SMTA International Conference Proceedings

A Novel & Cost-Effective Electroless Nickel Immersion Gold (ENIG) Surface Finish for Better Reliability of Electronic Assemblies

Authors: Kunal Shah, Ph.D.
Company: LiloTree
Date Published: 10/14/2018   Conference: SMTA International

Abstract: Conventional Electroless Nickel/Immersion Gold (ENIG) currently available in the market is prone to black-pad defects (hyper-corrosion related failures) associated with de-wetting of solder. ENIG also suffers from brittle solder joint failures. Due to these reasons, there are field failures and reliability concerns of electronic assemblies - component disconnection which lead to overall malfunction of electronic assemblies. Most ENIG manufacturers/suppliers provide cyanide-based gold chemistry which has health and ecological hazards. Moreover, gold layer thickness with conventional ENIG has very high thickness distribution and higher thickness is correlated nickel corrosion and additional gold consumption (expensive). The novel ENIG eliminates black pads- corrosion related issues, low gold thickness-small thickness distribution, achieves robust solder joints and provides improved quality and reliability of electronic assembly. Also, it uses cyanide-free chemistry for immersion gold process making it eco-friendly. This allows manufacturers to consume eco-friendly and cost-effective product while avoiding major field failures and resulting consequences. Novel ENIG eliminates black-pad related failures and lead to robust, high quality and reliable solder joints for electronic assemblies.

The root cause of black-pad defects has been identified as hyper corrosion activity at gold and nickel-phosphorous interface which involves nickel depletion and an enrichment of phosphorous in localized areas. Interfacial engineering approach had been used to successfully eliminate black pads by achieving marked improvement in corrosion resistance. Corrosion tests have been conducted using Potentiodynamic Polarization method and Tafel plots were generated between novel ENIG and conventional ENIG. The results show 10x improvement in corrosion resistance. Also, interfacial engineering led to smoother topography of Ni-P surface, low gold thickness and small thickness distribution. Also, it has also led to improved intermetallics at the solder joints leading to robust solder joints and elimination of brittle failures. Ball Shear and Ball Pull Tests (Industry Standard based testing: JEDEC Standard) were conducted on novel ENIG based solder joints and conventional ENIG based solder joints. No solder joints (intermetallics) failures found with novel ENIG compared to 80% of failures found at the solder joints with conventional ENIG. Also, the force to induce failure increased by more than about 50% with novel ENIG compared to conventional ENIG. A novel ENIG is eco-friendly and cost-effective with high corrosion resistance and robust solder joints for better reliability of electronic assemblies.

Key Words: 

Electroless Nickel/Immersion Gold, gold layer thickness distribution, solder joints reliability, black pads (hyper-corrosion).

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