Prognostication of system-state in lead-free electronics equipment under cyclic and steady-state thermo-mechanical loads

The steady-state input and output processes are considered for a birth-and-death queueing model with N waiting positions (0 ≦ N ≦ ∞), s servers (1 ≦ s ≦ ∞) and an arbitrary queueing discipline. Let an index n indicate that the quantity in question depends on the system state but not on time t. The instantaneous arrival rate is λ, the probability of balking (i.e., not trying to obtain service) being ξ n. The instantaneous departure rate, μn , of customers having joined the system is the sum of the rate of service completions and the rate of defections before service completion. Three cases are considered. We start by ignoring balking customers; in the first case treating a lost customer neither as an input nor as an output, then secondly as both. Finally, balking and lost customers are considered both as inputs and outputs.

Download Full-text

RELIABILITY EVALUATION OF BGA SOLDER JOINTS DURING ACCELERATED LIFE TEST

International Journal of Modern Physics B ◽

10.1142/s0217979206041677 ◽

2006 ◽

Vol 20 (25n27) ◽

pp. 4553-4558

Author(s):

OUK SUB LEE ◽

NO HOON MYOUNG ◽

DONG HYEOK KIM ◽

MAN JAE HUR ◽

SI WOON HWANG

Keyword(s):

Solder Joint ◽

Thermal Cycling ◽

Solder Joints ◽

Coefficient Of Thermal Expansion ◽

Accelerated Life Test ◽

Lead Free ◽

Lead Free Solder ◽

Metal Fatigue ◽

Mechanical Loads ◽

Free Solder

The use of BGA (Ball Grid Array) interconnects utilizing the lead-free solder joint has grown rapidly because of its small volume and diversity of application. Thus, it requires the continuous quantification and refinement of lead-free solder joint reliability. The lead-free solder creep and cyclically applied mechanical loads cause metal fatigue on the lead-free solder joint which inevitably leads to an electrical discontinuity. In the field application, BGA solder joints experience mechanical loads during temperature changes caused by power up/down events as the result of the CTE (Coefficient of Thermal Expansion) mismatch between the substrate and the Si die. In this paper, extremely small resistance changes at joint area corresponding to through-cracks generated by thermal fatigue were measured. In this way, the failure was defined in terms of anomalous changes in electrical resistance of the joint. Furthermore the reliability of BGA solder joints in thermal cycling is evaluated by using the modified coffin-Manson criterion which may define and distinguish failure. Any change in circuit resistance according to the accumulated damage induced by the thermal cycling in the joint was recorded and evaluated in order to quantitate reliability of solder joint.

Download Full-text

The Steady-State Thermo-Mechanical Analysis of Turbine Rotor

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.574.184 ◽

2014 ◽

Vol 574 ◽

pp. 184-189

Author(s):

Ming Zhuo ◽

Li Hua Yang ◽

Lie Yu

Keyword(s):

Steady State ◽

Stress State ◽

Gas Turbines ◽

Turbine Rotor ◽

Mechanical Analysis ◽

Mechanical Loads ◽

Tightening Force ◽

Thermal Boundary Conditions ◽

Steady State Temperature ◽

Rotor Assembly

Circumferential rod-fastened rotor is one kind of extensively applied structures of gas turbines which work at high temperature to expand hot gas and generate power. The steady-state temperature distribution of the turbine rotor as well as the thermal deformation and stress state were calculated through a thermo-mechanical analysis. A cyclic model of a four-disc rod-fastened turbine rotor assembly was built. A thermal analysis was carried out to obtain the steady-state thermal map of the turbine rotor with the thermal boundary conditions calculated through heat transfer empirical correlations. A static structural analysis was performed to derive the deformation and stress field under both thermal and mechanical loads which incorporate both the pre-tightening force of the rods and the centrifugal force of the rotor itself. The thermo-mechanical results are compared to the result with only mechanical loads applied. The comparison shows the steady-state thermal loads have an influence on the stress state of the rotor and the deformation of the rods.

Download Full-text

Methodologies for System-State Interrogation for Prognostication of Electronics Under Thermo-Mechanical Loads

Volume 5: Electronics and Photonics ◽

10.1115/imece2007-42560 ◽

2007 ◽

Author(s):

Pradeep Lall ◽

Madhura Hande ◽

Chandan Bhat ◽

Jeff Suhling

Keyword(s):

Health Monitoring ◽

Least Squares Method ◽

Residual Life ◽

Electronic System ◽

Minimal Risk ◽

Leading Indicators ◽

System State ◽

Electronic Warfare ◽

Mechanical Loads ◽

Marquardt Algorithm

Methodologies for prognostication and health monitoring can significantly impact electronic reliability for applications in which even minimal risk of failure may be unbearable. Presently, health monitoring approaches such as the built-in self-test (BIST) are based on reactive failure diagnostics and unable to determine residual-life or estimate residual-reliability [Allen 2003, Drees 2004, Gao 2002, Rosenthal 1990]. Prognostics health-monitoring (PHM) approach presented in this paper is different from state-of-art diagnostics and resides in the pre-failure-space of the electronic-system, in which no macro-indicators such as cracks or delamination exist. Applications for the presented PHM framework include, consumer applications such as automotive safety systems including front and rear impact protection system, chassis-control systems, x-by-wire systems; and defense applications such as avionics systems, naval electronic warfare systems. The presented PHM methodologies enable the estimation of prior damage in deployed electronics by interrogation of the system state. The presented methodologies will trigger repair or replacement, significantly prior to failure. The approach involves the use of condition monitoring devices which can be interrogated for damage proxies at finite time-intervals. The system’s residual life is computed based on residual-life computation algorithms. Previously, Lall, et. al. [2004, 2005, 2006] have developed several leading indicators of failure. In this paper a mathematical approach has been presented to calculate the prior damage in electronics subjected to cyclic and isothermal thermomechanical loads. Electronic components operating in a harsh environment may be subjected to both temperature variations in addition to thermal aging during use-life. Data has been collected for leading indicators of failure for 95.5Sn4Ag0.5Cu first-level interconnects under both single and sequential application of cyclic and isothermal thermo-mechanical loads. Methodology for the determination of prior damage history has been presented using non-linear least-squares method based interrogation techniques. The methodology presented used the Levenberg-Marquardt Algorithm. Test vehicle includes various area-array packaging architectures soldered on Immersion Ag finish, subjected to thermal cycling in the range of −40°C to 125°C and isothermal aging at 125°C.

Download Full-text