Sn-Ag-Cu Research Articles

Reliable Sn–Ag–Cu lead-free melt-spun material required for high-performance applications

AbstractThis study investigates the structural, mechanical, thermal and electrical properties of B-1 JINHU, EDSYN SAC5250, and S.S.M-1 commercial materials, which have been manufactured at China, Malaysia, and Germany, respectively. The commercial materials have been compared with the measurements of Sn–Ag–Cu (SAC) melt-spun materials that are only indicative of what can be expected for the solder application, where the solder will have quite different properties from the melt-spun materials due to the effects of melt-spinning technique. Adding Cu to the eutectic Sn–Ag melt-spun material with 0.3 wt.% significantly improves its electrical and mechanical properties to serve efficiently under high strain rate applications. The formed Cu3Sn Intermetallic compound (IMC) offers potential benefits, like high strength, good plasticity, consequently, high performance through a lack of dislocations and microvoids. The results showed that adding 0.3 wt.% of Cu has improved the creep resistance and delayed the fracture point, comparing with other additions and commercial solders. The tensile results showed some improvements in 39.3% tensile strength (25.419 MPa), 376% toughness (7737.220 J/m3), 254% electrical resistivity (1.849 × 10−7Ω · m) and 255% thermal conductivity (39.911 w · m−1 · k−1) when compared with the tensile strength (18.24 MPa), toughness (1625.340 J/m3), electrical resistivity (6.56 × 10−7Ω · m) and thermal conductivity (11.250 w · m−1 · k−1) of EDSYN SAC5250 material. On the other hand, the Sn93.5–Ag3.5–Cu3melt-spun solder works well under the harsh thermal environments such as the circuits located under the automobiles’ hood and aerospace applications. Thus, it can be concluded that the melt-spinning technique can produce SAC melt-spun materials that can outperform the B-1 JINHU, EDSYN SAC5250 and S.S.M-1 materials mechanically, thermally and electrically.

Microstructure, hardness, and shear behavior of Sn3.0Ag0.5Cu–Sn58Bi composite solder joint

In this study, Sn3.0Ag0.5Cu-Sn58Bi (SAC-SnBi) composite solder joint was obtained by two-step soldering process. The microstructure, hardness, and shear performance of the composite solder joint were investigated in comparison with the eutectic Sn58Bi (SnBi) and SnAgCu (SAC) solder joints. Experimental results showed that the SAC-SnBi had similar intermetallic compound (IMC) morphology and thickness with the SAC solder joints. Compared with the eutectic SnBi solder, the large Bi-rich matrix transforms into tiny Bi-rich grains in the SAC-SnBi solder bulk. Tiny Bi-rich grains, Cu6Sn5, and Ag3Sn distribute uniformly in the composite solder bulk. As the SnBi bulk melts into the SAC solder during the second soldering process, the formation and growth of large β-Sn dendritic in SAC solder is suppressed in the composite solder. Therefore, the SAC-SnBi composite joint shows higher hardness and shear strength than the other two.

Effect of isothermal aging on the microstructure, shear behavior and hardness of the Sn58Bi/Sn3.0Ag0.5Cu/Cu solder joints

In order to decrease the hardness and brittleness of eutectic Sn58Bi (SnBi) solder joint, Sn3.0Ag0.5Cu (SAC) bulk was added into SnBi/Cu by a two-step soldering process to obtain solder joint with superposition structure. The microstructure, shear behavior and hardness of Sn58Bi/Sn3.0Ag0.5Cu/Cu (SnBi/SAC/Cu) during isothermal aging were investigated in comparison with SnBi/Cu and SAC/Cu solder joints. Experimental results indicated that the addition of SAC bulk affected the formation and growth of the β-Sn dendritic in the SnBi bulk in SnBi/SAC/Cu. The relative area and grain size of β-Sn in the SnBi bulk were enlarged due to the increasing concentration of Sn. The atomic diffusion during aging led to the volume reduction of SAC bulk in the SnBi/SAC/Cu joint. The addition of SAC bulk suppressed the brittleness of SnBi/Cu and transformed its failure mode from brittle failure to brittle-ductile failure after reflow. Such effect was weakened and the shear force and failure mode of SnBi/SAC/Cu joint were similar to those of SnBi/Cu, as the solder joints were aged for 600 h at 80 °C. Furthermore, the addition of SAC bulk significantly decreased the hardness of SnBi/Cu before and after aging.

