SAC305 Lead-free Solder Research Articles

Influence of process parameters on SAC305 lead-free solder powder produced by centrifugal atomization

In the present work, a centrifugal atomizer was constructed in order to study the effects of operating parameters: rotating speed, melt feed rate, shape and size of atomizer, and oxygen content in the atomizer chamber, on the characters of SAC305 powder. It was evidenced from the experimental results that the median size of the atomized powders became smaller with increasing rotating speed, decreasing melt feed rate, and the use of larger atomizer. At same operating conditions, a cup shaped atomizer was able to give approx. 11% finer powder compared to that from a flat-disk shaped one. Median particle size appeared to be smaller with decreasing oxygen content in the chamber. SEM micrographs revealed that SAC305 particles atomized under atmospheric condition were found to form various shapes: ligament, teardrop, flake, and irregular. The shape of powder particles tends to be rounder with decreasing oxygen content in the chamber. Fine particles of SAC305 powder (−45μm) containing oxygen less than 100ppm could be synthesized by purging nitrogen gas into the atomizing chamber. Production yield of the SAC305 powder increased with increasing atomizer's rotating speed, lower melt feed rate, and larger atomizer.

Analysis of Pin in Paste Soldering on Printed Circuits Boards Assembly Using Lead Free Solder Paste

The THC (Through Hole Components) assembly in a SMT board using Pin-in-Paste (PIP) process was studied and implemented using SAC lead-free solder paste. The main idea of this process is to solder in the same thermal step THCs and SMDs (Surface Mount Devices), eliminating the step of wave soldering which is the most used in electronics assembly today for THCs. As results one could achieve reduction on production time and costs, as well as improvements in soldering quality and also environmental aspects. The experiment was conducted to identify the best PCB and stencil design parameters. Printing and reflow parameters were also considered to reach the best solder joints. Some problems could be found with solder excess but the solder quality of the reflowed boards was acceptable for almost all components.

In situ investigation of SnAgCu solder alloy microstructure

In situ X-ray diffraction experiments, using synchrotron radiation, were employed to analyze microstructure evolution of the 96.5Sn3Ag0.5Cu (wt.%)—SAC305 lead-free solder alloy during heating (30–240 °C), isothermal dwell (240 °C) and cooling (240–30 °C). The special emphasis was placed on the study of the melting and solidification processes, explaining formation, distribution and the order of crystallization of the crystal phases ( β-Sn, intermetallic compounds) in the solder alloy. Furthermore, thermal expansion behaviour of the main constituent phase β-Sn was analyzed prior to melting and after the consequent solidification.

IMC Growth Mechanisms of SAC305 Lead-Free Solder on Different Surface Finishes and Their Effects on Solder Joint Reliability of FCBGA Packages

Intermetallic compound (IMC) growth behavior of lead-free solder plays an important role in ball grid array (BGA) solder joint reliability for flip chip BGA (FCBGA) packaging applications. The growth mechanism of IMC is reported based on a diffusion model. Thermal treatment such as accelerated thermal cycling (ATC) and isothermal aging exposure also contribute to the growth rate and morphology of lead-free solder IMC. Among the lead-free solder alloys, Sn-3.0wt.%Ag-0.5wt.%Cu (SAC305) solder is a promising substitute for Sn-Pb because of its good mechanical properties and wettability with current surface finishes. After thermal exposure, BGA solder joint reliability is degraded due to IMC formation and growth. In this study, two different thermal treatments, ATC and isothermal aging, and two different pad surface finishes, solder on pad (SOP) and electroless Ni immersion gold (ENIG), are considered in terms of IMC growth rate and mechanical solder joint reliability. An SOP finished interface forms a thin ε-phase Cu3Sn layer and a scallop-like η-phase Cu6Sn5 layer. In contrast, the ENIG finished interface forms a thick (Cu,Ni)6Sn5 IMC layer and prevents overall IMC growth. Different surface finished test vehicles are evaluated in an ATC test in a 0°C to 100°C temperature range and the Ni diffusion layer shows a longer solder joint fatigue lifetime than the nondiffusion barrier interface based on the micro cross-section and dye penetration analysis results. In an isothermal aging test at 100°C and 150°C, the aging temperature and time are valid factors to decide mechanical shock reliability. Interfacial fractures are found in the 100°C aged test vehicle due to easier crack propagation at the interface between the thin Cu3Sn layer and the scallop-like Cu6Sn5 layer based on SEM microstructure analysis results. Finally, this investigation proposes how to improve solder joint reliability and prevent interfacial fracture for SAC305 lead-free application.

