3D Shape Measuring Apparatus Using Subsidiary Reference Beam
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Solution Overview
Problem
Conventional three-dimensional shape measuring apparatuses using interferometry face challenges in measuring the overall shape of objects with stepped structures efficiently, particularly for components like ball grid arrays (BGAs), due to low inspection speed and poor reflectivity differences at the highest and lowest points, which hinder accurate measurement and speed up inspection processes.
Innovation Solution
A three-dimensional shape measuring apparatus that employs a subsidiary reference beam generating unit with a plate beam splitter and a compensation plate to adjust focal distances and optical paths, allowing for simultaneous generation of interference patterns at the highest and lowest points of a target object by creating reference beams with the same focal distances and optical paths as the object beams, thereby improving measurement speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single interference pattern is obtained by joining the interference patterns for the highest point and the lowest point separately, then measurement accuracy is improved, but inspection speed deteriorates
Solution Approach 1:
The reference beam is divided into multiple beams (first reference beam and second reference beam) with different optical paths, allowing simultaneous measurement of multiple height levels. The plate beam splitter segments the reference beam to create separate measurement channels for the highest point and lowest point of the stepped structure.
Solution Approach 2:
The invention adds an optical path dimension by creating reference beams with different path lengths (first reference beam path and second reference beam path). This enables simultaneous interference pattern generation for different height levels by utilizing the additional optical path dimension rather than sequential measurement.
2Measurement precision
If the reflectivity of the reference surface coincides with the reflectivity of the highest point or lowest point, then measurement of that point is improved, but measurement of the other point deteriorates
Solution Approach 1:
The reference beam is segmented into multiple beams with different optical paths, allowing each segment to be optimized for different reflectivity conditions. This enables simultaneous measurement of points with different reflectivities by assigning appropriate reference beams to each measurement point.
Solution Approach 2:
Different reference beams are assigned to different measurement locations (highest point and lowest point) based on their local reflectivity characteristics. The first reference beam is optimized for one reflectivity condition while the second reference beam is optimized for another, allowing each local measurement to have optimal quality.
3Measurement precision
If the optical path length of the reference beam is adjusted to match the highest point, then measurement of the highest point is improved, but measurement of the lowest point deteriorates
Solution Approach 1:
The reference beam is divided into multiple segments (first reference beam and second reference beam) with different optical path lengths. Each segment is optimized for measuring specific height levels, allowing simultaneous accurate measurement of both highest and lowest points without compromising reliability.
Solution Approach 2:
The invention introduces an optical path length dimension by creating reference beams with deliberately different path lengths. This allows the system to simultaneously satisfy the optical path matching condition for both the highest point and lowest point by utilizing multiple reference beams with varying path lengths.
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 solution enables simultaneous interference pattern generation for both the highest and lowest points of a target object, enhancing inspection speed and efficiency by ensuring accurate measurement of stepped structures, even when reflectivity differences exist, and maintaining consistent beam characteristics.
Implementation Method 1
illumination light emitted from a light source is split into beams by a beam splitter
Implementation Method 2
a reference beam and an object beam respectively reflected by the reference mirror and the surface of the target object are joined by the beam splitter and interfere with each other to generate an interference pattern
Data Source
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AI summary
The three-dimensional shape measuring apparatus includes a light source; a beam splitter to split illumination light from the light source; a target object to be measured, having a height difference between the highest point and the lowest point; a reference mirror, on which another beam emitted from the beam splitter is irradiated; a light detecting element to detect an interference pattern generated by the interference of an object beam reflected by the surface of the target object and a reference beam reflected by the surface of the reference mirror; and a control computer to process an image detected by the light detecting element, wherein a subsidiary reference beam generating unit to change the optical path of the beam from the beam splitter to generate a subsidiary reference beam is provided between the beam splitter and the reference mirror.