Conformal Probe Card for μLED Single Touchdown Testing
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Solution Overview
Problem
Conventional probe cards are inadequate for simultaneously contacting and testing the large number of discrete semiconductor devices on highly-scaled monolithic μLED devices, such as those used in near-eye displays, due to their small feature sizes and high density, which limits their ability to efficiently screen and characterize these devices in a single 'touchdown' event.
Innovation Solution
The development of enhanced probe cards with an electrically-conductive, conformal, and elastic film that can simultaneously contact and provide input signals to all discrete semiconductor devices on a μLED die, utilizing either isotropic or anisotropic conductivity to enable testing and screening of individual μLEDs without damaging the contact pads, even in the presence of debris or variations in pad size and shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional probe cards are used to test highly-scaled monolithic μLED devices, then the testing process becomes simpler, but the ability to simultaneously contact and test all discrete semiconductor devices is insufficient due to small feature sizes and high density
Solution Approach 1:
The patent employs a conformal and elastic film as the contact element of the probe card. This flexible film can simultaneously conform to and make electrical contact with the small, densely-pitched contact pads on highly-scaled μLED devices, enabling reliable testing of all discrete semiconductor devices in a single touchdown event without damaging the pads
Solution Approach 2:
The probe card contact structure is divided into multiple discrete contact regions corresponding to individual μLED devices. Each region of the conformal film can independently contact its corresponding contact pad, allowing simultaneous addressing and testing of numerous discrete semiconductor devices across the monolithic substrate
2Productivity
If conventional probe cards attempt to contact small, densely-pitched contact pads, then the number of devices tested increases, but the risk of damaging contact pads increases
Solution Approach 1:
The elastic conformal film provides a compliant contact interface that adapts to the precise geometry of each contact pad without exerting excessive localized stress. This flexibility enables the probe card to safely contact numerous small, densely-pitched pads simultaneously while minimizing the risk of mechanical damage to the fragile contact structures
Solution Approach 2:
The conformal and elastic nature of the contact film provides inherent cushioning and stress distribution before contact is made. The film's elasticity allows it to deform and accommodate minor variations in pad height and position, preventing concentrated stress points that could cause damage during the touchdown event
3Ease of manufacture
If isotropic conductivity is used in the probe card contact, then manufacturing is simpler, but the ability to individually address and sense current draw from each discrete device is reduced
Solution Approach 1:
The probe card contact structure incorporates regions with different electrical conductivity characteristics. By creating anisotropic conductivity patterns in the conformal film, the system enables individual addressing and current sensing for each discrete μLED device while maintaining the overall conformal contact structure. This local differentiation of electrical properties allows precise control and measurement without compromising manufacturing feasibility
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
These enhanced probe cards allow for efficient and reliable testing and characterization of μLED devices by enabling a single 'touchdown' event to contact and test all discrete semiconductor devices on a die, reducing testing time and minimizing damage to the contact pads, while providing accurate electrical and optical measurements.
Implementation Method 1
The first contact may include a conformal and/or elastic sheet and/or film
Implementation Method 2
The embodiments include isotropic embodiments, where the electrical conductivity of the first contact is isotropic, and anisotropic embodiments, where the electrical conductivity of the first contact is anisotropic. As discussed throughout and due to the anisotropic conductivity of the first contact, the anisotropic embodiments may be enabled to individually address and sense the electrical current draw from each of the discrete semiconductor devices of the DUT
Data Source
AI summary
Enhanced probe cards, for testing unpackaged semiconductor die including numerous discrete devices (e.g., LEDs), are described. The die includes anodes and cathodes for the LEDs. Via a single touchdown event, the probe card may simultaneously operate each of the LEDs. The LEDs' optical output is measured and the performance of the die is characterized. The probe card includes a conductive first contact and another contact that are fabricated from a conformal sheet or film. Upon the touchdown event, the first contact makes contact with each of the die's anodes and the other contact makes contact with each of the die's cathodes. The vertical and sheet resistance of the contacts are sufficient such that the voltage drop across the vertical dimension of the contacts is approximately an order of magnitude greater than the operating voltage of the LEDs and current-sharing between adjacent LEDs is limited by the sheet resistance.