken into consideration.
  3. The total thermal contact of the thermal interface material. This value is determined based on the parameters in step 1 and step 2, which are published in the data sheet of the TIM supplier.