low-Ag Solder Research Articles

Applicability Evaluation of Nano-Al2O3 Modified Sn-Ag-Cu Solder in High-Density Electronic Packaging Subjected to Thermal Cycling

Recently, 3D packaging has been regarded as an important technical means to continue Moore’s Law. However, excessive stacking will increase the longitudinal dimension, and one chip with high-density bondings packaging is still needed. Thus, it naturally places higher demand on thermal cycling reliability due to the decreased joint size to satisfy high-density packaging. In this work, the nano-Al2O3 (1 wt.%) modified Sn-1 wt.% Ag-0.5 wt.% Cu low-Ag solder was applied as a solder sample to evaluate the associated thermal cycling reliability. The investigated results revealed that the nano-Al2O3 modified solder did present enhanced thermal cycling reliability, as evidenced by the delayed microstructure coarsening and the inhibited atom inter-diffusion at interface caused by the adsorption of nano-Al2O3 on grain surfaces, and the resultant pinning effect. Worthy of note is that the potential of the newly developed nano-Al2O3 modified solder for high-density packaging applications (e.g., BGA, QFN, and CCGA) was evaluated based on the Finite Element Modeling.

Synergic effect of Te, Ni and MWCNT on creep behavior and microstructural evolution of Sn-1.0Ag-0.7Cu low-Ag solder

Avoiding the weak interface bonding of multi-walled carbon nanotubes MWCNT with Sn-Ag-Cu solder matrix is vital to produce high performance large scale Sn-Ag-Cu solder alloys. In this work, Sn-1.0Ag-0.7Cu (SAC107) composite solders were developed by incorporating MWCNT in SAC107 alloy with Ni and Te. The results indicate that the MWCNTs and Cu can be instantaneously adsorbed at the surface-active of Te atoms to in situ compose the core multi-shell (Te/C/Cu/C) polygonal particles, linking MWCNT with SAC solder matrix. The polygonal particles are well dispersed through the Cu6Sn5, Ag3Sn, β-Sn, SnTe and (Cu,Ni)6Sn5 IMC precipitates. These structural variations produce a combination of increased creep resistance 15 times and enlarged creep life time (14 times) than that of plain SAC107 alloy. Although Ni and Te additions decreased the creep resistance of SAC, the SAC-Ni-Te-MWCNT composite alloy exhibits significant change in dislocation creep resistance with creep stress exponent of ~ 6.6 at 25 °C: the creep threshold stress is decreased by 58.8% (5 MPa) in SAC-Ni-Te alloy, while increased by 17.6% (1.5 MPa) in SAC-Ni-Te-MWCNT composite alloy owing to the presence of polygonal particles.

Laser Soldering Properties of MEMS Probe for Semiconductor Water Testing

In this study, the laser soldering process of microelectromechanical system (MEMS) probes and multilayer ceramic (MLC) substrates was optimized with Type 4 (T4) and Type 7 (T7) Sn-3.0Ag-0.5Cu (SAC305), Type 4 Sn-0.3Ag-0.7Cu (SAC0307), and Type 4 Sn-5.0Sb (SnSb) soldering, and the probe solder joint properties were compared. SAC0307 and SnSb were used to confirm the bonding property of the low-Ag solder and the high-temperature durability. We conducted a thermal cycling test (TCT) with 500 cycles at temperatures of -25 ℃ to 105 ℃ with a 10-min dwell time at each temperature. Before and after the TCT, the microstructure of solder joint as well as the shear strength between the probe and the MLC were examined. The results revealed that, after the TCT, the degradation rate of T7 SAC305 solder was lower than that of T4 SAC305, and the SnSb solder did not exhibit bonding strength degradation. The fracture mode of the SAC solder joint was ductile-brittle. In the case of the SnSb joint, brittle fracture was the major fracture mode because of the Sn-Sb intermetallic compounds. The SnSb solder had an excellent bonding strength and degradation property after the TCT, but the lack of toughness caused brittle fracture. These results confirm the applicability of T4 SnSb and T7 SAC305 solders for high-temperature response and fine pitch bonding.

