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Purpose -The purpose of this paper is to discuss the reliability of board level Sn-Ag-Cu (SAC) solder joints in terms of both thermal cycling and drop impact loading conditions, and further modification of the characteristics of low Ag-content SAC solder joints using minor alloying elements to withstand both thermal cycle and drop impact loads. Design/methodology/approach -The thermal cycling and drop impact reliability of different Ag-content SAC bulk solder will be discussed from the viewpoints of mechanical and micro-structural properties. Findings -The best SAC composition for drop performance is not necessarily the best composition for optimum thermal cycling reliability. The content level of silver in SAC solder alloys can be an advantage or a disadvantage depending on the application, package and reliability requirements. The low Ag-content SAC alloys with different minor alloying elements such as Mn, Ce, Bi, Ni and Ti display good performance in terms of both thermal cycling and drop impact loading conditions. Originality/value -The paper details the mechanical and micro-structural properties requirements to design a robust bulk SAC solder joint. These properties provide design and manufacturing engineers with the necessary information when deciding on a solder alloy for their specific application.

In this work, we investigate the effects of Ni doping on the thermoelectric (TE) properties of Yb 0.25 Co 4 Sb 12 sample. Yb 0.25 Co 4x Ni x Sb 12 (0 ≤ x ≤ 0.5) samples were prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The morphology of consolidated samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS). The thermoelectric properties of bulk samples were measured from room temperature to 800 K. The XRD analysis confirmed that, the successful formation of the Co 4 Sb 12 skutterudite phase and Ni is substituted into Co site of the skutterudite crystal lattice. Moreover, the electrical resistivity decreased to 14.6 μΩm at 785 K for Yb 0.25 Co 3.5 Ni 0.5 Sb 12 sample, due to increase of the electron concentration by Niaddition. The absolute Seebeck coefficient reached the highest value of 223 μV/K at 592 K for Yb 0.25 Co 3.7 Ni 0.3 Sb 12 sample, thus yielding a maximum value of power factor of 2.41 × 10 -3 W/mK 2 at 592 K. The highest dimensionless thermoelectric figure of merit value ZT of 0.49 at 692 K has been achieved for the Yb 0.25 Co 3.7 Ni 0.3 Sb 12 sample, compared to ZT=0.06 for the Yb 0.25 Co 4 Sb 12 sample at same temperature. This work indicates a strategy to improve the thermoelectric performance by Ni substitution of Co sites in the Yb 0.25 Co 4 Sb 12 skutterudite through simultaneous improvement of its electrical conductivity, Seebeck coefficient and reduction of its thermal conductivity. ABSTRAK Dalam kajian ini, kesan pendopan Ni ke atas sifat Yb 0.25 Co 4 Sb 12 telah dikaji. Sampel Yb 0.25 Co 4-x Ni x Sb 12 (0 ≤ x ≤ 0.5) telah disediakan dengan kaedah pengaloian mekanikal dan seterusnya digabungkan dengan pensinteran pencucuh plasma. Morfologi untuk sampel gabungan telah dicirikan oleh pembelauan sinar-X (XRD) dan imbasan mikroskop elektron berserta tenaga serakan X-ray spektroskopi (SEM-EDS). Ciri termoelektrik sampel telah diukur daripada suhu bilik ke 800 K. Analisis XRD mengesahkan bahawa Ni berjaya didopkan ke dalam Yb 0.25 Co 4-x Ni x Sb 12 CoSb 3 dalam fasa skutterudite, dengan Ni menggantikan beberapa lokasi Co dalam kekisi kristal skuterudit. Selain itu, kerintangan elektrik menurun kepada 14.6 μΩm di 785 K bagi sampel Yb 0.25 Co 3.5 Ni 0.5 Sb 12 , disebabkan oleh peningkatan bilangan pembawa cas elektron oleh Ni. Pekali Seebeck mutlak mencapai nilai tertinggi 223 μV/K pada 592 K bagi sampel Yb 0.25 Co 3.7 Ni 0.3 Sb 12 , lalu menghasilkan nilai maksimum faktor kuasa 2.41 × 10 -3 W/MK 2 pada 592 K. Angka merit, ZT yang optimum adalah 0.49 pada 692 K telah dicapai untuk sampel Yb 0.25 Co 3.7 Ni 0.3 Sb 12 . Kajian ini menunjukkan strategi untuk meningkatkan prestasi termoelektrik melalui penggantian Ni pada bahagian Co dalam bahan skutterudite Yb 0.25 Co 4 Sb 12 , sekaligus menambahbaik kekonduksian elektrik, pekali Seebeck dan pengurangan kekonduksian haba.

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