Elastic Behavior of Coarse-Grained SnAgCu (SAC) Solder Joints Based on an Anisotropic Multi-scale Predictive Modeling Approach

Lead-free electronic interconnections made of Sn-rich solder alloys usually contain only a few highly anisotropic grains, rendering their overall thermo-mechanical behavior highly dependent on each crystal’s morphology and orientation. Miniaturization and heterogeneous integration will further reduce the length-scale of interconnections and exacerbate this piece-to-piece variation among different solder joints. The objective of this paper is to predict the elastic response and intergranular stresses in coarse-grained SAC (SnAgCu) solder joints, starting with orientation sensitive anisotropic predictive models of the elastic behavior of single crystals. The properties of the single crystal are, in turn, predicted by a multi-scale method, where each grain is modeled as a collection of Sn dendrites embedded in a eutectic Sn-Ag matrix. The eutectic phase, in turn, is modeled as an effective homogenized composite material consisting of nano-scale Ag3Sn particles embedded in a highly anisotropic tin matrix. All homogenization for prediction of single-crystal elastic properties is based on composite micromechanics, using Eshelby’s method and Mori–Tanaka homogenization. Elastic response of a few-grained solder joints is then numerically predicted from the anisotropic behavior of the single crystal, by explicitly modeling the grain morphology in finite element analysis (FEA). Stress distributions along grain boundaries are simulated and analyzed in terms of the misorientation angle between neighboring grains. The mismatch in von Mises stress along the boundaries varies up to 55% for grain structures considered here. This multi-scale predictive modeling approach is explicitly sensitive to microstructural features such as the morphology of: (1) the intermetallic compound (IMC) reinforcements in the eutectic phase; (2) dendrites; and (3) grains. Thus, this modeling approach is ideally suited for: (1) parametric studies of the effect of microstructural tailoring on solder joint thermo-mechanical behavior and (2) examining the effects of microstructural evolution caused by static and cyclic thermo-mechanical aging. This work forms the starting point for future development of microstructurally based anisotropic models of crystal-scale inelastic behavior.

Suppressed Growth of (Fe, Cr, Co, Ni, Cu)Sn2 Intermetallic Compound at Interface between Sn-3.0Ag-0.5Cu Solder and FeCoNiCrCu0.5 Substrate during Solid-state Aging

High-entropy alloys (HEAs) are promising materials for next-generation applications because of their mechanical properties, excellent high-temperature stability, and resistance against oxidation and corrosion. Although many researchers have investigated high-temperature HEA applications, few have considered low-temperature applications. Here we demonstrate an unprecedented intermetallic compound of (Fe, Cr, Co, Ni, Cu)Sn2 at the interface between Sn-3.0Ag-0.5Cu (SAC) solder and FeCoNiCrCu0.5 HEA substrate after reflow at 400 °C. Significantly suppressed growth of intermetallic compound without detachment from the substrate was observed during thermal aging at 150 °C for 150 h. Sn grains with an average grain size of at least 380 μm are observed. The results reveal a completely new application for the fields of Sn-Ag-Cu solder and HEA materials.

