Ultrasonic Nondestructive Testing And Thermal Fatigue Evaluation Of Electronic Packaging

At this moment, a major paradigm change, from2D IC to3D, is occurring inmicroelectronic industry. Joule heating becomes more serious in3D IC. Research showsthat the failure rate of electronic components increases exponentially with temperaturegrowth. Its failure rate doubled if the operating temperature of electronic componentsincreased by10℃. Therefore the reliability concerns will be extremely important.The electronic packaging usually is surrounded in thermal cycling environment so thatthe temperature field and thermal stress field changing circularly result to produce thefatigue residual stress inside of it. A variety of defects such as micro-cracks, delaminationand void will appear while local fatigue stress is over the maximum of allowed stressbecause the electronic package is composed of multilayer and inhomogeneous materials.Vicious cycling speeds up the failure of electronic packages. It is significant important tocheck out the defects of electronic package in the process of quality control and overhaul ofelectronic system.In order to improve the reliability of the electronic packaging, structure defects shouldbe timely detected, and the evolution laws of these defects must be explored so that peoplehave enough time to take actions before these defects lead to catastrophic accidents. Basedon the failure mechanisms and thermal fatigue damage models, a thermal fatigue damageassessment methods for electronic packaging under thermal cycling was developed, andthermal fatigue damage assessment results were verified using the accelerated life test andultrasound microscopy detection technology. The main contents are as follows:(1) A thermal reliability evaluation method for electronic packaging is proposed basedon the physical of failure. First, the new rising Physics of Failure(POF) method and fatiguedamage models developed by previous scholars in the field of electronic packaging wasstudied and analyzed. Then based on thermal failure mechanism of electronic packaging, athermal fatigue damage assessment method was developed.(2) A set of practical SAM system was developed independently by our Lab. And itsdetection resolution was analyzed using high frequency focused transducers with centerfrequency ranging from20MHz to100MHz. The experimental results show that the lateral resolution of the ultrasonic transducer with100MHz central frequency can reach about40microns, which is consistent with calculated resolution. Comparing with Sparrow criteria,Rayleigh criteria is more coherent with the experimental results.(3) Based on heat propagation theory and thermal stress theory, the internaltemperature field and thermal stress distribution of electronic packaging was simulated withANSYS Workbench FEM software, under different heat generation rate and differentpackaging materials (different thermal conductive material). The simulation results willprovide some reference for the thermal fatigue damage assessment analysis of electronicpackaging under harsh temperature ambient.(4) The ultrasonic nondestructive evaluation method of thermal fatigue damage inplastic electronic packaging structure under thermal cycling loads was developed based onthe fatigue fracture theory. The crack propagation rate of plastic electronic packagingstructure was measured using the accelerated thermal fatigue test according toMIL-STD-883G standard1010.8temperature cycling test method and high-frequencyultrasound microscope (C-SAM) nondestructive testing technology. The experimentalresults are consistent with theoretical predictions using the developed thermal fatiguedamage evaluation method.（5）The non-equilibrium statistical theory uses Fokker-Plank equation as the kineticequation for the void evolution in metal materials. From the micro-mechanism of metal’selectromigration damage, void growth rate equation was obtained using spherical Weilvmodel and control diffusion theory, and then it was simplified based on appropriateassumptions. According to the probability density distribution function of void, a series ofmacro-mechanical characteristics caused by void growth can be calculated, such as: thecritical radius of the void nucleation, the average radius of void. Thus the correlationbetween the void microstructure evolution and the macroscopic properties of metals can beachieved.