Strength Of Solder Joints Research Articles

Fracture mechanism and strength-influencing factors of Cu/Sn–4Ag solder joints aged for different times

Tensile properties and fracture mechanisms of Cu/Sn–4Ag solder joints aged at 180 °C for different times were investigated at the strain rates of 1.25 × 10 −4 s −1 and 1.25 × 10 −1 s −1. At the low strain rate, it was found that the tensile strength of the solder joints decreased with increasing aging time in principle, though the tendency was not monotonously at the early stage of aging; and all the solder joints had similar tensile curves but different fracture morphologies and fracture processes. At the high strain rate, tensile strength of the solder joints was much higher and decreased monotonously with increasing aging time, with identical fracture process and fractographies. Evolution of the Cu/Sn–4Ag interfacial morphology during aging process and the effect of aging on tensile property of the Sn–4Ag alloy were also involved for further analysis. Based on the experimental results and observations, the fracture processes were revealed and some factors controlling the tensile strength of solder joints were discussed qualitatively.

An Assessment of Immersion Silver Surface Finish for Lead-Free Electronics

The worldwide transition to lead-free electronics has increased the usage of several lead-free pad finishes for electronic assembly manufacturers, including immersion silver, immersion tin, electroless nickel-immersion gold, and organic solderability preservatives. This study assesses and compares immersion silver as a circuit board finish in terms of its ease of use, wettability, solderability, shelf life, appearance, solder joint strength, intermetallic and void formation, reliability, and costs.

Effect of various Ni plating layers and aging on microstructure and shear strength of Sn–2.5Ag–2.0Ni solder joint

Sn–2.5Ag–2.0Ni alloy is used to solder silicon carbide reinforced aluminum matrix (SiC p/Al) composites substrate with various Ni coatings. An experimental study is carried out to assess the effects of various Ni coatings on the microstructure and reliability of solder joint. Three electroless Ni layers, including Ni–5 wt.%P, Ni–10 wt.%P and Ni–B, are investigated. The electroless Ni–B layer is found to have good wettability with solder and gives the lowest growth rate of Ni 3Sn 4 IMCs during aging. The formation of Ni 2SnP, which significantly affects the reliability of solder joints, is suppressed by using the low P content Ni–5 wt.%P layer. The electroless Ni–B layer has given the highest shear strength of solder joint while Ni–5 wt.%P layer yields the higher shear strength as compared to Ni–10 wt.%P layer. Growth of Ni 3Sn 4 IMCs and formation of crack are observed to be the major sources of failure for the solder joint with Ni–5 wt.%P, whereas, the failure of Ni–10 wt.%P solder joint is accounted for the formation of Ni 2SnP, P-rich Ni layer and Kirkendall voids after long term aging.

Effects of minor Fe, Co, and Ni additions on the reaction between SnAgCu solder and Cu

The reactions between Cu and the Sn2.5Ag0.8Cu solders doped with 0.03 wt.% Fe, Co, or Ni were studied. Reaction conditions included multiple reflows for up to 10 times and solid-state aging at 160 °C for up to 2000 h. In the multiple reflow study, Cu 6Sn 5 was the only reaction product noted for all the different solders used. Reflows using the solder without doping produced a thin, dense layer of Cu 6Sn 5. Adding Fe, Co, or Ni transformed this microstructure into a much thicker Cu 6Sn 5 with many small trapped solder regions between the Cu 6Sn 5 grains. In the solid-state aging study, both Cu 6Sn 5 and Cu 3Sn formed, but adding Fe, Co, or Ni produced a much thinner Cu 3Sn layer. Because the Cu 3Sn growth had been linked to the formation of micro voids, which in turn increased the potential for a brittle interfacial fracture, thinner Cu 3Sn layers might translate into better solder joint strength.