Investigation of mechanical shock testing of lead-free SAC solder joints in fine pitch BGA package

The lead-free Sn–Ag–Cu (SAC 305/405) solder that replaced the tin–lead eutectic solder tends to be more brittle in nature due to high stiffness and excessive solder interfacial reactions. This leads to higher occurrences of solder joints failure during surface mount assembly and handling operations as a result of PCB bending, shock impact and drop. In this work, mechanical tests simulating the shock impact were conducted on lead-free SAC of different weight percentages. These SAC materials were prepared for use in the solder joints of fine pitch ball grid array (BGA) components which were mounted onto the motherboard. After the mechanical shock tests, strain measurements were performed on the BGA components to gauge the solder joint integrity, which was shown to be related with the formation of intermetallics in the bulk and at the interface of the SAC solder. The ball pull tests were conducted to determine both the bulk and interfacial strength and the solder joint fracture, which was classified as either mode 1, 2 or 3. A correlation was made between the silver (Ag) and copper (Cu) weight percentages with the metallurgical reactions.

Estimation of the Thermal Fatigue Resistance and Creep Properties of the Co/Ni-Bearing SAC305 Lead-Free Solders by the Strain Rate Change Tensile Test

In the present paper, in order to evaluate the creep properties of Co/Ni-bearing SAC305 lead-free alloys, the strain rate change tensile (SRCT) test was conducted. Two parameters, m 0 and k, obtained from the SRCT test could be applied to estimate the thermal fatigue resistance and the creep properties for lead-free solder alloys. The m 0 value implied the material's creep resistance, and the k value revealed the stability of the creep resistance during the whole tensile test process. The Co/Ni-bearing SAC305 solder alloys showed much lower m 0 and k values than the conventional Sn37Pb solders which indicated that the Co/Ni-bearing SAC305 solder alloys possessed of excellent thermal fatigue resistance and higher creep resistance. For the lead free solder alloys, high temperature aging led to microstructural coarsening. After aging, the m 0 value increased meanwhile the k value decreased for the Co/Ni-bearing SAC305 solders. Furthermore, the two parameters showed a converse change tendency between the conventional Sn37Pb and Co/Ni-bearing SAC305 solders after high temperature aging, which implied that they have different creep mechanism. It can be deduced that, for the conventional Sn37Pb solder, the grain boundary slide is the dominant creep mechanism, whereas the Co/Ni-bearing SAC305 solders showed a dislocation glide/climb creep mode.

An Analytical Elasto-Creep Model of Solder Joints in Leadless Chip Resistors: Part 2—Applications in Fatigue Reliability Predictions for SnPb and Lead-Free Solders

For pt. 1 see ibid., p.681-94, (2007). In Part 1, a novel two-dimensional model was presented for multi-axial thermal stresses, elastic strains, creep strains, and creep energy density at the interfaces of solder joints in leadless chip resistor (LCR) assemblies. In this paper, the model is used to characterize the creep performance of SnPb and SAC lead-free solder joints in LCRs. For both the SAC lead-free and eutectic tin-lead solder joints the predicted cyclic stresses and strains exhibit ratcheting behavior, in good agreement with finite-element predictions. The model is also employed to assess the role of ramp rate and temperature variations in accelerated thermal cycling (ATC) tests. The predictions of the present model correlate well with the experimentally measured number of cycles-to-failure using the Coffin-Manson strain-based model for the SnPb solder and energy-based life prediction model for the SAC solder joints.