LED Array Probe Card for CMOS Image Sensor Wafer Testing
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Solution Overview
Problem
Conventional testing of CMOS image scan devices using halogen lamps is inefficient due to large size, high maintenance requirements, and difficulty in reconfiguring test setups, especially in wafer-scale device testing.
Innovation Solution
The use of a light emitting diode (LED) array as a light source for CMOS image scan device testing, where each LED corresponds to a CIS device chip, with phosphor illumination, aperture + lens arrangement for telecentric light, and uniformity filters for improved illumination uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a halogen lamp is used as the light source for CIS device testing, then sufficient illumination can be provided, but the system becomes large in size and requires significant maintenance
Solution Approach 1:
The single halogen lamp is segmented into multiple individual LED light sources, with each LED corresponding to a specific CIS device chip. This segmentation allows for a compact array configuration that provides sufficient illumination while dramatically reducing the overall system size and maintenance requirements compared to a single large halogen lamp.
Solution Approach 2:
The halogen lamp (thermal radiation source) is replaced with LED light sources (electroluminescence sources). This substitution transitions from a mechanical/thermal system to a solid-state electronic system, achieving compact size, low maintenance, and energy efficiency while providing adequate illumination for testing.
2Illumination intensity
If a halogen lamp is used for wafer-scale device testing, then illumination can be provided, but the system becomes difficult to reconfigure and requires significant maintenance
Solution Approach 1:
By segmenting the illumination system into individually addressable LED sources arranged in an array, each corresponding to a specific chip position, the system becomes highly reconfigurable. Test patterns can be easily modified by selectively activating different LED subsets, enabling flexible adaptation to various wafer sizes, chip layouts, and test requirements.
Solution Approach 2:
The LED array enables dynamic reconfiguration of the illumination pattern through electronic control. Different combinations of LEDs can be activated or deactivated programmatically, allowing the system to adapt to different testing scenarios, wafer sizes, and chip configurations without physical reconfiguration.
3Illumination intensity
If individual LED sources are used for each CIS device chip, then uniform illumination can be achieved, but the device complexity increases
Solution Approach 1:
Each LED in the array provides localized illumination optimized for its corresponding chip position. This local quality approach ensures uniform illumination across the entire wafer surface, with each LED tailored to illuminate its specific target area, compensating for variations in chip positions and orientations.
Solution Approach 2:
The LED array system serves multiple functions: it provides illumination for testing, enables selective activation of specific regions, supports different wafer sizes, and allows for flexible test pattern configuration. This multi-functionality justifies the increased device complexity by delivering comprehensive testing capabilities in a compact, reconfigurable platform.
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
The LED array provides a compact, low-maintenance, and easily reconfigurable light source that ensures uniform illumination across multiple CIS device chips, enhancing testing efficiency and reliability, especially in wafer-scale testing.
Implementation Method 1
The use of a light emitting diode (LED) array as a light source for CMOS image scan device testing
Implementation Method 2
The LEDs illuminate a phosphor which provides the light used for testing
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
Improved wafer-scale testing of optoelectronic devices, such as CMOS image scan devices, is provided. A probe card includes an LED light source corresponding to each device under test in the wafer. The LED light sources provide light from a phosphor illuminated by the LED. A pinhole and lens arrangement is used to collimate the light provided to the devices under test. Uniformity of illumination can be provided by closed loop control of the LED light sources using internal optical signals as feedback signals, in combination with calibration data relating the optical signal values to emitted optical intensity. Uniformity of illumination can be further improved by providing a neutral density filter for each LED light source to improve uniformity from one source to another and/or to improve uniformity of the radiation pattern from each LED light source.