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Low-Ag SAC solder will lead to a series of problems, such as increased the melting range and declined the solderability and so on. These research studies do not have too much impact on the improvement of solders’ performance but were difficult to achieve satisfactory results. It is urgent to develop new soldering technology to avoid the bottleneck of lead-free solder. low-temperature-stirring soldering and ultrasonic-assisted soldering was developed in the authors’ early work, but slag inclusion and pore would gather and grow up to lead decreasing of the shear strength. In this paper, Cu/SAC0307 +Zn power/Cu joints with ultrasonic-assisted at low-temperature was successfully achieved.

45um Zn-powder and SAC0307 No.4 solder powder were mixed to fill the Cu-Cu joint, and the content of Zn-powder were 0 and 5%, 7.5% and 10%, 12.5% and 15% respectively. During the soldering process under ambient atmosphere %252C the heating platform provided a constant 220%253 F and the ultrasonic vibrator applied a constant pressure of 4 MPa to the copper substrate. The soldering process was completed after holding 70 s at 300 W.

The Zn particles made the IMC at the joint interface and in the soldering seam from scallop-type Cu₆Sn₅ to flat-type Cu₅Zn₈. The shear strength of joints without Zn was only 12.43 MPa, the shear strength of joints with 10% Zn reached a peak of 34.25 MPa, and the shear strength of joints containing 10% Zn was 63.71% higher than that of joints without zinc particles, and then the shear strength decreased. In addition, with the increase of zinc content, the fracture mode of the joint changed from the brittle fracture of the original layered tears to the mixed tough and brittle fracture.

A new method that Zn micron-size powders and SAC0307 micron-size powders was mixed to fill the joint, and successfully achieved micro-joining of Cu/Cu under ultrasonic-assisted without flux at low-temperature.

The purpose of this paper is to discuss the design, materials, and assembly process aspects of a study, conducted by The High Density Packaging Users Group Consortium, into process development and solder joint reliability of high‐density packages on printed circuit boards using a low‐melting temperature lead‐free solder (Sn‐57 wt%Bi‐1 wt%Ag).

The components studied include several SMT package types and various lead configurations. The assembly process addresses the low‐temperature lead‐free assembly process, inspection and analysis of these boards and packages.

It was found that, the assembly process of the SnBiAg lead‐free test boards is very robust and the assembly yield is almost 100 percent.

The paper is of value by presenting a description of the rationale and material set used for an experiment to test SMT assembly and reliability characteristics using the 57Bi‐42Sn‐1Ag alloy, which has a melting point of 139°C.

The purpose of this paper is to investigate the thermal fatigue endurance of two lead‐free solders used in composite solder joints consisting of plastic core solder balls (PCSB) and different solder materials, in order to assess their feasibility in low‐temperature cofired ceramic (LTCC)/printed wiring board (PWB) assemblies.

The characteristic lifetime of these joints was determined in a thermal cycling test (TCT) over a temperature range of −40‐125°C. Their failure mechanisms were analyzed after the TCT using scanning acoustic and optical microscopy, scanning electronic microscope, and field emission scanning electronic microscope investigation.

The results showed that four different failure mechanisms existed in the test assemblies cracking in the mixed ceramic/metallization zone; or a mixed transgranular/intergranular failure occurred at the low temperature extreme; whereas an intergranular failure within the solder matrix; or separation of the intermetallic layer and the solder matrix occurred at the high temperature extreme. Sn3Ag0.5Cu0.5In0.05Ni was more resistant to mixed transgranular/intergranular failure, but had poor adhesion with the Ag3Sn layer. On the other hand, cracking in the mixed ceramic/metallization zone typically existed in the joints with Sn2.5Ag0.8Cu0.5Sb solder, whereas the joints with Sn3Ag0.5Cu0.5In0.05Ni were practically free of these cracks. The characteristic lifetimes of both test joint configurations were at the same level (800‐1,000) compared with joints consisted of Sn4Ag0.5Cu solder and PCSB studied earlier.

The study investigated in detail the failure mechanisms of the Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders under harsh accelerated test conditions. It was proved that these solders behaved similarly to the ternary SnAgCu solders in these conditions and no improvement can be achieved by utilizing these solders in the non‐collpasible solder joints of LTCC/PWB assemblies.

This study aims to research properties of Cu/SAC0307 mixed solder balls/Cu joints with different Zn-particles content at low-temperature under ultrasonic assisted.

A new method that 1µm Zn particles and Sn-0.3Ag-0.7 (SAC0307) with a particle size of 25–38 µm were mixed to fill the joint and successfully achieved micro-joining of Cu/Cu under ultrasonic-assisted at low temperature.

