Interface analysis of embedded chip resistor device package and its effect on drop shock reliability

In this study, the drop reliability of an embedded passive package is investigated under JESD22-B111 condition. Chip resistors were buried in a PCB board, and it was electrically interconnected by electroless and electrolytic copper plating on a tin pad of a chip resistor without intermetallic phase. However tin, nickel, and copper formed a complex intermetallic phase, such as (Cu, Ni)6Sn5, (Cu, Ni)3Sn, and (Ni, Cu)3Sn2, at the via interface and via wall after reflow and aging. Since the amount of the tin layer was small compared with the solder joint, excessive intermetallic layer growth was not observed during thermal aging. Drop failures are always initiated at the IMC interface, and as aging time increases Cu-Sn-Ni IMC phases are transformed continuously due to Cu diffusion. We studied the intermetallic formation of the Cu via interface and simulated the stress distribution of drop shock by using material properties and board structure of embedded passive boards. The drop simulation was conducted according to the JEDEC standard. It was revealed that the crack starting point related to failure fracture changed due to intermetallic phase transformation along the via interface, and the position where failure occurs experimentally agrees well with our simulation results.     

Phase Analysis in the Solder Joint of Sn-Cu Solder/IMCs/Cu Substrate

A joint assembly of solder/IMCs/copper was prepared and experienced a thermal aging test for 50, 100, 400, and 600 hours at 150°C. The morphology at the interface of the assembly was investigated with an optical microscope (OM) to measure the thickness of the intermetallic layer, and with secondary electron images (SEI) to evaluate the interfacial microstructure. X-ray color mappings using an electron probe microanalyzer (EPMA) of copper and tin were also applied to study the concentration variations near the interfaces in the joint assembly. According to the intensities of Cu and Sn, collected by color mapping, software was employed to construct series of statistical graphs, and the detailed concentration profiles at the interfaces of the assembly were investigated from these graphs. Two important results were derived. The first, is that analyses of the interfacial profiles exhibit Cu₃Sn-rich, Cu₆Sn₅-rich, and tin-rich phases, which match with the boundaries of solder/Cu₆Sn₅, Cu₆Sn₅/Cu₃Sn, and Cu₃Sn/copper, respectively. The second, is that the semi-quantitative measurements with a peak-fitting model employed suffices to evaluate the interfacial concentration profiles with a statistical variation less than 5 mol %.     

Interfacial morphology and concentration profile in the unleaded solder/Cu joint assembly

A joint assembly of lead-free solder/intermetallic layers/copper was prepared by hot-dipped solder coated on a copper substrate and then by thermal ageing at 100, 125, 150, and 170°C for 50, 100, 200, and 600 h, respectively. Results of interfacial morphologies and concentration profiles on the solder/copper joint were presented. Optical and scanning electron microscope (OM and SEM) were used to measure the thickness of intermetallic layers and then to illucidate the development of microstructure at the joint assembly. The phases of intermetallic compound were identified to be Cu₃Sn and Cu₆Sn₅ by both X-ray mapping in electron probe micro-analysis (EPMA), and X-ray diffraction. The intermetallic layers, subtracted from the initial thickness formed by hot dipping, showed a linear dependence on the square root of ageing time at various ageing temperatures. The diffusion coefficients of intermetallic compounds are estimated by an Arrhenius equation, and the pre-exponential terms of Cu₃Sn layer and Cu₆Sn₅ layer are 7.10×10^-7cm²s^-1 and 6.1×10^-3cm²s^-1, respectively. The associated activation energies of Cu₃Sn layer and Cu₆Sn₅ layer are 57.03kJmol^-1 and 83.76kJmol^-1, respectively. A model of a diffusion-controlled mechanism is used to fit the concentration profiles of the joint assembly, and exhibits a fairly good quantitative agreement with the measured data. The initial thickness formed as soldering proceeds is also taken into account to evaluate the apparent thickness by introducing a term of corrected ageing time. ©1999 Kluwer Academic Publishers     

Evolution of Intermetallic Compounds between Sn-0.3Ag-0.7Cu Low-silver Lead-free Solder and Cu Substrate during Thermal Aging