Coupling effects of rare-earth Pr and Al2O3 nanoparticles on the microstructure and properties of Sn-0.3Ag-0.7Cu low-Ag solder

Low-cost Al2O3 nanoparticles (NPs) are regularly incorporated into lead-free solder to improve its mechanical performance, but the poor wettability of Al2O3 NPs leads to weak Al2O3/solder interface bonding. In this work, a novel idea different from the common solution of pre-coating a metal layer on the surface of NPs was proposed to address the issue of weak interface bonding by simultaneously doping rare-earth (RE) Pr (0.06 wt%) and Al2O3 NPs (0–0.5 wt%) into Sn-0.3Ag-0.7Cu low-Ag solder. The coupling effects of RE Pr and Al2O3 NPs on the wettability, microstructures, shear force and creep resistance of prepared nanocomposite solder were systematically investigated. It was found that the coupling effects were concentration dependent. When the content of Al2O3 NPs was less than 0.06 wt%, a synergistic relationship between free Pr atoms and Al2O3 NPs was established. This is because the surface-active Pr atoms, acting as bridges between Al2O3 NPs and solder matrix, can be spontaneously adsorbed at the surfaces of Al2O3 NPs to in situ form Pr-coated Al2O3 NPs, which have much better wettability than the single Al2O3 NPs. However, increasing the doping content of Al2O3 NPs over 0.06 wt% led to a competitive relationship among free Pr atoms, Al2O3 NPs and Pr-coated Al2O3 NPs, which was probably caused by the emerged Al2O3 agglomerates occupying partial space of grain surfaces. The optimum doping content of Al2O3 NPs in SAC0307–0.06Pr solder was approximately 0.06 wt% and SAC0307–0.06Pr-0.06Al2O3 possessed the best wettability, a well-controlled growth of interfacial IMC layer, the highest shear force (∼61 N) and a superior room-temperature creep resistance with creep stress exponent (n) reaching approximately 11.7.

Enhancement on the high-temperature joint reliability and corrosion resistance of Sn–0.3Ag–0.7Cu low-Ag solder contributed by Al2O3 Nanoparticles (0.12 wt%)

In this study, the evolution of interfacial microstructures and mechanical properties of the joints soldered with Sn–0.3Ag–0.7Cu (SAC0307) and SAC0307-0.12Al2O3 nanoparticles (NPs) aged at 150 °C for different hours (72–840 h) were investigated. It was found the joint soldered with SAC0307-0.12Al2O3 displayed a significantly enhanced high-temperature joint reliability, reflected in a higher shear force than that of the original. This enhancement in shear force primarily benefited from the refinement in solder microstructure contributed by Al2O3 NPs. As aging time reached 840 h, a controlled growth of interfaical IMC layer resulted from the pinning effect of Al2O3 NPs contributed to the increase in shear force. Theoretical analysis showed 0.12 wt% Al2O3 NPs effectively lowered the growth constant of total interfacial IMCs (DT) from 3.19 × 10−10 to 1.02 × 10−10 cm2 s−1. Moreover, comparative studies on the corrosion resistances of SAC0307 and SAC0307-0.12Al2O3 were also conducted by electrochemical test and analyzed by electrochemical impedance spectroscopy (EIS). The results revealed SAC0307-0.12 Al2O3 solder displayed a stronger corrosion resistance (Rt; ~ 3.1 kΩ cm2 vs ~ 7.1 kΩ cm2). This is also related with the tailored microstructure, which provides more grain boundaries for the initial nucleation of passive film.

Effect of Additive Elements Bi/Ni/Ge on Crack Initiation and Propagation for Low-Ag Solders

This study discusses an effect of additive elements on crack propagation behaviour for low-Ag contain Sn1.0Ag0.7Cu lead-free solders at high temperature. A cyclic push-pull loading tests for four kinds of Sn1.0Ag0.7Cu solders were conducted at 313 K with a single hole specimen. Stress amplitude of solders containing additive element Bi were bigger than that of Bi-free solders. Crack initiation cycle of solders containing Bi were earlier than that of Bi-free solders. Low-Ag solders containing Bi had shorter crack propagation cycles than that of Bi-free solders. These results indicate that the additive element Bi have the effects on the crack initiation and propagation cycles, that is, Bi accelerates the crack propagation rate. We also discuss the adaptation of J-integral range parameter to the crack propagation rate evaluation for solders. J-integral range parameter evaluates the crack propagation rate for low-Ag solders independent of the additive elements.