Interfacial intermetallic growth and shear strength of lead-free composite solder joints

In the present study, varying weight percentages of carbon nanotubes (CNTs) were incorporated into Sn–Ag–Cu solder matrix, to form composite solders. Isothermal aging study was performed on solder joints, to investigate the formation and growth of the intermetallic compound (IMC) layer at the solder/metallization interface. Shear tests were also conducted on as-soldered and aged solder joints. Results revealed that after soldering, the initial interfacial IMC thickness of the unreinforced solder joint was comparable to that of the composite solder joints. However, after aging, the interfacial IMC layer of the unreinforced solder joint was observed to grow more significantly than that of the composite solder joints. Moreover, the composite solder joints also exhibited lower diffusion coefficient and this signified that the presence of CNTs was effective in retarding the growth of the IMC layer. Shear tests results revealed that as-soldered and aged composite solder joints had better shear strength than their monolithic counterparts and the shear strength of all aged solder joints decreased with increasing aging time.

Reliability Evaluation of QFP Solder Joint Using Sn-8Zn-3Bi Solder Paste during the Thermal Shock Test

The reliability of QFP (Quad flat package) solder joint using Sn-8Zn-3Bi solder paste under the thermal shock test was investigated. Considering the environmental restriction such as ROHS, the QFP Cu LF (Lead-frame) was coated with lead-free materials (Sn, Sn-3Bi). To analyze the reliability under thermal shock treatment, the samples were placed in the thermal shock chamber (248K/423K, Dwell time: 30min). During the thermal shock test, the solder joint cross-sections were observed every 500 cycles. No crack initiation and propagation was observed through all type of plated Cu LF. The measured pull strength slightly decreased, as the number of cycles increased. After 1000 cycles, the pull strength of Sn and SnBi plated Cu LF reduced by 30% and 20%, respectively, compared with that of initial condition. Observing the fracture surface morphology by FE-SEM, the fracture mode changed and the IMC fractured area on the both fracture surface was increased. The IMC was identified as γ-Cu5Zn8 by chemical composition analysis using EDS. The reduced pull strength was affected by IMC fracture and fracture mode change. However, the pull strength does not decrease steeply but gradually. Consequently, the Sn-8Zn-3Bi solder joint shows the reliable solder joint strength, fracture mechanism, and compatibility with lead-free plated Cu LF during the thermal shock temperature of 248K to 423K.

Effects of multiple reflows on interfacial reaction and shear strength of SnAgCu and SnPb solder joints with different PCB surface finishes

Abstract The effects of multiple reflows (1, 2, 4, 6, 8, 10 numbers of reflow) on interfacial reaction and shear strength of Sn3.8Ag0.7Cu (SAC) and Sn37Pb (SP) joints were systematically investigated using electrolytic Ni/Au and organic solderability preservative (OSP) finished pad. In the case of OSP finished substrate, the well-known intermetallic compound (IMC) Cu6Sn5 was observed for both solders. While for the Ni/Au finished substrate, the IMC Ni3Sn4 and (CuNi)6Sn5 were formed on the interface of SP and SAC joints, respectively. With the increasing number of reflows, the thickness of IMCs on all reaction couples increased gradually and the IMC grain coarsened. The IMC growth kinetics showed that the interfacial IMC Cu6Sn5 was controlled by grain boundary diffusion and that the IMCs (Ni3Sn4 and (CuNi)6Sn5) near Ni layer had interactive diffusion control of grain boundary and volume diffusion. Moreover, IMC growth at Cu interface was faster than that at Ni interface, irrespective of the solder type. Shear test results showed that the shear force did not change much until eight numbers of reflow for each reaction couple. The ductile fracture indicated that the shear strength of solder joints could not be significantly influenced by the thickness and morphology of the interfacial IMC.

TESTING METHOD FOR MEASURING IMPACT STRENGTH OF BGA SOLDER JOINTS ON ELECTRONIC PACKAGE

A pendulum-impact testing machine was developed to measure the impact strength of ball-grid-array (BGA) solder joints between an electronic package and a circuit board. Ball solders were connected to daisy-chain between a dummy electronic package and a circuit board. The upper side of the package was directly bonded to a load cell. The rear side of the circuit board was also bonded to an aluminum alloy block fixed on a base. A pendulum made of aluminum alloy was collided into the load cell to apply tensile impact to the solder joints through the load cell. The history of the impact load could be controlled by raising the angle of the pendulum. The fracture of a BGA solder joint was detected by measuring the resistance of the daisy-chain circuit on the board. Therefore, the impact strengths of the solder joints at electrical disconnection and mechanical breaking of all joints could be determined. The experimental results showed that this method is useful for measuring the impact strength of BGA solder joints.

