The Effect of Isothermal Ageing Treatment on Different PCB Surface Finishes: Simulation and Experimental

Abstract

AbstractThis research was conducted to investigate the effect of isothermal ageing treatment on different PCB surface finishes via simulation and experimental. The surface finishes selected in this study are electroless nickel immersion gold (ENIG) and hot air solder levelling (HASL). The Pb-free solder ball used is SAC-x Ni (x = 0.5 wt.% and x = 1.0 wt.%) with a diameter of 500 µm. All the samples were subjected to the isothermal ageing process. The intermetallic compounds (IMCs) formation and growth at tin-silver-copper-nickel/hot air solder levelling (SACN/HASL) and tin-silver-copper-nickel/electroless nickel immersion gold (SACN/ENIG) at the 230 °C reflows was investigated. The characterisation of IMCs after the isothermal ageing is also being analysed in terms of type and size. The thermal distribution had come out with the analysis of steady-state thermal and transient thermal from simulation analysis. These two analyses successfully simulate the thermal distribution on the PCB package. The total deformation and equivalent stress of the PCB package were yet to be determined. It can be observed that the equivalent stress decreased when the isothermal ageing duration was getting longer. The experimental result revealed that single scallop-shape morphology of IMC formed has been detected at the interface, known as (Cu, Ni)6Sn5 for both nickel percentages after reflow soldering. Meanwhile, duplex IMC was seen after being exposed to isothermal ageing. There is no Ni element detected in IMC composition due to no availability of Ni layer on HASL surface finish. During the ageing treatment, the intermetallic thickness was proportional to the ageing duration time and nickel percentages. In addition, the ENIG finish also shows thinner IMC thickness compared to HASL after isothermal ageing treatment. Therefore, it can be concluded that SACN30505/ENIG has lower growth kinetic rate compared to SACN30510/HASL.KeywordsReflow solderingLead-free solderIntermetallic compoundsIsothermal ageingElectroless nickel immersion gold (ENIG)Hot air solder levelling (HASL)