Technology Development

Low-Temperature Baked Paste for Au-Au Bonding

Tanaka developed a halogen-free gold paste that can be used for gold-to-gold bonds at 200°C by focusing on the low-temperature sintering properties of sub-micron size gold particles. This paste is made solely from sub-micron sized gold particles with a solvent that has low electrical resistivity (5.4μΩ-cm) and provides high thermal conductivity (150W/mK) metal bonds.

How to Use

  • A dispenser method and pin transfer method are used to supply the paste to the gold electrode on the circuit board.
  • After mounting the device (gold electrode), bonding is possible in 20 minutes without applying pressure by raising the temperature to 200°C (0.5°C/sec.). Bonding is possible in air or gas atmosphere and no washing is needed after bonding.
  • Additional heating at 200°C for about one hour is effective for increasing the bonding strength.

Exterior of AuRoFUSE™

Sintering behavior of Au particles

After heating at 200°C for five minutes in air,
bonding proceeds as a result of necking of the Au particles.

Comparison of Durability from Differences in Bonding Material

  • LEDs were flip-chip bonded to a metal circuit board using AuRoFUSE™ with gold-tin solder and silver-tin-copper solder. A LED module was created by mounting 12 LED elements connected in series of two rows. Subsequently, a thermal stress test was performed by applying a load of 24V at 350mA and turning the LEDs on and off (load time was 15 minutes). The results demonstrated a high bonding reliability of the LED devices connecting to gold particles.

Results of LED module bonding reliability test

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