AuLTRA^® 75/78/79 Off-Eutectic Preforms

Available Alloys

• 79Au/21Sn
• 78Au/22Sn
• 75Au/25Sn

Geometry

Guidelines for preform geometry can be derived from the die size. Generally, 90-100% of the die size indicates the preform’s x and y dimensions. Our AuLTRA® 75 off-eutectic AuSn alloys have thickness capabilities down to 0.005″. As for thickness, our Off-Eutectic AuSn alloys have thickness capabilities down to 0.0005″. The most critical attribute for a die bonding application is flatness. Due to process constraints, fixturing can be challenging and time consuming. Allowing the die to float freely on the preform can be advantageous. If the preform is not flat, it can skew the die during reflow and lead to failure. Proper processing is key to preserving flatness.

Alloy Chemistry

AuSn has a sensitive eutectic phase, which can be altered by Au-rich metallizations. This can result in areas that do not wet or flow properly, creating a weak solder joint. Adjustments with off-eutectic AuSn alloy compositions can be made to accommodate these metallizations, resulting in joint characteristics that are optimized for high reliability and performance.

Packaging

Packaging in waffle trays is the primary method for many die-attach applications while tape and reel is another similar technique that can be used. Both methods are suitable for automated assembly and offer excellent protection during transit and storage. Die-attach preforms can come in various sizes, so flexibility in design is important. We have an extensive library of trays and tape available.