Strength Of Solder Joints Research Articles

はんだ継手のせん断応力下における疲労・クリープ強度特性とき裂進展挙動に関する研究

Troubles of electric components and electronic devices are mainly caused by failure of solder joining parts, which results from thermal cycle fatigue due to the mismatch of thermal expansion coefficients among constituents. Therefore, it is an urgent problem to clear the fatigue and creep properties of solder joint and solder itself. In order to clarify the strength and crack growth behaviors of solder joint in fatigue and creep, a series of fatigue and creep tests was carried out on Cu/60Sn40Pb/Cu joints under shear stress condition. Results of fatigue tests under different loading frequencies indicate that fatigue lives can be evaluated uniformly by taking cumulative loading time to failure as a key parameter. Observations of shear strain behavior during fatigue and creep process make it clear that fatigue lives and creep rapture lives are well predicted by the minimum shear strain rate. Furthermore, results of crack growth tests in fatigue and creep under Mode II shear stress condition reveal that the modified J integral well governs the crack growth rate.

Growth kinetic studies of Cu–Sn intermetallic compound and its effect on shear strength of LCCC SMT solder joints

Growth kinetics of interfacial Cu–Sn intermetallic (IMC) layer and its effect on the shear strength on practical LCCC surface mount solder joints were studied for isothermal aging at 70, 120, 155 and 170°C. Only normal Cu 6Sn 5 ( η-phase) intermetallic was found in the interfacial IMC layer of as-soldered solder joint, whereas the duplex structure of both η-phase and ε-phase Cu 3Sn existed in all annealed joints. The growth kinetics of the overall interfacial IMC layer can simply be described by classical kinetic theory for solid-state diffusional growth with an activation energy of 1.09 eV and interdiffusion coefficient of 1.61×10 −4 m 2 s −1. The relatively higher activation energy, as compared with that found for bi-metallic couple of eutectic Sn–Pb solder on copper, is attributed to the dissolution of Ni from the component metallization into the bulk Sn–Pb solder. In addition, the shear fractures in all the solder joints investigated are shown to be ductile in nature and confined in the bulk solder rather than through the interfacial IMC layer. A linear reduction in shear joint strength was observed with an increase in intermetallic layer thickness up to ∼5.6 μm. Such a reduction in joint strength is due to a continuous removal of Sn from the bulk solder for the growth of interfacial IMC layer and flattening of the solder/IMC layer during isothermal aging of the solder joint.

Effects of three soldering techniques on the strength of high-palladium alloy solder joints

Statement of problem. Little information is available on the optimum technique for soldering high-palladium alloys, which have gained considerable popularity for prosthodontic applications. Purpose. The objective of this study was to compare the flexural stress at the proportional limit of four noble dental alloy specimens soldered with torch, oven, and infrared techniques. Materials and methods. The high-palladium alloys studied were Legacy XT (Jelenko), Freedom Plus (Jelenko), and IS 85 (Williams/Ivoclar). A gold-palladium alloy, Olympia (Jelenko), served as the control. Thirty round bars, 18 × 3 mm, were cast from each alloy, cut in half, aligned, and joined using Olympia Pre solder (Jelenko) for the gas-oxygen torch and the infrared technique and Alboro LF solder (Jelenko) for the oven technique. Each soldered bar was subjected to three-point bending, and the maximum elastic stress or strength of the solder joint was calculated at the proportional limit. Data were analyzed by two-way ANOVA and the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test at the 0.05 level of significance. Results. There was no significant difference between torch and oven-soldering, but both were significantly different from the infrared technique. ANOVA showed a significant difference between alloys, but this difference could not be detected with the REGW test. SEM examination of the fracture surfaces revealed grooves associated with the path of crack propagation. X-ray energy-dispersive spectroscopic analysis failed to detect copper in the solders, and there were no significant changes in the solder compositions after the melting procedures. Conclusions. All three techniques can yield satisfactory solder joints in high-palladium alloys. These joints should be well-polished to achieve optimal strength. (J Prosthet Dent 1998;79:677-84.)