Roles of direct current in ultrafast wetting of 3YSZ by Sn3.0Ag0.5Cu and joining to Ni

The purpose of this work was to develop a new strategy for the rapid and reliable joining of zirconia to metal. The wetting behavior of 3 mol% yttria-stabilized zirconia (3YSZ) by molten Sn3.0Ag0.5Cu (SAC) under the application of a direct current (DC) was investigated using a DC-coupled sessile drop method. Joining of 3YSZ with Ni using the SAC solder under the assistance of a DC was carried out in vacuum and the joint strength was evaluated by shear test. The interfacial microstructures were analyzed by SEM, EDS and XRD. The wettability was significantly improved when 3YSZ was connected to anode (represented by “+”) at temperatures higher than 723 K. Noticeably, the contact angle decreased from 143° to 43° in < 3 s under a DC of +10 mA at 1173 K. The underlying mechanisms were ascribed to the formation of substoichiometric ZrO2-x and the adsorption of metallic Zr at the interface, while the formation of a ZrSn2 phase at the interface played a negligible role. Reliable 3YSZ/SAC/Ni joint was obtained. The formation of a ZrSnNi phase at the interface played a key role in determining the bonding strength. The maximum shear strength reached 43 ± 4 MPa when the couples were brazed under a DC of +10 mA at 1073 K for 10 min. The effects of the current intensity and temperature on the joint microstructure and shear strength were discussed and the relevant mechanisms were addressed.

Comprehensive comparative analysis of microstructure of Sn–Ag–Cu (SAC) solder joints by traditional reflow and thermo-compression bonding (TCB) processes

Thermo-compression bonding (TCB) process has been considered an emerging alternative to the conventional reflow process because of its significantly fast bonding time due to rapid ramping and its ability to fabricate ultra-fine pitch 3D stacked interconnections to achieve package miniaturization, as is necessary in high bandwidth memory (HBM) modules. Since the TCB-process bonded joints are usually followed by additional solder reflow processes for bonding of other components, no attention has been solely dedicated to the reliability of TCB-only bonded joints. In addition, there has not been any fundamental and comparative studies between the conventional reflow bonding and the TCB process. A recent study showed that the TCB joints could be vulnerable to thermal cycling and electro-migration (EM), and therefore risk exhibiting early failures. A significant difference in bonding processes between the two processes may affect solder grain and crystallographic characteristics, thus affecting the reliability performance. Here, we show that the Cu6Sn5 intermetallic compound (IMC) morphology at Sn–Ag–Cu (SAC-305) solder joint interfaces and the β-Sn crystallographic orientation of the solder joint could explain for the premature EM failure in TCB-utilized solder joints. The effect of the IMC layer of TCB-processed solder joints on the diffusion of Cu and Ni atoms at the solder/bond pad interfaces is presented. Furthermore, the thermomigration (TM) caused by Joule heating for TCB-utilized solder joints is discussed. Lastly, statistical studies using electron backscatter diffraction (EBSD) results reveal the higher lattice coherency of β-Sn crystallographic texture for TCB-processed solder joints.

Comprehensive Comparative Analysis of Microstructure of Sn-Ag-Cu (SAC) Solder Joints by Traditional Reflow and Thermo-Compression Bonding (TCB) Processes

Thermal-compression bonding (TCB) process has been considered to successfully fabricate the 3D stacked interconnection with ultra-fine pitch I/O bumped thin flip-chip and achieve package miniaturization, such as high bandwidth memory (HBM) modules that exceed capabilities of traditional thermal reflow process. Until now, a conventional reflow process has been the de facto solder interconnection method in microelectronic packaging. The alternative, TCB process has not been employed commonly for solder interconnection method as TCB-bonded solder joints have yet failed to prove their reliabil-ity such as upon thermal cycling and electro-migration (EM). A significant difference in solder reflow (i.e. melting and solidi-fication) technique may affect solder grain and crystallographic characteristics, thus affecting the reliability performance of 3D package modules. In addition, there has not been any fundamental and comparative study between the conventional reflow bonding and TCB processes. Also, the degradation mechanism of TCB-processed flip-chip packages upon EM failure has not been clearly defined. Here we show that the Cu6Sn5 intermetallic compound (IMC) morphology at Sn-Ag-Cu (96.5 wt./3.0 wt./0.5 wt.% SAC-305) solder joint interfaces and the texture of β-Sn crystallographic orientation of SAC-305 solder joint upon TCB-utilized flip-chip fabrication drives premature EM failure. We found that the lack of the IMC layer of TCB-processed solder joints facilitates the diffusion of Cu and Ni atoms at the solder-Cu bond pad interfaces, and furthermore the thermomigration (TM) caused by Joule heating at the TCB interface could provide synergistic impact on the EM. In ad-dition, through statistical studies using EBSD results, higher lattice coherency of β-Sn crystallographic texture was observed for TCB-processed solder joint that adds to a much faster diffusion of Cu and Ni atoms during the EM test, which is respon-sible for leaving defects both within the solder and at the interfaces of the joint. Our results demonstrate an insightful deriv-ing force of EM from the solder joint the microstructure and the crystal orientation that allows for juxtaposition of two most widely used bonding technologies, reflow bonding and TCB.

