Reliability Of Lead-free Solder Joints Research Articles

Effect of Matte-Sn Electroplating Parameters on the Thermo-mechanical Reliability of Lead-free Solder Joints

Most of the Cu/Cu alloy lead-frames of electronic components used for automotive applications contain electroplated matte-Sn terminal finish to improve the wettability of Sn-based Pb-free solders during reflow soldering process. When the solder joints are subjected to combined thermal and mechanical cyclic loading, the influence of matte-Sn electroplating parameters can lead to early and brittle failure of the solder joint. To test this hypothesis, a factorial design of experiments (DOE) has been conducted with LFPAK-MOSFET (hereafter referred to as LFPAK) components plated with different matte-Sn electroplating parameters and reflow soldered with two solder alloys (SAC 305 and Innolot). The LFPAK solder joints were then subjected to thermo-mechanical in-phase cyclic loading under different strain amplitudes. No electrical measurement is done to eradicate the effect of electrical current on the solder joint. The response to the DOE is the crack percentage obtained in the LFPAK solder joints after 1000 and 2000 cycles. The Innolot solder joints exhibited lower crack percentages than the SAC 305. The level of organic additives in the electroplating process of matte-Sn influences the failure mode of the solder joint. Microstructural investigation attributes the nature of failure to the morphology of the (Cu,Ni)6Sn5 IMC phase that forms on the component side of the solder joint.

Study of Lead-Free Solder Joint Reliability

Solders are essential for the construction of many engineering materials. The use of soldering in electronic packaging has become increasingly critical in today's world. In the electronic manufacturing industry, alternative soldering materials based on tin metal have developed gradually over the last two decades. Manufacturing companies are primarily concerned about removing lead from electronic manufacturing and waste recycling by switching to the lead-free solder. Environmental and human health are adversely affected by exposure to high lead levels in consumer products. The manufacturing industry has switched to lead-free soldering to support their social responsibility initiatives. The three categories of lead-free solder are classified according to temperature range: high-temperature solder, medium-temperature solder, and low-temperature solder. This research is conducted based on the approach of study literature, which is obtained from some papers that generally explain lead-free solder. To provide additional knowledge which is expected to add new insights about the importance of lead-free usage and its behavior.

Fracture Behavior and Reliability of Low-Silver Lead-Free Solder Joints

Abstract Low-silver solders are increasingly being used because silver improves the tensile strength. In this study, the variation in fracture behavior with silver content in lead-free solder joints was studied using double cantilever beam specimens. Fracture tests were done with solder joints made with Sn-0.7Cu, SACX0307, and SAC305 solder materials. The critical energy release rate for crack-initiation (Gci) of the joint was correlated with the plastic zone just ahead of the precrack tip, intermetallic compound layer thickness, energy dispersive spectroscopy analysis, and scanning electron microscopy based fractography study. The Gci for Sn-0.7Cu solder joint was observed to be significantly higher than the other two solder joints. The fractography study revealed that the failure was ductile for Sn-0.7Cu and a mix of ductile and brittle for the other two solder joints. The extent of the plastic zone ahead of the crack tip, obtained from finite element modeling, was found to be significantly larger and the intermetallic compound layer was relatively thinner for Sn-0.7Cu solder joint compared to the other two solder joints. The ductile failure, significantly larger plastic zone size and thinner intermetallic compound layer resulted in significantly higher Gci for Sn-0.7Cu solder joint.

Reliability Analysis of Solder Joints on Rigid-Flexible Printed Circuit Board for MEMS Pressure Sensors Under Combined Temperature Cycle and Vibration Loads With Continuously Monitored Electrical Signals

Abstract The reliability of lead-free solder joints on flexible printed circuit board (PCB) has created significant new challenges in the industry, especially in automotive electronics, and possibly for future wearable electronics. In the automotive industry, thermal cycling test and random vibration test need to be conducted to certify every electronic product to be used in harsh automotive environments. In order to accelerate the testing time, we may need to subject the electronic components, in particular, sensors to both loadings such as thermal cycling and vibration. During all the experiments, the electrical signals of each specimen were continuously monitored by using an event detector. One advantage of this method is that any individual soldering interconnect failure will result in the diagnostic signal of the circuit, which could be detected in real-time. A simulation was used to confirm the possibility of the stress concentration location caused by the vibration and thermal cycling loads. The influence of vibration frequency and acceleration on the vibration fatigue life of solid joints was investigated. In this paper, the submodeling technique was used to construct the finite element model of the rigid-flexible printed circuit board (rigid-flexible PCB) coupled with a MEMS pressure sensor subjected to temperature cycle and random vibration loadings. The research results are helpful to effectively characterize the performance of the MEMS sensors under both thermal cycling test and vibration test. Two kinds of land shapes and two kinds of PCB assemblies were selected. In order to investigate the crack growth in the solder joint, the solder joint is sliced and the crack on the cross section of the solder joint was observed. Results of finite element modeling analysis were consistent with the experimental results. Two design parameters have been identified in our research as being important to soldering usage in automotive environments: pad type (teardrop versus nonteardrop) and pad size (big versus small, matching size for Cu-wire and pad). Experimental results also showed that the solder joint with a big land shape presented a relatively good thermal fatigue resistance.