Real‐time control of advanced solderability preservatives

Organic and immersion metallic coatings are being used as a replacement for the hot air solder level (HASL) process. Use of these coatings provides advantages for both the fabricator and assembler. Advantages to assemblers include flatter pads (0.25‐0.5 micron thickness), no limitations on fine pitch or small hole cleaning, and greater solder joint strength. Advantages to the fabricator include lower operating costs, little or no rejects/rework, reduced safety hazard and a more environmentally friendly process. Current problems associated with the organic and immersion coatings include the inability to assess the solderability of the bare copper or the integrity of the coating (organic). These coatings also present a critical concern due to their reduced shelf life and potential inability to survive mishandling in manufacturing. Real time, non‐destructive methods of rapidly assessing the integrity these coatings are currently not available to the electronics industry. Surface Spectroscopy measurement techniques have the potential to measure the structure and characteristics of the organic and metallic coatings, and surface oxides that develop with time and temperature. The measurement techniques are rapid, non‐contact, and relatively inexpensive to make when compared to existing methods. Surface Spectroscopy can also provide critical surface information that is needed to troubleshoot solderability problems. The American Competitiveness Institute in association with the Navy EMPF program is working with several industry partners to develop a usable surface spectroscopy tool that will assess the quality and integrity of the coatings and correlate that reading with a solderability evaluation.

Analytical and Experimental Hybrid Study on Thermal Fatigue Strength of Electronic Solder Joints. 2nd Report. Evaluation by Isothermal Mechanical Fatigue Tests.

An isothermal mechanical fatigue test method and fatigue testing equipment were developed to investigate the low cycle fatigue strength of Sn-Pb eutectic solder joints. Based upon the results of finite element analysis, it is found that the rate of inelastic strain components (plastic strain and creep strain) in the solder joints can be accurately controlled by the displacement rate of the linearactuator of the test equipment. The isothermal mechanical fatigue tests were carried out by controlling the displacement at a very high displacement rate, and a very low displacement rate, respectively ; only plastic strain was generated in the solder joints at the high displacement rate, and only creep strain at the low rate. It is found that the low cycle fatigue life of Sn-Pb eutectic solder joints is not grealty affected by the ratio of inelastic components. Therefore, it can be said that the low cycle fatigue life can be estimated from the equivalent inelastic strain range, and the relationship of the cycles to failure and the strain range follows Coffin-Manson's law. In comparison of the mechanical fatigue strength results with the results of the cyclic thermal tests, it was found that the mechanical fatigue test method can be used as a good accelerated test method for the thermal fatigue strength of Sn-Pb eutectic solder joints.

Analytical and Experimental Hybrid Study on Thermal Fatigue Strength of Electronic Solder Joints. 1st Report. Rationalization of Accelerated Thermal Cyclic Test and Evaluation of Thermal Fatigue.

Stress-strain analyses for Sn-Pb cutectic solder joints in a thin single outline package (STOP), a ball grid array (BGA) assembly, and a leadless ceramic chip carrier (LCCC) were carried out for investigation of plastic-creep behavior, and of stress relaxation behavior due to accelerated thermal cycling tests or the operating conditions. the temperature dependence of plastic behavior (yield stress) and creep behavior (creep properties) were taken into account in all numerical analyses. The results of finite element analysis (FEA) show that in an accelerated terperature cycling test, long high-temperature and low-temperature dweel times do not contribute to an increase in the cyclic inelastic equivalent strain range in solder joints, although the creep behavior occurring during the dwell times under operating conditions is very important in estimation of the fatigue life of solder joints. Based upon the results of the strain analyses, an efficient temperature cycling test process for microelectronic solder joints was proposed, and cycling tests were carried out. The experimental results show that the thermal fatigue life of microelectronic Sn-Pb eutectic solder joints can be predicted by an associated fracture parameter of total equivalent inelastic strain range, and the fatigue life of solder joints follows Coffin-Manson's law.

