Cu6Sn5 Intermetallic Compound Layer Research Articles

Effects of trace amounts of rare earth additions on the microstructures and interfacial reactions of Sn57Bi1Ag/Cu solder joints

The effects of trace amounts of rare earth (RE) additions on the melting property and microstructural evolution of SnBiAg/Cu solder joints were studied by differential scanning calorimetric test and microstructural observation. The results indicated that with the increase of RE additions, the solidus temperature decreased and the mushy temperature zone increased slightly in SnBiAg–xRE (x = 0.25, 0.5, 0.75 and 1.0) solder alloys. The microstructures of the Bi–rich dendrites in SnBiAg–xRE solder alloys were refined by the additions of minor RE elements. However, too many RE elements added into solder matrices led to the formation of large RE(Bi,Sn)3 intermetallic compound (IMC) which weakened the adsorption effect of RE elements on the Bi–rich dendrites. In addition, the thickness of the Cu6Sn5 IMC layers of SnBiAg–xRE/Cu solder joints were reduced remarkably due to the adsorption effect of RE elements at the interfaces of the Sn element and the Cu6Sn5 IMC layer.

Influence of minor Ag nano-particles additions on the microstructure of Sn30Bi0.5Cu solder reacted with a Cu substrate

The objective of this paper is to study the influence of minor Ag nano-particles additions on the microstructural evolution of Sn30Bi0.5Cu lead-free solder matrices and the interfacial reactions. Ag nano-particle reinforced SnBiCu–xAg (x = 1, 2, 5) composite solder pastes were prepared by a mechanical mixing method and then were reflowed on Cu substrates. Three cooling methods (furnace cooling, air cooling and water cooling) were adopted in this study. Microstructural evolution of composite solder matrices and the intermetallic compound (IMC) layers formed in solder joints were investigated by microstructural observation and phase analysis. The addition of Ag nano-particles did not change the microstructure of solder matrices apparently both in the furnace cooled and water cooled samples. In the air cooled samples, Bi-rich grains were refined in the composite solder matrices due to the adsorption of Ag3Sn micro-particles on them. The growth of Cu6Sn5 IMC layers in air cooled SnBiCu–xAg/Cu solder joints was influenced by the adsorption of Ag3Sn micro-particles both on the surface of Cu6Sn5 layers and on the surface of the Bi-rich grains.

Abnormal Failure Behavior of Sn-3.5Ag Solder Bumps Under Excessive Electric Current Stressing Conditions

Abnormal failure behavior of flip chip Sn-3.5Ag solder bumps with a Cu underbump metallurgy under excessive electric current stressing conditions is investigated with regard to electromigration lifetime characteristics and damage evolution morphologies. Abnormal behavior such as abrupt changes in the slope of the resistance versus stressing time curve correlate well with the changes in mean time to failure and the standard deviation with respect to␣the resistance increase ratio, which seems to be strongly related to highly␣accelerated electromigration test conditions of 120°C to 160°C and 3 × 104 A/cm2 to 4.6 × 104 A/cm2. This is closely related to changes in the damage evolution mechanism with time, even though the activation energy for electrical failure is primarily controlled by Cu diffusion through Cu-Sn intermetallic compound layers.

Electromigration Characteristics of Flip Chip Sn-3.5Ag Solder Bumpsunder Highly Accelerated Conditions

The e ects of severe current crowding and Joule heating on the damage morphology and the electromigration parameters were evaluated for ip chip Sn-3.5Ag solder bumps with Cu underbump metallurgy. in-situ electromigration testing in a scanning electron microscope was performed to correlate the statistical lifetimes with the detailed microstructural characteristics. The highly accelerated test conditions used led to an activation energy of 1.63 eV and a current density exponent of 4.6, which can be attributed to severe current crowding and Joule heating e ects. Real-time microstructural analysis revealed that interfacial voids nucleated around corners of the under-bump metallurgy layer, where electrons entered from the chip or the substrate interconnect line to the solder bump and then grew along the Cu6Sn5/solder interface, irrespective of the current ow's direction. Accelerated growth of Kirkendall voids was also observed at the Cu3Sn/Cu interface and within Cu3Sn. However, electrical failure of the bump resulted from electromigration-induced interfacial void propagation along the Cu6Sn5/solder interface, which can be explained in terms of the large di erence in Cu di usion ux between the Cu-Sn intermetallic compound layer and the solder itself.