Impact of inter-metallic compound thickness on thermo-mechanical reliability of solder joints in solar cell assembly

This study evaluates the impact of intermetallic compound (IMC) thickness on thermo-mechanical reliability of lead-free SnAgCu solder joints in crystalline silicon solar cell assembly with regard to fatigue life. Finite element modelling is used to simulate the non-linear thermo-mechanical deformation of the joints. Five geometric models of solar cell assemblies with different IMC thickness layers in the range of 1 to 4 μm are utilized. The models were subjected to accelerated thermal cycling from 40 °C to 85 °C employing IEC 61215 standard for photovoltaic panels. Creep response of each of the assembly's solder joints to the induced thermal load were simulated using Garofalo-Arrhenius creep model. Simulation results indicate that when IMC thickness grows incrementally to 1, 2, 2.5, 3 and 4 μm, thermo-mechanical fatigue life of solder joints diminishes to 13,800, 11,800, 10,600, 9400 and 7800 cycles to failure respectively. Thus, solder joint fatigue life decreases as the IMC thickness increases during service lifetime. Therefore, proper design of solder joint in crystalline silicon solar cell assembly must include consideration of IMC layer thickness to prevent premature failure and to ensure fulfilment of desired functional lifetime of 13,688 cycles to failure (25 years).

State of the Art of Lead-Free Solder Joint Reliability

AbstractThe state of the art of lead-free solder joint reliability is investigated in this study. Emphasis is placed on the design for reliability (DFR) and reliability testing and data analysis. For DFR: (a) the Norton power creep constitutive equations and examples for Au20Sn, Sn58Bi, Sn3.8Ag0.7Cu, and Sn3.8Ag0.7Cu0.03Ce, (b) the Wises two power creep constitutive equations and examples for Sn3.5Ag and Sn4Ag0.5Cu, (c) the Garofalo hyperbolic sine creep constitutive equations and examples for Sn3.5Ag, Sn3Ag0.5Cu, Sn3.9Ag0.6Cu, Sn3.8Ag0.7Cu, Sn3.5Ag0.5Cu, and Sn3.5Ag0.75Cu, Sn4Ag0.5Cu, Sn(3.5-3.9)Ag(0.5-0.8)Cu, 100In, Sn52In, Sn3.8Ag0.7Cu0.03Ce, and Au20Sn, and (d) the Anand viscoplasticity constitutive equations and examples for Sn3.5Ag, Sn3Ag0.5Cu, Sn3.8Ag0.7Cu, Sn3.8Ag0.7CuCe, Sn3.8Ag0.7CuAl, Au20Sn, Sn3.5Ag with temperature and strain rate-dependent parameters, and Sn1Ag0.5Cu, Sn2Ag0.5Cu, Sn3Ag0.5Cu, and Sn4Ag0.5Cu after extreme aging will be discussed. For reliability testing and data analysis: (a) the Weibull and lognormal life distributions for lead-free solder joints under thermal-cycling and drop tests, (b) the true Weibull slope, true characteristic life, and true mean life, and (c) the linear acceleration factors for various lead-free solder alloys based on: (i) frequency and maximum temperature, (ii) dwell time and maximum temperature, and (iii) frequency and mean temperature will be presented. Some recommendations will also be provided.

Book Review: Assembly and reliability of lead-free solder joints. Springer. (2020)

Book Review: Assembly and reliability of lead-free solder joints. Springer. (2020)

Influence of Thermal Aging on Lead-Free Solder Joints Reliability: A Review

The handheld electronic products currently turning to high density, high performances, and multifunctionality, which sets higher demands on the solder joints reliability in electronic packaging. Because of environmental conscious towards Pb-containing solders, Pb-free solder get attracted wide attention in the electronic industry. Challenges of the Pb-free solders in the microelectronics device are the microstructural evolution influence the mechanical behavior of the solder reliability. This paper analyses a short overview on the progress of the study on the relationship between structure and property, and possible concerns regarding reliability of Pb-free solders joints. Furthermore, the measures to enhance the solder joint reliability are evaluated which contribute to a further theoretical foundation for the research on the solder joints reliability of electronic devices in service life.

