Wafer Test Pad Contact Via Segmentation for Low-Force Probing
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Solution Overview
Problem
The introduction of three-dimensional integrated circuits (3DIC) leads to depth loading issues in wafer acceptance test (WAT) pads due to the planarization of passivation layers, requiring excessive probing force that can damage probe cards.
Innovation Solution
A WAT pad is electrically coupled to a top metal layer via a plurality of smaller contact vias, distributing them over the pad to avoid depth loading effects, ensuring minimal probing force is required for access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If passivation layers are planarized to provide a substantially planar top surface for 3DIC stacking, then planarity is improved, but excessive probing force is required to access WAT pads causing probe card damage
Solution Approach 1:
The patent segments the single large WAT pad into multiple smaller WAT pads arranged in an array. This segmentation allows the probing force to be distributed across multiple smaller contact points rather than concentrated on one large pad, reducing the force required per probe and preventing probe card damage while maintaining electrical connectivity to the underlying metal layer through the planarized passivation structure.
2Reliability
If a single large via is used to access the WAT pad through the planarized passivation layer, then electrical connectivity is achieved, but depth loading effects cause excessive probing force requirements
Solution Approach 1:
The patent divides the single large via structure into multiple smaller vias that are distributed across the passivation layer. Each smaller via provides a separate electrical connection path to the underlying metal layer, collectively achieving the same electrical connectivity function while distributing the mechanical probing force across multiple points, thereby reducing depth loading effects and the force required per probe.
Data Source
AI summary
A redistribution structure is provided. A redistribution structure according to the present disclosure includes a first dielectric layer, a mesh metal feature disposed in the first dielectric layer and including a base portion and a frame portion surrounding the base portion, a second dielectric layer disposed over the first dielectric layer and the mesh metal feature, a redistribution feature disposed over the second dielectric layer, a passivation structure disposed over the redistribution feature and the second dielectric layer, a pad opening extending through the passivation structure to expose a top surface of the redistribution feature. The redistribution feature includes a plurality of contact vias that extend through the second dielectric layer to land on the frame portion of the mesh metal feature.