Effects of α-Al2O3 nanoparticles-doped on microstructure and properties of Sn–0.3Ag–0.7Cu low-Ag solder

In order to enhance the properties of Sn–0.3Ag–0.7Cu low-Ag solder, α-Al2O3 nanoparticles with various content (0–0.5 wt%) were successfully doped into the solder paste with a self-designed dispersion step. After comprehensive study of the microstructures and properties of the novel nano-composite solder, several satisfactory modified results can be obtained. For instance, the wettability of solder was greatly improved with trace amount of α-Al2O3 nanoparticles-doped. The superior wettability was achieved by Sn–0.3Ag–0.7Cu–0.12Al2O3 solder with spreading area approaching to ~ 79 mm2. Detailed thermodynamic and kinetic analysis of how α-Al2O3 nanoparticles promoting the processes of solder wetting and spreading on Cu substrate were given. In addition, the joint soldered with Sn–0.3Ag–0.7Cu–0.12Al2O3 displayed the highest shear force (57.1 N) with a typical ductile fracture failure mode. This relates to the evidently refined microstructure as well as the well-controlled growth of interfacial Cu6Sn5 IMCs. Corresponding theoretical analysis shows 0.12 wt% Al2O3 nanoparticles-doped can decrease the growth rate constant of interfacial Cu6Sn5 IMCs from 5.08 × 10−10 to 1.71 × 10−10 cm2/s.

Effect of Pr addition on properties and Sn whisker growth of Sn–0.3Ag–0.7Cu low-Ag solder for electronic packaging

In this study, trace amount of rare earth Pr was added into Sn–0.3Ag–0.7Cu low-Ag solder to enhance properties of solders. Experimental results indicated that optimal amount of Pr addition (~0.06 wt%) can improve properties of wettability, shear force and ductility of Sn–0.3Ag–0.7Cu low-Ag solder. This is because that solder with optimal Pr addition not only had a refined microstructure but also owned a regular and thin interfacial IMC layer after soldering on Cu substrate. Meanwhile, we have explained the change of morphology and thickness of interfacial IMC layer after Pr addition based on Kim and Tu’s kinetic model of interfacial IMC growth. However, it was found excessive Pr addition led to the formation of PrSn3 phase, which was easy to be oxidized and became a great deterioration on the properties referred above. Besides, the fracture mode of solder joint also gradually changed from ductile fracture to cleavage fracture. Moreover, this oxidized PrSn3 became the birthplace of Sn whisker since it provided abundant supply of Sn sources and compressive stress for Sn whisker growth. By the in-situ observation of Sn whisker growth in 0.5 wt% Pr-doped solder joint, we obtained that the incubation period of Sn whisker is very short and its growth rate may have a great decrease with time extending. Besides, it was found after 1 day at room temperature, spindly and rod-like Sn whiskers also grew in 0.5 wt% Pr-doped solder joint besides dot-shaped Sn whisker that grew in 0.5 wt% Pr-doped solder matrix. We suggest this may be related with the extra compressive stress provided by interfacial IMC layer growth in 0.5 wt% Pr-doped solder joint.

Effect of Bi Addition on Microstructures, Properties and Interfacial Intermetallic Compound Growth of Low-Ag Sn-Cu Lead-Free Solder

The research on a new low-Ag lead-free solder has become a hot spot in the field of electronic packaging. In this work, the effects of Bi addition on microstructure, melting temperature, wettability of low-Ag solder, shear strength of solder joint and the growth of interfacial intermetallic compound (IMC) before and after thermal cycling were investigated. A moderate amount of Bi element resulted in the microstructural refinement and melting temperature reduction of Sn-0.2Ag-0.7Cu solder. Wetting test results showed that a small amount of Bi produced the significant effect on improving the wettability. In addition, it is shown that the thickness of interfacial IMC during thermal cycling decreased first and then increased; the shear strength of solder joint increased with the increase of Bi.

Microstructure and elemental composition of electrochemically formed dendrites on lead-free micro-alloyed low Ag solder alloys used in electronics

The Electrochemical Migration (ECM) behaviour of lead-free, micro-alloyed, low Ag solder alloys was investigated using Scanning Transmission Electron Microscopy (STEM), Energy Disperse X-ray Spectroscopy (EDS) and electron diffraction methods. Different solder alloys were investigated by Water Drop (WD) tests to stimulate ECM failure mechanism. After WD tests, differently structured dendrites were formed depending on the solder alloy types. The results showed that micro-alloying components (e.g. Sb) also played role during the ECM processes. The novelty of this study is the demonstration that Sb can take part in the ECM process; the ECM model of Sb is also discussed.

