A Novel Precision Die Attach Technique for Opto-Electronics Packaging

Semiconductor Laser diodes that emit visible light have various interesting applications such as sensing, high density optical storage and projection displays. In any opto-electronic package, the laser diode chips are typically attached or soldered to metal or ceramic substrates that have good thermal conductivity and are well-matched in coefficient of thermal expansion using solder. Some applications require a critical alignment of the front facet of the laser diode to the front edge of the substrate onto which the laser diode chip is attached to. Depending on the application, the alignment precision could be varying from 20 μm to being as stringent as 0.5 to 1 μm. In many of these applications, the cost of packaging is also a very important factor. In such applications, it is essential to develop a laser diode chip bonding process that can meet such stringent die alignments along with a low cost manufacturing process. Therefore, the objective of this research work is to provide a low cost alternative solution for die attach process that can guarantee alignment precision of 0.5 to 1 microns and can be easily adapted to high volume manufacturing. The novel technique proposed in this work uses primarily gravity force for the facet alignments between the two components. In this passive-gravity assisted precision (P-GAP) assembly process, the laser diode (LD) chip is placed on the substrate using a traditional pick and place machine and later the substrate and the chip are tilted such that the chip slides on the substrate due to the gravity and touches a mechanical stop in-front of them. This does not involve any active alignment. In addition, we have provided few ideas to improve the sliding when gravity is used. This technique has been implemented on several samples and the feasibility of achieving the alignment precision to within a micron was demonstrated.