Microstructure transformation of Sn base solders under isothermal aging and thermal shearing cycling conditions

The diffusion of atoms and the growth behaviour of intermetallic compounds (IMCs) at both Sn–3·5Ag–0·5Cu/Cu and 63Sn–37Pb/Cu interfaces under isothermal aging and thermal shearing cycling conditions have been investigated. The results show that a Cu6Sn5 IMC layer is formed at both the Sn–Ag–Cu/Cu and Sn–Pb/Cu interfaces, and the morphology of Cu6Sn5 changes gradually from scallop structure to plate-like structure with increasing number of thermal shearing cycling, while two IMCs, Cu6Sn5 and Cu3Sn, are formed at the Sn–Ag–Cu/Cu and Sn–Pb/Cu interfaces after isothermal aging for 100 h. The IMC growth follows parabola growth kinetics, implying that the IMC growth is controlled by the diffusion of Cu atoms. In Sn–Ag–Cu solder, Ag3Sn, forming uniform particles after reflowing, congregates gradually to be chunk-like.

The formation and evolution of intermetallic compounds formed between Sn–Ag–Zn–In lead-free solder and Ni/Cu substrate

The formation and evolution of intermetallic compounds (IMCs) layer between the Sn–3.7Ag–1.0–In–0.9Zn lead-free solder and Ni/Cu substrate were investigated for different reflow time. The morphology and thickness of the IMCs layer formed at the interface varies apparently with increasing the reflow time. At the early reflow stage, a thin continuous Ni3Sn4 dissolved with small amount of Cu is observed. As the reflow time going on, a thick Sn–Ni–Cu ternary intermediate compound layer is formed at the interface after the plated Ni layer is consumed totally. When the reflow time is long enough, a final Cu6Sn5 IMC layer dissolved with minor Ni will be formed. The IMCs layer grows very slowly until the plated Ni layer was completely consumed. Once the plated Ni layer disappears, the corresponding growth rate of the IMC layer increases apparently.

Evolution of intermetallic compounds layers in the soldered Sn–3.7Ag–1.0In–0.9Zn/Cu interface

The formation and evolution of intermetallic compounds (IMCs) layer between the Sn–3.7Ag–1.0In–0.9Zn lead-free solder and Cu substrate were investigated for different soldering periods. The structure of the IMCs layer in the soldered interface varies apparently with increasing the soldering time. The interface soldered for 1 min is composed of a thick Cu5Zn8 layer and a thin Cu6Sn5 IMCs layer, which are separated by an intermediate solder layer. When the soldering time reaches 3 min, both the Cu5Zn8 and Cu6Sn5 layers grow thicker towards the middle solder layer, with the Cu5Zn8 layer much thicker than the Cu6Sn5 one. Later the Cu5Zn8 layer will decomposed completely and the Cu6Sn5 layer will grow prominently when the soldering time reaches 4 min. The evolution of the soldered interfacial structure was discussed in view of the governing factor for the atomic diffusion through the intermediate solder layer.

Effect of Bi on the Interfacial Reaction between Sn-3.7Ag-xBi Solders and Cu

It was reported in previous studies that the addition of Bi could improve the wettability and reduce the melting temperature of Sn-Ag solders. This work investigates the effect of Bi on the interfacial reaction between Sn-Ag-xBi solders and the Cu substrate reflowed at 250°C for different times and thermally aged at 150°C for different durations. Five types of Sn-Ag-based solders, Sn-3.7Ag-xBi (x = 0 wt.% to 4 wt.%), were used in this study. The microstructure of the interfacial Cu-Sn intermetallic compound (IMC) layers between the solders and the Cu substrate was studied, and the thickness of the Cu-Sn IMCs in different solder/Cu systems has been measured. It was found that the thickness of the Cu-Sn IMC layer decreased with increasing amount of Bi in both the reflow and thermally aged condition. The effect of Bi addition on the interfacial reaction between the solder and the Cu substrate was discussed based on the experimental results.

