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Second Round Robin Evaluation of iNEMI Creep Corrosion Qualification Test
The paper reports the results of the iNEMI creep corrosion qualification test and compares them to the first round robin test and recent mixed-flowing gas test results.
Technical Paper
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Authored By:
Prabjit Singh and Larry Palmer
IBM Corporation
NY, USA
Haley Fu
iNEMI, Shanghai, China
Dem Lee and Jeffrey Lee
iST-Integrated Service Technology, Inc.
Taiwan
Karlos Guo and Jane Li
Lenovo (Beijing) Limited Corporation
Beijing, China
Simon Lee and Geoffrey Tong
The Dow Chemical Company
Tao Yuan Hsien, Taiwan
Chen Xu
Nokia
NJ, USA
Summary
Creep corrosion on printed circuit boards (PCBs) is the corrosion of copper metallization and the creeping of the copper corrosion products across the PCB surfaces to the extent that they may electrically short circuit neighboring features on the PCBs. The paper will report the results of the second-round robin evaluation of the iNEMI creep corrosion qualification test and compare them to the first round robin test and to the recent mixed-flowing gas test results on the same iNEMI test PCBs. The modifications to and the differences in the 1st and the 2nd round robin test will be presented and discussed. The 2nd round robin test consisted of three 5-day test runs: the first 5 days at 31% relative humidity provided by MgCl2 saturated salt solution; the 2nd 5 days at 59% relative humidity provided by NaNO2 saturated salt solution; and the 3rd 5 days at 81% relative humidity provided by KCl saturated salt solution. The paper will show the round robin test results from three companies on immersion silver (ImAg), gold on electroless nickel (ENIG) and organic solderability preservative (OSP) finished PCBs soldered using organic acid (OR) and rosin (RO) fluxes. In the 1st round robin test, the ENIG finished PCBs suffered the most creep corrosion whereas in the 2nd round robin test, the ImAg finished PCBs suffered the most creep corrosion. As expected, the OSP finished PCBs suffered very little creep corrosion. The paper will also list the copper and silver corrosion rates experienced during the test runs and discuss means of better control of these corrosion rates.
Conclusions
The iNEMI taskforce on creep corrosion has developed an innovative, general-purpose FoS corrosion chamber that is inexpensive and easy to maintain. A creep corrosion qualification test has been developed that has been successful in two round robin tests at three companies on test PCBs from two different lots, with three different finishes (ImAg, ENIG and OSP) soldered with two different fluxes (rosin flux and organic acid flux). In the first-round robin, the ENIG finished boards suffered the most creep corrosion and the OSP finished boards suffered the least creep corrosion. In the second-round robin test, the ImAg finished boards suffered more creep corrosion than the ENIG finished boards and the OSP finished boards suffered the least creep corrosion. The change in the order of creep corrosion propensity between ENIG and ImAg finished boards may be explained based on the processing chemicals trapped at the solder mask edge reacting and passivating the neighboring copper and thus changing the creep corrosion behavior of the PCBs.
Initially Published in the SMTA Proceedings
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