Investigation of NiAu surface finishes using Thermal Humidity Bias test

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Dr. Medgyes Bálint Károly
Department of Electronics Technology

Electrochemical migration (ECM) is a type of short formation mechanism, which can be formed together with surface moisture (e.g. condensation) on given conductor – insulator- conductor (e.g. pectinate) structures. Under voltage bias due to the creation of moisture film disolution of metals begins in the conductor - insulator pattern, which causes expansion in the conductive filamnets (dendrites) until a circuit is formed. To examine this topic, I chose 3 types of metallization: pure Cu surface panel, NiAu-, and Ni surface coated test panels, and variants of these treated with NaCl as potential contaminant. Concentration of the created solution matches the average NaCl content of seawater (3,5 wt%). For my method of examination, I chose dew point test using a climate chamber followed by SEM-EDS (scanning electron microscope - with energy disperse spectroscopy) analysis and water drop test. I have investigated the different mechanish on surface using the dew test and optical microscope methods. This was followed by a water droplet test with which I determined the dendrite growth direction. After creating a summary of the dew point test ordered by the migration test, the samples with the surface coating were the first ones to become damaged before panels that had “clean” Cu conductors. For this reason, I concluded that the protective coatings accelerated the failed mechanism caused by ECM. From the composition point of view, the dendrites are dominated by Cu and if they contain Ni, are dominated by Ni, in the case of precipitation dendrites are more differentiated. For the reliability of the measurements I got to these conclusions by doing minimum 10 measurements of each type, to ensure that incidental mistakes have a minimal effect. In the future, I would like to continue this subject with the analysis of further metallization types and migrations of solder alloys.


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