Quantitative Analysis of Film Thicknesses of Multi-Layer Plating Used on Cards

Importance of the Topic

The reliable measurement of multi-layer metal plating on electronic contacts is critical for ensuring device performance, material conservation and cost efficiency. Non-destructive X-ray fluorescence (XRF) techniques enable rapid, in situ thickness evaluation without damaging delicate IC and SIM card surfaces.

Objectives and Overview of the Study

This work aims to demonstrate a standard-free quantitative method for determining the deposition amount and film thickness of gold (Au), nickel (Ni) and copper (Cu) layers applied to contact areas on IC chips and SIM cards. The thin-film fundamental parameter (FP) approach is applied using small analysis spot sizes.

Methodology and Instrumentation

• Samples: Certified reference material (NMIJ CRM 5208-a), commercial IC chip, SIM card
• Technique: XRF spectrometry with thin-film FP method
• Analysis diameters: 1 mmφ and 3 mmφ
• Instrument: Shimadzu EDX-8000/7000 EDX system
• X-ray source: Rhodium target at 50 kV
• Detector: Silicon drift detector, in air, no primary filter, 100 s integration, max 30 % dead time
• Analytical lines: Au Lα, Ni Kα, Cu Kα

Key Results and Discussion

• CRM validation yielded errors within 5 % for Au, Ni, Cu deposition values.
• Measured deposition on IC and SIM: Au ~71–76 μg/cm2, Ni ~1 700–1 780 μg/cm2, Cu ~23 900–25 300 μg/cm2.
• Calculated film thicknesses: Au 0.037–0.040 μm, Ni 1.88–2.00 μm, Cu 26.8–28.3 μm.
• Assuming an infinite Cu layer corrected Au and Ni quantitation in thick regions.
• Repeatability tests (10 replicates) showed coefficients of variation <0.6 % for Au and Ni layers.
• Upper quantitation limit for Cu film thickness is ~18 μm before X-ray intensity saturation.

Benefits and Practical Applications

• Non-destructive, high-sensitivity measurement from nanometer to micrometer scale.
• Localized analysis enables spot measurements on electronic contacts with minimal sample preparation.
• Supports quality control in plating processes and assessment of precious metal usage, aiding recycling and cost management.

Future Trends and Potential Applications

• Expanding measurement capability with larger spot sizes for very thick films.
• Applying the FP XRF approach to other valuable coatings such as platinum, palladium and rhodium.
• Integrating XRF thickness mapping into automated production and inline quality assurance systems.

Conclusion

The thin-film FP XRF method offers an effective, non-destructive solution for accurate quantitation of multi-layer Au/Ni/Cu platings on electronic components, enhancing process control, material stewardship and device reliability.

Reference

Estimated mass and price of gold on the SIM card: 80 μg (80 μg/cm2 × 1 cm2); cost approx. 0.37 yen per card (London Metal Exchange, Oct. 13, 2017).