SMT Magazine

SMT-Sept2017

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64 SMT Magazine • September 2017 by Bob Wettermann BEST INC. BGA component package dimensions con- tinue to get thinner as more are being used in handheld device applications. End-use device requirements include the need to maintain their interconnections, even when dropped, thus necessitating underfill. The increased de- mand for higher board densities requires neigh- boring or mirrored devices during the rework process to be more challenging. Higher reflow temperatures of lead-free rework increases the pressure for properly shielding the neighbor- ing components. These developments are caus- ing BGA rework challenges. This summary will discuss the most challenging aspects of BGA re- work and options for solutions. Warped BGAs One of the challenges in reworking BGAs at this time is the warping of the packages as ever thinner packages lead to a va- riety of problems. A largely noted issue of a warped BGA is the 'Head in Pillow' (HiP) de- fect (Figure 1). This defect may or may not be detectable during the X-Ray inspection. In this solder joint defect, the solder paste de- posit will wet the pad, but does not fully wet the ball. This is due to the ball of the package being 'pulled away' during the device warp- ing. The result is a solder joint with enough of a connection to have electrical integrity , but not sufficient mechanical strength. With- out the strength, these components may fail with a small amount of mechanical or ther- mal stress. This potentially costly defect is not FEATURE Figure 1: Head-in-pillow defect.

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