A study of the strength and shape of surface mount technology leadless chip solder joints

A method that directly pulled the components off printed circuit boards was used as a means for testing the bond quality of surface mount technology leadless chip solder joints. Components D7243, CC1206, RC1206, RC1210 and CC1812 were selected for the study. It was found that the ultimate tensile force that breaks a component off the printed circuit board has the potential to be used as a parameter for measuring the quality of the solder joint. The failure modes of the joints were recorded and are discussed. The effect of solder thickness on the strength of a joint has also been investigated. The shape of joints soldered by two methods, wave soldering and infra-red reflow, were compared. Joints at the two ends of a component produced by infra-red reflow were found to be more uniform than the ones produced by wave soldering. A recommendation is made here for the wave soldering approach in achieving uniform solder joints. The effects of solder shape on the joint strength were further investigated by finite element analysis. A convex joint was found to be marginally more robust than a concave joint.

Fatigue Behavior of Solder Joint under Simple Shear Stress.

In order to clarify the simple shear strength of solder joint, we carried out static strength tests, fatigue tests, fatigue crack growth tests and creep crack growth tests on Cu/60Sn·40Pb/Cu joint under simple shear stress. Major conclusions obtained in this study are summarized as follows : 1) The maximum simple shear stress increased with the increase in the simple shear strain rate. 2) The effect of the width of the solder on the fatigue strength were not observed. 3) The fatigue cyclic crack growth rates were governed by neither the stress intensity factor range nor the maximum stress intensity factor. 4) The fatigue and creep loading time crack growth rates were governed by the modified J integral. 5) The fatigue and creep crack growth behaviors depended on the process zone (small scale creep zone) at the crack tip.

Electroless Bumped Bare Dice on Flexible Substrates

Modern semiconductor technologies have advanced to the level of sophistication where the benefits of the high functional and power density, high speed, low defect rate and low wafer processing cost can seldom be fully utilised at the final equipment or even at the single packaged semiconductor component level due to the limitations of wire bonds and lead frame fan‐outs. This paper suggests a new assembly method where low‐cost contact bumps are deposited on semiconductor wafers and then the dice are reflow soldered or gang bonded to the substrate. The bumps are electroless nickel deposited and coated with a protective layer of gold. As the nickel bumps are non‐collapsible, they are better suited to Extra High Density Interconnections (EHDI) than the more usual solder bumps. The amount of solder must be accurately dispensed either on the die bumps or on the substrate bonding pads using various methods. Essential to the high volume assembly is fast pick‐and‐place operation and simultaneous soldering of all components in a reflow furnace. In certain applications bonding of the bumped device (one die at a time) can be done using reflow or thermocompression gang bonding by applying a heated thermode to the backside of the die. In this case, the bonding energy will be transferred through the die to the bumps. Tentative solder joint strength and reliability aspects are discussed. Further process and design improvements are suggested.

A Method of Determining Reliability Testing Conditions for Solder Joints of Electronic Devices.

A method is proposed for determining the temperature cycling test conditions for solder joints of electronic devices. First, the purpose of the temperature cycling test is clearly expressed. Next, the concept of the fatigue damage rate based on Miner's law is introduced. The fatigue damage rate is obtained from the finite element analysis of the solder joint and the fatigue strength data of the solder. In this method, the testing conditions are determined so that the damage rate during the temperature cycling test equals that in the Hield after the reliability guaranteed period. The influence of temperature and cycling frequency on the fatigue strength of the solder and the dispersion of the strength of solder joints are considered in determining the testing conditions. Finally, an example of the proposed method is shown.

The effect of production variables on the strength of brass/Sn-Pb-Sb solder joints: A statistical analysis

Tomlinson and Cooper's data on solder joint strength have been used to illustrate the additional benefits, in terms of useful results, that can be obtained from the application of stepwise regression techniques to production process data. This technique provides extra quantitative information in three main areas. First, those production variables of importance can be identified and the exact effect of such variables on joint strength determined. Secondly, linear versus non-linear association between such production variables and joint strength can be tested. Finally, the degree and significance of interaction effects can be estimated. Using this stepwise regression technique it was found, contrary to Tomlinson and Cooper's paper, that the relationship between strength and antimony content was, in all cases, non-linear, whilst all other relationships were linear. The significant main effect variables were furnace cooling, cooling time and antimony content with the latter being the most important explanatory variable. However, the effects of these and other interaction explanatory variables were not minor as Tomlinson and Cooper suggest. Important interaction effects were also identified particularly so between gap size and antimony content.

