Non-uniform Probe Card Pad Geometry Mitigates Misalignment
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Solution Overview
Problem
Probe pin to pad misalignment issues in automated test equipment (ATE) due to manufacturing errors and coefficient of thermal expansion (CTE) mismatch, leading to failed electrical contact during testing of semiconductor devices.
Innovation Solution
A non-uniform pad array design with elongated pads having unique spatial parameters such as tilt angles and varying widths based on distance from the center, which accommodates thermal expansion and manufacturing errors, ensuring reliable electrical contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform pad array design is used, then manufacturing is simpler, but probe pin to pad misalignment occurs due to thermal expansion and manufacturing errors
Solution Approach 1:
The pad array transitions from a uniform design to a non-uniform design where each pad's spatial parameters (tilt angle, width, position) are locally optimized based on its distance from the array center. Pads farther from the center have larger tilt angles and dimensions to compensate for greater thermal expansion and alignment errors, while central pads maintain smaller, more precise geometries. This local adaptation ensures reliable electrical contact across all pads despite manufacturing variations and thermal effects.
Solution Approach 2:
The invention systematically varies key geometric parameters of the pads including tilt angle, width, length, and position along the first direction. These parameters are not fixed but change continuously or discretely based on the pad's location in the array, specifically its distance from the centroid. This parameter modulation compensates for cumulative alignment errors and thermal expansion effects that increase with distance from the center.
2Reliability
If pads are made larger to accommodate misalignment, then electrical contact reliability improves, but the area available for other circuit elements decreases
Solution Approach 1:
Instead of uniformly enlarging all pads, the invention applies local quality by making each pad's dimensions proportional to its specific needs. Pads at the periphery, which experience greater misalignment, are enlarged in width and length, while central pads maintain compact sizes. This selective sizing achieves the necessary contact reliability where needed without unnecessarily consuming board area in regions where smaller pads suffice.
Solution Approach 2:
The pad geometry introduces asymmetry through non-zero tilt angles relative to the first direction, and asymmetric dimensioning where pads farther from the center have larger widths and lengths. This asymmetric design efficiently distributes the contact area where it is most needed for alignment tolerance, optimizing the trade-off between contact reliability and area utilization.
3Adaptability or versatility
If the probe card assembly uses multiple stacked circuit boards, then testing capability increases, but alignment precision between boards decreases
Solution Approach 1:
The non-uniform pad design acts as a pre-compensation mechanism that anticipates and cushions against cumulative alignment errors from multiple stacked boards. By incorporating larger tolerance margins in the form of tilted, elongated pads at critical locations, the design absorbs the effects of stacking misalignment before they can cause contact failures, thereby maintaining testing capability across multi-board assemblies.
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 non-uniform pad array design significantly reduces probe pin to pad misalignment, enhancing testing reliability by providing a larger conductive surface and maintaining minimum spacing from edges, thus ensuring consistent electrical contact across varying temperatures and manufacturing tolerances.
Implementation Method 1
mismatch of coefficient of thermal expansion
Data Source
AI summary
A probe card in an automated test equipment (ATE) and methods for operating the same for testing electronic devices. The probe card may be a portion of a vertical-type probe card assembly in which pads on a circuit board are contacted by probe pins. The probe card has a pad geometry that compensates for misalignment with corresponding probe pins due to manufacturing error or a mismatch of coefficient of thermal expansion, enabling reliable operation of the ATE over a wide range of test temperatures. The pad array may have a plurality of elongated pads, each of uniquely designed size, tilt angle, and/or center location, with the characteristics of each pad being dependent on a distance between each pad and a centroid of the pad array, such that a probe pin to pad location errors can be mitigated.