Copper-Aluminum Wirebond Interconnects
Automotive electronics is migrating to copper, palladium-coated copper and silver wire for wirebonding. Copper and Silver wire is finding increasing applications in high power electronics operating at 50V-300V used for propulsion, transmission and control in emerging hybrid electric (HEV) and electric vehicles (EV). Potential advantages of transition to Cu-Al wire bond system includes low cost of copper wire, lower thermal resistivity, lower electrical resistivity, higher deformation strength, damage during ultrasonic squeeze, and stability compared to gold wire. However, the transition to the copper wire brings along some trade-offs including poor corrosion resistance, narrow process window, higher hardness, and potential for cratering. Research focuses on development of corrosion life prediction models during operation at high voltage at extreme temperatures.
High Strain-Rate Constitutive-Behavior of Electronic Materials
Material constitutive behavior of electronic materials at small-length scales and high strain-rates is not well-understood. Lack of material data limits the prediction capability and accuracy of computational models for transient dynamics of electronics subjected to shock and vibration. Electronic materials being studied include leadfree solders, low-k dielectrics, underfills, thin-film adhesives, fine-pitch copper traces and conformal coats.
Light Emitting Diodes (LED)
Light emitting diodes may shift in color and degrade in the luminous flux output during operational life. An excessive color shift or excessive degradation in the luminous flux output, usually to 70% of the initial luminous flux, constitutes the failure of the product. In the current state of art a color shift of Δu’v’ less than 0.007 after 6,000 hours of operation is achievable. Degradation in the luminous flux and the color shift is attributed to a number of factors including – exposure to high temperatures, change in the refractive index of the lens and encapsulant, discoloration of the reflector, corrosion and depolymerization. Research focus is on the development a life prediction model, early defect detection, lifetime prognostics and color shift prognostics
MEMS devices also known as micro-electro mechanical systems have found wide spread applications in numerous sensing applications including accelerometers, pressure sensors, microphones, and gyroscopes. Several military and defense applications require reliable operation of the MEMS sensors under long period of thermal storage followed by deployment in high-g environments. Examples include missile-applications which often require acceleration exposure of 10,000 to 100,000g. Further, MEMS devices deployed in consumer products such as automotive airbags may be subjected to high temperature and high-g during impact and subsequent deployment of the airbag. This research area focuses on the development of multi-physics models, performance drift prediction models, and life prediction techniques for survivability of MEMS in harsh environments.
Electronic components may be subjected to significant deformation under the action of thermal and mechanical loads during operation and storage. The use of thin material layers in addition to fine embedded interconnects limits the possibilities for the integration of sensors to measure deformation and strain. Previously, deformations in in electronic components and assemblies have been measured using optical methods including moiré interferometry and digital image correlation – both of which require the cross-sectioning of the solder joint to gain access to the joint of interest for the purpose of strain and deformation measurement. Cross-sectioning is an invasive technique which requires discarding a portion of the package. In addition, the measurements are often limited to line of sight allowing measurement of only the optically visible cut-section. In this research area, methods are being studied for non-contact measurement of displacements in electronics layers and interconnects, non-invasively using a combination of x-ray computed tomography and digital volume correlation. The new class-of-methods does not require cross-sectioning of the part for the purpose of deformation and strain measurement. In addition, the measurements are not limited to the joints in the line of sight.
Prognostics Health Management of Electronic Structures
Leading indicators-of-failure are being developed for interrogation of material state significantly prior to appearance of any macro-indicators. The research focus is on determination of residual life of electronic systems via on-board sensing, damage-detection algorithms and data processing. Environments being studied include single, sequential, simultaneous thermo-mechanical, hygro-mechanical and dynamic loads.
Transient-Dynamics of Microcircuits and MEMS in Shock and Vibration
Micro-circuits and Micro-electromechanical systems are subject to accidental drop, shock-impact, large velocity deformation, and shock due to nearby impact in portable electronic applications. Damage initiation and progression in materials and interfaces, methodologies for survivability-prediction are not well understood. Applications being studied include – cellular phones, PDAs, notebook computers, missiles, tanks and unmanned airborne vehicles.
Thermo-mechanics of Electronics in Harsh Environments
Electronics in harsh environments is exposed to temperature (100 to 200°C), humidity (100% RH), pressure (vacuum-to-high-pressure). Deformation and failure response of commercial fine-pitch electronics in harsh environments is not well understood. Environments being studied include – automotive underhood, on-transmission, unmanned airborne vehicles (UAV), unmanned ground-vehicles (UGV), tank, missile, avionics and space applications.