scope:

Description of Driving Event:

On MIDAS, thin ceramic boards (1-inch x 1-inch x .030-inch thick) were bonded to a 1-inch hollow copper cube. The bond was cured at 75C, and then the assembly was cooled to 75K for operation. It was found that some boards would shatter for what seemed like no reason, even though an identical procedure was used for ones that survived many cycles undamaged.

It was eventually found that the stresses on the boards were intimately related to their exact mounting configuration. If the boards were mounted on the cube such that two edges were in contact, the shrinkage created by taking the assembly down to cryogenic temperatures caused the edges of the boards to push on each other and stressed the boards to failure at the edges. Thus, testing the epoxy by bonding substrates to flat copper test pieces was not sufficient to ensure a successful bond.