Patent ID: 9576888
Date: 2017-02-21
CPC Classifications: H01L

Claim:
1. A method comprising: attaching a semiconductor die on a first side of a bottom package, wherein the bottom package comprises a plurality of metal bumps formed on the first side of the bottom package, and wherein a metal bump of the plurality of metal bumps comprises an upper portion rectangular in shape and a lower portion trapezoidal in shape, wherein a top surface of the upper portion is higher than a top surface of the semiconductor die and a top surface of the lower portion is lower than the top surface of the semiconductor die; forming an underfill layer over the first side of the bottom package; patterning the underfill layer to expose upper portions of the metal bumps; mounting a top package on the bottom package, wherein the top package comprises a plurality of solder balls; and applying a reflow process so that the bottom package and the top package form a package-on-package structure, wherein the solder balls and respective metal bumps form a joint structure, and wherein the joint structure comprises the metal bump and a solder ball, and wherein, from a top view, a center of a top surface of the upper portion of the metal bump overlaps a center of the solder ball, and wherein the solder ball extends from a boundary of the upper portion and the lower portion of the metal bump.