Effects of Trace Amounts of Rare Earth Additions on Microstructure and Properties of Sn-Bi-Based Solder Alloy

The effect of trace amounts of rare earth additions on the microstructure and properties were studied for the Sn-58Bi and Sn-58Bi-Ag solder alloys. At the same time, the intermetallic compounds (IMCs) in the solder alloys and intermetallic layer (IML) thickness at the solder/Cu substrate interface were investigated, both as-reflowed and after high-temperature aging. The results indicate that adding trace amounts of rare earth (RE) elements has little influence on the melting temperature and microhardness of the solders investigated, but adding RE elements improves the wettability and shear strength of the Sn-58Bi and Sn-58Bi-Ag solder alloys. In addition, it was found that the addition of RE elements not only refines the microstructure and size of the IMC particles, but also decreases the IML thickness and shear strength of the Sn-58Bi solder joint after high-temperature aging. Adding trace amounts of RE elements is superior to adding trace amounts of Ag for improving the properties of the Sn-58Bi solder. The reason may be related to the modification of the microstructure of the solder alloys due to the addition of trace amounts of RE elements.

Effect of rare earth addition on shear strength of SnAgCu lead-free solder joints

In the present study, the effect of adding trace amount of rare earth (RE) on the shear strength of Sn3.8Ag0.7Cu lead-free solder joints has been investigated. The shear strength of the solder joints as-reflowed and after aging at 150 °C for 168 and 336 h was measured at a constant loading rate of 0.3 mm/min and room temperature. The investigation indicates that the shear strength of Sn3.8Ag0.7Cu0.1RE solder joints is lower than that of Sn3.8Ag0.7Cu solder joints. The shear strength of both Sn3.8Ag0.7Cu solder joints and Sn3.8Ag0.7CuRE solder joints was reduced after aging at elevated temperature. However, the shear strength reduction rate of the Sn3.8Ag0.7Cu solder joints was much faster than that of Sn3.8Ag0.7CuRE solder joints. Moreover, the fracture surfaces were examined by scanning electron microscopy (SEM) and the thickness of intermetallic compounds layer (IML) in the solder joints that join Cu substrate was measured. The results indicated that the addition of rare earth elements suppresses the growth of the thickness of intermetallic compounds layer.

Strength and Corrosion Resistance of Solder Joint in Ultrasonic Soldering of Aluminum using Quasi-Melting Solder

Strength and Corrosion Resistance of Solder Joint in Ultrasonic Soldering of Aluminum using Quasi-Melting Solder

719 異種接合体の損傷シミュレーションに関する研究(OS4.電子デバイス・電子材料と計算力学(4),オーガナイズドセッション)

Purpose of the present study is to develop a method to simulate damage evolution of dissimilar material joint. Solder joint is one of the examples of target of the research in which intermetalic compounds are generated along the boundary between solder and interconnection. Evaluation of solder joint strength usually requires time consuming experiment. To reduce the time need, development of numerical method is desired. Cellular automata simulation method is employed. As a first step, numerical method of simulating diffusion process and formation of inter metallic materials along interface of materials has been developed.

