Ricky Valentin

Remaining life assessment of aging electronics in avionic applications

This paper describes an assessment of the remaining life of solder interconnects for 13 different insertion mount packages used in an engine control electronics. The assessment consisted of using simulation to determine the mean time to failure of solder joint interconnects between the package leads and printed wiring boards under applied temperature cycle conditions. The simulation results were confirmed by accelerated testing for a 132-pin grid array (PGA) and field data for a 40-lead side-brazed dual in line package (DIP). Loading conditions include an accelerated test condition of -45/spl deg/ to 100/spl deg/C and a service loading condition of 10/spl deg/ to 75/spl deg/C with an extended dwell at 60/spl deg/C. Predicted mean interconnect life expectancy ranged from 4,000 in the worst case to 130,000 cycles. Results indicate a brazed leaded ceramic dual inline package with 40 leads is likely to fail first and a 2 lead plastic encapsulated axial capacitor is the least likely to fail. The early failure of the 40-lead side-brazed DIP was confirmed by the service performance data. The service life remaining after failure of the 40-lead side-brazed DIP was estimated to be 7,800 cycles.

Model for life prediction of fatigue-creep interaction

This paper discusses the development of a procedure for computing creep and stress relaxation at the critical location in a through-hole structure. A high-speed methodology was developed for calculating cyclic creep and stress relaxation at critical locations of a pile on elastic foundation subjected to cyclic thermomechanical loading. This simplified analysis was exercised for two cases involving a pile on elastic foundation problem with different thermomechanical loading. The simplified analysis exhibited no computational problems and gave a stable solution for the full dwell times. Comparisons made with experimental results for these cases gave an excellent agreement at a much faster computing time. This simplified procedure is expected to be even much faster when an entire pile on elastic foundation assembly is analyzed.

Study of the Thermomechanical Inelastic Energy Response of Backward Compatible Solder Joints Made With Sn-3.8Ag-0.7Cu versus Reballed Sn37.0Pb Components

Conflicting results in reliability tests for backward compatible and Pb-free soldered assemblies has motivated RoHS-exempted industries to practice reballing. Reballing is the name given to the process of removing Pb-free solder balls from the copper (Cu) pads of the Ball Grid Array (BGA) components received through the supply chain and replacing them with SnPb solder balls. Recent studies on the subject of reballing have shown the possibility that the removed Pb-free solder ball leaves behind some intermetallic remnants of the Pb-free solder alloy and the Cu from the pads. A modeling approach based on physics of failure (PoF) is presented that quantifies the interactions between different thermal cycles applied to reballed Ball Grid Arrays (BGA) with remnants of the Pb-free solder alloy on the Cu pads. These resulting interactions are compared to backward compatible Sn-3.8 Ag-0.7Cu (SAC) balls soldered with eutectic SnPb paste for the same thermal cycles. For the latter, the risk of having improper mixing during the assembly process is also studied. The approach is formulated at the microscale, incorporating physical mechanisms of the intermetallics created with Cu, and at the macroscale, capturing the creep phenomenon of the bulk solder as dominant failure driver. Simulation results show that the reballed cases have higher inelastic energy density per cycle averaged over damage volume near the copper pads and that the inelastic energy density is higher across the bulk of the improperly mixed backward compatible solder balls when compared to properly mixed backward compatible solder balls. The results of this study permit extrapolation of laboratory results to field life predictions and to explore the design of accelerated re-balled or backward compatible BGA tests that relate better to application-specific usage environments.Copyright

Pb-Free Synthesis: Decision Matrix as a Tool for Alloy Selection

For aerospace products, there is no current legislation or directive that sets a schedule for transitioning to Pb-free electronics; however, the aerospace industry is likely to be swept along because of its dependence on the larger commercial electronics industry which has already changed its materials, components, and assemblies to Pb-free. In this article, we present a synthesis of Pb-free solders along with critical factors affecting selection and deployment. A decision matrix methodology is introduced as a valuable tool to assist the alloy selection process based on specific criteria and life cycle conditions.

Canaries Development via Combinatorial Materials Science Techniques for Prognostics and Health Management in Electronics Systems

The design of a canary in a system aims at the detection of failures without causing an error in the system. The idea behind a canary is to have a system that will provide an early warning in a way that a fault-tolerant system will continue its intended function despite the potential presence of hardware errors. This paper presents methods to collect and analyze life-cycle environmental and usage data for in-situ health assessments. The FARM method is also provided to develop a canary life cycle monitoring plan, that encompasses the selection of environmental and usage parameters. The multidimensional failure space of a system is analyzed with combinatorial material science. A case study is presented to illustrate the methodology.Copyright

Functionalized nanowires from electrospun polymer nanofibers

The ability to pattern materials in three dimensions is critical for several emerging technologies, including photonics, μfluidics, MEMS, and biomaterials. Electrospinning allows one to functionalized and rapidly fabricate materials in complex three-dimensional shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in functionalization techniques are reviewed with an emphasis on the push toward patterning finer feature sizes. Effects of material and process parameters on the diameter of electrospun Poly Ethylene Oxide (PEO) fibers were experimentally investigated. Experiments were conducted at the settings of solution flow rate, voltage and the collector distance. It also imparted the evaluation of the significance of each parameter on the resultant fiber diameter. All the factors were found statistically significant in the production of nanoscale fibers. Opportunities and challenges associated with electrospinning of polyacrylonitrile fibers are also highlighted.

Modeling the Behavior of Insertion-Mounted Components — Part 1

Insertion mount, or trough hole, technology has historically been considered a fatigue-free method for soldering components to printed circuit boards; recently, though, applications implementing this technology have experienced use lifetimes sufficient to warrant investigation into fatigue failure. Although much research has been done into failure mechanisms and rapid failure prediction methods for surface mount components, there have been on such studies in the area of insertion mount technology. Therefore, this paper will be the first in a series of two papers introducing a rapid failure assessment approach for components fixed using insertion mount technology. The purpose of this paper will be to introduce the methodology used in this study, as well as to provide a method for determining the critical lead forces quickly and accurately.Copyright