Instead of the operator viewing the superimposed alignment of the bumps and pads, the alignment regiment may require the operator to use fiducial recognition. In this case, the vision system looks at two or more registration marks that have been added along the periphery of the substrate's artwork. User-defined fiducials may be used for locating flip chip bumps and flex pads prior to placement. The pattern of the chip's bumps and flex pads are drawn, then added to the fiducial library. Any distinctive artwork feature, such as traces or pads, is learned by the vision system and used to locate the component placement position.
Pattern recognition is very user-friendly and versatile.
With a semiautomatic system equipped with a cube beam splitter, the operator initiates the placement cycle once the bump and pads are in alignment. The viewer retracts and the pickup head holding the chip lowers to gently place the chip onto the flex bond pads under a preprogrammed load. To ensure good reflow, each of the chip bumps must be touching a bond pad on the substrate. When solder is used, applying only a small amount of bond load and then retracting is necessary. However, for some applications the chip needs to be held at a higher bond load.