The ever-increasing demand for high-temperature reliability and extended fatigue life requirements in more demanding electronic applications, has motivated further investigation on high-reliability lead-free solder alloys. The novel Alloy 10 solder alloy presented here exhibits exemplary thermomechanical and mechanical reliability in extreme operating conditions, ideal for the future needs of high-reliability electronics, such as in the automotive industry. Recent results showing excellent performance of Alloy 10 when compared to another leading high-reliability alloy, have also raised questions on which features are responsible for such performance. In this work, we present the latest results of a collaborative in-depth study to understand the mechanisms behind the Alloy 10 solder alloy’s improved performance. Solder joint samples are studied for the detailed composition and distribution of phases after reflow and aging treatment under varying aging times. The effect of aging time and temperature on the evolution of the microstructure of the solder joints is then studied. A redistribution of elements and phases are observed after aging; microconstituents are observed to be uniformly distributed after prolonged aging, while intermetallic compounds grow and become distinctly visible upon aging. This discussion is then further expanded by discussing the mechanical behaviour of Alloy 10 as measured by a custom designed micro-precision mechanical tester, which was used to perform isothermal creep, monotonic and fatigue testing of solder test specimens under shear at room temperature. Thermal cycling has also been performed on BGA solder joints in extreme temperature conditions and results have been discussed.

Research and development of next-generation high- reliability solders has been motivated by the ever-increasing demand for reliability at higher operating temperatures and extended life requirements in the more demanding automotive electronic applications. The combination of harsh operating conditions, increased power densities, and miniaturization has added to the complexity of assembly designs in the automotive electronics space for which traditional surface mount solders are no longer suitable. Suitability and selection of a solder alloy for such electronics assembly is primarily defined by the thermo-mechanical reliability of solder alloys, in which solder joint performance can be evaluated using various reliability tests. This work presents a next-generation high-reliability solder alloy for automotive electronics that uses a combination of complex metallurgy such as solid solution strengthening, precipitation strengthening, grain refinement and diffusion modifiers for achieving enhanced performance over traditional Sn-Ag-Cu alloys. Micro-additives contribute to intermetallic compound (IMC) formation and strength retention at high operational temperatures. The novel alloys showed significantly higher thermal cycling performance in two different test profiles of -40°C to 125C and -40C to 150°C, both using 30 minutes holding times. This new ultra- high reliability alloy exhibits significant step function improvement in the thermal cycling characteristic life over other high-reliability alloys and has considerably higher drop shock performance. Such results are also confirmed by solder joints cross-sections, IMC thickness measurements and microscopic analysis. The above performance results are very encouraging and demonstrate the potential and suitability of this novel high-reliability solder to be used in surface mount applications with challenging reliability requirements such as automotive electronics.

Assemblies for automotive applications can require minimum operational temperature of 125°C, while soldering temperature need to be within 250°C for compatibility in surface mount processing. For fulfilling such harsh operating conditions requirements, an optimum combination of macro- and micro-alloying additives is necessary, so: i) melting point does not exceed to maintain reflow peak temperature within 250°C, ii) creep properties and fatigue life are improved, and iii) high mechanical strength and elongation at extreme temperatures is more balanced. This is exemplified here by comparing a high-reliability alloy referred to as High Rel Alloy and a newly developed alloy, Alloy 10.

Requirements for high-reliability lead-free solder alloys in automotive electronics are becoming more challenging as assembly designs require increased powder densities and miniaturization in combination with harsh operating conditions. Thermal cycling performance has been the primary factor for deciding on the suitability of a solder alloy for such applications. Solder joint reliability under thermal and mechanical stresses depends on the solder, packages, PCB, and assembly, including global and local CTE mismatch. Automotive electronic assemblies for critical applications commonly require operational temperatures around 150oC, while soldering temperatures need to be as low as possible (<250oC). To resolve performance gaps in Sn-Ag-Cu solders for such applications, alloying additives can be used for: i) lowering the melting temperature, ii) improving creep properties, and iii) improving fatigue life. This is exemplified here by comparing a high reliability alloy, commonly known as “Innolot” and SAC305. This work reviews some of the aspects related to such board level accelerated reliability tests and discusses these experimental results in terms of alloy composition, microstructure, and mechanical properties.

The eutectic 42Sn58Bi alloy showed promising results as a low temperature solder in the first generation of lead-free solders, but its excessive brittleness has greatly limited its use in the electronics industry. Minor changes in the eutectic SnBi, such as addition of Ag or other micro-additives, was shown to successfully improve its thermal and mechanical reliability, although still far from the SAC305 performance. Driven by increased miniaturization, complexity, and design integration in electronics, a third generation of SnBi alloys has been recently introduced and shown to enable low temperature soldering while delivering superior drop shock and thermal cycling performance. In this paper, a fourth generation of SnBi solder alloys is introduced, and its performance is compared with previous SnBi solders and SAC305. Testing including melting behaviour and solder joint formation, tensile tests at room temperature and at 75oC, high temperature creep, and other physical properties are discussed here.

