VDI Notes on Diode Mount and Solder

The following notes are some general guidelines and details that may be helpful when flip-chip mounting/soldering VDI diodes to circuits. The procedure noted here is essentially the procedure used by VDI. The VDI diode solder contact pads are Au thin films. Process times and temperatures are variable and depend upon the Customer’s circuits or substrates being used. This outline is simply intended to give some general guidelines for diode flip-chip mounting and soldering.

• Adhere circuit or substrate (that will receive diode) to a glass slide; all surfaces should be clean and free of debris, contamination, or residue. VDI diodes are typically soldered to Au circuit traces.
• Prepare flux. Place one drop solder flux onto new cover slide on hotplate at 120° C for 1 to 3.5 minutes until flux thickens, then apply tiny amounts of prepared flux to circuit or substrate pads with clean probe.
• Use small, Indium based solder spheres having a melting temperature of approximately 160 C or less. Position appropriate small solder sphere to center of circuit pad in flux. To pre-melt solder, heat slide at 150-170° C for 5-20 seconds. Times and temperatures will vary depending on equipment, environment and substrate materials being used.
• Re-clean solder surface. Rinse in heated DI water 10-60 seconds and shake off excess water, then dry without melting solder by cycling on/off hot plate for several 3-15 second periods. Lightly blow dry with nitrogen.
• Place diode on top of solder pads and carefully align. Gently lower weighted cover slide over circuit and diode. Carefully place the carrier slide on a hotplate and heat/solder at 150-170° C for 10-40 seconds. Remove weighted cover slide, rinse, and dry as above.
• Remove circuit or substrate from glass slide.