Conventional die attach machines are used in automated semiconductor equipment to accurately deliver components, such as semiconductor dice, onto semiconductor substrates (e.g., lead frames). An example of such conventional die attach machines is a die bonding machine, which transfers cut or sawn wafer dice or chips from a wafer table onto a substrate in a pick-and-place operation. Typically, a bonding device having a bond arm and a bond head is used to perform a pick-and-place operation.
During a pick-and-place motion, in order to ensure the placement and rotation accuracy, usually alignment is performed between a pick-up position and a placement position. At the pick-up position, the bonding device using the bond head detaches a die from for example an adhesive tape on which the die is mounted. In conventional methods for die rotation recognition and die center measurement, an up-look camera is used. To capture an image of edges of the die from a bottom side of the die, the bond arm holding the die using the bond head, moves to an up-look position or photo capture position after picking up the die and before placing the die at a target position. At the up-look position, the die is typically placed at a station for measurement of the orientation of the die. A mirror and a look-up camera located underneath the die are commonly used to capture an image of the die from a bottom side thereof. The mirror is positioned to project an image of the die to the look-up camera. At the up-look position a two dimensional image (also referred to herein as a 2D image) of a bottom surface of the die is captured. The bottom surface of the die is referred to herein as a surface of a die facing away from the bond head.
For a precise bonding, it is important that the die to be bonded is correctly aligned before bonding and that a bonding position, for example a center of the die, is reliably determined. Conventionally, the center and the orientation of the die are calculated from 2D image data captured by an up-look camera. Before bonding the die at the bonding position and during movement of the die from the up-look position to the bonding position, the bond head is used to adjust orientation of the die, for example an angle about the Z-axis of the bond head, and an X-Y-position of the die in an Cartesian X, Y, Z coordinate system stated in metric units.
However, this approach, which relies on the bottom edges of the die, imparts an uncertainty and variation in determining the position of the die and a center of the die. Since semiconductor dice are usually sawn from a wafer, edges of the dice are often not even after the sawing process. In particular, the shapes of top and bottom surfaces of a die may differ from each other. Illustratively, after a sawing process, the die does not have a shape of a rectangle from a side view, but may rather have a shape of a trapezoid. That means a width of the die at a bottom surface of the die may be smaller than a width of the die at a top surface of the die, or vice versa. When the center of the die is calculated from a 2D image captured from a bottom side of the die, the shape of the die at a top side thereof is not taken into account. Thus, calculation of the center of a die according to the prior art typically does not take into account the shape of the die at a top surface thereof.
Consequently, since the die is not correctly aligned, electrical contacts at a bottom surface of the die may not be correctly aligned to bonding contacts on a substrate in a bonding process due to misalignment of the die with bonding contacts on the substrate. Moreover, problems may occur when a die is bonded in a misaligned manner on a substrate by the bond head, and, thus, loss of productivity may result. Thus, errors in the calculation of a center of the die occur due to differences between the top and bottom surfaces of the die. As a result, the bottom surface of the die is not reliable for calculating a center of the die. In addition, an up-look station including an up-look camera is needed between the die picking and bonding positions. Therefore, additional time is spent at the up-look station leading to the loss of throughput and resulting in higher costs.