Effect Of Grain Refinement Process Using Equal Channel Angular Pressing On The Properties And Corrosion Behaviour Of Sn-3.0ag-0.5Cu Solder
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Date
2019-01-01
Authors
Abu Bakar, Nur Adriana Nazifa
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Due to the inherent toxicity of Pb, environmental regulations have been
enforced to eliminate the usage of Pb-based solders in electronic devices. Sn-Ag-Cu
alloys is an attractive candidate due to good mechanical properties, good wettability
and low melting temperature. However, the reliability of SAC solders is still a serious
concern especially under long term exposure to heat or in corrosive environment.
There is potential to improve the corrosion behavior and increase solder joint
reliability by using Equal Channel Angular Pressing (ECAP) as a grain refinement
process. The aim of this project was to evaluate the microstructure, mechanical
properties and corrosion behavior of SAC305 alloy subjected to ECAP up to 4 passes.
In this study, the mechanical properties showed that the 4 passes ECAPed SAC305
alloy exhibited the highest hardness value (17.5 HV) with improvement of shear
strength (70.5 MPa). ECAP was used to alter the microstructure of SAC305 alloy by
reducing the large Sn dendrites into fine and equiaxed grains (5.51 μm). ECAP also
was observed to result in smaller IMC particles and better distribution of them in the
Sn matrix. It also showed the smallest crystallite size (0.28 μm) and the highest lattice
strain (4.36X10-1). ECAP process resulted in improved wettability based on largest
spreading area and smallest wetting angle compared to the others. As a result of grain
refinement and more evenly distributed IMCs, solder had higher hardness after ECAP.
The corrosion resistance was also improved based on lowest weight loss, lowest
corrosion rate and more positive value of corrosion potential. The morphology on
surface of immersion test samples showed rounded shape particles and then was
replaced with root-like film. ECAP 4 passes sample after potentiodynamic
polarization was uniformly covered with plate-like shape corrosion product while the
other samples suffered from selective corrosion with evidence of pits on the surface.
Phase and elemental analyses revealed the formation of several corrosion product such
as SnO2, SnCl2 and Sn3O(OH)2Cl2 on the surface. The increase number of passes can
induced grain refinement in SAC305 samples with better mechanical properties,
wettability behavior and corrosion resistance.