Optimization Of Test Profile And Feasibility Analysis Of Defect Activation For PQFP

Reliability Enhancement Testing (RET) is a brand-new method of reliability test. It can stimulate the defects of electronic products and expose their weakness in design stage by imposing high enough stress on them, which will result in the higher test efficiency. So RET has been widely spread and applied in the western developed countries. However, RET is followed in our country since the beginning of this century. Especially, how to implement RET efficiently is still lack of scientific guidance. Consequently, founded by a Major Armament Preparatory Research Project and regarded the quad flat package device (PQFP) as the specific object, the distribution of stress and strain, fatigue life of the solder joints and leads are studied under thermal cycling tests and vibration tests. Moreover, the test efficiency of the two types of vibration environment is compared in this thesis. The goal of this research is to provide the theory guidance for RET of electronic products.The shape of solder joint is predicted in accordance with the principle of minimum energy and the constitutive equation of solder is analyzed in detail because the results calculated are strictly effected by the shape of solder joint and the constitutive equation of solder. On the basis of these results and the finite element analysis software ANSYS, the finite element model of PCB on which the PQFP is mounted is built. The main contents and the conclusions of this thesis are as follows:1. At first, the rules of the distribution of stress and strain of solder joints are analyzed under thermal cycling tests. Then, the effects of temperature profile (up-dwell temperature, down-dwell temperature, up-dwell time, down-dwell time, ramp-up rate and ramp-down rate) on the distribution of stress and strain, fatigue life of solder joints and the thermal cycling test time are studied. At last, the common principles are built in choosing the appropriate temperature profile during the thermal cycling tests;2. The effects of voids and cracks on the fatigue life of solder joints and leads are analyzed, respectively. Then, the localization of thermal cycling tests in exposing the defects of solder joints and leads is deeply researched;3. The excitation effects of vibration tests in exposing the defects of solder joints and leads are studied and discussed detailedly. The results show that the defects of solder joints and leads of PQFP can be exposed more efficiently under vibration tests than thermal cycling tests. Hence, vibration tests can be regarded as the forceful supplement to thermal cycling tests;4. Under the different vibration tests, the excitation effects on the cracks of leads are analyzed. The results of research show as following. The stimulating energy of repetitive shock vibration environment is limited in low frequency. Therefore, single axis random vibration environment is better than repetitive shock vibration environment in exposing cracks of leads.At last, the theory analysis results are validated by tests. The results in the thesis will contribute not only to the design of electronic products but also to RET of theirs.