Custom Case Study
The customer’s optical transceiver design required the mounting of a laser diode on a substrate. The accuracy required when mounting this type of component, to ensure the laser output hits the lens and provides optimal performance, is largely unachievable using standard solder preforms and paste, as placement tolerances are very tight and are measured in mils (thousandths of an inch).
The final design would also need to withstand the temperature cycling testing required by the application.
The customer’s design had a pre-determined and specific location for the laser diode on the sub-mount and incorporated a resistor and edge-wrap patterning.
The Vishay EFI thin film manufacturing process is able to sputter AuSn up to a 7 µ layer with a tolerance of just 1 µ, and in a 15 mil by 15 mil square with tolerance of ± 0.5 mil, which is well below the customer’s initial design target of 1 mil.
The AuSn material is a purer eutectic solder material that makes it less susceptible to solderability degradation due to environmental issues like moisture. The alloy is also much thinner than solder paste and much more predictable, allowing it to be located much closer to the heatsink for further performance improvement.
For this design, the AuSn pad was deposited on the bottom side of the substrate, over the conductor layer, with 1 mil pulled back from the pattern edge.
This solved our customer’s problem because they are now able to fully automate the precision of their laser diode mounting process, without the need for additional preforms.
Sputtered 80/20 AuSn patterned on alumina
Sputtered 80/20 AuSn pads on top Au conductors
The Vishay EFI high accuracy AuSn patterning enabled the fine-tuning of the end customer’s automated component placement and assembly processes to meet the most demanding design requirements necessary when incorporating high accuracy optical signals in a circuit.
In addition, Vishay EFI's 80/20 eutectic AuSn allows for better thermal transfer than traditional preforms.
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