Qualification Test Development for Creep Corrosion, Phase 3 (The Effect of Relative Humidity on Creep Corrosion)
- Prabjit Singh (IBM)
- Simon Lee (Dow Chemical)
White Paper & Reports
(December 12, 2017) (this is for iNEMI members only)
Statement of Work and Project Statement
Finalize the FoS test setup and procedure. Determine the threshold relative humidity below which creep corrosion will not occur even in corrosive environments high in sulfur-bearing gases and chlorine.
Electronic hardware can be susceptible to creep corrosion in corrosive environments. Creep corrosion is the corrosion of metallization (generally copper and silver) and the migration of the corrosion product (typically copper and silver sulfides) across the printed circuit board (FR-4 and solder mask) surfaces. In environments high in sulfur-bearing gaseous contamination, the extent of creep corrosion may be so high as to electrically short circuit adjacent pads and traces, causing the circuit boards to malfunction.
To help eliminate creep corrosion, industry has initiated significant effort to better understand its cause and mitigation. iNEMI had an experimental program studying creep corrosion since October 2009. The iNEMI project on creep corrosion testing using mixed-flowing gases (MFG) was successful in identifying the role of finishes and fluxes on creep corrosion. MFG test is complex and expensive. Only a handful amongst the major electronics companies worldwide have MFG test capability. The MFG chamber (iNEMI creep corrosion test condition: H2S = 1200 ppb; NO2 = 200 ppb; Cl2 = 20 ppb; SO2 = 200 ppb; 40?, RH 70-75%) has copper corrosion rates much higher than silver corrosion rates. However, indoors, the copper corrosion rate is much lower than silver corrosion; whereas, outdoors, the opposite is true. There is motivation to explore the use of flowers of sulfur chambers as a means of qualifying PCBs that will survive the harsh, corrosive field environments without suffering creep corrosion.
Significant experiments have been done in Phases 1 and 2 to design the FoS test chamber, and to develop the test procedures to demonstrate creep corrosion and to compare with field failures. The major remaining challenge is to control the humidity level within sulfur-bearing gases and chlorine gas. If we can run the FOS test at much lower humidity, then the FoS test could be used to determine the threshold relative humidity below which creep corrosion will not occur even in corrosive environments high in sulfur-bearing gases and chlorine.
Objectives of Phase 3
The Creep Corrosion team is looking for donations for test method validation. We expect to use PCBs from lots that suffered creep corrosion in the field, to prove the test is capable of determining the propensity for creep corrosion. We are recruiting companies that have such PCBs to participate in the project or donate boards for anonymous testing.
- Improve the test setup to achieve several relative humidity levels (10-80%)
- Study the effect of relative humidity on creep corrosion.
- Validate the test using PCBs from lots that suffered creep corrosion in the field.
- Compare the test resutls with MFG test.
- Document the Test Procedure and deploy in the industry.
Qualification Test Development for Creep Corrosion Using Flower-of-Sulfur (FOS) Chamber, presented at SMTA China East 2018 (April 25, 2018; Shanghai, China). This iNEMI presentation was recognized as best presentation of Technology Conference Two at SMTA China East 2018.
Round Robin Evaluation of iNEMI Creep Corrosion Qualification Test; Prabjit Singh (IBM Corporation); APEX (February 2018)
Round Robin Testing of Creep Corrosion Dependence on Relative Humidity; Prabjit Singh (IBM Corporation); SMTAI (September 18, 2017; Rosemont, Illinois, USA)
Second Round Robin Evaluation of iNEMI Creep Corrosion Qualification Test; Chen Xu (Nokia Bell Labs), SMTA International, October 15, 2018 (Rosemont, Illinois).
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