Quantitative Assessment And Analysis Of BGA Micro Pad Failure Risk Of Board Level PCB Assembly

In recent years,due to the widespread use of artificial intelligence,big data and the Internet of Things,Make the printed circuit board more and more to the direction of high-density development,resin and glass fiber in dielectric materials have the characteristics of weak bonding strength,which leads to the risk of pad cratering.Therefore,the requirements for the reliability of printed circuit boards are also getting higher and higher,such as pad spacing and size.In this paper,the problem of interface delamination between copper foil and bonding layer is analyzed by combining simulation and experiment,and the failure risk of pads is quantified.The main contents and results are as follows:(1)Based on the simulation,the easy-to-fail positions of BGA pad of PCB assembly are obtained.Describe pad pull tester equipment and test methods for cohesion parameters.By establishing the simulation model of board-level PCB components,the thermal stress simulation analysis is carried out.The warpage deformation and equivalent stress of each component of the board-level PCB are obtained from the diagonal and perpendicular directions of the PCB board,respectively.In addition,a 3D simulation model of a single BGA micro pad is established,and under a certain tension,the stress strain and bonding strength of each layer of the PCB board are obtained.The results show that the deformation of the pads at the corners of the BGA package is the largest,and the stress on the chip is the largest,followed by the pads;the concentration point of stress and strain is the edge of the outer circle of the pads.(2)The influence and trend of key influencing factors on bonding strength of pads.On the one hand,the experimental scheme of the pad pull-out strength detector was formulated.On the other hand,using DMA Q800 experimental equipment,the range of elastic modulus was obtained,which provided support for the determination of cohesion parameters below.A 2D finite element simulation model is established based on the assumed cohesive force parameters,to obtain the trend of various factors on the bonding strength of pads with the single-variable method of changing material parameters and test conditions.The results show that the thicker the sample material,the greater the elastic modulus,and the size of the pad has the greatest influence on its bonding strength,followed by the drawing angle and the drawing speed.(3)Based on the comparative analysis of experimental results and simulation results,obtaining the quantitative assessment of pad failure risk through normal distribution.The sample was pulled out by a pad bonding strength tester to determine the average tensile force value of the pad.According to the principle and formula of energy release rate,the cohesion parameter is determined.Repeated experimental tests were performed on the samples with a pad pull-out tester to determine the tensile force value at which the BGA pads failed.Based on the experimentally obtained tensile force values,a risk quantitative assessment of the pad failure is carried out through a normal distribution.The results show that the deviation of tension peak value between simulation results and experimental results is within ±2N;The quantitative assessment of pad failure risk is based on the theoretical value,and the deviation between the measured actual value and the theoretical value is within 5%.In this paper,cohesion parameters can predict the initiation and propagation of cracks at the copper foil-prepreg interface.The simulation analysis and the quantitative assessment of pad failure risk have certain reference significance to improve the bonding strength and failure prediction of PCB pad.