Transient TIM measurements for in-situ thermal characterization of microprocessors

In this article a method for the in-situ testing of TIM2 type materials is introduced. A sample holder was designed for this purpose which is capable of hosting boards as they are used in the normal operation. The setup provides pneumatic control of the fixing force on the sample. On the bottom of the holder board a ring cold plate like structure was used to ensure lateral heat flow in the board and isothermal termination at defined geometry on the ring. Electrical connections to a transient tester are provided. Measurements were performed in three different boundary conditions, such as dry package surface; silicon elastomer foil between the package and heat sink; thermal grease as TIM. The results showed well the differences between these materials in an arrangement which is very similar to the real environment. Beside the information on the TIM materials the method gives information on the total heat conduction path, too; including cooling mount or BGA underfill characteristics.