Wafer Probe Magnetic Circuit Testing with Adaptive Field Compensation
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Solution Overview
Problem
Wafer probe testing of magnetic circuits is costly and inaccurate due to variations in the magnetic field at different test sites and with magnet rotational angle, temperature, probe needle height, and calibration, which affect the accuracy of test results.
Innovation Solution
A wafer probe test system with a rotary magnet, magnetic sensor, and controller that measures and models magnetic flux density in multiple directions as a function of rotational angle and probe needle height, allowing concurrent testing of multiple sites with adaptive magnetic field compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If multiple sites are tested concurrently in a single touch-down, then testing time is reduced, but variations in magnetic field at different sites and with magnet rotational angle affect test accuracy
Solution Approach 1:
The system dynamically adjusts test parameters including magnetic field strength, rotational angle, and probe needle height to compensate for variations across different test sites. The controller modifies these parameters in real-time based on feedback from magnetic sensors to maintain consistent test conditions despite concurrent multi-site testing
Solution Approach 2:
Magnetic sensors provide real-time feedback on the magnetic field conditions at each test site during concurrent testing. The controller uses this feedback to adjust the magnet rotation and probe positioning, ensuring accurate measurements across all sites simultaneously tested
2Loss of time
If testing is performed during less than a full rotation of the magnet, then testing time is reduced, but variations with magnet rotational angle affect test accuracy
Solution Approach 1:
The system performs preliminary characterization of the magnetic field across different rotational angles before actual testing. This pre-established data is stored and used to select optimal rotation angles for testing, allowing accurate measurements to be obtained during a partial rotation rather than requiring a full 360-degree rotation
Solution Approach 2:
The controller dynamically adjusts the magnet rotational angle parameter during testing based on pre-characterized field distributions. By selecting specific angular positions where the magnetic field provides optimal sensitivity for the test, accurate measurements are achieved without requiring complete rotation cycles
3Adaptability or versatility
If probe needle height varies, then testing can accommodate different wafer positions, but variations in applied magnetic field affect test accuracy
Solution Approach 1:
Magnetic sensors measure the actual magnetic field strength at each test site, providing feedback on the effect of probe needle height variations. The controller uses this feedback to compensate for field strength changes by adjusting test parameters or magnet positioning, maintaining measurement accuracy despite height variations
Solution Approach 2:
The system adjusts multiple parameters including magnet-to-wafer distance, rotational angle, and magnetic field strength in response to detected probe needle height variations. These dynamic parameter changes compensate for the altered magnetic field conditions caused by height variations, preserving test accuracy
4Productivity
If calibration readings are taken with in-line or on-board magnetic sensors, then testing efficiency is improved, but variations in calibration readings affect test accuracy
Solution Approach 1:
The system continuously monitors calibration readings from in-line or on-board magnetic sensors and uses this feedback to detect drift or variations. When variations are detected, the controller automatically adjusts test parameters or triggers recalibration, maintaining measurement accuracy while preserving the efficiency benefits of continuous monitoring
Solution Approach 2:
The magnetic sensors perform self-calibration by comparing their readings against reference values stored in the controller. This automatic self-correction eliminates the need for manual recalibration while maintaining measurement accuracy, thereby preserving testing efficiency without sacrificing precision
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 enables accurate and efficient testing of magnetic sensing performance across multiple sites, reducing testing time and costs by compensating for variations in the magnetic field and hardware performance, ensuring reliable pass/fail assessments independent of probe hardware variations.
Implementation Method 1
the rotary magnet is rotatable around an axis of an orthogonal third direction to provide a magnetic field to the wafer
Implementation Method 2
measuring a magnetic field of a rotary magnet rotating about an axis along the third direction at different rotational angles using a magnetic sensor of the wafer probe test system
Data Source
AI summary
A wafer probe test system having a probe card with a probe head, a rotary magnet, a magnetic sensor positioned to sense the magnetic field of the rotary magnet and a controller coupled to the probe card, where the probe head has probe needles to engage features of test sites of a wafer in a wafer plane of orthogonal first and second directions, and the rotary magnet is rotatable around an axis of a third direction to provide a magnetic field to the wafer, in which the controller includes a model of magnetic flux density in the first, second and third directions at the respective test sites of the wafer as a function of a rotational angle of the rotary magnet, a probe needle height along the third direction and a measured magnetic flux density of the magnetic sensor.