Issue link: https://iconnect007.uberflip.com/i/322206
66 SMT Magazine • June 2014 ray image (slice plane = ball centre of the bot- tom row). This BGA will probably fail, if it will be mechanically or thermally loaded. Such tilt- ing may be caused by wandering components that settled under the BGA. The fault scenario of the head-in-pillow ef- fects has already been discussed. One approach to evaluate this fault scenario in a safe and re- producible way would be to use the tear drop pad design. Here, terminal pads of the BGA are not round, but rather tear drop shaped. Figure 6 illustrates that in an X-ray image. When a ball melts and fuses with the under- lying solder paste, the typical tear drop shape will be visible. If the ball doesn't fuse with the solder paste, it will keep its circular shape and can be identified by parameters like roundness, axis ratio or ball area. The tear drop design often cannot be used with smaller pitches. The tear shape decreases THe TROuBLe WITH BgA SOLDeR JOInTS continues arTICLe figure 6: "resting" balls (head in pillow) visible due to tear drop pad design. figure 7: different radiographic views using 2d, 2.5d and 3d technologies.