Effect of the soldering time on the formation of interfacial structure between Sn–Ag–Zn lead-free solder and Cu substrate

The evolution of interfacial structure between the Sn–3.7%Ag–0.9%Zn lead-free solder and Cu substrate were systematically explored for different soldering times (1, 5, and 10 min). According to microstructural observations, it is found that the longer the soldering time is, the thicker the soldered interface becomes. The interface soldered for 1 min is composed of the Cu5Zn8 intermetallic compounds (IMCs) layer locating above the Cu6Sn5 IMCs layer. The interfaces soldered for 5 and 10 min are mainly made up of the Cu6Sn5 IMCs with some bulk Ag3Sn IMCs randomly distributing within it. The evolution of the IMCs layer in the soldered interface can be divided into three stages: the Cu5Zn8 IMCs firstly forms, then Cu6Sn5 IMCs separated out from the bottom (controlled by diffusion of Sn in the Cu5Zn8), finally, subsequent growth of the Cu6Sn5 IMCs layer is controlled by diffusion of Sn in Cu6Sn5 IMCs.

Intermediate decomposition of metastable Cu5Zn8 phase in the soldered Sn–Ag–Zn/Cu interface

Abstract The structural evolution process of the soldered interface between Sn–3.7%Ag–0.9%Zn lead-free solder and Cu substrate with different soldering time (less than 10 min) was explored by microstructural observations. It is found that a metastable Cu5Sn8 intermetallic compounds (IMCs) layer was firstly separated out close to the Cu substrate, then a stable Cu6Sn5 layer formed above it, as a result of the decomposition of the metastable Cu5Sn8 layer. It is proved that the existence of an intermediate decomposition of metastable Cu5Sn8 layer in the evolution of the soldered interface slightly accelerates the diffusion of Sn atoms in the formed Cu6Sn5 IMCs layer.

Effect of Isothermal Aging on the Growth and Morphology of the Intermetallic Compounds Formed at the Solder/Cu Interface of the Lead - Free Solder Joint

The growth and morphology of the intermetallic compounds (IMC) formed at the interface between the solder ( Sn–3.5Ag–0.5Cu ) and the Cu substrate of the lead - free solder joint have been investigated by means of isothermal aging at 125°C. The scalloped Cu6Sn5 intermetallic compound layer was formed at the interface between the solder and Cu substrate upon reflow. The thickness of Cu6Sn5 layer increased with aging time. Cu3Sn appeared between Cu6Sn5 layer and Cu substrate when isothermally aged for 100 hours. Compare to Cu6Sn5 , the thickness of Cu3Sn was rather low, and nearly did not increase with aging time. In this paper, the comparison was made among the Sn-Pb and the Sn-Ag-Cu(SAC) solders which were pre-treated differently before soldering.

Isothermal Aging Effects on the Microstructure, IMC and Strength of SnAgCu/Cu Solder Joint

The formation and evolution of the intermetallic compound (IMCs) between SnAgCu lead-free solder and Cu substrate, after isothermal aging at 150°C for 24, 48, 120, 240 and 480 hours, were studied. Scanning electron microscope (SEM) was used to observe the microstructure evolution of solder joint during aging. The IMC phases were identified by energy dispersive X-ray (EDX). The results showed that IMCs layer of Cu6Sn5 was formed at the interface of solder and Cu during reflowing. With the increase of aging time, the grain size of the interfacial Cu6Sn5 increased and the morphology of the interfacial Cu6Sn5 column was changed from scallop-like to needle-like and then to rod-like and finally to particles. At the same time, the rod-like Ag3Sn phase formed at the interface of solder and the IMCs layer of Cu6Sn5 with the aging time increased. In addition, large Cu6Sn5 formed in the solder with the aging time increased. The tensile strength was measured for the solder joints. The results showed that the tensile strength increases slightly at beginning and then decreases with the aging time. SEM was used to observe the fracture surface and it showed that the fracture position moved from solder matrix to the interfacial Cu6Sn5 IMCs layer with the aging time increased. The weakening of the solder matrix is caused by the coarsening of the eutectic solder structures. The weakening of the interfacial IMCs layer is caused by the evolution of morphology and size of the interface Cu6Sn5 layer.

