Electrical analysis and solder joint quality of PCB land-pad design for QFP E-pad package

In traditional Quad Flat Package(QFP), solder joint quality and electrical analysis always been a critical issue. In original PCB land pad design, thermal opening is the same size of QFP thermal pad. In this design, solder joint yield is about 87.5%. In order to overcome this problem, this paper proposes a new PCB land pad design as a solution. Let PCB thermal opening 25% of QFP thermal pad size. Sacrifice some thermal function to have better solder joint yield. Test the reliability to samples. Including Temperature Cycle Test(TCT), -40~125°C, through 0,500,1000 cycle, then through lead pull test. Make sure that samples have ideal solder joint. On the other side, randomly selected five samples from 240 samples. And measure the electrical performance of the samples. Measuring 100%, 75%, 50%, 25%, 0%size of QFP thermal pad design. In result, 25% and 0% land pad design have 100% yield in solder joint. In electrical analysis, 25%land pad design has almost the same performance with original design. In conclusion, 25% PCB thermal land pad can easily overcome solder joint yield problem without affecting the electrical performance.