Dependence of shear strength of Sn–3.8Ag–0.7Cu/Co–P solder joints on the P content of Co–P metallization

The mechanical properties of solder joints highly depend on the interfacial reaction between the solders and the metallization on substrates. In this work, we electroplated Co–P films with various compositions on the Cu pads of printed circuit boards and fabricated Sn-3.8 wt% Ag-0.7 wt% Cu/Co–P ball grid array (BGA) solder joints. The BGA solder joints were annealed at 150 °C for 100, 200, 500, and 1000 h and the shear strength of these joints was measured. When the P content of the Co–P metallization was increased from 2.3 to 18.8 at.%, the shear strength after 1000 h annealing initially rose to 107.9 MPa at a P content of 8.5 at.%, then decreased to 84.3 MPa at a P content of 12.5 at.%, and again increased to 96.0 MPa at a P content of 18.8 at.%. The enhancement of the shear strength of the joints with Co-8.5 at.% P, Co-12.5 at.% P, and Co-18.8 at.% P films was 109.5%, 63.7%, and 86.4% in comparison to the joints without Co–P metallization, respectively. The interfacial reaction between the Sn–Ag–Cu (SAC) solder and Co–P films during annealing and the fractured surfaces of the solder joints after the shear test were studied. For the joints with Co-8.5 at.% P and Co-18.8 at.% P films, a thick layer of CoSn3 was formed at the interfaces during annealing, which enhanced the shear strength. For the joints with Co-12.5 at.% P metallization, a thin layer of Co–Sn–P was formed at the interfaces and was peeled off layer by layer with prolongation of the annealing time. The spalled Co–Sn–P was mixed with the solder matrix, increasing the shear strength of the solder joints. The shear strength of the SAC/Co-12.5 at.% P joints was less than that of the joints with Co-8.5 at.% P and Co-18.8 at.% P films because no CoSn3 formed. Therefore, the composition of Co–P metallization played an important role in the interfacial reaction of the SAC/Co–P solder joints, which in turn affected the shear strength of the solder joints. Our experimental results show that the electroplated Co–P film is a promising candidate as the metallization for BGA solder joints.

Studies of the solidification characteristics in Sn-Ag-Cu-Bi solder alloys.

Because of the environmental health implications of Pb, and legislation backing Restriction on Hazardous Substances (RoHS) in electronic devices, Sn-based lead-free solders are developed. Near eutectic Sn-Ag-Cu (SAC) compositions is the most widely used Pb-free solder in the electronic industries. However, its high melting temperatures (>217 ℃) remains a concern. The addition of Bi to a Sn-based alloy can be used to lower melting temperature because of the presence of a deep valley eutectic in the Bi-Sn system. The effects of such additions in SAC on solidification path are rarely considered. The effects of Bi substitution for Sn on solidification of near eutectic SAC alloy are followed with differential thermal analysis (DSC). It is found that the solidus temperature of SAC-Bi alloy mixes is considerably lowered. For low concentrations of Bi, melting range (ΔTr) were generally less than 4 ℃. However, (ΔTr) considerably widens when the Bi content exceeds 2 wt. %. The DSC and X-ray diffraction (XRD) studies suggested that a higher concentration of Bi in SAC would lead to far eutectic solidification that is attended by a formation of primary Bi phase. The existence of primary Bi phase in a solidified solder would lead to embrittlement and thus would affect the integrity of soldered joints. This work suggests that the use of Bi in SAC solders should be restricted to less than 2 wt. % (by varying %Wt of Bi).