The growth, transformation, and lattice structure of intermetallic compounds formed between Sn–0.3Ag–0.7Cu lead-free solder and copper substrate were investigated. Dip soldering was used to initiate the reaction between the solder and substrate. An η-Cu6Sn5 intermetallic phase possessing a hexagonal lattice structure was found at the as-soldered interface. Thermal aging at a number of conditions resulted in the formation of a Cu3 Sn intermetallic phase between the Cu6Sn5 layer and the copper substrate. ε-Cu3 Sn with an orthorhombic lattice structure was found together with hexagonal Cu3 Sn. Subsequently, the activation energies of the intermetallic phases were calculated and compared to results obtained from the literature. The comparison showed that good agreement existed between the findings from this study and literature data within a similar temperature range.     

Sn2.5Ag0.7CuxRE钎料时效焊点界面IMC研究

以Sn2.5Ag0.7CuxRE/Cu钎焊为研究对象,借助于扫描电镜和X衍射检测手段,研究了二硫化钼介质下时效焊点界面IMC组织结构特征及生长行为。实验结果表明:时效焊点界面Cu6Sn5IMC呈现由波浪状→扇贝状→层状的形态变化。焊点界面Cu6Sn5和Cu3Sn IMC的生长厚度与时效时间平方根呈线性关系,Cu6Sn5IMC具有较小的生长激活能、较大的生长系数。添加0.1%(质量分数)RE时,界面Cu6Sn5和Cu3Sn IMC的生长激活能最大,分别为81.74 kJ/mol和92.25 kJ/mol,对应焊点剪切强度最高。     

Effect of Bismuth on Intermetallic Compound Growth in Lead Free Solder/Cu Microelectronic Interconnect

The intermetallic compound (IMC) growth kinetics in pure Sn/Cu and Sn10 wt%Bi/Cu solder joints was studied, respectively, after they were aged at 160-210°C for different time. It was found that the total IMC in Sn10 wt%Bi/Cu joint developed faster than it did in pure Sn/Cu solder joint, when they were aged at the same temperature. And the activation energy Qa for total IMC in Sn10 wt%Bi/Cu joint was lower than that for pure Sn/Cu interconnect. The IMC growth process was discussed. The IMC Cu6Sn5 was enhanced in compensation of reduced IMC Cu3Sn growth. The work reveals that Bi element containing in lead free solder alloys with 10 wt% can enhance IMC growth in lead free solder/Cu joint during service.     

Effects of trace amount addition of rare earth on properties and microstructure of Sn–Ag–Cu alloys

Ternary lead free solder alloys Sn–Ag–Cu were considered as the promising alternatives to conventional SnPb alloys comparing with other solders. In the present work, effects of trace amounts of rare earth Ce on the wettability, mechanical properties and microstructure of Sn–Ag–Cu solder have been investigated by means of scanning electron microscopy and energy dispersive X-ray analysis systematically. The results indicate that adding trace amount of rare earth Ce can remarkably improve the wettability, mechanical strength of Sn–Ag–Cu solder joint at different temperature, especially when the content of rare earth Ce is at about 0.03%, the tensile strength will be 110% times or more than that of the lead free solder joint without rare earth Ce addition. Moreover, it was observed that the trace amount of rare earth Ce in Sn–Ag–Cu solder may refine the joint matrix microstructure, modify the Cu₆Sn₅ intermetallic phase at the copper substrate/solder interface, and the intermetallic compound layer thickness was reduced significantly. In addition, since rare earth Ce possesses a higher affinity to Sn in the alloy, adding of rare earth Ce can also lead to the delayed formation and growth of the intermetallic compounds of Ag₃Sn and Cu₆Sn₅ in the alloy.     

