Tin-lead Solder Alloys Research Articles

EFFECT OF GAMMA RADIATION ON MICROMECHANICAL BEHAVIOR OF SNPB SOLDER ALLOY

Tin-lead (SNPB) alloys are widely used in microelectronic packaging industry. It serves as a connector that provide the conductive path needed to achieve the connection from one circuit element to another circuit element. In this research, the effect of gamma irradiation on the micromechanical behaviour of tin-lead (SNPB) solder alloy has been investigated using the nano-indentation testing. Gamma radiation with a Cobalt-60 source were exposed to SNPB solders with different doses from 5 Gy to 500 Gy. In this study, the nano-indentation technique was used to understand the evolution of micromechanical properties (hardness and reduced modulus) of SNPB solder joints subjected to gamma irradiation. The results showed that the hardness of the SNPB alloys was enhanced with increasing of gamma radiation. The hardness was greatest at dose of 500 Gy of sample, 25.6 MPa and had the lowest value at un-irradiated sample. However, the reduced modulus was decreased by increasing the irradiation of gamma due to the intrinsic properties and the atomic bonding of the material.

Optimized cerium addition for microstructure and mechanical properties of SAC305

PurposeThis paper aims to analyze the effect of cerium addition on the microstructure and the mechanical properties of Tin-Silver-Copper (SAC) alloy. The mechanical properties and refined microstructure of a solder joint are vital for the reliability and performance of electronics. SAC305 alloys are potential choices to use as lead-free solders because of their good properties as compared to the conventional Tin-Lead solder alloys. However, the presence of bulk intermetallic compounds (IMCs) in the microstructure of SAC305 alloys affects their overall performance. Therefore, addition of cerium restrains the growth of IMCs and refines the microstructure, hence improving the mechanical performance.Design/methodology/approachSAC305 alloy is doped with various composition of xCerium (x = 0.15, 0.35, 0.55, 0.75, 0.95) % by weight. Pure elements in powdered form were melted in the presence of argon with periodic stirring to ensure a uniform melted alloy. The molten alloy is then poured into a pre-heated die to obtain a tensile specimen. The yield strength and universal tensile strength were determined using a fixed strain rate of 10 mm per minute or 0.1667 mm s^(−1). The IMCs are identified using X-ray diffraction, whereas the elemental phase composition and microstructure evolution are, respectively, examined by using electron dispersive spectroscopy and scanning electron microscopy.FindingsImprovement in the microstructure and mechanical properties is observed with 0.15% of cerium additions. The tensile test also showed that SAC305-0.15% cerium exhibits more stress-bearing capacity than other compositions. The 0.75% cerium doped alloy indicated some improvement because of a decrease in fracture dislocation regions, but microstructure refinement and the arrangement of IMCs are not those of 0.15% Ce. Different phases of Cu_6 Sn_5, Ag_3 Sn and CeSn_3 and ß-Sn are identified. Therefore, the addition of cerium in lower concentrations and presence of Ce-Sn IMCs improved the grain boundary structure and resulted refinement in the microstructure of the alloy, as well as an enhancement in the mechanical properties.Originality/valueCharacterization of microstructure and evaluation of mechanical properties are carried out to investigate the different composition of SAC305-xCerium alloys. Finally, an optimized cerium composition is selected for solder joint in electronics.

Investigation of Intermetallic Phases Formed in Lead-Free Solders

Industry should gradually replace the tin-lead solder alloys used traditionally in the soft soldering technology by lead-free soldering alloys, which raises a lot of new technological and scientific problems to be solved. The introduction and application of lead-free alloys caused a number of soldering defects not observed earlier; mechanisms of their formation are still unclear. One of such defects is whisker formation, another one is intensified formation of intermetallic phases. The appearance of undesired intermetallic phases in the soldering material spoils its mechanical properties; therefore it is particularly important that these phases do not form in electronic components. Besides, the formation of intermetallic compounds may occur in the soldering bath, thus making the soldering process difficult or even impossible.Tin-copper-nickel and tin-silver-copper alloys are suitable for the replacement of tin-lead alloys. The components of these alloys were studied. After metallographic examination of the specimens the occurrence of intermetallic phases was determined by the XRD method. The identification of intermetallic phases was carried out by using literature data and phase diagrams.

