Low Temperature Diffusion Bonding of Semiconductor Devices

Laser diodes (LD) have many desirable properties, e.g. small size and high electrical-to-optical efficiency. For ease of use, most applications require coupling the LD photons to an optical fiber. Attaching the LD-die to a heat-sink is a key packaging procedure. The heat-sink material is generally copper since it is the lowest thermal-resistance metal but its CTE (coefficient of thermal expansion) is significantly larger than the LD-die. Unless compensated, this CTE mismatch leads to mechanical stress which in turn degrades LD performance, lifetime and fiber-coupling efficiency. The use of a malleable-metal solder, consisting of either an indium-based or a lead-based alloy, is the present solution to the CTE mismatch problem between the LD and a copper heat-sink. Unfortunately, indium-alloy solders are subject to thermo-migration and electro-migration whereas lead-alloy solders do not comply with RoHS (Restriction of the Use of Certain Hazardous Substances) regulations. SRL¡¦s revolutionary solution to this key technical problem is to use a low-temperature (<125oC) diffusion bond, namely Au-In that has two properties that solve the CTE mismatch: „« It is applied at temperatures as low as 75oC and; „« It is simultaneously malleable and stable.