The reliability of lead-free solder joint subjected to special environment: a review

With the rapid development of electronical products, many primary challenges arise in the field of design and manufacture, among which the property of electronical packaging materials is a crucial factor. Compared with lead-containing solder, the performance of lead-free solder alloy is hardly noticed before but is being concerned recently due to the restriction of lead application, which still could not meet the actual requirement. Moreover, the increasingly severe service conditions of electronical equipment such as specific temperature, high-density current and corrosion, which would result in the degradation of microstructure and property of lead-free solder alloy, have requested a great raise in the reliability of solder joint. Therefore, a great number of studies to enhance the reliability of lead-free solder joint subjected to special environments have been conducted in the last decade and it has been proved that the increasing reliability could be obtained by the addition of element and nanoparticle, as well as the enhanced substrate. In this article, a systematic review of the progress on the reliability investigation of lead-free solder joint is given to try to provide some theoretical support for the further investigation and application of lead-free solder alloy.

Void Formation and Their Effect on Reliability of Lead-Free Solder Joints on MID and PCB Substrates

Since the introduction of lead-free solder alloys, the impact of voids in solder joints has rapidly gained in importance. Particularly in power electronics, voids in solder joints can reduce their reliability due to less heat dissipation and a significant reduction of the cross-sectional area. While void formation in the printed circuit board (PCB) technology has been the focus of many research projects, the increasing application of molded interconnect devices (MIDs) demands a vivid understanding of void formation and its impact on reliability. This report will show that those processes specific to MID technology do not significantly influence the void formation in SAC305 solder deposits. The processed different roughness levels on Vectra, Vestamid, and FR4 substrate materials show no significant impact on void formation. The surface finish metallization was detected as the most important factor. Especially, the chemical-Sn (iSn) surface finish is inclined to having more voids compared to a nickel–phosphor–gold (NiP-Au) finish. Furthermore, three solder processes were investigated: convection, condensation, and vacuum-condensation soldering. The vacuum-condensation processes significantly reduced the voids in the Sn–3.0Ag–0.5Cu (simplified as SAC305) solder joints of CR0805, MLF20, and switches on all the investigated substrates. An accelerated thermal cycling test of these components according to JESD22-A104D demonstrates no significant effect of the void content of <19% on the solder joints’ reliability. Finally, the result of accelerated thermal cycling shows the possibility to achieve an equivalent lifetime of the solder joints on Vectra in comparison to the FR4 substrate.

Study on the Reliability of Carbon Nanotube-Reinforced Sn-58Bi Lead-Free Solder Joints

The wettability, microstructure and mechanical properties of multi-walled carbon nanotube (CNT)-reinforced Sn-58Bi composite solder joints were investigated. The results indicate that the wettability of the Sn-58Bi solder is improved and the growth of interfacial intermetallic (IMC) compounds for solder joints is restrained by CNTs. The thickness of the IMC layers is decreased with increasing CNTs concentration. The microstructure of the Sn-58Bi composite solders is refined, the maximum tensile strength and shear strength are obtained by adding the optimum CNTs content about 0.01 wt.%. However, excessive content of CNTs addition can deteriorate the properties. The creep rupture life of Sn-58Bi solder joint and Sn-58Bi-0.01CNTs solder joint is decreased with increasing load, temperature and current density. The average creep rupture life of Sn-58Bi-0.01CNTs composite solder joint is 60% higher than that of the plain solder joint.

Reliability study of package-on-package stacking assembly under vibration loading

The vibration reliability of lead-free solder joints of Package-on-Package (PoP) is investigated by experimental tests and finite element method (FEM) simulations in this paper. A 14×14mm two-tier PoP module was selected for this study. The natural frequencies and modes were determined by FEM and verified by experimental tests. The printed circuit board (PCB) assemblies are tested under harmonic vibration. Vibration test results show that the vibration reliability of top package is better than the bottom package, and the outermost corner solder joints of the bottom package are the critical solder joints for the PoP under vibration loading. The stress characteristics of solder joints obtained by FEM are well correlated with the experimental results. Failure mechanism analysis indicates that the bottom solder joints become the most vulnerable part of the PoP under vibration due to the bigger relative displacements between the PCB and the bottom package. The micro-structural analysis indicates that cracks usually originate in the bottleneck position of the solder balls, extend within bulk solder and then propagate along the interface between the IMC layer and the bulk solder. The influence of bottom solder joints standoff for vibration reliability was analyzed by FEM as well. Results show that the higher the bottom solder joints' standoff, the more difficult the failure for the PoP assembly.