Influence of Liquid Structure Change on Microstructure and Properties of SnZnBi Solder Alloy

Currently, Pb-free is the primary trend of development for solder alloys, and the existing Pb-free solder alloys are still difficult to replace the traditional tin-lead solder alloys. How to further improve the welding properties of Pb-free solder alloys is the issue we currently faced. In this paper, through melt overheating treatment, the influence of liquid-liquid structure change (LLSC) on the structure and properties of SnZn8Bi3 Pb-free solder alloy has been studied. Experimental results show that the LLSC has obvious effects on the solidification process and solidified microstructure of SnZn8Bi3 alloy: bigger solidification undercooling degree in the solidification process, finer and more dispersed solidification structure, and more importantly, the mechanical and welding properties of the solder alloy have also been obviously improved.

Pb-free v/s Tin-Lead Reliability Comparison for Telecom/High Reliability Applications

With the European Union's (EU's) RoHS directives coming into force in July 2006 for consumer electronics products, the transition to lead-free (Pb-free) solder has occurred at a rapid pace. This push has driven many OEM suppliers/manufacturers to adopt Pb-free solder and End of Life many of their conventional Tin-Lead (Sn-Pb) components. This has forced telecom or high reliability applications to adopt Pb-free solder compositions with many reliability anomalies unanswered. While there have been many studies published on long term reliability of Pb-free solder joints at the component level, there have been few studies focused on the time zero reliability of the joints at the printed circuit board assembly (PCBA) level. The goal of this study is to help the OEM suppliers and their customers (like service providers) to come up with a common PCBA test methodology that will help identify and weed out early, marginal manufacturing and design defects that would crop up due to transition to the Pb-free solder. A normalized reliability data comparison and impact of the test on Pb-free and Tin-Lead solder alloys using test vehicles is presented in this study. The sequential PCBA level evaluation methodology involves a series of tests that include Thermal Aging, Mechanical Shock, Vibration, Functional test over elevated temperature and Destructive Analysis (Dye & Pry and Cross-sectional analysis) . The solder joint reliability comparisons for different components are presented against this methodology using different PCBA constructions (test vehicles).

A General Methodology to Predict Fatigue Life in Lead-Free Solder Alloy Interconnects

The ubiquitous eutectic tin-lead (Sn–Pb) solder alloys are soon to be replaced with lead-free alternatives. In light of this transition, new computational tools for predicting the fatigue life of lead-free solders are required. A fatigue life prediction methodology was developed, based on stress-strain, creep, and isothermal fatigue data; the latter generated using a double lap-shear (DLS) test assembly. The proposed fatigue life prediction methodology builds on current practices in fatigue prediction for solder alloys, particularly the concepts of unpartitioned energy methods in finite element analysis (FEA) and continuum damage mechanics. As such, the current state of these fields is briefly discussed. Next, the global and local FEA simulations of the DLS test assembly are detailed. A correlation is then made between the empirical data and the FEA simulations. A general fatigue life prediction methodology is next described in detail. Finally, this methodology is tested and verified against the empirical data.

Microstructure, electrical, mechanical and thermal properties of melt-spun bismuth–tin eutectic alloy

Microstructure, electrical, mechanical and thermal properties of melt-spun Bi58Sn42 eutectic alloy have been investigated using scanning electron microscopy, X-ray analysis, the double bridge method, dynamic resonance method, Vickers hardness measurement and thermal analysis. The structure and physical properties of this alloy are affected by the preparation method (rapid solidification technique). The bismuth–tin eutectic alloy has good properties as a lead-free solder alloy, such as low melting point and adequate cost and mechanical properties when compared with commercial tin–lead solder alloys.

