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Effects of mould on electrochemical migration behaviour of immersion silver finished printed circuit board
Pan Yi1, Kui Xiao2, Chaofang Dong2
1Corrosion and Protection Center, University of Science and Technology Beijing, Beijing 100083, PR China.
Abstract:
The role played by mould in the electrochemical migration (ECM) behaviour of an immersion silver finished printed circuit board (PCB-ImAg) under a direct current (DC) bias was investigated. An interesting phenomenon is found whereby mould, especially Aspergillus niger, can preferentially grow well on PCB-ImAg under electrical bias and then bridge integrated circuits and form a migration path. The cooperation of the mould and DC bias aggravates the ECM process occurring on PCB-ImAg. When the bias voltage is below 15V, ECM almost does not occur for Ag coating. Mechanisms that explain the ECM processes of PCB-ImAg in the presence of mould and DC bias are proposed.
Insights
Mould, particularly Aspergillus niger, accelerates electrochemical migration (ECM) on printed circuit boards (PCBs) with immersion silver finishes under direct current (DC) bias. This microbial growth bridges circuits, forming migration paths and worsening PCB-ImAg degradation, especially above 15V.
Area of Science:
- Materials Science
- Microbiology
- Electrochemistry
Background:
- Immersion silver (ImAg) finishes are used on printed circuit boards (PCBs) for their excellent solderability and cost-effectiveness.
- Electrochemical migration (ECM) is a reliability concern in electronic components, leading to conductive filament formation and circuit failure.
- The influence of biological factors, such as mould growth, on ECM in PCB finishes is not fully understood.
Purpose of the Study:
- To investigate the role of mould in the electrochemical migration (ECM) of immersion silver (ImAg) finished printed circuit boards (PCBs) under direct current (DC) bias.
- To understand the synergistic effect of mould growth and DC bias on ECM acceleration.
- To propose mechanisms for ECM in PCB-ImAg with mould presence.
Main Methods:
- Direct current (DC) bias was applied to PCB-ImAg samples.
- Mould inoculation, specifically Aspergillus niger, was performed on the samples.
- Microscopic observation and analysis were used to study mould growth and migration path formation.
- ECM behaviour was monitored under varying bias voltages.
Main Results:
- Mould, particularly Aspergillus niger, preferentially grew on PCB-ImAg under electrical bias.
- Mould growth bridged integrated circuits, creating a conductive path for electrochemical migration.
- The combined effect of mould and DC bias significantly aggravated the ECM process on PCB-ImAg.
- ECM was minimal for Ag coating when the bias voltage was below 15V.
Conclusions:
- Mould actively participates in and accelerates the electrochemical migration (ECM) of immersion silver (ImAg) finishes on printed circuit boards (PCBs).
- The synergistic interaction between mould growth and direct current (DC) bias poses a significant reliability risk for PCB-ImAg.
- Understanding these mechanisms is crucial for developing strategies to mitigate ECM failures in electronic devices exposed to microbial environments.
