Attaching Planar Waveguide Dies to Aluminum Using Low-Stress Thermal Conductive Adhesives

We analyzed stress and heat transfer in attached planar waveguides. Die attaching adhesives were known to be the key to avoiding stress buildup in and dissipating heat from waveguides. When adhesives have a shear modulus of less than 1 MPa and a thermal conductivity of 2 w/mk, a 0.1-0.2-mm-thick layer of adhesive can eliminate stress-related effects and efficiently dissipate 30-50 mW/mm² of heat, even if aluminum is used as a substrate. Supersoft thermal conductive adhesives were thus developed and used to attach 60-mm-long AWG dies to aluminum with excellent results.