Coarsening mechanisms, texture evolution and size distribution of Cu6Sn5 between Cu and Sn-based solders (original) (raw)
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Electronic Packaging Technology …, 2009
During the reflowing procedure, the Cu concentration in the solder affects the coarsening mechanisms of intermetallic compound (IMC) grains. For the Sn3Cu solder, the mean radius of the IMC grains was proportional to the cube root of the reflowing time; while it follows the square root relation with the reflowing time for the SnAgCu and Sn solders. It is proposed that the flux from the substrate was only consumed to coarsen the IMC grains for Sn3Cu solder, while it was separated into two fluxes for the SnAgCu and Sn solders at the reflowing initial procedure. For the Sn3.8Ag0.7Cu/Cu and Sn/Cu couples, the size distribution of the IMC grains well agrees with the modified flux driven ripening (FDR) model when the value of r/ r is above 1; while it would closely match with Marqusee and Ross analysis when the value of r/ r is below 1. For Sn3Cu/Cu couple, the size distribution of IMC grains shows good agreement with the FDR model. However, for SnPb/poly-Cu, during the solid-state aging procedure, the mean radius of the IMC grains was proportional to the cube root of the aging time. And the size distribution of IMC grains is well consistent with the FDR model.
Journal of Electronic Materials, 2003
Intermetallic-layer formation and growth in Pb-free solder joints, during solder reflow or subsequent aging, has a significant effect on the thermal and mechanical behavior of solder joints. In this study, the influence of initial intermetallic morphology on growth rate, and kinetics were examined in a Sn-3.5Ag solder reflowed on Cu. The initial morphology of the intermetallic was tailered by cooling in water, air, or furnace conditions. Solder aging was conducted at 100°C, 140°C, and 175°C and aged for 0-1,000 h. Cooling rate, aging temperature, and aging time played an important role on microstructure evolution and growth kinetics of Cu 6 Sn 5 (η) and Cu 3 Sn (ε) intermetallic layers. Prior to aging, faster cooling rates resulted in a relatively planar Cu 6 Sn 5 layer, while a nodular Cu 6 Sn 5 morphology was present for slower cooling. Intermetallic-growth rate measurements after aging at various times, indicated a mixed growth mechanism of grain-boundary and bulk diffusion. These mechanisms are discussed in terms of the initial intermetallic thickness and morphology controlled by cooling rate, diffusion kinetics, and the competition between Cu 6 Sn 5 and Cu 3 Sn growth.
Growth of Sn and intermetallic compounds in Sn-Ag-Cu solder
Journal of Electronic Materials, 2004
The microstructure of the SnAg -Cu solder is examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt. Focus is on the size and orientation of Sn grains as indicated by cross-polarized, light optical microscopy, and pole figures from x-ray diffraction. We find that both composition and cooling rate have strong influences on Sn grain size, with Sn grain size increasing an order of magnitude as Cu concentration increases from 0% to 1.1%. Cyclic growth twinning, with twinning angles near 60°, is observed in SnAg -Cu alloys near the composition Sn-3.9Ag-0.6Cu.
The effect of Ni addition on Cu-Sn intermetallic growth rate values in the SAC solder
2018
Due to environmental concerns, lead free solders were introduced in replacing the lead based solders in microelectronic devices technology. Among many lead-free solders, the Sn-3.5Ag-1.0Cu solder is the potential replacement for the Sn-Pb solder. This research was carried out to improve the properties of the Sn-3.5Ag-1.0Cu solder in terms of the reaction with copper substrate by adding small amount of Ni into the solder. The composite solders were synthesized via the powder metallurgy route, which consist of blending, compacting and sintering process. After soldering on copper substrate, the solder joint was aged at 150 o C for 1000 hours. The thickness of Cu 6 Sn 5 and Cu 3 Sn were measured and hence the growths kinetic of the intermetallics (k) were calculated. The results show that the SAC-0.05Ni solder has the lowest k value for Cu 6 Sn 5 intermetallic and SAC-0.5Ni has the lowest k value for Cu 3 Sn intermetallic.
Evolution of CuSn intermetallics between molten SnAgCu solder and Cu substrate
Acta Materialia, 2008
The evolution of SnCu intermetallic compounds (IMCs) between a molten SnAgCu alloy and the Cu under-bump metallization (UBM) throughout reflow is presented based on interruption of soldering reactions in experiments by removing the liquid solder from the substrate. This allows to capture and visualize interfacial reactants at arbitrary moments of the soldering process, and to gain an insight into their formation characteristics. The results show that the interfacial Cu 6 Sn 5 /Cu 3 Sn structure is formed at an early stage of reflow and is maintained throughout the process. Based on the experiments, formation mechanisms of interfacial CuSn IMCs are discussed.
