Recessed Stack Via Structure Without Capture Pads

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Solution Overview

Problem

Conventional stack via structures require large capture pads for improved placement accuracy, which reduces design flexibility due to reduced routing space and increases stress on via bottoms, affecting reliability.

Innovation Solution

A stack via structure is proposed where vias are stacked directly on top of each other without intermediate capture pads, featuring a recess in the top via to accommodate the bottom portion of the upper via, enhancing structural integrity and design flexibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If large capture pads are used for stack vias, then placement accuracy is improved, but routing space is reduced and design flexibility is worsened

Engineering Contradiction:

Improveplacement accuracyVSAvoiddesign flexibility

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent extracts the capture pad from the conventional stack via structure, eliminating the need for large landing pads. The via structure directly connects to the pad without requiring an intermediate capture pad, thereby removing the constraint that forced large pad dimensions while maintaining placement accuracy through direct via-to-pad alignment.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a recess feature in the via wall that extends in the vertical dimension, allowing the via to mechanically interlock with the pad structure. This vertical dimension solution provides structural support and alignment without requiring increased horizontal pad area, thus preserving routing space and design flexibility.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If large capture pads are used for stack vias, then placement accuracy is improved, but stress on via bottoms is increased, affecting reliability

Engineering Contradiction:

Improveplacement accuracyVSAvoidvia bottom stress

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies a recess feature locally at the via bottom region, creating a localized structural modification that redistributes stress. The recessed portion provides mechanical support and stress relief at the critical via-bottom interface without requiring overall via enlargement, thus maintaining reliability while enabling accurate placement.

Inventive Principle:

Principle #3Local quality

3Reliability

If conventional stack via structures are used, then via connectivity is achieved, but structural integrity is reduced due to stress concentrations

Engineering Contradiction:

Improvevia connectivityVSAvoidstructural integrity

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The recess feature acts as a pre-designed stress-relief structure that cushions mechanical loads before they reach the via bottom. This beforehand cushioning prevents stress concentration at the via-pad interface, protecting the via structure from failure while maintaining electrical connectivity and structural integrity.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS12230552B2Recess structure for padless stack via

Publication Date: 2025.02.18 QUALCOMM INC

AI summary

Disclosed is a stack via structure in which a plurality of vias are stacked over each other. At least one via is a via that has a recess formed from a top surface thereof. Another via above the via is formed such that a bottom portion of the another via is in the recess of the via. In this way, no capture pad is needed between the via and the another via. Also, contact area between the via and the another via is enhanced.