SMTA International Conference Proceedings

Understanding Electrical Leakage And Electrochemical Migration In Electronics

Author: Eric Camden
Company: Foresite
Date Published: 10/13/2013   Conference: SMTA International

Seika Machinery, Inc.

Abstract: Electrochemical Migration is caused by three key conditions being met on an electronic assembly. The “fire triangle” conditions for dendrite growth are voltage differential (>1.5 volts), fluid media for metal salt transportation, and corrosive ions (not just halides) to initiate a deplating cell and metal salt transport of the corroding metal. Since voltage differential exist on many areas of the electronic assembly it cannot be changed, and almost all electronics are exposed to airborne moisture and humidity conditions, even in controlled environments. The only variable that can be controlled is the level of contamination found on the bare boards, components, and housing surfaces of the fielded hardware.

This paper describes what residues are found after board fabrication, SMT, after full or selective wave, and after hand soldering on the PCBA. We will also showcase three electrochemical failures showing the SEM/EDS analysis and comparing it to localized C3 steam extraction and Ion Chromatography analysis to determine root cause and corrective action. These failures are due to flux and other fabrication residues causing electrical leakage and/or dendrite growth and shorting hardware in a normal end use environment, including samples under conformal coating.

Key Words: 

Reliability, electrical leakage, electrochemical migration, dendrite, failures

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