Publications

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The development and operational sustainment of renewable (geothermal) and non-renewable (fossil fuel) energy resources will be accompanied by increasingly higher costs factors: exploration and site preparation, operational maintenance and repair. Increased government oversight in the wake of the Gulf oil spill will only add to the cost burden. It is important to understand that downhole conditions are not just about elevated temperatures. It is often construed that military electronics are exposed to the upper limit in terms of extreme service environments. Probably the harshest of all service conditions for electronics and electrical equipment are those in oil, gas, and geothermal wells. From the technology perspective, advanced materials, sensors, and microelectronics devices are benefificial to the exploration and sustainment of energy resources, especially in terms of lower costs. Besides the need for the science that creates these breakthroughs - there is also a need for sustained engineering development and testing. Downhole oil, gas, and geothermal well applications can have a wide range of environments and reliability requirements: Temperature, Pressure, Vibration, Corrosion, and Service duration. All too frequently, these conditions are not well-defifined because the application is labeled as 'high temperature'. This ambiguity is problematic when the investigation turns to new approaches for electronic packaging solutions. The objective is to develop harsh environment, electronic packaging that meets customer requirements of cost, performance, and reliability. There are a number of challenges: (1) Materials sets - solder alloys, substrate materials; (2) Manufacturing process - low to middle volumes, low defect counts, new equipment technologies; and (3) Reliability testing - requirements documents, test methods and modeling, relevant standards documents. The cost to develop and sustain renewable and non-renewable energy resources will continue to escalate within the industry. Downhole electronics can provide a very cost-effective approach for well exploration and sustainment (data logging). However, the harsh environments are a 'game-changer' in terms defining materials, assembly processes and the long-term reliability of downhole electronic systems. The system-level approach will enable the integration of each of these contributors - materials, processes, and reliability - in order to deliver cost-effective electronics that meet customer requirements.

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Thick film conductors provide the circuitry for hybrid microcircuit (HMC) assemblies. The integrity of solder joints made to those conductors is a function of the solid-state interface reactions that occur under long-term service environments. A study was performed, which examined the mechanical strength of 63Sn-37Pb (wt.%, Sn-Pb) solder joints made to the thick film conductor, 76Au-21Pt-3Pd (Au-Pt-Pd), on 96% Al2O3 substrates. The Au-Pt-Pd layer was 18±3 μm thick. Isothermal aging accelerated the solder/thick film interface reaction, which resulted in the growth of an intermetallic compound (IMC) layer and consumption of the thick film layer. The aging temperatures were 70°C, 100°C, and 135°C. The aging times were 5-5000 hours. The sheppard's hook pull test was used to assess the strength of the Sn-Pb solder joints at two displacement rates: 10 mm/min and 100 mm/min. A measurable loss of joint strength was observed after aging, which did not generate a great deal of IMC layer growth. The aging effects occurred at the thick film/Al2O3 interface as concluded by other authors. However, the present investigation showed those strength losses to be reversible after more extended aging times at elevated temperature. The strength and failure modes were sensitive to displacement rate when IMC layer development was minimal. Extensive growth of the IMC layer was accompanied by the formation of a Pb-rich layer ahead of it, which was responsible for a gradual decrease in the pull strength. In this case, pull strength and failure mode were less sensitive to displacement rate. The solder joints maintained a nominal level of pull strength, even after nearly all of the thick film conductor had been consumed by IMC layer formation. Copyright © 2010 MS&T'10®.

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A unified creep plasticity damage (UCPD) model for Sn-Pb solder is developed in this paper. Stephens and Frear (1999) studied the creep behavior of near-eutectic 60Sn-40Pb solder subjected to low strain rates and found that the inelastic (creep and plastic) strain rate could be accurately described using a hyperbolic Sine function of the applied effective stress. A recently developed high-rate servo-hydraulic method was employed to characterize the temperature and strain-rate dependent stress-strain behavior of eutectic Sn-Pb solder over a wide range of strain rates (10{sup -4} to 10{sup 2} per second). The steady state inelastic strain rate data from these latest experiments were also accurately captured by the hyperbolic Sine equation developed by Stephens and Frear. Thus, this equation was used as the basis for the UCPD model for Sn-Pb solder developed in this paper. Stephens, J.J., and Frear, D.R., Metallurgical and Materials Transactions A, Volume 30A, pp. 1301-1313, May 1999.