The results showed that with a continuous increase in the Zn-particle content, the interfacial intermetallic compounds (IMCs) of the upper and lower interfaces of joints gradually changed from scallop-shaped Cu₆Sn₅ to wavy-shaped Cu₅Zn₈. Moreover, the IMC thickness of the upper/lower interface of joints first decreased and then increased with increasing Zn-particle content. The shear strengths of joints increased with Zn-particle content, the shear strength of joints went to a maximum of 29.76 MPa when the Zn-particle content was 40%, an increase of 62.6% compared to joints without Zn particles. However, as the Zn-particle content continued to increase, the shear strengths of the joints decreased. Additionally, when the Zn content increased to 50%, because the oxidation degree of Zn particles increased, the joints were mainly broken among Zn particles.

A new method that 1µm Zn particles and Sn-0.3Ag-0.7 (SAC0307) with a particle size of 25–38 µm were mixed to fill the Cu/Cu joint at 180°C.

The High Density Packaging Users Group Consortium has conducted a study of process development and solder‐joint reliability of high‐density packages on printed circuit boards (PCB) using a low‐melting temperature lead‐free solder. The purpose of this paper is to investigate the reliability tests (e.g. temperature cycling and shock and vibration) and failure analysis (FA) of high‐density packages on PCB with the low‐melting temperature lead‐free solder (Sn‐57 wt%Bi‐1 wt%Ag).

The design for reliability, materials, and assembly process aspects of the project have been discussed in “Design, materials, and assembly process of high‐density packages with a low‐temperature lead‐free solder (SnBiAg)” also published in this journal issue. In this study, reliability tests (e.g. temperature cycling and shock and vibration) and FA of high‐density packages on PCB with the low‐melting temperature lead‐free solder (Sn‐57 wt%Bi‐1 wt%Ag) are investigated.

Lead‐free solder‐joint reliability of high‐density packages, such as the PBGA388, PBGA256, PBGA208, PBGA196, PBGA172, PQFP80, and TSSOP56 were determined by temperature cycling, shock, and vibration tests. Temperature cycling test data for over 8,100 cycles between 0 and 100°C in a 44 min. cycle were statistically analyzed. Shock and vibration test data based on the HP Standard Class Bi‐II Products SPEC have also been reported.

Currently there is a lack of experimental and simulation data and field experience in respect of one of the critical issues for industry – that of solder joint reliability in lead‐free soldering. The paper contains some important research results and recommendations.

This study aims to evaluate the effect of thermal aging temperature on the properties of Cu/Cu joints.

A new method that 1 um Zn-particles and Sn-0.3Ag-0.7Cu (SAC0307) with a particle size of 25–38 µm were mixed to fill the joint and successfully achieved the micro-joining of Cu/Cu under ultrasonic-assisted at low-temperature, and then the effect of thermal aging temperature on the properties of Cu/Cu joints was researched.

The composition of the intermetallic compounds (IMCs) on the upper and lower interfaces of Cu/SACZ/Cu joints remained unchanged, which was Cu₅Zn₈ in aging process, and the thickness of the IMCs on the upper and lower interfaces of the Cu/SACZ/Cu joints increased accordingly. Compared with the as-received joints, the thickness of the upper and lower interfaces IMCs of the soldering aged time for 24 h increased by 404.7% and 505.5% at 150ºC, respectively. The IMCs formation tendency and the IMCs growth rate of the lower interface are larger than those of the upper interface because the soldering seam near the IMCs at the upper and lower interfaces of the as-received joints were mostly white SAC0307 balls black Zn-particles, respectively. The growth activation energy of IMCs in the upper and lower interfaces is about 89.21 and 55.11 kJ/mol, respectively. Under the same aging time, with the increase of the aging temperature, the shear strength of Cu/SACZ/Cu joints did not change significantly at first before 150ºC. When the aging temperature reached 150ºC, the shear strength of the joints decreased significantly; the shear strength of the joints was the smallest at 150ºC for 24 h, which was 39.4% lower than that of the as-received joints because the oxidation degree of Zn particles in the joint with the increase of aging temperature and time.

Cu/Cu joints were successfully achieved under ultrasonic-assisted at low-temperature.