Investigation on the intermetallic compound layer growth of SnZnGa/SnZnGaNd solder joints

Growth kinetics of intermetallic compound layers (IMCs) formed between SnZnGa/SnZnGaNd solders for re-flow soldering and Cu substrate during aging was investigated at temperatures between 100 and 150 °C. The Cu₅Zn₈ IMCs could be found by reacting SnZnGa/SnZnGaNd solders on Cu substrate, and it was found that the addition of rare earth Nd can decrease the thickness of the IMCs of SnZn/Cu solder joints. The apparent activation energies of Cu₅Zn₈ which were calculated as 48.76 kJ/mol (SnZnGa) and 56.99 kJ/mol (SnZnGaNd). The shear force of Sn9Zn0.5Ga0.08Nd solder joint after aging treatment was remarkably higher than those of Sn–9Zn and Sn9Zn0.5Ga solder joints. The results would provide support to the superiority of Sn9ZnGaNd solder which can be used in the electronic packaging instead of traditional SnPb solder.     

Effect of thermal ageing on (Sn-Ag, Sn-Ag- Zn)/PtAg, Cu/Al2O3 solder joints

As-fabricated solders of eutectic Sn-Ag and ternary Sn-3.5 wt% Ag-1 wt% Zn alloys are coupled with metallized substrates including PtAg/Al2O3 and Cu/Al2O3 to simulate the solder joint in microelectronics. The growth mechanism of intermetallics and the mechanical properties of solder joints after thermal ageing (150 °C and 200 °C) are evaluated. In this study, a 1206 passive device/solder/metallization/Al2O3 surface mount technology (SMT) assembly is employed, and a Cu stud is attached on the ceramic substrate assembly to evaluate mechanical properties and the fracture morphology by the pull-off test. In addition, microstructure evolution of the interfacial morphology, elemental and phase distribution are probed with the aid of scanning electron microscopy (SEM), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) techniques. There are two intermetallics (Cu3Sn and Cu6Sn5) formed at the eutectic Sn-Ag solder/Cu metallized layer interface, while only Cu6Sn5 is observed in the Sn-3.5 Ag-1Zn/Cu system. However, in the PtAg metallized substrate, only Ag3Sn is present, regardless of which solders are employed. Cu6Sn5 and Ag3Sn in the Sn-3.5 Ag-1Zn system contain 2–5 at% Zn due to the higher solubility of Zn in both Cu and Ag. The adhesion strength decreases as the time increases for all solder joint systems in the thermal ageing test. The solder joint with eutectic Sn-Ag alloy exhibits higher fracture load than that with Sn-3.5 Ag-1Zn alloy. From the fracture surface analysis, as the ageing time increases, the fracture takes place from the solderconductor interface toward the inside of the IMC (intermetallic compound). © 1998 Kluwer Academic Publishers     

Interfacial reaction and mechanical reliability of eutectic Sn–0·7Cu/immersion Ag-plated Cu solder joint

Abstract

In this study, the interfacial reaction and joint reliability of immersion Ag-plated Cu substrate with the Sn–0·7Cu (wt-%) ball–grid array (BGA) solder was investigated. During reflow, the Ag plating layer was dissolved completely into the molten Sn–Cu solder and some of the Cu layer was also dissolved into the molten solder. The dissolved Ag and Cu were precipitated as Ag₃Sn and Cu₆Sn₅ intermetallic compounds (IMCs) in the solder matrix. Upon reflow, the Sn–Cu solder exhibits an off-eutectic reaction to produce the eutectic phase and precipitate (Cu₆Sn₅ and Ag₃Sn). The Cu–Sn IMC layer was formed at the solder/Cu interface after reflow, and the IMC layer grew during aging treatment. During the shear tests, the failure mode switched from a bulk-related failure to an interface-related failure. After aging for 250 h, the joint failed partially at the solder/Cu₆Sn₅ interface. The brittle fracture was linked to the formation of thick Cu–Sn IMC layer.     