The effect of CNT and Cu on interfacial intermetallic growth of Sn-Ag-Cu solder

In this study, the effect of copper and carbon nanotubes (CNT) composition on interfacial growth of various Sn-Ag-Cu (SAC) solder joints were investigated. SAC is proven to have good reliability and mechanical properties but lacking in terms of melting point and wettability. Thus, Sn-4.0 wt%Ag-0.3wt%Cu (SAC403) and Sn-4.0 wt%Ag-0.7 wt%Cu (SAC407) were reinforced with CNT with various weight percentages of 0 to 0.1wt%. The wetting angle and intermetallic compound (IMC) thickness is measured using optical microscope (Olympus BX5/M) and Olympus Stream Essentials software. The high Cu content alloys formed a long Cu6Sn5 whisker which act as an obstacle to crack propagation. CNT improves wettability and IMC layer growth for both SAC403 and SAC407 by lowering the wetting angle and IMC thickness compared to the plain solder.

Evolution of the Microstructure of Sn58Bi Solder Paste with Sn-3.0Ag-0.5Cu Addition During Isothermal Aging

Eutectic Sn58Bi (SnBi) solder paste mixed with 0 wt.%, 3 wt.%, 5 wt.%, 8 wt.% and 15 wt.% of Sn-3.0Ag-0.5Cu (SAC) paste was prepared by mechanical mixing. The effects of SAC paste additions on the microstructure evolution of SnBi-SAC/Cu composite solder joints during isothermal aging were investigated. The results indicated that the number of large Bi-rich phases decreased and the relative areas of β-Sn increased with increasing SAC content. Moreover, 1-μm Bi-rich particles were found near the Bi-rich phases. During the isothermal aging process, the diameter of the 1-μm Bi-rich particles in the solder bulk increased by about 50% with aging time by Ostwald ripening. The thickness of the interfacial intermetallic compound in all the solder joints increased slightly during the aging process. The formation of Cu6Sn5 was suppressed by the Bi-rich phases above the Cu6Sn5 layer with the aging time increasing. In addition, the solder bulk showed many cracks along the β-Sn grain boundaries after isothermal aging when the content of SAC paste was 5 wt.%. With 8 wt.% or 15 wt.% SAC, fractures were more obvious near the interface than away from the interface.

Characterization of SAC – x NiO nano-reinforced lead-free solder joint in an ultra-fine package assembly

PurposeThis study aims to investigate the NiO nano-reinforced solder joint characteristics of ultra-fine electronic package.Design/methodology/approachLead-free Sn-Ag-Cu (SAC) solder paste was mixed with various percentages of NiO nanoparticles to prepare the new form of nano-reinforced solder paste. The solder paste was applied to assemble the ultra-fine capacitor using the reflow soldering process. A focussed ion beam, high resolution transmission electron microscopy system equipped with energy dispersive X-ray spectroscopy (EDS) was used in this study. In addition, X-ray inspection system, field emission scanning electron microscopy coupled with EDS, X-ray photoelectron spectroscopy (XPS) and nanoindenter were used to analyse the solder void, microstructure, hardness and fillet height of the solder joint.FindingsThe experimental results revealed that the highest fillet height was obtained with the content of 0.01 Wt.% of nano-reinforced NiO, which fulfilled the reliability requirements of the international IPC standard. However, the presence of the NiO in the lead-free solder paste only slightly influenced the changes of the intermetallic layer with the increment of weighted percentage. Moreover, the simulation method was applied to observe the distribution of NiO nanoparticles in the solder joint.Originality/valueThe findings are expected to provide a profound understanding of nano-reinforced solder joint’s characteristics of the ultra-fine package.

