New Assembly Technology for VCSEL arrays comprising ultra-thin diodes

Objective of this paper is the development of an assembly technology for VCSELs 360 micron by 360 micron in size and a thickness of 72 micron with high positioning accuracy for automated production. Due to special customer requirements, a final thickness of the conductive glue of about 50 micron is necessary. For highest reliability, gold wire bonding of the top side contact of the VCSEL to a silicon substrate with gold metallization and printing gold-based conductive glue have been used. One VCSEL array contains 512 diodes. Special design features of the VCSEL secure that the relatively high thermal resistance of the cured conductive glue layer does not impair the optical properties or the life time of the VCSELs. Die bonding has been carried out with a Datacon EVO machine. The singulated laser chips were picked from a blue tape. For the interconnection of the top side contact we used gold wire and a Stand-Off Stich Bond process with special loop geometry. With an optimized screen printing process we did get a reproducible height of the conductive glue of about 50 micron with low standard deviation, as required, and no shorts at the silicon substrate. The position tolerance of the VCSELs meets the customer requirements. Gold wire bonding delivered excellent results, meeting the customer specification. For the first prototypes we did get a total yield of 99.9%. The optical spectrum of the VCSELs and other measurements indicate that the assembly processes do not harm the diodes or their optical properties.