Influence of TiO2 nanoparticles on IMC growth in Sn–3.0Ag–0.5Cu–xTiO2 solder joints during isothermal aging process

The influence of TiO₂ nanoparticles on the growth of intermetallic compound (IMC) between Sn–3.0 wt% Ag–0.5 wt% Cu–x wt% TiO₂ (x = 0, 0.02, 0.05, 0.1, 0.3, and 0.6) composite solder and the Cu substrate during isothermal aging process at temperatures of 120, 150, and 190 °C has been investigated in this study. Scanning electron microscopy was used to observe the microstructural evolution of the solder joints and measure the thickness of IMC layer. The IMC phases were identified by energy-dispersive X-ray spectroscopy and X-ray diffractometry. Results show that two intermetallic layers, Cu₆Sn₅ and Cu₃Sn phase are formed at the interface and the morphology of the Cu₆Sn₅ phase transforms from scallop-type to layer-type in Sn–3.0Ag–0.5Cu–xTiO₂ solder joints. The addition of nano-TiO₂ has a strong influence on the growth of overall IMC layers, and the thickness of overall IMC layers rapidly increase with aging temperature and time. The growth rates and activation energies of the IMC growth of six solder alloys were determined. Results reveal that, for three different ageing temperatures, the growth rates of overall IMC layers decrease with an increase in nano-TiO₂ proportion. The activation energies for the growth of overall IMC layers range from 48.34 to 63.61 kJ/mol. Adding nano-TiO₂ to Sn–3.0Ag–0.5Cu solder could evidently increase the activation energy of overall IMC layers, reduce the atomic interdiffusion rate, and thus inhibit excessive growth of overall IMC layers.     

Microstructure and kinetic analysis of the properties and behavior of nickel (Ni) nano-particle doped tin–zinc–bismuth (Sn–8Zn–3Bi) solders on immersion silver (Ag)-plated copper (Cu) substrates

In order to identify the effect on the properties and behavior of tin–zinc–bismuth (Sn-8 wt% Zn-3 wt% Bi or Sn-13.6 at.% Zn-1.6 at.% Bi) based solders produced by adding nickel (Ni) nano-particles, the interfacial microstructure between plain and composite solders with newly developed immersion silver (Ag) plated copper (Cu) substrates has been investigated as a function of reaction time, at various temperatures. For plain Sn–8Zn–3Bi solder joints, a scallop-shaped Cu–Zn–Ag intermetallic compound layer was found to adhere to the surface of the immersion Ag-plated Cu substrate. However, after addition of Ni nano-particles into the Sn–8Zn–3Bi solder, Cu–Zn–Ag (at the bottom) and (Cu, Ni)–Zn (at the top) intermetallic compound layers were observed at the interfaces. In addition, these intermetallic compound layer thicknesses increased substantially with increases in the temperature and reaction time. In the solder ball region, needle-shaped α-Zn rich phase and spherically-shaped Bi-particles appeared to be homogeneously distributed throughout a beta-tin (β-Sn) matrix. However, after the addition of Ni nano-particles, needle-shaped α-Zn rich phase appeared that exhibited a fine microstructure, due to the heterogeneous nucleation of the Ni nano-particles. The calculated activation energy for the Cu–Zn–Ag intermetallic compound layer for the plain Sn–8Zn–3Bi solder/immersion Ag-plated Cu system was 29.95 kJ/mol—while the activation energy for the total [Cu–Zn–Ag + (Cu, Ni)–Zn] intermetallic compound layers formed in the Sn–8Zn–3Bi–0.5Ni (Sn-13.6 at.% Zn-1.6 at.% Bi ~1 at.% Ni) composite solder/immersion Ag-plated Cu system was 27.95 kJ/mol. Addition of Ni nano-particles reduces the activation energy which enhanced the reaction rate as we know that lower the activation energy indicates faster the reaction rate.     

Relation between Kirkendall voids and intermetallic compound layers in the SnAg/Cu solder joints

Several different kinds of intermetallic compound (IMC) layers were fabricated through adding trace elements into the Sn-3.5Ag solder, to investigate the relationship between the Kirkendall void (KV) and the IMC layers. The results show that a considerable amount of KVs were observed at the Cu₃Sn/Cu interface in the Sn-3.5Ag/Cu joint after isothermal aging. A proper amount of Zn (0.5 wt%) and Ge (0.1 and 0.3 wt%) were found to effectively suppress the formation of the Cu₃Sn layer, and no obvious KVs were observed at the Cu₆Sn₅/Cu interface, while more Zn induced the formation of the Cu₆Sn₅ plus Cu–Zn mixed IMC layer, and voids (not KVs) were observed at the Cu₆Sn₅/Cu–Zn interface. (Cu,Ni)₆Sn₅ IMC layer replaced the initial Cu₆Sn₅ at the SnAg-Ni/Cu joints, likewise, the Cu₃Sn was suppressed at the thermal aging stage. Moreover, voids were found at the IMC/solder interface, while not at the IMC/Cu. Therefore, the formation of KVs is greatly determined by the characteristic of the IMC layer, this is consistent with the previous reports. On other hand, the KV can be suppressed by controlling the interfacial phase through adding trace elements into the solder.     

