A Study of Intermetallics in Cu-Sn system and Development of Sn-Zn Based Lead Free Solders

In the electronic industry Pb-Sn solder is a very important material but Pb is toxic and has adverse effects on the environment and human beings. Due to the harmful effects of the Pb the use of the Pb-Sn solder alloys are being avoided and new Pb-free solder alloys are being used for electronic applications. This study is mainly based on the intermetallics that are formed in the Cu-Sn system and development of Sn-Zn based lead free solders. The aim was to understand the solidification of Cu-Sn alloys, the various intermetallics formed and their morphology. Thermal analysis of Sn-Zn based lead free alloys and their wetting characteristics has been analysed. The Pb-Sn solders are being replaced by the Sn-Cu, Sn-Ag, Sn-Ag-Cu, Sn-Zn and Sn-Zn-Bi alloys. Here the intermetallics formed between Cu-Sn during solidification of the molten solder on the Cu electrical contacts are also studied. The intermetallics are brittle in nature and this leads to fracture of the solder. In order to understand the Sn-Cu or Sn-Zn based lead free solder alloys it is essential to is understand the solidification of the molten alloys. This is why a few compositions of Cu-Sn alloy are selected and the various intermetallics formed during the solidification of the molten Cu-Sn alloys are analyzed. At high temperatures diffusion of Cu and Sn increases and as a result intermetallics of Cu-Sn are formed. The common intermetallics formed are Cu3Sn and Cu6Sn5. Sn-8.8Zn and Sn-8Zn-3Bi solder alloys has been developed. DSC analysis of these alloys has carried out to determine their melting points. It has been also observed that the addition of Bi increases the wettability and decreases the melting point of these alloys

Study On The Wetting Properties, Interfacial Reactions And Mechanical Properties Of Sn-Zn And Sn-Zn-Bi Solders On Copper Metallization [TK7870. R165 2007 f rb].

Secara praktiknya kesemua pemasangan elektronik masa kini menggunakan pateri eutektik Sn-Pb pada antara penyambung. Akibat pertambahan penggunaan peranti elektronik dalam industri serta untuk kegunaan peribadi, maka penggunaan pateri penyambung juga bertambah. Practically all microelectronic assemblies in use today utilize Sn-Pb eutectic solder for interconnection. Due to the increase in the use of electronic devices within the industry as well as personal use, the usage of solder connections has increased

A Study on Process, Strength and Microstructure Analysis of Low Temperature SnBi-Containing Solder Pastes Mixed with Lead-free Solder Balls

As the traditional eutectic SnPb solder alloy has been outlawed, the electronic industry has almost completely transitioned to the lead-free solder alloys. The conventional SAC305 solder alloy used in lead-free electronic assembly has a high melting and processing temperature with a typical peak reflow temperature of 245ᵒC which is almost 30ᵒC higher than traditional eutectic SnPb reflow profile. Some of the drawbacks of this high melting and processing temperatures are yield loss due to component warpage which has an impact on solder joint formation like bridging, open defects, head on pillow, and other drawbacks which include circuit board degradation, economic and environmental factors, and brittle failure defects in the circuit board like pad cratering. To overcome this, a detailed study has been carried out on low temperature lead-free solder paste that utilizes Bi bearing alloys. Three low temperature lead-free solder pastes, Sn-58Bi, Sn-57Bi-1Ag and Sn-40Bi-Cu-Ni with the melting temperatures of 138ᵒC (which is 45ᵒC below eutectic SnPb and 79ᵒC below SAC) were printed on Cu-OSP finish test boards. These pastes were then assembled with SAC305, Sn99CN and Sn100C solder spheres. The range of Bi concentrations for various mixtures used in this study was calculated to be in the range of 2 to 4 wt%. The mixtures were reflowed under two different low temperatures reflow profiles; (a) a traditional SnPb profile with a peak temperature 217ᵒC and (b) a low temperature SnBi profile with a peak temperature 177ᵒC (recommended by the paste manufacturer). After the assembly process, the mixed solder joints were shear tested to study the failure modes and shear strength at rate of 27.50mils/sec. Cross sectioning was performed to evaluate the possible microstructural changes at room temperature and after aging conditions that may have led to the changes in failure mode observed in shear testing. The isothermal aging condition used in the study is 125ᵒC for 200 hours, which mimics 21 years of field storage at 25ᵒC degrees using Arrhenius extrapolation for Cu6Sn5 intermetallic formation. Our study suggests that high temperature reflow profile (217ᵒC peak profile) had better mechanical strength than the low temperature reflow profile (177ᵒC peak profile). A metallurgical explanation for the improvement is presented in this paper. Thus, this paper describes that by generating a robust reflow assembly process for SnBi solder paste, the shear strength can be increased, cost of manufacturing can be reduced and high temperature assembly process (SAC) issues can be minimized which may improve product yield in production