Interfacial Reaction and Joint Strength on Cu UBM with Pb-Free Flip Chip Solder Bumps

The interfacial reaction and joint strength of the Pb-free flip chip solder joints were investigated. Microstructural investigations were conducted using scanning electron microscopy (SEM), and phase analysis of the intermetallic compound (IMC) was carried out using energy dispersive spectrometer (EDS). Cu6Sn5 IMC layer was formed at the as-reflowed state, and Cu3Sn was additionally settled at the interface between the Cu6Sn5 and Cu under bump metallurgy (UBM). Growth of the IMC layers followed the parabolic law, while the IMC layer growth was not highly affecting the mechanical properties of the solder joints. The shear force of the solder joints decreased because of the microstructural coarsening within the solder region.

Interfacial Reaction of Cu/Sn-Ag/ENIG Sandwich Solder Joint during Aging

The interaction between Cu/Sn-Ag and Sn-Ag/Ni interfacial reactions has been studied during isothermal aging at 150°C for up to 1000h using a Cu/Sn-3.5Ag/ENIG sandwich solder joint. A typical scallop-type Cu-Sn intermetallic compound (IMC) layer formed at the upper Sn-Ag/Cu interface after reflowing. On the other hand, a (Cu,Ni)6Sn5 IMC layer was observed at the Sn-Ag/ENIG interface. The Cu in the (Cu,Ni)6Sn5 IMC layer formed on the Ni side has to be contributed from the dissolution of the opposite Cu metal pad or Cu-Sn IMC layer. When the dissolved Cu arrived at the interface of the Ni pad, the (Cu,Ni)6Sn5 IMC layer formed on the Ni interface, preventing the Ni pad from reacting with the solder. Although a long isothermal aging treatment at 150°C was performed, any Ni was not detected in the Cu-Sn IMC layer formed on the Cu side. Compared to the single Sn-Ag/ENIG solder joint, the formation of the (Cu,Ni)6Sn5 IMC layer of the Cu/Sn-Ag/ENIG sandwich joint retarded effectively the consumption of the Ni from the electroless Ni-P layer.

SnZn系はんだ合金のアトマイズ効果

Sn-Zn based solder alloys are expected to be a potential candidate as a lead-free low temperature solder because of its melting point close to that of Sn-Pb. There are, however, several problems in practical application. Cu-Zn intermetallic compound (IMC) layer formed at the solder and Cu substrate interface leads to degradation of adhesion strength. In order to prevent the formation of Cu-Zn IMC, we have added some additives (Ni and Cu) to the Sn-Zn solders. We have also investigated the quenching effect by the atomization process in these Sn-Zn-(Ni and Cu) solders. For the pre-atomized solders, Cu-Zn IMC layer is formed at the interface. On the other hand, for the atomized solders, Cu-Sn IMC layer which is usually seen in Sn-Pb solder is observed instead.

The effect of CuSn intermetallics on the interstrand contact resistance in superconducting cables for the large hadron collider

The large hadron collider superconducting cables are submitted to a 200 °C heat treatment in air in order to increase the resistance between the crossing strands (RC) within the cable. During this treatment the as-applied Sn–Ag alloy strand coating is transformed into a CuSn intermetallic compound layer. The microstructure, the surface topography, and the surface chemistry of the nonreacted and reacted coatings have been characterized by different techniques, notably focused ion beam, transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. Based on the results obtained by these techniques the different influences that the intermetallics have on RC are discussed. The desired RC is obtained only when a continuous Cu3Sn layer is formed, i.e., a sufficient wetting of the Cu substrate by the tinning alloy is crucial. Among other effects the formation of the comparatively hard intermetallics roughens the surface and, thus, reduces the true contact area and it strongly affects the oxide growth on the strand surface. The oxide formed on the fully reacted coatings, which may essentially contain Cu oxides, appears to be more stable, both mechanically and thermally, as compared to the oxide formed on the tinning alloy.