Mechanical Properties of Metal Connectors Soldered by Gas Torch Versus an Infrared Technique

The ultimate tensile strength and percentage elongation of solder joints of three alloy systems were tested. Solder joints were formed using either an infrared soldering machine or gas-oxygen torch. Intact solder materials were used as controls. There were no significant differences in percentage elongation among different treatment methods of the solders or among various solder materials. All intact solder materials possessed significantly higher ultimate tensile strength than the joints made with either method. For high-noble and noble alloy solders, there were no significant differences in ultimate tensile strength of joints made with either method. For base metal alloy solder, the ultimate tensile strength of joints made with the infrared technique was significantly higher than that made with the gas-oxygen torch technique. The infrared technique can be used as an alternative to the gas-torch technique for soldering high-noble and noble alloys. It is superior to the gas-torch technique for soldering a cobalt-chromium alloy.

Predicting Scooping and Skipping in Solder Paste Printing for Reflow Soldering of SMT Devices

This paper examines the rôle that the squeegee plays in the solder paste printing process. Although the printing of solder paste is only one stage of many in the surface mount assembly process, it is crucial to deposit the correct amounts of solder paste cleanly onto the substrate. The amount of solder paste deposited affects the reliability and strength of the reflowed solder joint. Surface mount component lead pitches are continually being reduced due to the requirements of packing more and more components into a given space on the PCB, and this necessitates a proper understanding of the printing process and in particular of the squeegee which plays an important part in determining paste heights and the occurrence of defects. The paper outlines a model which predicts scooping and skipping in the stencil printing of solder pastes used in the reflow soldering of surface mounted devices. The model is based on the forces acting on the squeegee blade, which determines the paste flow pattern ahead of the squeegee, and on the stencil aperture geometry. The paper also examines the interactions between the paste properties and squeegee material properties. These interactions produce printing defects such as scooping, skipping and wet bridging. Results of an experimental comparison of different types of squeegee blade used in the stencil printing of solder pastes for reflow soldering in SMT, as well as the experimental results for squeegee deformation into stencil apertures, were used for validating the model. The empirically enhanced model which results takes into account the force on the squeegee due to solder paste flow and some of the non‐Newtonian properties of the solder paste. The main utility of the proposed model is the control of solder paste printing quality.

Comparison of tensile strength of solder joints by infrared and conventional torch technique

Fabrication of a fixed partial denture may require a soldering step. This study compared soldering by a conventional torch procedure with an infrared soldering technique. Comparisons were made for tensile strength, porosity, and time efficiency between the two methods. No significant difference was found in ultimate tensile strength between the two types of solder joints and the nonsoldered control samples. Random samples photographed with a scanning electron microscope revealed no difference in joint porosity between the two techniques. Torch soldering took consistently less time that infrared soldering.

A Study of the Effects of Infra‐red Reflow Profile on Solder Joint Strength and Structure

The effects of varying reflow profiles on the tensile pull strength and structure of solder joints of components with tin plated and nickel‐palladium plated leads were studied. It was found that, in the case of tin plated leads, the structure and the tensile pull strength of the resultant solder joints were not significantly affected by varying the reflow conditions from Profile 1 (peak temperature range: 174°C to 195°C, reflow time 24 seconds) and Profile 2 (peak temperature range: 198°C to 218°C, reflow time 30 seconds). On the other hand, the mean pull strength of solder joints of nickel‐palladium plated lead was found to be significantly higher for joints reflowed with profile 2 than that of joints reflowed with Profile 1. Also, for both reflow profiles, the pull strengths of joints of nickel‐palladium plated leads were significantly higher than those of tin plated leads. This higher average pull strength may be due to the dissolution of palladium in the solder and/or the increased density of intermetallic precipitates in the solder fillet, and the increased intermetallic layer thickness at the lead/solder interface.

