Solderable Case Study
Assembly of Miniature Optical Components
Very small components of glass and ceramic were mounted to a carrier board with high quality epoxy. Over time the epoxy shrank slightly and altered the alignment, causing device failure. In one case where high radiation resistance was required, the epoxy failed completely.
Polymers alter structure during an extended period of "final cure".
They also absorb water, causing expansion and contraction with environmental changes. Radiation will often destroy even the best epoxy or polyamide resins.
Coursen Coating Labs Solution:
A solderable, highly adherent coating was applied to the components and the carrier. Using tin/silver solder in a reducing atmosphere, it was possible to bond the components in a permanent stable fashion. Pull tests show that the glass will fail before the joint. CCL type 3LPT system was used. For some solders, a gold flash can be supplied on top of the platinum bonding layer to enhance wetting.
Case Study Results:
Stable optical assemblies able to maintain alignment during heat, cold, humidity and immersion testing were possible. The bonds appear to withstand radiation exposure beyond other components in the systems. The assembly method shows great promise.