Creep Corrosion, Investigation of Factors that Influence Creep Corrosion, Phase 3
Friday, June 19, 2020
Section: Board Assembly

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Project Leaders


Chair: Xiaodong Jang,
Alcatel-Lucent

Co-chair: Mason Hu,
Cisco

Co-chair: Simon Lee,
Dow Electronic Materials




 

Statement of Work and Project Statement 


Background

Since October 2009, iNEMI has taken a phased approach to investigate creep corrosion. Phase 1 consisted of a survey to collect the data on creep corrosion failures and related factors in the electronics industry. The team also communicated with ASHRAE, IPC 3-11g and Lawrence Berkeley National Laboratory on related issues. In Phase 2, the team analyzed the output from Phase 1 and narrowed down the major factors that influenced creep corrosion.

Phase 3 is currently performing laboratory-based experiments to further investigate the sensitivities of the influencing factors, including surface finish, flux, solder mask geometry, solder paste coverage, reflow and wave soldering, and mixed flowing gas (MFG) test conditions (corrosive gas concentration, humidity, temperature).

The team believes more experiments, based on previously published work, could help:
  • Understand the sensitivities of the already identified contributing factors
  • Validate the effectiveness of a few mitigation approaches
  • Correlate experimental test conditions to environment classification standards (e.g. ISA G1, G2, etc.)
Testing to date has used ImAg, OSP and Pb-free HASL-finished boards with reflowed Pb-free solder paste on the top side of the test vehicle and wave solder on the bottom side — some with no-clean organic acid flux and others with no-clean rosin-flux. Boards were subjected to a mixed-flowing gas environment with gaseous composition adjusted to achieve the targeted 500-600 nm/day copper corrosion rate.

Results were as follows:
  • Copper creep corrosion was observed primarily on the ImAg- finished boards that were wave soldered with no-clean organic acid flux.
  • Pb-free HASL-finished boards experienced some severe but localized creep corrosion due to exposed copper metallization.
  • Creep corrosion was most severe in the wave soldered boundary areas where no-clean organic acid flux residue was present.


Papers & Presentations


For Additional Information

Haley Fu
haley.fu@inemi.org