Stepped Metal Pillars to Prevent Solder Sidewall Wetting

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Solution Overview

Problem

The challenge in packaging integrated circuits is the wetting of solder regions on the sidewalls of metal pillars, which can hinder the allocation of Independent Passive Devices (IPDs) due to insufficient standoff height.

Innovation Solution

The formation of metal pillars with lower portions wider than upper portions, featuring stepped sidewalls with controlled slant angles, prevents solder wetting and increases standoff height, allowing space for IPDs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If metal pillars with vertical sidewalls are used, then manufacturing is simple, but solder wetting occurs on sidewalls reducing standoff height

Engineering Contradiction:

Improvestandoff heightVSAvoidmetal pillar structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The metal pillar sidewalls are formed with asymmetric angles relative to the vertical axis. The first sidewall has a first angle and the second sidewall has a second angle, where the angles are different. This asymmetric configuration prevents solder from wetting uniformly on both sidewalls, thereby maintaining adequate standoff height while avoiding the complexity of completely redesigning the pillar structure.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The angles of the sidewalls are specifically controlled within certain ranges (e.g., 80-85 degrees for the first sidewall, 85-90 degrees for the second sidewall) to optimize solder behavior. By adjusting these angular parameters, the patent achieves prevention of solder wetting while maintaining manufacturability through standard fabrication processes.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If solder regions wet on sidewalls of metal pillars, then manufacturing is easier, but space for IPDs is insufficient

Engineering Contradiction:

Improvesoldering processVSAvoidspace for IPDs

Core Design Contradiction:

Ease of manufactureVSArea of stationary object

Solution Approach 1:

By creating asymmetric sidewall angles, the patent controls solder flow during the soldering process. The unequal angles cause solder to preferentially wet one sidewall over the other, preventing complete circumferential wetting. This maintains adequate spacing for IPDs while still allowing the soldering process to proceed with standard manufacturing techniques.

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS20250336818A1Metal pillars preventing wetting on sidewalls and method forming same

Publication Date: 2025.10.30 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A package includes a first package component, which includes a bottom dielectric layer, a micro-bump protruding below the bottom dielectric layer, and a metal pillar protruding below the bottom dielectric layer. The metal pillar has a top width and a bottom width greater than the top width. The package further includes a die underlying and bonding to the micro-bump, a solder region underlying and joining to a bottom surface of the metal pillar, and a second package component underlying the first package component. The second package component includes a conductive feature underlying and joining to the solder region.