Recent advances of conductive adhesives as a lead-free alternative in electronic packaging: Materials, processing, reliability and applications

Abstract Tin–lead solder alloys are widely used in the electronic industry. They serve as interconnects that provide the conductive path required to achieve connection from one circuit element to another. There are increasing concerns with the use of tin–lead alloy solders in recognition of hazards of using lead. Lead-free solders and electrically conductive adhesives (ECAs) have been considered as the most promising alternatives of tin-lead solder. ECAs consist of a polymeric resin (such as, an epoxy, a silicone, or a polyimide) that provides physical and mechanical properties such as adhesion, mechanical strength, impact strength, and a metal filler (such as, silver, gold, nickel or copper) that conducts electricity. ECAs offer numerous advantages over conventional solder technology, such as environmental friendliness, mild processing conditions (enabling the use of heat-sensitive and low-cost components and substrates), fewer processing steps (reducing processing cost), low stress on the substrates, and fine pitch interconnect capability (enabling the miniaturization of electronic devices). Therefore, conductive adhesives have been used in liquid crystal display (LCD) and smart card applications as an interconnect material and in flip–chip assembly, chip scale package (CSP) and ball grid array (BGA) applications in replacement of solder. However, no currently commercialized ECAs can replace tin–lead metal solders in all applications due to some challenging issues such as lower electrical conductivity, conductivity fatigue (decreased conductivity at elevated temperature and humidity aging or normal use condition) in reliability testing, limited current-carrying capability, and poor impact strength. Considerable research has been conducted recently to study and optimize the performance of ECAs, such as electrical, mechanical and thermal behaviors improvement as well as reliability enhancement under various conditions. This review article will discuss the materials, applications and recent advances of electrically conductive adhesives as an environmental friendly solder replacement in the electronic packaging industry.

Lead-free 0201 manufacturing, assembly and reliability test results

The trend towards smaller, faster and cheaper electronic devices has led to an increase in the use of 0201 ( L ∼ 0.02 in.; W ∼ 0.01 in.) and even smaller sized passive components. The size advantages of the 0201 component make it a popular choice among design engineers but not among manufacturing engineers. From a manufacturing perspective, the size of the 0201 package poses significant challenges to the printed circuit board (PCB) assembly process. The many challenges with 0201 assembly can be attributed to the solder paste volume, pad design, aperture design, board finish, type of solder paste, pick-and-place and reflow profile. If these factors are not optimized, they will introduce undesirable manufacturing defects. The small size of 0201 packages and undetected manufacturing defects will also raise concerns about their second level interconnect reliability, especially for lead-free solder alloys and surface finishes, with new processes and higher reflow requirements. To determine the optimum conditions, a design-of-experiment (DOE) study was carried out to investigate the effects of these parameters on assembly defects and solder joint reliability. This paper presents the test results and comparative literature data on the influence of a few key manufacturing parameters and defects associated with the 0201 component using lead-free and tin–lead solder alloys. Data pertaining to component shear strength before and after isothermal aging at 150 °C and intermetallic growth up to 500 h of aging are presented. A number of test vehicles were also subjected to thermal cycling (1500 cycles) in the range of −55/100 °C to determine the solder fatigue behavior. Shear test results for test vehicles subjected to thermal cycling is also presented. In addition, optical microscopy analysis of solder joint behavior during thermal cycling showing the progress of the solder damage and cross-sectional photos taken at 1500 cycles is included.

Effect of volume in interfacial reaction between eutectic Sn-3.5% Ag-0.5% Cu solder and Cu metallization in microelectronic packaging

The Sn-3.5Ag-0.5Cu (wt.%) is the most promising replacement for the eutectic tin-lead solder alloy. Here, an investigation has been carried out to compare the interfacial reactions of the Cu pad of a ball grid array (BGA) substrate with molten eutectic Sn-3.5% Ag-0.5% Cu solder having different volumes. Two different sizes of BGA solder balls were used: 760-µm and 500-µm diameter. Scanning electron microscopy (SEM) was used to measure the consumed thickness of the Cu and also the thickness of the intermetallic compound (IMC). The soldering reaction was carried out at 230°C, 240°C, and 250°C for 1 min, 5 min, 10 min, and 20 min. The Cu consumption was much higher for the Sn-Ag-Cu solder with higher volume. On the other hand, the mean thickness of the intermetallics for solder with smaller volume was thicker than that of the bigger solder balls. The Cu3Sn compound was also observed at the interface between the Cu6Sn5 IMCs and Cu substrate for longer reflow for the both solder balls. Larger Cu6Sn5 IMCs were observed in the bulk of the solder with bigger volume. A simplistic theoretical approach is carried out to find out the amount of Cu6Sn5 IMCs in the bulk of the solder by measurement of the Cu consumption from the substrate and the thickness of the IMCs that form on the interface.