Transient liquid phase bonding of Sn–Bi solder with added Cu particles

The aim of this study was to apply the transient liquid phase (TLP) bonding technique to low-temperature Sn–Bi-based solders to enable their use in high-temperature applications. The microstructure of the eutectic Sn–Bi solders with and without added Cu particles was investigated with the solders sandwiched between two Cu substrates. The flux of the Cu atoms successfully consumed the Sn phase and resulted in the formation of Sn–Cu intermetallic compounds and a Bi-rich phase in the solder joint. This caused the melting point of the solder joint to increase from 139 to 201 °C. The results of this study show the potential of using low-temperature solders in high-temperature applications. This study also provides new insight into the advantages of using particles in the TLP bonding process.     

The effects of Mn powder additions on the microstructures and tensile property of SnAgCu/Cu solder joints

In this paper, the effects of Mn powder on fusion property of Sn3.0Ag0.5Cu solder alloy and microstructures as well as tensile property of the solder joints of Sn3.0Ag0.5Cu/Cu were investigated by differential scanning calorimetry analysis, scanning electron microscopy and tensile tests. The results showed that the addition of Mn dramatically suppressed under cooling of SnAgCu solder alloy. Mn addition contributed to the growth of Cu₆Sn₅ intermetallic compound layers since it provided nucleation sites for Cu₆Sn₅ at the solder joints. Moreover, Mn addition increased the hardness of the solder alloys and reduced the tensile strength of SnAgCu/Cu solder joints. During aging, the growth of IMC layers of SnAgCuMn/Cu solder joints was slower than that of SnAgCu/Cu solder joints, and the tensile strength of all the solder joints increased after aging.     

Premelting behavior and interfacial reaction of the Sn/Cu and Sn/Ag soldering systems during the reflow process

The early interfacial reaction and premelting characteristics of the Sn/Cu and Sn/Ag soldering systems, and the formation and morphology transition of interfacial intermetallic compounds in the two systems during the reflow soldering process were investigated by using a differential scanning calorimeter. Results show that the initial interfacial eutectic reaction arising from atomic interdiffusion in solid-state Sn/Cu and Sn/Ag systems results in the premelting at each interface of the two systems at a temperature 4.9 and 10.6?°C respectively lower than the actual melting point of pure tin, and consequently both of the Sn/Cu and Sn/Ag soldering systems exhibit morphology change of the intermetallic compound (IMC) as the solder experiences a transition from solid-state to liquid-state in a very small temperature range. The change in the interfacial energy between the solid (or liquid) Sn-rich phase and IMC phase is the essential factor leading to the morphology transition of the interfacial IMC in the Sn/Cu and Sn/Ag soldering systems.     

Interfacial reactions and intermetallic compound growth between indium and copper

The growth kinetics of intermetallic compound layers formed between pure indium solder and bare Cu substrate by solid-state isothermal aging were examined at temperatures between 343 and 393 K for 0–4×10⁶ s. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. Experimental results showed that the Cu₁₁In₉ intermetallic compound was observed for bare copper substrate. Additionally, the thickness of the Cu₁₁In₉ intermetallic compound was increased with the aging temperature and time. The layer growth of the intermetallic compound in the couple of the In/Cu system followed a parabolic law over the given temperature range. As a whole, because the values of time exponent (n) were approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion mechanism over the temperature range studied. The apparent activation energy of Cu₁₁In₉ intermetallic compound in the couple of the In/Cu was 34.16 kJ mol^–1.     

