June 12, 2012 — Electronics manufacturing and design services provider ESCATEC added package-on-package (PoP) capability at its Heerbrugg, Switzerland, facility, adding a dipping unit for ball grid array (BGA) packages on its Siplace assembly line.

Figure 1. PoP stack before soldering.

The dipping unit wets about 50% of each ball on the package with paste/flux. Before reflow, both BGA components are stacked on each other and then both are soldered in one process step. During the soldering, the upper device sinks down, eliminating any gap between the stacked packages in the final assembly.

Figure 2. PoP stack after flow soldering.

Verification of accurate bonding between the layers of the PoP stack is checked using X-Ray inspection. Darker balls in Figure 3 are from the upper BGA and lighter balls are from the lower BGA.

Figure 3. Xray of PoP stack.