Creep Properties of Composite Solders Reinforced with Nano- and Microsized Particles

In the present work the creep properties of Sn37Pb- and Sn0.7Cu-based composite solders reinforced with metallic nano- and microsized Cu and Ag particles have been studied. First, a series of volume percentages of reinforcements were selected to optimize the content of reinforcing particles. Then, the composite solder with optimum volume fraction of reinforcement particles, corresponding to the maximum creep rupture lifetime, was selected to investigate the effect of applied stress and temperature on the creep rupture lifetime of the composite solder joints. In the creep rupture lifetime test, small single-lap tensile-shear joints were adopted. The results indicate that composite solders reinforced with microsized particles exhibit better creep strengthening than composite solders reinforced with nanosized particles, although the mechanical tensile shear strength of composite solder joints reinforced with nanosized particles may be higher than those reinforced with microsized particles. Moreover, the creep strengthening action of the reinforcement particles is more obvious under conditions of lower applied stress or lower test temperature. Strengthening by metallic Cu or Ag reinforcement particles decreases with increasing temperature or applied stress. The Sn0.7Cu-based composite solder reinforced with microsized Ag particles is a low-cost lead-free solder that is easy to process and may have good market potential.

Influence of Content of Ni and Ag on Microstructure and Joint Strength of Lead-Free Solder Joint with Sn-Ag-Cu-Ni-Ge

An influence of content of Ni and Ag in a Sn-Ag-Cu-Ni-Ge lead-free solder has been investigated on microstructure and joint strength of the soldered joint under heat exposure conditions. The growth kinetics of the reaction layer formed at the joint interface has been investigated, and the apparent activation energy of the reaction layer growth has been also examined. Moreover, the soldered joints with Sn-Ag and Sn-Ag-Cu solders were prepared and were compared with the joints with the Sn-Ag-Cu-Ni-Ge solders.

Electromigration Reliability and Morphologies of 62Sn–36Pb–2Ni and 62Sn–36Pb–2Cu Flip-Chip Solder Joints

The near-eutectic Sn-Pb-Cu and Sn-Pb-Ni ternary solder alloys were developed based on the consideration of strength and fatigue reliability enhancement of solder joints in part via the altering of formation of interfacial intermetallic compounds. In this work, we examine electromigration reliability and morphologies of 62Sn-36Pb-2Ni and 62Sn-36Pb-2Cu flip-chip solder joints subjected to two test conditions that combine different average current densities and ambient temperatures: 5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 150 degC and 20 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 3 degC. Under the test condition of 5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 150 degC, 62Sn-36Pb-2Cu is overwhelmingly better than 62Sn-36Pb-2Ni in terms of electromigration reliability. However, under the test condition of 20 kA/cm2 at 30 degC, the electromigration fatigue life of 62Sn-36Pb-2Ni shows a profuse enhancement and exceeds that of 62Sn-36Pb-2Cu. Electromigration-induced morphologies are also examined on the cross sections of solder joints using scanning electron microscopy.

Effects of multiple reflows on intermetallic morphology and shear strength of SnAgCu–xNi composite solder joints on electrolytic Ni/Au metallized substrate

Abstract The present work prepared composite lead free solders by adding 0.5, 1 and 2 wt.% of dendrite Ni micro-particles to Sn3.8Ag0.7Cu solder paste. Melting behaviors of composite solders were determined by differential scanning calorimeter (DSC). The wetting ability was evaluated with the spread area on Ni/Au finished Cu pad. The interface microstructure, morphology and shear strength were examined for composite solder joints on the electrolytic Ni/Au metallized Cu substrate with one, two, four, and six reflows, respectively. It was found that the intermetallic compound (IMC) shifted from the needle-like (CuNi) 6 Sn 5 on the non-composite joint to dual layers of facet-like (CuNi) 6 Sn 5 and boomerang shape (NiCu) 3 Sn 4 with 0.5 wt.% Ni addition, and only boomerang shape (NiCu) 3 Sn 4 was formed at the interface between the composite solder and Ni layer when Ni addition exceeded 1 wt.%. The thickness of IMC increased with the increasing number of reflows. Regardless of the number of reflows, the shear strength of composite solder joints showed increased trend as Ni content increased. The fracture of all joints happened in the solder bulk, which revealed that the failure was ductile.

