Looking at the drawing for Laird Thermoelectric Assembly DL-210-24-00-00-00, we see a number of holes on the top of the body. The six holes around the outside are used by the customer for mounting. The three down the center are used to compress the assembly together on the Thermoelectric Modules (TEMs). These compression holes come up from under part and have screw ends in them, with only one or two threads exposed, These should not be used by the customer.
All mounting screws should have spring washers to hold compression when mounting to the cold block. As temperature varies, metals expand and contract. Spring washers are used to hold compression as the metal expands and contracts with the temperature.
A thermal pad or grease should always be used between two surfaces if the maximum heat is to be transferred. No matter how flat the surfaces are, there is always a point to point contact and the pad or grease will fill the microscopic air gaps.
The torque specification is up to the customer and the pad manufacturer. The Laird thermoelectric modules recommend a torque to achieve 250 to 300PSI of compression on a TEM. If grease is used, it is recommended to retorque after grease has pumped out (approximately one to two hours later).
Laird’s Thermoelectric Handbook contains this information and much more, including calculations for torque and all the basics on Thermoelectrics. This handbook is available from the Laird Thermal Systems website.