Bond Wire Loop Height Measurement Using Optical Focusing
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Solution Overview
Problem
Existing methods for measuring the loop height of bonded wires, especially in high-density semiconductor designs with overlapping wires, are inaccurate, cumbersome, and unable to handle multiple planes, leading to complex and costly inspection processes.
Innovation Solution
A method utilizing an optical system with XY & Z motor integration to capture focused images at multiple planes, combined with low-angle illumination and interpolation of coordinates, allows for precise measurement of bond wire profiles, including those obstructed by overlapping wires, and enables faster inspection by focusing on critical areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If prior art methods (U.S. Pat. No. 7,145,162 B2) are used to measure wire loop height with reflected light and height gauges, then measurement capability is provided, but the apparatus is bulky, requires frequent calibration, is complex to control and setup, and has high cost making the design difficult to scale
Solution Approach 1:
The patent replaces the mechanical height gauge system with an optical imaging system consisting of a camera, light source, and lens. Instead of using physical contact measurement with a height gauge, the system captures images of the wire loops and calculates heights through image processing and coordinate transformation, eliminating the need for mechanical calibration and reducing apparatus complexity.
Solution Approach 2:
The patent creates an optical copy (image) of the wire loop structure and processes this copy to extract measurement information. By capturing images at different focal planes and processing them through coordinate transformation, the system obtains height measurements without direct mechanical interaction, simplifying the measurement process and reducing calibration requirements.
2Measurement precision
If the optical device is moved up and down to obtain a focused image of the dark area for height determination, then height measurement is achieved, but the imaging system becomes bulky resulting in reduced speed of inspection
Solution Approach 1:
The patent uses periodic focusing at multiple discrete focal planes (first focal plane, second focal plane, etc.) to capture images at different depths. Instead of continuous movement, the system performs periodic image capture at specific focal positions, then uses coordinate transformation to calculate heights, maintaining measurement precision while improving inspection speed.
Solution Approach 2:
The patent performs preliminary image capture at multiple focal planes before conducting the actual height calculation. By pre-capturing the necessary image data at different depths and storing the coordinate information, the system prepares all required measurement data in advance, enabling faster processing and reducing inspection time.
3Measurement precision
If low-angle illumination with shallow focal depth is used for single plane bonding wire measurement, then height determination is possible, but the concept cannot be applied to overlapping bond wires in multiple planes
Solution Approach 1:
The patent extends the measurement from a single plane to multiple planes by introducing the focal depth dimension. By capturing images at different focal planes (Z-axis) in addition to the standard X-Y plane, the system can distinguish between overlapping wires at different heights, enabling measurement of complex multi-plane wire structures that were previously inaccessible.
Solution Approach 2:
The patent changes the focal plane parameter (Z-coordinate) to access wires at different depths. By varying the focal distance and capturing images at multiple focal positions, the system can isolate and measure individual wires even when they overlap in the two-dimensional image plane, significantly expanding the applicability to complex wire configurations.
4Measurement precision
If multiple images at different focal planes are captured and coordinates are interpolated to determine wire profiles, then accurate measurement of overlapping wires is achieved, but processing complexity increases
Solution Approach 1:
The patent introduces coordinate transformation as an intermediary process between image capture and height measurement. By establishing a relationship between coordinates at different focal planes through transformation equations, the system creates a mathematical bridge that simplifies the extraction of wire profiles from multiple images, reducing the overall processing complexity despite capturing multiple focal planes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate and consistent measurement of bond wire loop heights across multiple planes, increasing inspection speed and reducing errors, while maintaining high precision and reliability.
Implementation Method 1
the reflected light incident from the wire loop is coupled to a height gauge
Implementation Method 2
the focus of an optical means is brought into a desired point of the object to be inspected
Implementation Method 3
the focal depth of the optical device is designed to be shallow. A dark area appears in the central portion of the wire at the focal point of the optical system
Data Source
AI summary
An apparatus and method for measuring loop height of overlapping bonded wires, interconnecting the pads of a single or stacked silicon chips to the pads of a substrate taking the steps of: focussing of an optical assembly at multiple points of the bond wire including overlapping bond wires, capturing an image of the bond wire at each of the predetermined focused points; calculating the height of each point of the wire with respect to a reference plane; and tabulating the height data using the X, Y and Z coordinates.