Rate dependent strengths of some solder joints

The shear strengths of three lead-free solder joints have been measured over the range of loading rates 10−3 to ∼105 mm min−1. Binary (SnAg), ternary (SnAgCu) and quaternary (Castin: SnAgCuSb) alloys have been compared to a conventional binary SnPb solder alloy. Results show that at loading rates from 10−3 to 102 mm min−1, all four materials exhibit a linear relationship between the shear strength and the loading rate when the data are plotted on a log–log plot. At the highest loading rate of 105 mm min−1, the strengths of the binary alloys were in agreement with extrapolations made from the lower loading rate data. In contrast, the strengths of the higher order alloys were found to be significantly lower than those predicted by extrapolation. This is explained by a change in failure mechanism on the part of the higher order alloys. Similar behaviour was found in measurements of the tensile strengths of solder joints using a novel high-rate loading tensile test. Optical and electron microscopy were used to examine the microstructures of interest in conjunction with energy dispersive x-ray analysis for elemental identification. The effect of artificial aging and reflow of the solder joints is also reported.

Observations of nucleation catalysis effects during solidification of SnAgCuX solder joints

While modification of a strong (high Cu) Sn-Ag-Cu (SAC) solder alloy with a substitutional alloy addition (X=Co, Fe, Zn, and Ni) for Cu has been demonstrated to enhance solder joint strength and ductility after aging at 150°C for 1,000 h, control of the as-solidified SAC+X solder joint microstructure is also needed to inhibit under cooling and nucleation of brittle pro-eutectic phases (e.g., Ag3Sn). Bulk undercooling measurements of SAC+X alloys and microstructural analysis of SAC+X solder joints were used to rank the effectiveness and consistency of low-level (X < 0.15 wt.%) substitutional additions to a base SAC composition, Sn-3.5Ag-0.95Cu (wt.%). This SAC composition was selected to favor thermodynamically the nucleation of pro-eutectic Cu6Sn5 over that of Ag3Sn and the formation of an enhanced ternary eutectic fraction in the joint microstructure, while retaining a pasty range that is only 3°C. Using differential scanning calorimetry with sample pans that serve as either inert (aluminum) or actively wetting (copper) substrates, reflow cycles were studied that simulated surface mount (1.5°C/s) and ball-grid array (0.17°C/s) cooling rates. Of the SAC+X solders tested with copper pans, X = Zn appeared to be most effective and consistent, providing catalytic enhancement of the nucleation temperature for even the minimum concentration (0.05 wt.%) and lowest cooling rate.

Effect of reflow numbers on the interfacial reaction and shear strength of flip chip solder joints

The effects of multiple reflows on the microstructural variation and joint strength of the flip chip solder joints were investigated. Conventional Sn–37Pb and a representative Pb-free Sn–3.0Ag–0.5Cu were used, and a popular low cost under bump metallurgy (UBM) of immersion Au/electroless Ni–P plating was employed. In case of Sn–37Pb, only Ni 3Sn 4 intermetallic compound layer was formed during multiple reflows. In case of Sn–3.0Ag–0.5Cu, (Cu,Ni) 6Sn 5 intermetallic compound layer was observed after a single reflow, while (Ni,Cu) 3Sn 4 layer was additionally settled at the interface between the (Cu,Ni) 6Sn 5 layer and Ni–P UBM. The thicknesses of the intermetallic compound layers increased and coarsened. The shear force of the both joints slightly decreased during the multiple reflows. The decrease of the joint strength was caused by different softening phenomena between the two cases, and that is discussed in the main text.

Evaluation of solder joint strengths under ball impact test

The ball impact test (BIT) was developed based on the demand of a package-level measure of the board-level reliability of solder joints in the sense that it leads to brittle intermetallic fracturing, similar to that from a board-level drop test. The BIT itself stands alone as a unique and novel test methodology in characterizing strengths of solder joints under a high-speed shearing load. In this work, the BIT apparatus, characteristics of measured impact force profiles, and induced failure modes are introduced. We also present BIT results conducted on 63Sn–37Pb, 95.5Sn–4Ag–0.5Cu, and 98.5Sn–1Ag–0.5Cu package-level solder joints, bonded on substrate pads of different surface finishes, under an impact velocity of 1 m/s or 1.25 m/s.