Empirical Modelling of Surface Mount Solder Joints from 132 Pin Quad Flat Pack Components

Tensile pull strength tests were used to study the strength of solder joints of 25 mil gull wing leads on 132 pin quad flat pack components. The authors generated quadratic and linear models which can be used to predict the pull strength of a solder joint given its geometry. The shape parameters studied were stand‐off height between the lead and substrate, height of heel fillet, radius of curvature of heel fillet, length of heel fillet, height of solder at toe region, and thickness of solder on the lead. The most significant parameters in determining the tensile pull strength of the solder joint are the height and length of the heel fillet. A study was performed to quantify the effect of lead finish on the accuracy of these models. The lead finish was found to have a significant effect on the solder joint strength. The effect of lateral misregistration on the tensile pull strength of solder joints was also investigated. No correlation between the extent of lateral misregistration and joint pull strength has been found.

Strength of tin-based soldered joints

Single overlap joints of copper and brass soldered with tin and tin-based solders containing (wt%) 1% Cu, 3.5% Ag, 5% Sb, 57% Bi, and 2% Ag 36% Pb, have been tested in shear at 20 and 100 °C, and with strain rates of 0.05 and 50 mm min−1. Six specimens were tested under each condition, and the average value and coefficient of variation of the 0.2% yield stress, ultimate shear stress, elongation, and work to fracture, determined. Brass joints were generally slightly stronger than copper joints, and tended to show more scatter. Ranking in terms of strength depended on the test conditions. The solders containing silver generally gave the strongest joints. Strain-rate sensitivities were less than 0.1, and activation energies for deformation were very low. Overall, there did not appear to be any regular pattern between the properties, solders, and test conditions.

Reliability evaluation of electronic devices

Stresses due to thermal oxidation and film deposition processes during the fabrication of a semiconductor are analysed. The strengths of plastic encapsulants, silicon chips, bonding wires and adhesive interfaces in integrated-circuit (IC) plastic packages are evaluated using fracture mechanics and other techniques. The thermal fatigue strength of solder joints is then estimated using the fatigue test data of solder specimens and simplified modelling of IC packages.

面実装はんだ接合部の疲労損傷評価 評価手法の検討

Fatigue in solder joints in thermal cycling is one of the problems in surface mount technology. This paper proposes the evaluation method of fatigue damage (fatigue crack length) in solder joint by the measurement of residual strength (peeling strength) of solder joint. An attempt was made to evaluate quantitatively the fatigue damage in solder joint, paying attention to the residual strength of cracked solder joint. The fatigue damage in solder joints was given by a four-point bending mechanical fatigue test of the substrate, on which some packages were mounted. After the fatigue test, the peeling test of each solder joint and the observation of each fracture surface by a scanning electron microscope were carried out to investigate the relationship between the fatigue damage and the residual strength. On the other hand, numerical analyses were carried out to estimate the residual strength of the cracked solder joint. The elasto-plastic finite element method was employed for these analyses. Furthermore, the effects of solder material, solder volume and package lead shape on the fatigue damage were investigated. Two kinds of solder materials (35Pb63Sn2Ag and 96.5Sn3.5Ag) were used in these solder joints.It was found that the fatigue damage can be evaluated quantitatively by the residual strength of solder joint, and the residual strength can be estimated by the finite element analysis.

Temperature Variations in Soldering and Their Influence on Microstructure and Strength of Solder Joints

Since the introduction of surface mounting technology (SMT), interest in solder joints has increased greatly. In this work soldered joints were examined for different kinds of components. Factors which influenced the temperature cycle most strongly were the component size and its placing on the circuit board. These factors led to significant differences in maximum temperature and cooling rate between different solder joints on one and the same circuit board. The microstructure of the solder joints could then be related to their individual cooling rates. The near ternary eutectic Sn‐Pb‐Ag solder presented large variations in microstructure for the interval of cooling rates which was investigated. Strengths of the joints are therefore expected to vary because of the relation between microstructure and strength. Dissolution of elements from metallised coatings can also influence markedly the structures and properties in the solder joints.