SMTA International Conference Proceedings

Copper Corrosion Effects From Cleaning Agent Entrapment

Authors: David Thomas Lober and Mike Bixenman, D.B.A; and Linda Woody
Company: Kyzen Corporation and Lockheed Martin Missiles and Fire Control
Date Published: 10/13/2013   Conference: SMTA International

Abstract: With the increasing complexity and decreasing size of electronic assemblies, the cleanliness of electronics is becoming increasingly critical to the reliability of the final assembly. Contaminants, such as flux, left from the assembly process can cause electrochemical migration (ECM), or conductive anodic filament (CAF), current leakage, or simple corrosion, all of which are detrimental to the reliability of the product. To mitigate these risks, electronics manufacturers are increasingly turning towards cleaning to solve these and other issues. Most commonly, the completed assembly is cleaned at the end of the manufacturing processes, although it is becoming more common to clean at certain critical stages during the manufacturing process in addition to at the end of the manufacturing process.

There are several cleaning options available, such as vapor degreasing, semi-aqueous cleaning, and aqueous cleaning. Aqueous cleaning is the predominate cleaning process in the United States, and consists of diluting a cleaning agent with water and using the cleaning agent-water mixture to clean the assembly usually, sprayed in air in an in-line cleaning machine and then rinsed with water.

With increasingly complicated and small electronic components, there are ample opportunities for the cleaning agent, with the dissolved contaminants, to become entrapped, such as in connectors, inductors, and in vias. These trapped residues become dried onto the assembly. There is increasing concern that these residues can contribute to corrosion of exposed copper in the assembly or may contribute to the aforementioned failure modes. A study was conducted to ascertain the corrosion rate and products of cleaning agent residues and cleaning agent with flux residue on copper to assess the risk to the completed assembly. Corrosion rates were measured and the corrosion products were analyzed by Scanning Electron Microscopy Energy Dispersive X-ray spectroscopy (SEM-EDX).

Key Words: 

Cleaning, reliability, corrosion

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