Brazing copper and alumina metallized with Ti-containing Sn0.3Ag0.7Cu metal powder

A Sn-based metallization layer was successfully prepared on the surface of alumina at 900 °C by using Ti-containing Sn0.3Ag0.7Cu (SAC, wt.%) metal powder. Reliable alumina/copper joints were obtained by brazing pre-metallized alumina and copper using SAC filler at 580–660 °C for 5 min. The typical interfacial microstructure of brazed joint was copper/Cu₃Sn layer/Cu₆Sn₅ layer/β-Sn layer containing Ti₆Sn₅ phase and Al₂O₃ particles/alumina. As brazing temperature increased, the Cu–Sn intermetallic layers thickened rapidly and the amount of β-Sn phase reduced. When brazing temperature exceeded 640 °C, Kirkendall voids and microcracks formed at copper/Cu₃Sn interface. The joints brazed at 580–620 °C possessed high shear strength and the highest average shear strength of 32 MPa was achieved when brazed at 620 °C. Fracture analyses indicated that the joints mainly fractured inside of the Cu₆Sn₅ layer and β-Sn layer. The joints brazed above 620 °C demonstrated low shear strength due to the formation of Kirkendall voids which caused the joints fractured along the Cu/Cu₃Sn interface.     

水下搅拌摩擦焊对铝/铜接头组织与性能的影响

目的 采用搅拌摩擦焊,对比分析大气环境和水下环境下铝/铜接头的组织与性能,以期获得力学性能更优异的铝/铜焊接接头。方法 利用搅拌摩擦焊,在焊接速度为40 mm/min、旋转速度为1 000 r/min的条件下,分别在大气环境和水下环境下对厚度为9 mm的6061铝合金板和T2纯铜板进行焊接。然后,对铝/铜界面、焊核区进行扫描电镜及能谱分析,并对铝/铜界面及焊核区进行物相分析,确定产物相组成。最后,对铝/铜试样进行拉伸及硬度检测。结果 铝/铜接头均无裂纹、气孔等缺陷。铜颗粒弥散分布在焊核区,铝/铜界面形成金属间化合物层。水下搅拌摩擦焊下界面元素扩散距离明显变短,且金属间化合物厚度更薄。铝/铜接头的金属间化合物为AlCu和Al4Cu9。大气环境焊接下接头的抗拉强度为130.6 MPa,断裂方式为脆性断裂;水下焊接下接头的抗拉强度为199.5 MPa,断裂方式为韧性断裂。水下环境下的接头硬度值更高,其中热影响区的硬度最低值约为65HV。结论 水下搅拌摩擦焊铝/铜接头无裂纹、气孔等缺陷。组织上,水下搅拌摩擦焊的铝/铜接头界面元素扩散距离更短,硬脆的金属间化合物更少;性能上,水下搅拌摩擦焊的铝/铜接头强度更高,抗拉强度达到199.5 MPa,达到母材的74.4%。     

Liquid-state and solid-state interfacial reactions between Sn–Ag–Cu–Fe composite solders and Cu substrate

The growth kinetics and morphology of the interfacial intermetallic compound (IMC) between Sn–3Ag–0.5Cu–xFe (x = 0, 0.5 wt%, 1 wt%) composite solders and Cu substrate were investigated in the present work. The Sn–Ag–Cu–Fe/Cu solder joint were prepared by reflowing for various durations at 250 °C and then aged at 150 °C. During soldering process, Fe particles quickly deposited in the vicinity of IMC, resulting in the formation of Fe-rich area. Isothermal equation of chemical reaction and phase diagrams were used to explain the effect of Fe on the growth kinetics of IMC during liquid-state interfacial reaction. It was shown that Fe could effectively retard the growth of interfacial Cu₆Sn₅ and Cu₃Sn layers during liquid-state reaction and reduce the size of Cu₆Sn₅ grains. Small cracks were observed in the Cu₆Sn₅ grains after reflowing for 2 min while they were found in the other composite solders reflowing for about 30 min. The Fe tended to suppress the growth of the Cu₃Sn layer during solid-state aging. However, the total thickness of IMCs (Cu₆Sn₅ + Cu₃Sn) for the composite solders with Fe particles was similar to that for SnAgCu without Fe particles.