A reflow oven replaces the solder wave. Solder alone forms the electrical and mechanical link between the BGA and the underlying circuit board. Thus, BGA manufacturers must use exactly the right size solder balls, and they must position them properly. To ensure the quality of the small solder balls and their proper placement, they rely on automated inspection systems. The system may come as part of the BGA assembly equipment, or the BGA manufacturer may have added it later.
Many companies supply complete inspection systems as well as individual machine-vision components.
A wire bonder connects the die's contacts to contacts on the substrate. Instead of individual fragile leads such as those found on the outside edges of a quad flatpack, the BGA package provides an array of conductive pads on its underside. An epoxy material encapsulates the assembly. Solder balls attached to the opposite side of the substrate provide electrical and mechanical connection to a larger PCB that holds other circuitry. BGAs may have hundreds of individual pads, so inspection for proper solder-ball placement is a must.