3RD INTERNATIONAL CONGRESS ON TECHNOLOGY - ENGINEERING & SCIENCE - Kuala Lumpur - Malaysia (2017-02-09)

Effect Of Post-reflow Cooling Rate And Isothermal Aging On Imc Formation Between Sacn30505 Lead-free Solders & Enimag
The surface finishes of printed circuit board (PCB) produce a critical interface between the bare copper of PCB and the electronic component. It act as protection for underlying copper from oxidation and provide solderability and wettability of the surface. Electroless Nickel/Immersion Gold (ENIG) finish is one of the surface finishes that offered the best characteristics for printed circuit board (PCB). However, ENIG is a costlier finish because the price of gold is very expensive. With the optimization and development of a new alternative surface finish, Electroless Nickel/Immersion Silver (ENImAg) hopefully can offer better price and properties compared to ENIG. In this study, the effect of post-reflow cooling rate and isothermal aging on formation and growth of the intermetallic compound (IMC) between Sn-3.0Ag-0.5Cu-0.5Ni (SACN30505) lead-free solders and Electroless Nickel/Immersion Silver (ENImAg) was investigated. SACN30505 lead-free solder alloy with solder ball diameter of Ø500 µm has been used. The morphology, thickness, type and size of the intermetallic compounds formed was observed from three different cooling medium which are furnace-cooled, air-cooled and water-cooled at reflow state and four different isothermal aging times which are 250 hours, 500 hours, 750 hours and 1000 hours. The characterization of intermetallic compound formed was made by using Optical Microscope (OM), Field Emission Scanning Electron Microscope (FESEM) and energy dispersive X-ray analysis (EDX). The result showed that water cooled media is the faster cooling rate followed by air-cooled then furnace-cooled media. However, in term of intermetallic compound thickness revealed that the thickness of IMC through furnace-cooled is thicker compared to the air-cooled followed by water-cooled. Regarding the formation of IMC, there is one layer of (Cu,Ni)6Sn5 IMC formed between SACN30505 solder and ENImAg after reflow soldering. For isothermal aging treatment, a new layer of IMC has been detected between (Cu,Ni)6Sn5 IMC and ENImAg known as (Cu,Ni)3Sn4. The results also shows that the morphology of IMC is changing from irregular circle and rod-like shape to irregular polygonal and rod-like shape during isothermal aging process and then become bigger and compact as the aging times increase. The thickness of IMC formed is directly proportional to the isothermal aging time and cause the IMC become brittle as the time increase. Other than that, the period of failure during shear test for furnace-cooled specimen is shorter compared to air-cooled followed by water-cooled which mean the IMC for furnace-cooled specimens is brittle compare to air-cooled and water-cooled specimens. Specimen that undergo longer period of isothermal aging shows a short period of failure during shear test which mean the specimen is brittle compare to specimens that undergo shorter period of isothermal aging.
ZOLHAFIZI JAIDI, SALIZA AZLINA OSMAN