An empirical study was conducted to determine the thermal fatigue behaviour of 1.27 mm pitch, J‐bend and gullwing surface mount solder joints, manufactured with four low‐temperature solders. Selected solder alloys were: 58Bi‐42Sn (wt %), 43Sn‐43Pb‐14Bi, 52ln‐48Sn and 40ln‐40Sn‐20Pb. Accelerated thermal cycling was used in conjunction with metallographic analysis and mechanical (pull) strength measurement to test their behaviour. The relative merit of each solder composition was determined by comparing it with 63Sn‐37Pb solder, subjected to identical testing conditions. The strength decreased linearly with increased number of thermal cycles for gullwing solder joints of all four solder alloys. The fatigue lifetime was relatively longer for 58Bi‐42Sn and 40ln‐40Sn‐20Pb than for other alloys, but significantly lower than that obtained with 63Sn‐37Pb solder. No discernible degradation of strength was observed with the J‐bend solder joints of any solder alloy, even after the completion of 6000 thermal cycles. Thermal fatigue resistance of the latter joints was attributed to a more favourable coefficient of thermal expansion (CTE) mismatch. Solder joint cracking occurred only in gullwing components soldered with 52ln‐48Sn, 40ln‐40Sn‐20Pb and 43Sn‐43Pb‐14Bi alloys, after 1000 or 2000 thermal cycles. The crack initiated on the outside surface of the solder fillet, and appeared to propagate through both phases of the microstructure. The stress‐induced heterogeneous coarsening of the microstructure was evident only with 43Sn‐43Pb‐14Bi solder, although not as prevalent as that usually observed with eutectic Sn‐Pb solder. Fatigue cracks were absent from solder joints of 58Bi‐42Sn and 63Sn‐37Pb alloys.

The mechanical properties of eight solder alloys from the Pb‐Sn‐In‐Ag alloy systems were determined over the temperature range ‐200°C to 100°C, using uniaxial tensile tests, dynamic mechanical analysis (DMA), acoustic pulse methods and dilatometry. In general, the strength and elastic modulus of the alloys studied was inversely dependent on temperature. PbSn, PbIn and SnIn alloys were observed to turn superplastic with elongations over 100 per cent at temperatures of 50°C or above. The Pb‐based and In‐Sn eutectic solders possessed superplasticity at temperatures greater than 50°C. From these results, deformation and fracture processes are reviewed, and the appropriate fracture mechanism is proposed.

This paper aims to investigate the effects of different ultrasonic-assisted loading degrees on the microstructure, mechanical properties and the fracture morphology of Cu/Zn+15%SAC0307+15%Cu/Al solder joints.

A new method in which 45 μm Zn particles were mixed with 15% 500 nm Cu particles and 15% 500 nm SAC0307 particles as solders (SACZ) and five different ultrasonic loading degrees were applied for realizing the soldering between Cu and Al at 240 °C and 8 MPa. Then, SEM was used to observe and analyze the soldering seam, interface microstructure and fracture morphology; the structural composition was determined by EDS; the phase of the soldering seam was characterized by XRD; and a PTR-1102 bonding tester was adopted to test the average shear strength.

The results manifest that Al–Zn solid solution is formed on the Al side of the Cu/SACZ/Al joints, while the interface IMC (Cu₅Zn₈) is formed on the Cu side of the Cu/SACZ/Al joints. When single ultrasonic was used in soldering, the interface IMC (Cu₅Zn₈) gradually thickens with the increase of ultrasonic degree. It is observed that the proportion of Zn or ZnO areas in solders decreases, and the proportion of Cu–Zn compound areas increases with the variation of ultrasonic degree. The maximum shear strength of joint reaches 46.01 MPa when the dual ultrasonic degree is 60°. The fracture position of the joint gradually shifts from the Al side interface to the solders and then to the Cu side interface.

The mechanism of ultrasonic action on micro-nanoparticles is further studied. By using different ultrasonic loading degrees to realize Cu/Al soldering, it is believed that the understandings gained in this study may offer some new insights for the development of low-temperature soldering methodology for heterogeneous materials.

This paper aims to review recent reports on mechanical properties of Sn-Bi and Sn-Bi-X solders (where X is an additional alloying element), in terms of the tensile properties, hardness and shear strength. Then, the effects of alloying in Sn-Bi solder are compared in terms of the discussed mechanical properties. The fracture morphologies of tensile shear tested solders are also reviewed to correlate the microstructural changes with mechanical properties of Sn-Bi-X solder alloys.

A brief introduction on Sn-Bi solder and reasons to enhance the mechanical properties of Sn-Bi solder. The latest reports on Sn-Bi and Sn-Bi-X solders are combined in the form of tables and figures for each section. The presented data are discussed by comparing the testing method, technical setup, specimen dimension and alloying element weight percentage, which affect the mechanical properties of Sn-Bi solder.

The addition of alloying elements could enhance the tensile properties, hardness and/or shear strength of Sn-Bi solder for low-temperature solder application. Different weight percentage alloying elements affect differently on Sn-Bi solder mechanical properties.

This paper provides a compilation of latest report on tensile properties, hardness, shear strength and deformation of Sn-Bi and Sn-Bi-X solders and the latest trends and in-depth understanding of the effect of alloying elements in Sn-Bi solder mechanical properties.