Issue link: https://iconnect007.uberflip.com/i/881969
October 2017 • SMT Magazine 73 RELIABILITY OF ENEPIG BY SEQUENTIAL THERMAL CYCLING AND AGING vehicle was assembled using a vapor-phase re- flow machine. The real-time 2D X-ray of the two package assemblies revealed no shorts or excessive sol- der balling and are acceptable. This build was re- peated one more time and achieved acceptable quality results. Figure 4 shows the overall X-ray of the side with the LGA1156. It also shows the corner solder joints at a higher magnification. The X-ray shows the internal configurations of the LGA and the fine pitch packages. During real-time examination of the X-ray images at higher magnifications, there were no apparent unusual solder anomalies except the existence of large voids. ENEPIG Microstructure after 200 TC (-55°C/+125°C) for LGA1156 LGA1156 assemblies on ENEPIG finished PCB were subjected to thermal cycling followed by isothermal aging prior to cross-sectioning for microstructural changes. LGA1156 assemblies were subjected to thermal cycling in the range of -55°C to +125°C with a 2−5°C/min (target 3°C/min) heating/cooling rate. After 200 ther- mal cycles, one of the LGA packages was cut in half diagonally for cross-sectioning. Figure 5 shows cross-sectional images of a LGA1156 with the package dimensional values including die size, die thickness, and solder joint height length. Images include both optical and scan- ning electron microscopy (SEM). Figure 6 shows representative optical and SEM images at high magnification providing details on microstructural features after 200 thermal cycles (-55°C to +125°C). The observa- tion of no cracks confirms the result from the Figure 4: X-ray photomicrograph images of a section of a test vehicle with plastic LGA1156 showing solder joint voids. Figure 5: Representative photomicrographs of LGA1156 after thermal cycling showing die size relative to the package.