The technical and economic benefits derived from lowering the reflow temperatures have motivated the evaluation of new SnBi low temperature alloys for soldering. Eutectic Sn-Bi alloy is usually described as having a brittle nature, not being able to sustain mechanical shock and thermal cycling stresses as well as Sn3Ag30.5Cu (SAC305) solder. A new non-eutectic Sn-Bi solder with 2 wt.% additives (generally called here as alloy A) is evaluated here and compared with other eutectic Sn-Bi alloys and SAC305.Tensile tests at -55 oC, -25 oC, +25 oC, +75 oC and +125oC were performed to provide insights on their relative mechanical properties. Mechanical drop shock tests of BGA84 and LGA84 were performed as per the JESD22-B111 standard, while thermal cycling tests were performed from -40oC (10 min) to +125oC (10 min) as per the IPC 9701 standard. The BGA84 was used for thermal cycling in situ monitoring, while BGA169, SOT223, QFP44 and 1206 chip resistors were also used for evaluating the effect of thermal cycling on IMC thickness, shear strength and tin whiskers. The results show that, for the aforementioned packages, assembly and testing conditions, alloy A is a viable replacement for SAC305. The joints formed with alloy A have the mechanical (drop) shock and thermal cycling performance as good as, or, in some cases, better than the same joints formed with SAC305.

High-Ag, low-Ag, high-Ag plus additives: Which alloy fits best certain application? Here we present a comprehensive report on the thermal and mechanical reliability of alloys ranging from 0.3 to 3.8% Ag, with and without presence of additives such as Bi, Ni and Sb. CTBGA packages with 84 I/Os were assembled using SAC105, SACX Plus 0307, SAC125N, SAC305, Innolot and Maxrel Plus spheres. Test vehicle assembly used SAC305 solder paste for all alloys, except for Maxrel Plus BGAs, which were evaluated with both SAC305 and Maxrel Plus solder pastes. Single ball shear, drop shock and thermal cycling were used to evaluate these alloys performance for BGA packages applications. Our results expand the perspective over the usual belief that high-Ag Sn-Ag-Cu alloys result in better thermal cycling and lower drop shock performance than when using low-Ag alloys. Alloying additions can be used to improve single ball shear, drop shock and thermal cycling properties. In order to obtain maximum performance and cost benefit, solder alloys need to be paired to the correct application. Based on the results shown, we recommend: i) SACX Plus 0307 for applications that require maximum drop shock and reasonable thermal cycling performance. ii) SAC305 for applications requiring good drop shock and thermal cycling properties. iii) Maxrel Plus for applications that require higher shear strength, drop shock and thermal cycling, including automotive under the hood, high efficiency LEDs and semiconductor packaging.

Wafer-Level Chip-Scale Packaging (WLCSP) has become increasingly popular in portable electronics. One of its main characteristics is its reduced scale and that the solder balls are attached directly to the device. One of the main challenges in WLCSP is how to overcome the effects of thermal mismatch between the silicon die and the printed circuit board that arise from these characteristics. Use of new solder alloys is one of the ways to mitigate thermal fatigue stresses resulting from coefficients of thermal expansion mismatch. Tensile tests and high temperature creep tests were used for initial screening of the alloys and understanding the potential impact of each addition on the reliability of the solder in the final application. Here improvements in thermal, mechanical and metallurgical properties of the new alloy Maxrel Plus are discussed and compared to SAC405. Based on drop shock test, single ball shear test (high temperature storage, PCT and MSL1), thermal cycling test and intermetallics measurement results, we conclude that Maxrel Plus is specially recommended for use in WLCSP.

Copper sulphide (CuS) nanomaterials with interesting morphology were synthesised using copper nitrate trihydrate, thiourea and water as a solvent by a simple hydrothermal route. A systematic investigation was carried out to investigate the effect of reaction time (5, 16 and 24h) at 150 degrees C on the morphology of the materials. Without the use of any template or additives, shape controlled synthesis of CuS nanocrystallites were achieved. The possible mechanism for the formation of the various nanostructures of CuS in this system is discussed. The prepared materials were characterised by X-ray diffraction, field emission scanning electron microscopy (FE-SEM) and DRS-UV-Vis absorption analysis. The UV-Vis spectrum shows that it is the promising material which can absorb in the visible region and hence could be used for photocatalytic applications. In addition, the electrochemical characteristic of the synthesised material was investigated by cyclic voltammetric analysis, which shows that CuS could be used for electrocatalytic applications.