Study Of Thermal-hygroscopic Mechanical Properties For PBGA Electronic Package Polymer And Its Packaging Reliability

This thesis carries out an experimental analysis of polyurethane polymer encapsulation materials, thus to work out its stress-strain curve and the transformation law of mechanical properties under the influence of heat and humidity. Use the ABAQUS finite element software to simulate large deformation tensile experiment, compare and analyze the experimental results, and obtain the constitutive model of polyurethane polymer encapsulation materials related to this experiment through fitting, which is chosen to conduct a theoretical analysis on cavitation unstable growth. Use the FEA software to simulate the distribution of temperature field, humidity field, stress concentration and hygrothermal stress, and meanwhile, analyze the effects that thermal and hygroscopic have on the reliability of PBGA encapsulation.(1) With the polyurethane polymer encapsulation materials being put in the high/low temperature constant humidity chamber in different time (eight routines according to distinct time), nonmetallic material universal testing machine works on the eight-routine materials separately to do a large deformation tensile experiment, which drives to the stress-strain curve, and polyurethane change law under the hither effect. The conclusion is:With the increase of test cycle, the mechanical properties such as elasticity modulus, yielding strength, stress at definite elongation are decreased.(2) By means of ABAQUS FEA software simulated stretch experience and numerical fitting, compare the two stress strain curves from experimental data and from different strain-energy functions fitting, a fact that only the contact ratio of Yeoh model fitting stress-strain curve and trial curves quite high is found, which illustrates that Yeoh model fits for imitation of large changing stretch experience and could be used as constitutive model of polymeric materials, and its data can be got through imitation result.(3) Make use of finite deformation theory and void theory to theoretically research and analysis encapsulating material "popcorn" lose resulting from void, and the most important part is to reason the analytic relationship of ratio of cavity f and σbased on certain strain-energy function. Via analyzing the datum of its analytic relationship, a theory that inside of polymer electronic package material happen to "popcorn" lose or not has much to do with constitutive model is found.(4) Based on thermodynamics theory, the moisture analysis theory, steam pressure analysis theory, the equivalent thermal stress analysis theory, etc, the author chooses PBGA package which is sensitive to heat and humidity to establish the finite element model for analysis, including thermal finite element analysis and wet finite element analysis.1) Thermal analysis:to study its temperature distribution and stress distribution under different working conditions. The analysis result of finite element shows that around the chip temperature is highes, the conclusions is encapsulation device failure caused by the stress concentration problem.2) Wet analysis:The electronic packaging device in humid environment, different moisture conditions due to different materials. Stress concentration caused by the different CME in different interface. Thus the author probes into possible failure modes of electronic packaging in different situations and studies the reliability of PBGA packaging through finite element simulation analysis.