Effect of addition of GO Nanoparticles on the tensile properties and deformation temperature of Sn-3.5Ag-0.7Cu lead free solder alloy

The advantage of lead-liberated welding is the melting point of Sn-Ag-Cu (SAC) alloys in the Sn-rich alloy. The nanoparticles welding with lowering melting point near to the Sn-Pb eutectic point is found more interest. Latterly, the phase persistence of nanoparticles has been the project of massiveness of academic and experiential investigations. In this study, graphene nanoparticles (GNPa) with 0.3 percentages wt.% were successfully added into Sn-3.5Ag-0.7Cu lead-free solder. The effects of graphene nanoparticles (GNPa) on the microstructure, tensile properties, wettability, corrosion resistance, and hardness were subsequently investigated. The results show that graphene nanoparticles (GNPa) refine the microstructure with different features and enhance the wettability efficiently. Stress-strain tests discover that the combined solder with 0.3 wt.% GNPa exhibits about 15% and 25% enhancement in tensile strength and hardness, respectively. In addition, the total elongation of Sn-3.5Ag-0.7Cu is 22% greater than that of the pure Sn-3.5Ag-0.7Cu+0.3GO solder alloy. The enhancing mechanism of 0.3GO on the achievement of combined samples is also studied. Stress strain experiments were inspected under different five strain rates ranging from 5.4x10-5 S-1 to 2.9x10-3 S-1 and different five temperatures extended from R.T. (298K) to 383 K for two alloys. The activation enthalpy suggests that the dominant mechanism is the grain bounding diffusion (GBD). Also, X-ray diffraction examination display the permanence of both β-Sn rich phase and the intermetallic compound Ag3Sn and very little particles or residue from the intermetallic composition γ-In Sn4.

Mechanical Property of SAC305 Ball-Grid Array and Epoxy Sn-58Bi Solder Joints with 85 °C/85% Relative Humidity Environmental Conditions.

The ball-grid array (BGA) is widely used to reduce component size and it had advantages such as high I/O pins and fine pitch. Typical Sn-Ag-Cu (SAC) solder alloys are used for formation of BGA because SAC solder has excellent characteristics among lead-free solders. However, the electronic components assembled by SAC solder were easily damaged by heat during manufacture process because SAC solder had high melting point of 220 °C. To prevent these thermal damages, SAC305 BGA component assembled by Sn-58Bi solder paste has been studied because Sn-58Bi solder had low melting point of 139 °C. In generally, Sn-58Bi solder was improved by additional elements or polymer such as epoxy because Sn-58Bi had a brittle property. However, the epoxy Sn-58Bi solder did not guaranteed high environmental reliability such as high-temperature high-humidity (HTHH) test. Thus, we evaluated the shear strength of solder joints assembled by SAC305 BGA components with Sn-58Bi solder paste and epoxy Sn-58Bi solder paste. The shear strength of solder joints was evaluated by die shear test after HTHH test at the 85 °C/85% RH conditions. The Cu6Sn5 intermetallic-compound (IMC) at the interface of solder joints was observed by scanning electron microscope (SEM). The IMC thickness of Sn-58Bi solder joints was smaller than that of epoxy Sn-58Bi solder. The shear strength was improved up to 20% by epoxy addition. The shear strength of epoxy Sn-58Bi solder joints dramatically decreased after HTHH test for 100 h.