Effect of Sn-xCu Solder Alloy onto Intermetallic Formation After Laser Soldering

The awareness of lead-free solders can be attributed to their environmental and human-health related benefits. Due to this consciousness, research toward lead-free solder alloy became a concern. Tin-copper (SnCu) solder alloy is one of the candidates that can meet the characteristic of tin–lead (SnPb). The objective of this study is to analyse the wetting behaviour, intermetallic compound (IMC) thickness and also the spread ratio by varies the copper weight percentage (Cu wt%) in SnCu solder alloy. Solder alloy used was Sn-xCu, where x = 0.0, 0.3, 0.5, 0.7, 1.0 which was soldered onto electroless nickel immersion gold (ENIG) substrate using carbon dioxide (CO2) laser. Parameters used for laser soldering was 35 W for the laser power, focal length was kept constant, scanning time was 0.04 s, and scanning speed was 100 mm/s. Then these sample were subjected to isothermal aging with the duration of 0, 200, 500, 1000 and 2000 h. In the final analysis, the IMC thickness and wetting behaviour characteristics were characterized by metallographic microscopy. The results showed that the higher the Cu percentage in the solder alloy, the higher the thickness formed at the solder joint interface. Besides that, the morphology of IMCs additionally changed with aging time whereby it changed into much uniform and continuous shape, Nonetheless, its thickness was found to be increasing upon aging duration. Furthermore, the spread factor and spread ratio increase, but the equilibrium contact angle decreases with increasing Cu content. These results were the proof that Sn-0.7Cu/ENIG offers a good solder joint performance as compared to other copper percentage

Study On The Wetting Properties, Interfacial Reactions And Mechanical Properties Of Sn-Zn And Sn-Zn-Bi Solders On Copper Metallization

Secara praktiknya kesemua pemasangan elektronik masa kini menggunakan pateri eutektik Sn-Pb pada antara penyambung. Practically all microelectronic assemblies in use today utilize Sn-Pb eutectic solder for interconnection

Properties and behaviour of Pb-free solders in flip-chip scale solder interconnections

Due to pending legislations and market pressure, lead-free solders will replace Sn–Pb solders in 2006. Among the lead-free solders being studied, eutectic Sn–Ag, Sn–Cu and Sn–Ag–Cu are promising candidates and Sn–3.8Ag–0.7Cu could be the most appropriate replacement due to its overall balance of properties. In order to garner more understanding of lead-free solders and their application in flip-chip scale packages, the properties of lead free solders, including the wettability, intermetallic compound (IMC) growth and distribution, mechanical properties, reliability and corrosion resistance, were studied and are presented in this thesis. [Continues.

Structural Integrity Investigation Of SAC305 Lead Free Solder

Improvement in solder strength is instantly becoming one of the most important concerns in the electronics industry, particularly in Printed Circuit Board (PCB) applications. Because of the design and mounting of electronic components on a substrate or PCB, solder in electronic connections may crack and deform to certain factors. These causes device failures and massive costs, and the true impact of crack caused losses in the industrial sector is not widely communicated. As a result, mechanical strength of solder is now one of the most complicated issues, and it has received increased attention in recent years as a result of increased product warranties, advanced technologies, and phase changes brought about by recent laws affecting the electronics sector. In addition, a delicate and unstudied characteristic of SAC305 solder on copper was limited. Therefore, this project was conducted to study the mechanical properties of SAC305 solder. The reflowed SAC305/Cu solder with the temperature of 220℃ at 60 seconds was investigated. The microstructure, structural phase, and hardness of the formed intermetallic compounds were investigated. The interfacial IMC formed between SAC305 and the Cu substrate after solder reflow is Cu6Sn5 and Ag3Sn. The IMCs where visible in SEM and detected in XRD. The effect of IMCs in the terms of hardness was investigated using Vickers hardness test and nanoindentation. A specific indentation array was performed on four different horizontal cross sections of the solder with different heights and diameters. The hardness values increased gradually from the top cross sections towards adjacent to the solder/substrate interface