Effect of reflow time on interfacial reaction and shear strength of Sn–0.7Cu solder/Cu and electroless Ni–P BGA joints

The interfacial reaction and shear strength between the eutectic Sn–0.7wt.% Cu solder and two different kinds of ball grid array (BGA) substrates (Cu and Au/Ni–P/Cu) during reflow at 255°C for up to 30min were studied. With the solder joints between the Sn–0.7Cu solder and Cu substrates, a Cu6Sn5 intermetallic compound (IMC) was formed at the interface. In the case of the electroless Ni–P substrate, the IMC formed at the interface was mainly (Cu, Ni)6Sn5. Also, a P-rich Ni (Ni3P) layer was observed as a by-product of the Cu–Ni–Sn reaction. The Ni3P layer was between the (Cu, Ni)6Sn5 IMC and the electroless Ni–P layer. The thickness of the Cu6Sn5, (Cu, Ni)6Sn5 and Ni3P layer was found to increase with the reaction time. The growth of the Cu6Sn5 IMC layer for Cu substrate was faster than that of the (Cu, Ni)6Sn5 IMC layer for electroless Ni–P substrate. The Ni content in the (Cu, Ni)6Sn5 IMC layer formed at the interface increased with increasing reaction time. In the ball shear tests, the shear strength value did not change much as a function of reflow time. In all samples, the fracture mainly occurred in the bulk solder. However, for the Sn–0.7Cu/electroless Ni–P joint reflowed for 10min, the fracture occurred in ductile and slightly brittle mode.

Effect of Cu stud microstructure and electroplating process on intermetallic compounds growth and reliability of flip-chip solder bump

In electroplating-based flip-chip technology, the Cu stud and solder deposition processes are two of the most important factors affecting the reliability of solder joints. The growth of Cu-Sn intermetallic compounds (IMC) also plays a critical role. In this paper, the effect of Cu stud surface roughness and microstructures on the reliability of solder joint was studied. The surface roughness of the Cu stud was increased as the Cu electroplating current density increased. The microstructural morphology of the Cu-Sn IMC layer was affected by Cu stud surface structure. We found the growth rate of IMC layer increased with the increasing of Cu stud grain size and surface roughness during aging test. The growth kinetics of Cu-Sn intermetallic compound formation for 63Sn/37Pb solder followed the Arrhenius equation with activation energy varied from 0.78 eV to 1.14 eV. The ratios of Cu/sub 3/Sn layer thickness to the total Cu-Sn IMC layer thickness was in the range of 0.5 to 0.15 for various Cu microstructures at 150/spl deg/C during thermal aging test. The shear strength of solder bump was measured after thermal aging and temperature/humidity tests. The relationship between electroplating process and reliability of solder joints was established. The failure mode of solder joints was also analyzed.

Effect of randomness of Cu-Sn intermetallic compound layer thickness on reliability of surface mount solder joints

A statistical reliability analysis on thermal fatigue lifetime of surface mount solder joints, considering randomness of Cu-Sn intermetallic compound (IMC) layer thickness, is presented. Based on published thermal fatigue life test data, the two-parameter Weibull distribution of the thermal fatigue lifetime for a fixed IMC layer thickness is found, and a K-S goodness-of-fit test is conducted to examine the goodness of fit of the assumed Weibull distribution. Then, the Weibull parameters as functions of IMC layer thickness are obtained. Considering the randomness of IMC layer thickness, the MTTF and reliability of surface mount solder joints on thermal cycles are analyzed. For surface mount solder joints formed under the same conditions and loaded during the same thermal cycling as stated in the publication, numerical results of the MTTF and reliability are presented. The results show that when the mean value of MC layer thickness is low (e.g., smaller than 1.5 /spl mu/m), the effect of randomness of IMC layer thickness is significant; i.e., the MTTF has strong dependence on IMC layer thickness distribution; and the reliability is significantly different at high thermal cycles. When the mean value of IMC layer thickness is high (e.g., greater than 2.0 /spl mu/m), the effect of randomness of IMC layer thickness is negligible. Therefore, the presented results are important to the reliability study of surface mount solder joints. Even though the validity of the presented results based on the test data remains to be verified from other sources of data, the proposed statistical method is generally applicable for thermal fatigue reliability analysis of surface mount solder joints. By combining the proposed method with the forming mechanism of IMC layer under varying manufacturing and loading conditions, a comprehensive reliability analysis on thermal fatigue lifetime of surface mount solder joints can be expected.