6-Joyce-Board Test Workshop 2005.pdf

Definition of Board Flexure• When a board is assembled it is stressed—andtherefore strained—in many directions. This“board flexure” puts stress on the solder jointsand causes the package to flex, too. The cornersolder balls are usually under the most stress.BGA PackageRegions ofroughly equalstress4Highest Stressis in the corner• We do not have a way to directly measure thestress or strain on the solder balls, so wemeasure the strain on the PCB near the cornerof the package.