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In integrated circuit packaging, a solder ball, also a solder bump (ofter referred to simply as "ball" or "bumps") is a ball of solder that provides the contact between the chip package and the printed circuit board, as well as between stacked packages in multichip modules. The solder balls can be placed manually or by automated equipment, and are held in place with a tacky flux.
A coined solder ball is a solder ball subject to coining, i.e., flattening to a shape resembling that of a coin, to increase contact reliability.
References
Solder ball Wikipedia(Text) CC BY-SA