The automatic measurement device for wire tail length and free air ball size on a wire bonder operates through visual imaging, displacement sensing, and closed-loop control logic. It captures real-time parameters such as residual wire tail length, ball diameter, roundness, and height, performs automatic error judgment, and feeds back adjustments to the wire bonder process.
1. Wire Tail Length Measurement Principle
1.1 Detection Process
After the wire bonding of a single die is completed, the wire clamp releases the wire, and the bond head moves to the preset inspection station while carrying the wire with the residual tail.
A CCD area scan camera captures a high-resolution image of the tail area. Through edge extraction and contour matching algorithms, the system locates the bonded ball and the wire break point at the clamp, then calculates the axial distance between them, which is the residual wire tail length.
For highly reflective gold wire, some systems use a contact displacement probe to measure the tail length by detecting the displacement difference at the tail end, avoiding interference from light reflection.
1.2 Error Judgment and Process Feedback
The measured value is compared with a preset tolerance, typically 0.3 to 0.8 times the wire diameter in accordance with IPC-A-610E 2020 electronic packaging process requirements. If the value exceeds the threshold, the system triggers an audible and visual alarm or automatically adjusts the wire feed length for the next cycle.
2. Ball Size Measurement Principle
2.1 Detection Process
After the free air ball is formed by electric spark discharge at the wire end, the bond head moves the ball to the inspection station.
Images are captured from both vertical and lateral directions. A sub-pixel edge detection algorithm extracts the ball contour and calculates diameter, roundness, and protrusion height relative to the bond head end face.
Advanced high-speed wire bonders may also use laser displacement sensors to scan the three-dimensional profile of the ball and obtain micron-level dimensional data.
2.2 Error Judgment and Process Feedback
The measured dimensions are compared with standard parameters. The ball diameter should normally be 1.2 to 2.5 times the wire diameter, and roundness error should not exceed 5%. If the ball size is out of specification, the system automatically adjusts the electric spark current and burning duration. Some models will also skip the subsequent bonding process for the defective ball.
3. Integrated Control Logic
The inspection data of tail length and ball size are transmitted in real time to the PLC control system of the wire bonder, forming closed-loop feedback for process control.
Multiple sets of inspection data are simultaneously stored in the factory MES for process traceability and statistical process control analysis.
The inspection unit for high-speed wire bonders can complete detection of a single bonding point within 50 ms, ensuring no negative impact on overall production rhythm.
For non-standard visual inspection fixtures, sensor mounting brackets, or calibration blocks used in these measurement devices, Hansheng Automation can provide custom-machined parts according to equipment specifications to support stable measurement repeatability.
