The Effects of Non-filled Microvia in Pad on Pb-Free Solder Joint Reliability of BGA

An experiment was done by the High Density Packaging Users Group (HDPUG) Consortium investigating the effect of nonfilled microvias and the associated solder voids in SMT solder joint pads compared to identical packages without microvia in pad on the reliability of the Pb-free solder joints in air to air thermal cycling. Three different BGA's with different solder ball sizes (Ceramic BGA with 0.89mm diameter solder balls, 192PBGA at 0.8mm pitch with 0.46mm diameter solder balls, BGA84 at 0.5mm pitch with 0.3mm diameter solder balls) and a QFN72 with and without microvia in pad construction are investigated. Weibull plots of the failure distributions are presented. Failure analysis results are detailed, and a correlation of the void size as measured by X-ray to the cycles to failure is also detailed. Background Voids from solder joints have shown to have an impact on solder joint life 1,2,3,4,5,6 . The impact of the void varies depending on the size and number of the void(s), and in particular the location of the voids relative to the crack or failure path. Microvia in pad constructions using non-filled (conformal) microvias result in a small void associated with the microvia in pad 7 . With SnPb soldering, microvia in pad constructions, when properly fabricated, and the associated small voids located at the base of the solder joint have virtually no impact on BGA thermal cycle reliability as shown in the example of figure 1 8 . This is primarily since the failure location is virtually always on the package side of the component, away from the small void formed above the microvia as shown in Figure 2.