Vishay Fine-Tuning Assembly Process with AuSn Patterning

Challenge

The accuracy required to mount a laser diode on a substrate to ensure the laser output hits the lens and provides optimal performance is achieved using standard solder preforms and paste, as placement tolerances are extremely tight and measured in mils. Additionally, the final design would need to withstand the temperature cycling testing required by the application.

Solution

Restrictions for this customization included a pre-determined and specific location for the laser diode on the sub-mount, an incorporated resistor, and edge-wrap pattering.

The Vishay EFI thin film manufacturing process can sputter AuSN up to a 7µ layer with a tolerance of only 1µ and in a 15mil x 15mil square with a tolerance of ±0.5mil, well below the engineer's initial design target of 1mil. The AuSn material is a pure eutectic solder material that makes it less susceptible to solderability degradation due to environmental issues such as moisture. The alloy is also thinner than solder paste and more predictable, enabling it to be located much closer to the heatsink for greater performance improvement.

For this design, the AuSn pad was placed on the bottom side of the substrate, over the conductor layer, with 1mil pulled back from the pattern edge. This solved the problem because the engineer is now able to fully automate the precision of their laser diode mounting process without the need for additional preforms.

Benefit

The Vishay EFI high-accuracy AuSn patterning enables the fine-tuning of the engineer's automated component placement and assembly processes to meet the demanding design requirements of incorporating high-accuracy optical circuits in a circuit.