Probe Card Space Transformers for Thermal Distortion
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Solution Overview
Problem
Conventional probe cards face issues with thermal distortion and complex fabrication, particularly when testing larger wafers with smaller chip pads, leading to probe tip misalignment and difficulty in repair.
Innovation Solution
A modular probe card design featuring space transformers with a multi-layered printed circuit board, interposer array, and flatness adjustment screws, utilizing materials with low thermal expansion coefficients like Invar and Kovar to minimize thermal mismatch and facilitate easy repair by replacing individual probe units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional probe card with ceramic substrate is used, then thermal expansion matching is improved, but probe tip misalignment occurs due to excessive thermal expansion difference between silicon and ceramic
Solution Approach 1:
The patent changes the material parameter (thermal expansion coefficient) by using Invar alloy instead of conventional ceramic. Invar has a thermal expansion coefficient of about 1.2 ppm/°C, which is much closer to silicon's 2.6 ppm/°C than ceramic's 6.0 ppm/°C, thereby resolving the thermal mismatch problem and preventing probe tip misalignment during temperature changes
Solution Approach 2:
The patent employs composite material structure by combining Invar alloy with other materials in the probe card assembly. The Invar substrate is used specifically for its low thermal expansion properties to match silicon, while other materials are used for their respective advantages, creating a composite structure that optimizes both thermal stability and mechanical properties
2Stability of the object's composition
If cantilever-type probes are bonded on ceramic substrate, then thermal mismatch is minimized, but fabrication complexity and repair difficulty increase
Solution Approach 1:
The patent divides the probe card into modular probe units, each containing probes mounted on individual Invar substrates. This segmentation allows each probe unit to be independently fabricated, tested, and replaced, significantly simplifying the overall fabrication process and enabling easy repair by replacing only defective probe units rather than the entire probe card
Solution Approach 2:
The patent introduces an intermediary Invar substrate layer between the probes and the final mounting structure. This Invar substrate serves as a mediator that provides both thermal expansion matching and a standardized mounting interface, simplifying the bonding process and enabling modular probe unit construction that facilitates repair
3Area of stationary object
If probe card size increases for larger wafers, then testing capability is improved, but thermal distortion and probe misalignment worsen
Solution Approach 1:
The patent changes the thermal expansion parameter of the substrate material to Invar alloy, which has a thermal expansion coefficient closely matching silicon. This parameter change ensures that even as the probe card size increases to accommodate larger wafers, the thermal distortion remains minimal and probe tip alignment with chip pads is maintained across the entire card area
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 design effectively mitigates thermal distortion and simplifies fabrication and repair processes, ensuring stable contact with chip pads and improving test performance by allowing for precise flatness adjustment and easy replacement of probe units.
Implementation Method 1
the thermal expansion coefficients of the silicon and ceramic are 2.6 ppm/°C and 6.0 ppm/°C, respectably. For example, when the temperature increases about 150 degree, the position displacement around the edge of the 12 inch wafer are 59 μm and 153 μm for the ceramic and the silicon
Data Source
AI summary
A probe card of a semiconductor test apparatus having a plurality of space transformers supporting probe units of the probe card is provided. A probe card of the present invention includes a plurality of probe units, each comprising a guide member and at least one probe secured by the guide member and contacting a chip pad to be tested; a plurality of space transformers arranged below the respective probe units, each space transformer having wires electrically connected to lower terminals of the probes; a frame having a plurality of guide holes for fixedly positioning the respective probe units; an interposer array arranged below the space transformers for supporting the space transformers, interposer array comprising electrical connection means for supplying test signals to the wires of the space transformers; and a printed circuit board arranged below the interposer array for supporting the interposer array and electrically connected to the electrical connection means for supplying the test signals. In the probe card of the present invention, the probe units are independently supported by respective space transformers such that it is possible to reduce thermal distortion of the probe card and simplifying the manufacturing and repairing processes.