Thermal cycling effect on the drop reliability of BGA lead-free solder joints

PurposeThe purpose of this paper is to study the drop reliability of ball-grid array (BGA) solder joints affected by thermal cycling.Design/methodology/approachThe drop test was made with the two kinds of chip samples with the thermal cycling or not. Then, the dyeing process was taken by these samples. Finally, through observing the metallographic analysis results, the conclusions could be found.FindingsIt is observed that the solder joint cracks which were only subjected to drop loads without thermal cycling appeared near the BGA package pads. The solder joint cracks which were subjected to drop loads with thermal cycling appear near the printed circuit board pads.Originality/valueThis paper obtains the solder joint cracks picture with drop test under the thermal cycling.

Cu/SnAgCu/Cu TLP with different thicknesses for 3D IC

PurposeThis paper aims to investigate Cu/SnAgCu/Cu transient liquid phase (TLP) bonding with different thicknesses for three-dimensional (3D) integrated circuit (IC).Design/methodology/approachThis paper includes experiments and finite element simulation.FindingsThe growth rate of the intermetallic compound layer during TLP soldering was calculated to be 0.6 μm/s, and the small scallop-type morphology Cu6Sn5 grains can be observed. With the decrease in thickness in solder joint, the thickness of intermetallic compounds represents the same size and morphology, but the size of eutectic particles (Ag3Sn, Cu6Sn5) in the matrix microstructure decrease obviously. It is found that with the increase in thickness, the tensile strength drops obviously. Based on finite element simulation, the smaller value of von Mises demonstrated that the more reliability of lead-free solder joints in 3D IC.Originality/valueThe Cu/SnAgCu/CuTLPbondingwithdifferentthicknessesfor3D IC was investigated.

Anand constitutive model of lead-free solder joints in 3D IC device

Anand constitutive relation of SnAgCu and SnAgCu-nano Al solders were studied under uniaxial tension, and the constitutive model was used in the finite element simulation to analyze the stress-strain response of lead-free solder joints in 3D IC devices. The results showed that the nine parameters of the Anand model can be determined from separated constitutive relations and experimental results. Based on Anand model, the finite element method was selected to calculate the stress-strain response of lead-free solder joints, it was found that in the 3D IC device the maximum stress-strain concentrated in the concern solder joints, the stress-strain of SnAgCu-nano Al solder joints was lower than that of SnAgCu solder joints, which represented that the addition of nano Al particles can enhance the reliability of lead-free solder joints in 3D IC devices.

Effect of Ni and Sb additions and testing conditions on the mechanical properties and microstructures of lead-free solder joints

Nowadays, one of the strategies to improve the reliability of lead-free solder joints is to add minor alloying elements to solders. Therefore, the aims of this study are to investigate the effect of Ni and Sb, as well as that of the testing conditions (temperature and strain rate), on the mechanical properties of two new lead-free solder joints, Sn-3.8Ag-0.7Cu-3Bi/Cu and Sn-3.8Ag-0.7Cu-3Bi0.2Ni1.54Sb/Cu. The changes, after testing, in their respective microstructure will also be investigated. The procedure to fabricate appropriate joint samples is described in this research. The shear tests were conducted by micro-tensile machine at temperatures between room temperature and 125°C and strain rates between 2.0×10−4s−1 and 2.0×10−2s−1. The experimental results indicate that, with additions of Ni and Sb in Sn-3.8Ag-0.7Cu-3Bi, the ultimate tensile strength (UTS) and the yield stress (σy) are improved. Moreover, both temperature and strain rate may have substantial effects on the mechanical behavior and the microstructural features of the solder alloys. During the shear tests, the strength decreases with the increase of the test temperature and/or the decrease of the strain rate. The enhanced strength is attributed to the solid solution hardening effects of Sb in the Sn matrix and the refinement of the microstructure with the addition of Ni. Ni and Sb additions lead to the formation of new (Cu, Ni)6Sn5 and Ag3(Sn, Sb) IMCs. Needle-like (Cu, Ni)6Sn5 appeared in the Sn-3.8Ag-0.7Cu-3Bi0.2Ni1.54Sb/Cu, instead of the globular-like Cu6Sn5 inSn-3.8Ag-0.7Cu-3Bi/Cu. In addition, the nine Anand material parameters are identified using the shear stress-strain data and a non-linear least square fitting and its validity is checked by means of the experimental data. The findings found that these Anand parameters are also in good agreement with data given in literature for other solder alloys. The obtained material parameters of the Anand constitutive model were utilized to analyze the stress-strain response of an Insulated Gate Bipolar Transistor (IGBT) under thermal cycling. Furthermore, the SEM analysis of as-fabricated joint specimens as well as fractured specimens at different testing conditions was done to observe the effects of these factors on the microstructure of the solder alloys.

