Coupling effect in Pt/Sn/Cu sandwich solder joint structures
ABSTRACT The interaction between Sn/Cu and Sn/Pt interfacial reactions in Pt/Sn/Cu sandwich joint structures was studied. We found the interfacial Sn/Pt reaction to be greatly influenced by the opposite Sn/Cu reaction. The PtSn4 interfacial compound formation rate was very sluggish compared with that of the single Sn/Pt reaction case. On the other hand, the growth rate of the Cu6Sn5 compound at the Sn/Cu interface was not affected by the opposite Sn/Pt reaction, which has a rate similar to that of the single Sn/Cu reaction case. However, the morphology of the Cu6Sn5 grains was different than in the single Sn/Cu reaction case (i.e. it had the conventional scallop-type shape). In the sandwich case, the Cu6Sn5 grains had a column-like appearance. The column-like morphology of the Cu6Sn5 grains is due to the small interfacial energy, γsolder/Cu6Sn5, caused by the dissolution of Pt from the molten solder. Also, we found that the Pt dissolution would also cause a reduction in the solubility of Cu in the molten solder. The above two parameter changes lead to a diminishing of the ripening flux among Cu6Sn5 grains. Hence, smaller Cu6Sn5 grains would not be depleted and the separation distance between Cu6Sn5 grains would not be widened.
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ABSTRACT: The effect of adding 0.5–1.5 wt.% Zn to Sn–3.8Ag–0.7Cu (SAC) solder alloy during reflow and solid state ageing has been investigated. In particular, the role of the Zn addition in suppressing interfacial Intermetallic Compound (IMC) growth on Cu and Ni–P substrates has been determined. Solder–substrate couples were aged at 150 °C and 185 °C for 1000 h. In the case of 0.5–1.0 wt.% Zn on Cu substrate, Cu3Sn IMC was significantly suppressed and the morphology of Cu6Sn5 grains was changed, leading to suppressed Cu6Sn5 growth. In the SAC–1.5Zn/Cu substrate system a Cu5Zn8 IMC layer nucleated at the interface followed by massive spalling of the layer into the solder, forming a barrier layer limiting Cu6Sn5 growth. On Ni–P substrates the (Cu,Ni)6Sn5 IMC growth rate was suppressed, the lowest growth rate being found in the SAC–1.5Zn/Ni–P system. In all cases the added Zn segregated to the interfacial IMCs so that Cu6Sn5 became (Cu,Zn)6Sn5 and (Cu,Ni)6Sn5 became (Ni,Cu,Zn)6Sn5. The effect of Zn concentration on undercooling, wetting angles and IMC composition changes during ageing are also tabulated, and a method of incorporating Zn into the solder during reflow without compromising solder paste reflow described.Journal of Alloys and Compounds 01/2012; 511(1):176–188. · 2.73 Impact Factor
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ABSTRACT: There is a continuing demand for the development of fast, sensitive and reliable sensors for applications in harsh industrial environments. Gas sensors are finding great importance in fuel and energy sectors. Monitoring and control of combustion related emissions result in efficient use of fuels and subsequent energy savings. Microelectronic gas sensors have advantages like small size, low power combustion, and possibility of in situ control and monitoring. These gas sensors are commonly employed in fire detectors, emission control system, CO2 operated enhanced geothermal system (EGS), supercritical water systems, organic rankine cycles used in binary power plants, high temperature gas-reactors in next-generation nuclear power plants and in gas processing. Packaging of microelectronic devices is equally important to the development practice. Input/Output connections are fabricated on these systems during this process. Thermo-mechanically strong lead attachments on sensor devices are necessary for high temperature applications. The conventional joining techniques like soldering, wire bonding, flip chip bonding and lead welding show failure in high temperature operative microelectronic systems. Present work is focused on the development and characterization of Pb free packaging of Pt micro-heaters, a main functionary of the gas sensors. Thick film Pt heater printed on ceramics substrate has been interconnected to Cu metal using Indium interlayer. The thermal and mechanical strengths of the interconnect specimen are determined and analyzed. The ultimate tensile strength (UTS) and ultimate shear strength (USS) values are plotted for different reaction parameters. The isothermal solidification morphology and crystallography are examined and discussed. The tests of thermal shock, pressure, operating life and vibration have been performed in an environmental lab to predict the compatibility of the packaging for deployment in harsh environments.Fuel 10/2013; 112:550-556. · 3.41 Impact Factor
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ABSTRACT: While the Sn–Ag–Cu (SAC) family of solders are considered good candidate as lead-free solder replacement materials, their relatively short processing history and application result in a host of materials as well as reliability problems. For good metallurgical bonding and electrical connection, a thin, even layer of intermetallic compound (IMC) is required but excessive growth of the IMC layer will cause various reliability problems. This is especially critical for miniaturized solder pitches in very large scale integration circuits. This work adopts the composite approach of adding 0.15 and 0.30 wt.% of Pt into Sn–3.8Ag–0.7Cu alloy to study the effect of these additions to the IMC layer thickness between the solder and substrate. Alloys were isothermally aged at 150 °C for up to 1000 h to observe contribution of Pt in suppressing excessive IMC growth. It was found that when more Pt was added to the alloy, the IMC layer became more even and continuous. Voids and IMC layer thickness were reduced. This is attributed to the role of Pt in replacing Cu in the solder and thus impeding excessive diffusion.Microelectronics Reliability 08/2014; · 1.21 Impact Factor