Authored By:
Carrillo, C., Garcia, J., Labonte, A., Larson, S., Gudeczauskas, D., and Valentine, P. PhD
Uyemura
CT, USA
Summary
There is a lack of industry consensus on the recommended plating thicknesses of Electroless Palladium / Immersion Gold (EPIG) final finish. This article aims to identify the effect on the reliability of palladium and gold thicknesses in EPIG deposits. Determining the optimal EPIG palladium and gold thicknesses will allow the electronics industry to achieve stronger solder joints and robust wire bonds. Increased ruggedness of solder joints and wire bonds provides the benefits of reduced scrap costs and increased printed circuit board (PCB) reliability over time.
This study focuses on determining the effects of palladium and gold thicknesses to ensure dependable solder joints and wire bonds. The overall research consists of an in-depth literature review, design of experiments (DoE), solder joint and wire bonding testing, and statistical analysis. The results suggest that plating thicker palladium will yield higher solder joint shear results, while plating thicker gold yields a higher wire bond pull strength. Targeting these plating thicknesses will positively impact the electronics industry by eliminating scrap and the cost of poor quality.
Conclusions
The EPIG final finish is currently not governed by an industry standard. Without an optimized standard, the threat of solder joint and wire bond failures is present. The DoE completed provided the primary contributing factor levels for optimizing solder joint and wire bond reliability. Looking at these contributing factor levels, solder joint reliability is primarily affected by palladium thickness, while wire bond integrity is affected by gold thickness (see Figure 4, Figure 6).
The following conclusions are provided to optimize solder joint and wire bonding reliability in the EPIG process:
1) Palladium quartile 4 yielded the highest solder joint shear results
2) Gold quartile 3 yielded the highest wire bond pull strength results
Optimizing plating thickness ranges for EPIG can significantly impact the electronics industry. Establishing industry standard plating thickness ranges reduces plating thickness ambiguity amongst OEMs, PCB manufacturers, and chemical suppliers. Optimized thicknesses can reduce the possibility of solder joint and wire bond failures. Decreasing scrap and the cost of poor quality in the EPIG process will positively impact the industry.
Initially Published in the SMTA Proceedings
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