Influence of assembly parameters on lead-free solder joints reliability in Package-on-Package (PoP) technology

Purpose – The purpose of this paper is to evaluate the influence of assembly parameters on lead-free solder joints reliability in Package-on-Package (PoP) Technology and demonstrate factors important for this issue. Design/methodology/approach – Two types of soldering materials and three different assembly procedures were used for assembly of PoP system. The reliability properties of assembled PoP systems were investigated using accelerated aging and periodic resistance measurements of daisy-chain solder joints systems. The purpose of such approach was to determine which soldering material (flux or solder paste) as well as which assembly process parameter (dipping depth of upper component in soldering material), would provide better reliability properties of the solder joints in the PoP system. Findings – It was stated that both selected flux and solder paste dedicated to assembly of PoP systems can be utilized in soldering of PoP applications. More reliable PoP systems applications require larger attention regarding materials selection and assembly parameters. It is recommended 50 per cent dipping depth of ball’s height into soldering material during upper PoP component assembly for more reliable applications. For less demanding PoP systems, the process window from 30 up to 70 per cent is acceptable. All observed failures after thermal shocks occurred in upper PoP components. Originality/value – This paper explains how materials and assembly parameters have influence on lead-free solder joints reliability in PoP systems. Especially, influence of process window for dipping procedure of upper components balls into soldering material was presented.

Effects on the Reliability of Lead-Free Solder Joints under Harsh Environment

Pb-free solder joints undergo microstructural and mechanical evolution due to alloy coarsening and growing intermetallic compounds which degrade the joint electrical performance. Electronics assemblies containing solder joints are frequently exposed to elevated temperatures for prolonged periods of time. The purpose of the study is to discover the effect of isothermal aging on the reliability of Sn-Ag-Cu (SAC) assemblies. After studied different surface finishes, we employed Immersion Ag (ImAg), Immersion Sn (ImSn), Electroless Ni/Immersion Au (ENIG) and Electroless Ni/Electroless Pd/Immersion Au (ENEPIG) which have potential for higher reliability and better performance and received increased attention for both packaging and subtracted applications. A full experiment matrix with varying aging temperatures and solder alloys was considered. Package sizes ranged from 19mm, 0.8mm pitch ball grid arrays (BGAs) to 5mm, 0.4mm pitch μBGAs and in additional, 0.65mm MLF and 2512 resistors be particularly tested. Storage condition are temperatures leveling up from 25°C, 55°C, 85°C, 100°C and 125 °C with aging over time periods of 0, 21 days, 6 months, 12 months and 24 months. Afterwards, the specimens all subjected to accelerated thermally cycled from −40°C to 125°C with 15 min dwell times at the high and low peak temperature. The paper presents the experimental data to justify the investigation of the degradation on the characteristic lifetime of SAC alloy on ImAg and ImSn surface finish in elevated temperature environments.

Reliability of Lead-free Solder Joints in WLCSP Device with Finite Element Simulation and Taguchi Method

Abstract In this paper, we research the thermo-mechanical reliability of lead-free solder joints in WLCSP assembly subjected to an accelerated thermal cyclic loading based on finite element simulation and Taguchi method. Effects of different control factors, including solder materials, height of solder ball, chip thickness and substrates thickness on the reliability of the lead-free solder joints were examined and calculated. The corner solder joint is the most critical solder joints in the assembly, the top surface of the solder joint is the crack propagated location. The optimal design in the WLCSP assembly has the combination of the SnAgCuAl, height of solder ball at 0.25 mm, chip thickness at 0.6 mm, substrate thickness at 1.0 mm. Moreover, the solder materials is the most important factor among the control factors in the WLCSP assembly.

Reliability of lead-free solder joints in CSP device under thermal cycling

Finite element method and Garofalo–Arrheninus creep model were combined and used to evaluate the reliability of different lead-free solder joints (SnAgCu, SnAg, SnSb and SnZn) and SnPb solder joints in chip scale package (CSP) 14 × 14 device under thermal cyclic loading. The results show that von Mises stress and equivalent creep strain in each of the four lead-free solder joints and SnPb solder joints were strongly different, increasing in the order SnPb < SnAg < SnSb < SnZn < SnAgCu. It is found that maximum stress–strain concentrates on the top-surface of corner solder joints in the CSP device for all solder joints, and SnAgCu solder joints shows the highest fatigue life among those five kinds of solder joints.