It is observed that hardness testing is required for electroplated gold bumps, whereas this step is not performed for other metal electroplating—why? What are the applications of gold bumps?
The most common application is in LCD driver ICs (COG packaging), where Au bumps are flip-chip bonded to ITO electrodes on a glass substrate.
Properties of gold:
- Oxidation resistance
- High electrical conductivity
- Good compatibility, suitable for bonding with gold wire, solder paste, and ACF
- Very soft—pure gold can be scratched slightly with a fingernail
Why anneal gold?
Low-temperature annealing (150–300°C) after gold electroplating improves the grain structure of gold, increases its density, and enhances hardness—up to 70–90 HV.
Why does electroplated gold need higher hardness?
In COG, FOG, TCB and other packaging methods, Au bumps are mechanically bonded. As bump pitch decreases, if the gold layer is too soft, it can easily flatten or overflow during bonding. This can cause metal bridging (short circuits) between gold bumps. Therefore, electroplated gold must have sufficient hardness.
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