Research On Defects Inspection And Life Prediction Of Solder Joint Based On Eddy Currrnt Pulsed Thermography

In many forms of advanced packaging, ball grid array(BGA) package has become a reliable electrical interconnection method. BGA package uses solder bumps to provide both mechanical and electronic interconnections between chips and substrates,meeting the requirements of high density 、 small size and optical performance. With the development of solder bumps towards higher density and finer pitch, the chip power density will increase dramatically, which makes the heat dissipation and the mismatch in package become a significant problem in the production and service process of the chip. Solder joint defect detection and reliability assessment has become one of the key issues to be solved in BGA package technology.In order to solve tiny defect detection for the high density solder joints in BGA package, this paper proposes firstly feasibility study on the effect of detectability as well as classification based on eddy current pulsed thermography(ECPT). At the same time, the life prediction and reliability evaluation of solder joints are studied.The main contributions are:(1) The mechanism of solder joint defecet inspection is deliberated. The impact of excitation parameters,such as current density、frequency and coil location, on the detection results in the process of BGA solder joint defect inspection based on eddy current pulsed thermography(ECPT), is analysed and the suitable parameters are determined. The 3D finite element inductive heat model of ball grid array is built to investigate disturbance on the temperature field and the eddy field for different kind of defects such as cracks, voids, missing, etc. The temperature variation between defective and non-defective solder balls on the upper surface is monitored for defects classification and assessment.(2) The influence of the defect size on temperature is analysed quantitatively. The simulation model of induction heating is established to analyse the influence of defect size on the solder upper surface when the defects are at different location. The temperature regularities of the solder surface with the change in defect size are achived through quantitative analysis. At the same time, the influence of solder joint size on defect testability is discussed and the feasibility of defect detection in different solder joints based on eddy current pulsed thermography is analysed.(3)The reliability of BGA solder joints is studied. Through the Darveaux thermal fatigue simulation model, the stress-strain relationship of solder joints during thermal cycling is studied. According to the stress-strain relationship, the location of the failure solder joint is determined;The rule of fatigue crack propagation is analysed in the process of solder joint fatigue failure. By analyzing the impact of fatigue crack on induction heat temperature of the solder upper surface, the fatigue life prediction and reliability assessment of solder joint based on eddy current pulsed thermography are proposed.(4) The experimental study of solder joint defect detection is conducted. The experimental platform is constructed. The experiment is conducted on the solder joints array with the defects.The solder diameter is 0.4mm, 0.5mm, 0.76 mm respectively. And the feasibility of solder defects detection based on eddy current pulsed thermography is verified. And then, the experimental thermal images are processed by a series of thermal image data processing method, such as absolute temperature method, normalization method, high-pass filtering, which reduces the thermal noise and improve the capability of defect recognition and detection in the thermal image.In this paper, the inspection of the common defects on BGA solder joint array is realized based on eddy current pulsed thermography. And,the experiment verifies that defects,such as crack,void,minssing can be detected effectively on the solder joint arrays with the diameter of 0.4mm,0.5mm,0.76 mm respectively.Meanwhile, this paper applies eddy current pulsed thermography to asses the reliability of solder joint according to the analysis of the fatigue crack propagation rule.