Enhancement of Microstructural and Physical Properties of Sn-0.7Cu Lead-Free Solder with the Addition of SiC Particles

Nowadays, composite solder has gained researcher’s attention due to its promising improvement in physical and mechanical properties for lead-free solder. To improve the properties of Sn-0.7Cu (SnCu): the promising lead-free candidate, addition of silicon carbide (SiC) as a reinforcement was used into this study. However, its limitation on solderability as compared with SnAgCu (SAC) make it not an attractive alternative lead-free solder. This study was carried out to investigate the effect of SiC particle on microstructure evolution and physical properties of SnCu based solder alloys. SnCu-SiC composite solders were synthesized by powder metallurgy method (PM), which consists of several processes such as mechanical blending, compaction and sintering. Five different weight percentages of SiC particle; 0.00, 0.25, 0.50, 0.75 and 1.00 were mechanically blended with SnCu lead-free solder. The result shows that the addition of SiC particle has decreased the β-Sn area and refined the microstructure of composite solder. In addition, the improvement in microhardness of composite was achieved.

A Breakthrough in Pb-Free Solder Electroplating

The progression in the electronics industry is toward further minimization and the global semiconductor assembly community is striving for a robust replacement for leaded solders due to increased environmental regulations. A family of Pb-free solder alloys based on Sn-Ag-Cu (SAC) compositions has shown promise, but due to reliability issues in certain assembly and operating environments, quaternary (Mn, Ni, Zn, and Al-doped SAC) solders are currently under investigation. With more computing power, higher performance is needed for smaller areas. The ball-grid-array (BGA) packaging system with a decreased size, is likely to be replaced by chip-scale packages (CSPs) (i.e. µBGA) and Copper Pillar Bumps (CPBs). There are several methods to form solder bumps such as screen printing, evaporation and electroplating. As the pitch and the bump size decrease, electroplating becomes the only efficient way to fabricate bumps with small size, fine pitch and low cost. Electroplating is considered to be the only feasible technique to form the copper pillar and the solder cap to realize the CPBs. Currently, solder electroplating is limited mainly to binary compound plating and there exist no stable solutions for electroplating of ternary alloys due to a large gap in electrochemical reduction potentials between different elements. For example, in order to perform SAC electroplating Karim et al. had to use sequential plating from two separate binary SnCu and SnAg plating solutions [1]. However, if developed, ternary alloy plating solutions may not be practical under manufacturing conditions considering that it is hard to maintain bath and alloy composition even for binary plating solutions. Obviously the development of a plating solution for quaternary alloy is even less probable. In order to deposit alloy with precise composition, multilayer electroplating method is proposed instead. The method lies in the sequential electroplating of each of the solder components from a separate bath and a consequent reflow to form uniform alloy. Unfortunately to warrantee the reliability the electroplating sequence should be carefully watched [2]. To overcome inter-diffusion limitation and achieve a uniform and fast reflow, low thickness of each layer is necessary and a proportional increase of layers number makes the process time-consuming and impractical from a conventional electroplating point of view due to multiple switching between solution baths. The present work will show how using a new concept in electroplating, based on multiple Dynamic Liquid Drop/Meniscus (DLD/DLM), is possible to realize multilayer approach to plate binary, ternary and even quaternary solder alloy at high throughput, high precision and low cost. The DLD/DLM [3] represents a constantly refreshed confined electrolyte volume in touch with a substrate surface. The plating concept lies in assembling multiple independent DLD/DLM in a sequential array (one or many for each plating component intercalated by a rinse DLD/DLM) into a multiple plating head. Thus scanning the plating head over the wafer surface will allow consequent plating of a layer of each of the component. Each pass of the plating head leads to deposition of the multilayered structure representing consequent components layers (grains) with a required proportion. Total thickness of the alloy depends on the number of passages and can be varied in a wide range. Using the proposed technique various solder compositions were deposited. As a proof-of-concept, SAC305 and SAC405 layers with 30µm thickness were deposited containing more than 350 layers of each element. A detailed investigation of SAC and quaternary SAC+Mn alloys composition will be presented; EDX analysis before and after reflow proving that the high number of layers an homogenous solder is obtained independently of metal deposition sequence and even without reflow. The proposed breakthrough technique offers the unique opportunity to deposit any kind of binary, ternary and quaternary Pb-free alloy solder from single bath solutions without any kind of cross contamination. Such technique poses a key milestone to obtain ternary and/or quaternary Pb-free solder alloy for the CSPs and CPBs allowing to tune the correct solder alloy in order to finally solve reliability issues. [1] Z. S. Karim and J. Martin, “Lead-free solder bump technologies for flip-chip packaging applications”, SMTA (2001). [2] Qinghua Zhao, Anmin Hu, Ming Li, Jiangyan Sun, “Effect of electroplating layer structure on shear property and microstructure of multilayer electroplated Sn-3.5Ag solder bumps” Microelectronics Reliability 53 (2013) 321–326 [3] Konstantin Kholostov, et al. “High uniformity and high speed copper pillar plating technique” IEEE 64th Electronic Components and Technology Conference (ECTC), 2014, 1571-1576 Figure 1 shows the SEM pictures and EDX analysis of SAC 305 μBGA by multiple DLD/DLM technique. Figure 1

