Study On Board Level Drop Reliability Of WLCSP Package

Along with the electronic packaging devices developing to miniaturization, high density, and lead-free, the reliability of solder joints has already became one of the key factors affecting the quality of electronic products. During using of portable electronic products, it is easy for them to drop or suffer other shock by accident, so it is particularly important to improve the drop reliability of solder joint. For this reason, this thesis focused on the drop reliability of WLCSP and BGA packaging.The study of fracture mode and crack growth of WLCSP components after different drop times under the shock condition with the peak acceleration of1500g and duration of0.5ms that raised by JEDEC standard indicates:in the300drop times, only resin cracks was found, the crack generated between150and200drops, then grew linearly with the drop times.The study of drop300times under the shock condition with the peak acceleration of1500g and duration of0.5ms coupling aging under the temperature of125℃and thermal cycling during-55℃～125℃indicates:the fracture mode of WLCSP component is just resin crack, after aging or thermal cycling for150h, the fracture mode has not been changed, both Cu6Sn5IMC layers that generated near the component side and PCB side continuously grow with extension of time. After same time heat treatment, the Cu6Sn5IMC layer after aging is thicker and smoother than that after thermal cycling. Obviously IMC layers can been seen after100h and150h aging, however, this phenomenon is not found in component after thermal cycling.Five failure modes has been found in WLCSP component after5000drops under the shock condition with the peak acceleration of2900g and duration of0.3ms. The following failure modes is ranged from easy generate to hard:resin crack, crack between Cu and RDL, crack in the RDL, and crack inside the solder or crack mix inside the solder and IMC layer interfacial.The research of200drops failure strain threshold value of WLCSP component indicate: the value is between2400με～2500με, fracture mode is resin crack, as the drop condition become rigorous, the strain that generated on the PCB board increases. The length of cracks that generated in the solder joints which are located at the same position is directly proportional to the strain value. The study of strain and fracture behavior of WLCSP components that after300drops under the shock condition with the peak acceleration of1500g and duration of0.5ms or1ms indicates:after drop same times with the same peak acceleration and different duration, the bigger the duration is. the longer deformation time the corner of WLCSP component will go through. So. large duration can generates higher strain, and reduce the reliability of components.The worst damage usually generate in the solder joints that located near the corner of the components which also near to the edge of PCB, and directly proportional to the drop energy and drop times. No obviously fracture can be found in the solder joints that located at the middle position. As a result, the strength of resin of PCB is the primary factor that damage the reliability of this WLCSP component. Components located at position A and D are easier to fail than those located at the position B and C which near to the center of PCB, and more sensitive to...