Printed Thin Film On Copper And Pcb For Corrosion Application

Corrosion resistance is promptly one of the most critical issues in the electronics sector, especially in Printed Circuit Board (PCB) applications. The solder in electronic connection also experience corrosion as it may expose to the atmosphere, due to the design and mounting of electronic component on a substrate or PCB. Corrosion causes device failures and massive costs, and the real impact of corrosion-caused losses is not widely presented in the industrial sector. As a result, corrosion is now one of the most complicated issues, and it is gaining attention in recent years due to higher product warranties, advanced technologies, and phase changes brought by the recent laws affecting the electronics sector. Furthermore, a delicate and unstudied characteristic of SAC305 thin film solder on copper characteristic was limited. Therefore, this project was conducted to study the corrosion characteristic of SAC305 thin film solder in acidic medium. The corrosion behaviour of as-reflowed SAC305/Cu thin film solder with the temperature of 250℃ at 480 seconds was investigated by using a galvanic corrosion test in a 30% sodium chloride (NaCl) solution. The microstructure, structural phase, and hardness of the intermetallic compounds formed were determined. After solder reflow, the interfacial IMC formed between SAC305, and Cu substrate are Cu6Sn5 and Ag3Sn. The corroded surface was mainly composed of SnO and SnO2 for as-reflowed SAC305/Cu. These results clearly indicate the corrosion characteristics of SAC305 thin film solder in acidic media, as well as prospective guidance for electronic device maintenance to ensure safe operation and extended in-service lifetime

Effect of Ag on Sn-Cu Lead Free Solders

Lead free solders are expected to replace the traditional Sn-Pb alloys due to environmental concern. The Sn-Cu lead free solder alloys are found to be a potential alternative to the Sn-Pb alloys compared to other solders. Eutectic Sn-0.7Cu (wt.%) solder has been used for interconnecting and packaging electronic component due to the good wettability between the Sn-Cu solder and the Cu substrates. Three compositions Sn-0.7Cu, Sn-1Cu and Sn-2Cu and three compositions containing Ag, Sn-2Ag-0.7Cu, Sn-2.5Ag-0.7Cu and Sn-4.5Ag-0.7Cu were considered here for the study. Ag was added to the eutectic Sn-0.7Cu composition in order to decrease the melting temperature of the eutectic alloy and to enhance the mechanical properties of the alloy such as hardness. But the amount of Ag was more increases hardness was decreases. The wettability of the Sn-Cu solder on the Cu substrate was also enhanced by the addition of Ag. Structure and morphology of the solder alloys were analyzed using a SEM, XRD and EDX. The microstructural observation reveals the formation of â-Sn matrix and presence of intermetallic phases like Cu6Sn5 and Ag3Sn. Furnace cooling was employed for solidifying the lead free solder alloys. Thermal analysis of the solder alloys were done with the help of a differential scanning calorimeter (DSC). Trace additions of Ag have been found to significantly reduce the melting temperature of these alloys

INFLUENCE OF SURFACE ROUGHNESS OF COPPER SUBSTRATE ON WETTING BEHAVIOR OF MOLTEN SOLDER ALLOYS

The objective of this study is to understand the effect of surface roughness of the Cu substrate on the wetting of molten solder alloys. Eutectic Sn-Pb, pure Sn and eutectic Sn-Cu solder alloys and Cu substrates with different surface finish viz., highly polished surface, polished surface and unpolished surface were used in this work. Highly polished surface was prepared in Metallography lab, University of Kentucky while other two substrates were obtained from a vendor. Surface roughness properties of each substrate were measured using an optical profilometer. Highly polished surface was found to be of least surface roughness, while unpolished surface was the roughest. Hot-stage microscopy experiments were conducted to promote the wetting behavior of each solder on different Cu substrates. Still digital images extracted from the movies of spreading recorded during hot-stage experiments were analyzed and data was used to generate the plots of relative area of spread of solder versus time. The study of plots showed that surface roughness of the Cu substrate had major influence on spreading characteristics of eutectic Sn-Pb solder alloy. Solder showed better spreading on the Cu substrate with least surface roughness than the substrates with more roughness. No significant influence of surface roughness was observed on the wetting behavior of lead free solders (pure Sn and eutectic Sn-Cu)