Superior Reliability of SAC105 Solder on BGA Package Pad with NiPdAu Coating

The reliability of Sn-Ag-Cu (SAC) solder welded with Cu-organic solderability preservative (OSP) and NiAu- or NiPdAu-coated ball grid array (BGA) package pads has been investigated after isothermal aging. Moreover, the interfacial reaction and diffusion reaction are discussed. The intermetallic compound (IMC) layer was found to be too thick to withstand large stresses, leading to poor reliability of the solder joints on Cu-OSP pads. Additionally, for NiAu-coated pads, not only irregular Au-rich phases but also more diffused Ni without the barrier effect of Pd promoted formation of IMC in the solder balls, resulting in a potential mismatch with the initial solder. Compared with the NiAu-coated pad, the IMC layer that formed between the NiPdAu-coated pads and SAC105 solder was thinner, indicating an effective diffusion barrier effect of the Pd layer in the NiPdAu coating. Hence, SAC105 solder showed superior reliability on BGA package pads coated with NiPdAu.

Investigating the Microstructural and Mechanical Properties of Pure Lead-Free Soldering Materials (SAC305 &amp; SAC405)

Abstract The Sn–Ag–Cu (SAC) solders with low Ag or Cu content have been identified as promising candidates to replace the traditional Sn–Pb solder. In this study, an extensive discussion was presented on two major area of mechanical properties and microstructural investigation of SAC305 and SAC405. In this chapter, we study the composition, mechanical properties of SAC solder alloys and microstructure were examined by optical microscope and SEM and mechanical properties such as tensile tests, hardness test and density test of the lead solder alloys were explored. SAC305 and SAC405 alloys with different Ag content and constant Cu content under investigation and compare the value of SAC305 and SAC405. From this investigation, it was reported that tensile strength is increased, with an increase of Ag content and hardness and density were also increases in the same manner.

Property alterations of Sn-0.6Cu-0.05Ni-Ge lead-free solder by Ag, Bi, In and Sb addition

Abstract The Sn-Cu-Ni-Ge solder is a strong challenger to the Sn-Ag-Cu (SAC) solders as a replacement for the Sn-Pb eutectic solder. This research investigated the effects of addition of Ag, Bi, In, and Sb on the physical properties of the Sn-0.6Cu-0.05Ni-Ge (SCNG) lead-free solder and the interfacial reaction with the Cu substrate. The melting behavior, microstructure, tensile strength, and wettability of the SCNG–x (x=Ag, Bi, In, Sb) solders were examined. The findings revealed that the introduction of Ag, Bi, In, and Sb minimally altered the solidus temperature, liquidus temperature, and tensile strength of the solder. However, the cooling behavior and solidified microstructure of the solder were affected by the concentration of the alloying elements. The wettability of the SCNG solder was improved with the doping of the alloying elements except Sb. The thickness of intermetallic layer was increased by the addition of the alloying elements and was related to the cooling behavior of the solder. The morphology of intermetallic layer between the SCNG–x solders and the Cu substrate was different from that of the typical SAC solders. In conclusion, alloying the SCNG solder with Ag, Bi, In or Sb is able to improve particular properties of the solder.