53rd Electronic Components and Technology Conference, 2003. Proceedings., 2003
The adoption of Pb-free solders will affect manufacturing processes and joint reliability for electronics packages. Since SAC solder has a higher melting temperature than eutectic Pb-Sn solder, higher processing temperatures will be required. The higher processing temperatures allow for increased solubility of some elements, such as Ni, within the solder melt. The specific selection of pad metallurgies can influence both the type of intermetallics that form at the pad interfaces, and the age related evolution of those intermetallics. In joints where both Nt and Cu pad metallurgies are present, the fast diffusing Cu species can allow the intermetallic compound, (Cu,Ni)6Sns to form at the opposite, Ni, interface. The absence of a Cu pad can starve the system of Cu and effectively stop the growth of this (Cu,Ni)& intermetallic compound. The Ag component of the SAC solder can, under proper conditions, result in the growth of AgJSn plates in the solder melt before the Sn phase nucleates. This is controlled by the specific concentration of Ag in the solder, by the coolmg rate of the solder, and by the tendency of the solder joints to undercool by a typical 30°C before the Sn phase nucleates. The critical cooling rate for the onset of this phenomenon is between 3'Cisec. and 0.3"C/sec., within the range of normal reflow practices of the electronics industry. 101 Relatively small amounts of additional elements such as Cu or Ag are added to Sn to reduce the melting point of the solder alloy, and improve its mechanical and wetting properties. These constituents dramatically affect the mechanical properties of the solder, and possibly the reliability as well. Therefore it is important to understand the evolution of the distribution of these constituents during reflow and long term aging, including changes in the morphology of the intermetallic compounds (IMC's) formed along with Sn by these elements. In SnAg -Cu alloys, Cu&n5 and Ag3Sn form in the equilibrium state, with distinct morphologies, platelets for AglSn and hollow, hexagonal rods for Cu6Sn5. [l-71 We consider the evolution of IMC's during reflow, particularly Ag3Sn, including cooling to the solid state, and during long term aging.
Journal of Electronic Packaging, 2016
The sandwich structure Cu/Sn/Cu solder joints with different thicknesses of the solder layers (δ) are fabricated using a reflow solder method. The microstructure and composition of the solder joints are observed and analyzed by scanning electron microscopy (SEM). Results show that the thickness of intermetallic compound (IMC) and Cu concentration in the solder layers increase with the decrease of δ after reflow. During thermal aging, the thickness of IMC does not increase according to the parabolic rule with the increase of aging time; the solder joint thickness affects markedly the growth rate of IMC layer. At the beginning of thermal aging, the growth rate of IMC in the thinner solder joints (δ ≤ 25 μm) is higher than that in the thicker ones (δ ≥ 30 μm). The growth rate of IMC (δ ≤ 25 μm) decreases in the thinner solder joints, while increases in the thicker solder joints (δ ≥ 40 μm) and is nearly invariable when the δ equals to 30 μm with aging time extending. The growth rate of...
The Effect of Increased Cu Content on Microstructure and Melting of Utilized Sn-0.3Ag-0.7Cu Solder
Research Papers Faculty of Materials Science and Technology Slovak University of Technology, 2018
The influence of increased Cu and Ag contents on the microstructure evolution in the utilized Sn-0.3Ag-0.7Cu (wt. %) solder was studied. The utilized solder was exploited in the wave soldering process at the temperatures of about 260 °C for several days. The samples investigation involved the differential scanning calorimetry, the scanning electron microscopy including the energy dispersive X-ray spectroscopy, and the X-ray diffraction techniques. To predict phase equilibria at various temperatures and temperature dependences of heat capacity, the Thermo-Calc software and the COST531 lead-free solder database were used. The original and the utilized solders were found to be very similar regarding the phase occurrence, but slightly differ from one another in microstructure evolution due to higher bulk contents of Cu in the latter solder. The obtained results contribute to both the better understanding of the microstructure evolution in low-silver Sn-Ag-Cu solders and the determinatio...
The effect of adding Zn into the Sn–Ag–Cu solder on the intermetallic growth rate
Journal of Materials Science: Materials in Electronics, 2014
Due to toxicity of lead in the commercial solder, lead-free solders were proposed. Among the potential leadfree solders, the SnAg -Cu solders were considered as a potential replacement. To further improve the solder properties, a fourth element was added into the SnAg -Cu solder. The present study investigates the effect of different weight percentage of Zn (up to 0.7 wt%) into the Sn-3.5Ag-1.0Cu solder on intermetallic and growth rate (k) after long time thermal aging. The solders were prepared using powder metallurgy method and X-ray diffraction analysis shows that there were Cu 6 Sn 5 , Cu 3 Sn, CuZn and Ag 3 Sn phases present after solder preparation. The solders were reacted with Cu substrate at 250°C for 1 min and aged at 150°C until 1,000 h. The morphology of the intermetallic was observed under scanning electron microscope and the elemental distribution was confirmed by energy dispersive X-ray. Intermetallic thickness and growth kinetic result show that the additions of 0.4 % zinc is sufficient in retarding the Cu 6 Sn 5 and Cu 3 Sn intermetallic growth.