A comparative fatigue study of solder/electroless-nickel and solder/copper interfaces

The fatigue resistance of the interface between electroless–nickel and the eutectic tin–lead solder alloy was examined in the as-reflowed and aged conditions and compared to fatigue behavior of the copper/solder interface under the same conditions. In the as-reflowed state, the fatigue resistance of the solder/electroless-nickel interface was slightly superior to that of the solder/copper interface. However, after long-term aging, the fatigue resistance of the solder/electroless-nickel interface became far worse in the high crack growth rate regime. Examinations of interfacial microstructures and crack growth mechanisms indicated that the differences in fatigue resistance between the two interfaces were not directly related to the thickness of the intermetallic phase at the interface, as commonly believed, but were due to differences in crack growth mechanisms.

Fatigue analysis and testing of adhesive joints : Krenk, S., Jonsson, J., and Hansen, L.P. Eng. Fract. Mech. (1996) 53 (6), 859–872

Tin–lead solder alloys are widely used in the electronic industry. They serve as interconnects that provide the conductive path required to achieve connection from one circuit element to another. There are increasing concerns with the use of tin–lead alloy solders in recognition of hazards of using lead. Lead-free solders and electrically conductive adhesives (ECAs) have been considered as the most promising alternatives of tin-lead solder. ECAs consist of a polymeric resin (such as, an epoxy, a silicone, or a polyimide) that provides physical and mechanical properties such as adhesion, mechanical strength, impact strength, and a metal filler (such as, silver, gold, nickel or copper) that conducts electricity. ECAs offer numerous advantages over conventional solder technology, such as environmental friendliness, mild processing conditions (enabling the use of heat-sensitive and low-cost components and substrates), fewer processing steps (reducing processing cost), low stress on the substrates, and fine pitch interconnect capability (enabling the miniaturization of electronic devices). Therefore, conductive adhesives have been used in liquid crystal display (LCD) and smart card applications as an interconnect material and in flip–chip assembly, chip scale package (CSP) and ball grid array (BGA) applications in replacement of solder. However, no currently commercialized ECAs can replace tin–lead metal solders in all applications due to some challenging issues such as lower electrical conductivity, conductivity fatigue (decreased conductivity at elevated temperature and humidity aging or normal use condition) in reliability testing, limited current-carrying capability, and poor impact strength. Considerable research has been conducted recently to study and optimize the performance of ECAs, such as electrical, mechanical and thermal behaviors improvement as well as reliability enhancement under various conditions. This review article will discuss the materials, applications and recent advances of electrically conductive adhesives as an environmental friendly solder replacement in the electronic packaging industry.

Creep-fatigue life prediction of in situ composite solders

Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are incorporated into eutectic tin-lead alloy by rapid solidification processes to formin situ composite solders. In this study, thein situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage mechanism ofin situ composite solders is proposed to be growth of cavities. A constrained cavity growth model is applied to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed processes can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, based on a critical cavity size of failure. Calculated lives are compared to experimental data under several fatigue histories, which include fully reversed stress-controlled fatigue, zero-tension stress-controlled fatigue, stress-controlled fatigue with tension hold time, fully reversed strain-controlled fatigue, and zero-tension straincontrolled fatigue. The model predicts the creep-fatigue lives within a factor of 2 with the incorporation of an appropriate compressive healing factor in most cases. Discrepancy between calculated lives and experimental results is discussed.

Mixed-mode fatigue and fatigue damage mechanisms of tin-lead solder alloys: Cortez, R. Diss. Abstr. Int. (May 1993) 53 (11)

Mixed-mode fatigue and fatigue damage mechanisms of tin-lead solder alloys: Cortez, R. Diss. Abstr. Int. (May 1993) 53 (11)

Surface tension and density of liquid tin-lead solder alloys

Surface tension and density of liquid tin-lead solder alloys