Hard Gold Plating Control: Thickness, Hardness, and Wear Resistance Optimization

This document focuses exclusively on the process control variables that determine hard gold coating performance: bath chemistry stability, current density distribution, temperature control, and contamination management. It explains how to achieve uniform thickness across all fingers, control grain structure, and manage internal stress to avoid microcracking. Engineers will find quantitative process windows and control methodologies.

Core Content 

1. Hard Gold Coating Functional Requirements

• Low & stable contact resistance.
• High wear resistance (hardness 150–200 HV).
• Strong Ni-Au adhesion.
• Uniform thickness for predictable wear life.

2. Plating Bath Chemistry Control

• Gold concentration: 2–10 g/L.
• Alloying agents: Co or Ni (0.1–0.3%, ppm-level control).
• pH: 4.0–5.5, temperature: 50–65°C.
• Additives: grain refiners, wetting agents.

3. Current Density & Thickness Uniformity

• Typical current density: 0.5–2.0 A/dm².
• Edge effect: higher current at edges → overplating.
• Mitigation: shielding plates, auxiliary cathodes, optimized rack design.

4. Grain Structure & Internal Stress

• Fine grains = higher hardness, better wear resistance.
• Coarse grains = lower hardness, higher wear rate.
• Internal stress → microcracking risk.

5. Surface Roughness Control

• Too rough: high localized stress, accelerated wear.
• Too smooth: insufficient friction, fretting susceptibility.
• Controlled roughness required for stable contact.

6. Process Monitoring

• XRF thickness measurement (Au/Ni).
• Statistical Process Control (SPC) for thickness and hardness.
• Bath chemistry analysis (gold concentration, additives, contaminants).