Microstructure, Wettability and IMC Formation of Low-Ag SAC Solder on Cu Substrate

This Paper Reports the Microstructure, IMC Evaluation and Wettability of Low-Ag Sn-Ag-Cu(SAC) (0.3 Wt% Ag and 0.5 Wt% Ag) and SAC305 Solder Alloys in Reflowed and Agedconditions. Reflow was Done at 250°C and Thermal Aging at 150°C For100 Hours. Microstructure of Bulk Solder and the IMC Formed at Interfacebetween Solder and Cu Substrate were Observed Using SEM Equipped with EDX. Microstructureobservation Showed Finer β-Sn Dendrites at 0.3%Ag Indicating a Possiblerefining Effect of Lower Ag on Bulk Solder Microstructure. SEM Result Showedfiner Ag3Sn Distributed in the Solder but the IMC Thickness of Bothreflowed and Aged Solder Joint Seems to Increase with Decreasing Ag Content.This could be due to Finer β-Sn Dendrites which Provide more Diffusion Paththrough Grain Boundaries and Increase IMC Thickness. Similarly, Lower Ag Content Appears to have Detrimental Effect on Wettability and Wetting Angle Ofsolder Joint.

Effect of Strain Rate on Tensile Properties of Miniature Size Specimens of Several Lead-Free Alloys

The effect of strain rate on tensile properties of several lead-free solder was investigated using miniature size specimens. High-temperature lead-free solder which are Sn-Cu and Sn-Sb alloys were prepared. Moreover, low-Ag lead-free solder which are Sn-1Ag-0.7Cu (SAC107, mass%) based alloys were prepared. Sn-3Ag-0.5Cu (SAC305) was also prepared for comparison. Tensile strength is proportion to the logarithm of strain rate in all solder investigated. Although 0.1% proof stress decreases at high strain rate in high-temperature solder, it scarcely changes in low-Ag solder. Elongation somewhat increases with increasing strain rate in high-temperature solder. It increases with increasing strain rate in low-Ag solder although it is lower than that of SAC305. Chisel point fracture mainly occurred except Sn-13Sb. In Sn-13Sb, brittle fracture occurred and thus elongation was lower than those of other solder. Sn-8.5Sb and Sn-1Ag-0.7Cu-1Bi-0.2In show mechanical properties similar to SAC305.

低 Ag鉛フリーはんだの実力

低 Ag鉛フリーはんだの実力

Evolution of microstructure, thermal and creep properties of Ni-doped Sn–0.5Ag–0.7Cu low-Ag solder alloys for electronic applications

For development of lead-free solder for advance electrical components, the correlation of microstructure with thermal and creep properties of novel Ni-doped Sn–0.5Ag–0.7Cu (SAC (0507)) lead free solders has been investigated. Results showed that addition of 0.05Ni into the lead-free SAC (0507) solder led to the microstructural refinement, more uniform distribution of the Ag3Sn, (Cu,Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. However, the SAC (0507)–0.1Ni alloy has relatively high fraction of the primary β-Sn phase and the IMCs appeared coarse within the matrix compared with the other examined alloys. DSC results showed that the addition of Ni did not produce any significant effect on the melting behavior. Interestingly, 0.05wt.% Ni addition exhibited a drastically reduced undercooling to be 6.3°C. In terms of creep behavior, the SAC (0507)–0.05Ni gave the highest creep resistance due to the fine dispersion of IMCs. Furthermore, 0.05wt.% Ni addition can evidently increase the creep–rupture life, about 2.0 times greater than that of the baseline SAC (0507) and approximately 5.0 times better than that of SAC (0507)–0.1Ni solder. Meanwhile, the SAC (0507)–0.1Ni alloy shows lower creep resistance which is mainly attributable to smaller volume fraction of the precipitate phases. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.

Electrochemical Migration of Micro-alloyed Low Ag Solders in NaCl Solution

The reliability investigation of the lead-free solders is still a current issue. In this paper, Electrochemical Migration (ECM) behavior of novel lead-free micro-alloyed low Ag content solders were investigated by water drop test in NaCl solution. The results were compared to commonly used lead-free and lead bearing solder alloys. It was found that some micro-alloyed solders can have similar low ECM susceptibility than lead bearing ones. X-ray photoelectron spectroscopy was also carried out to find the root cause of different ECM behaviour of micro-alloyed solders. The results of water drop test and x-ray photoelectron spectroscopy were in good agreement relating electrochemical migration susceptibility. Since SAC0807 solder alloy has shown higher corrosion rate than SAC0307 and has also higher ability for ECM as well. It is concluded, that some lead-free micro-alloyed low Ag content solder alloy (e.g.: SAC0807) could have a high reliability risk in the electronic devices during operation.