Copper Pillar Interconnect Structure for Fine-Pitch Solder Wetting
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Solution Overview
Problem
Semiconductor device packages face challenges in accommodating sophisticated features that impact reliability, performance, and cost, particularly in forming fine-pitch interconnects with minimal solder bridging and voiding.
Innovation Solution
The formation of copper pillars with a proximal and distal portion, where the distal portion has a roughened sidewall surface to promote solder wetting, allowing for a slim profile and fine-pitch arrangement that minimizes solder bridging and voiding, while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If copper pillars are arranged in fine-pitch configuration, then interconnect density and performance are improved, but solder bridging risk increases
Solution Approach 1:
The copper pillar distal portion is selectively roughened only on its sidewalls, creating localized surface quality variation. This local roughening promotes solder wetting precisely where needed (on the pillar sidewalls) while maintaining smooth top and bottom surfaces for reliable bonding interfaces, thus enabling fine-pitch arrangements without increasing solder bridging risk
Solution Approach 2:
The sidewall roughening is performed in advance before the final soldering process. This preliminary surface treatment prepares the copper pillar distal portion to actively promote solder wetting during subsequent reflow, ensuring that even in fine-pitch configurations, solder flows properly along the roughened sidewalls without bridging to adjacent pillars
2Reliability
If copper pillar distal portion is roughened to promote solder wetting, then solder joint reliability is improved, but manufacturing complexity increases
Solution Approach 1:
Rather than roughening the entire copper pillar surface or using complex multi-step processes, the invention selectively roughens only the distal portion sidewalls. This localized treatment achieves the solder wetting promotion function with minimal additional manufacturing complexity, as it can be accomplished through targeted etching or surface treatment processes applied only to the distal region
Solution Approach 2:
The invention changes the surface roughness parameter of the copper pillar distal portion sidewalls. By controlling the roughness parameter (creating a roughened surface with increased surface area and irregular topology) only in the distal region, the process achieves improved solder wetting without requiring fundamental changes to the overall manufacturing flow, thus balancing reliability improvement with acceptable manufacturing complexity
3Manufacturing precision
If copper pillars are formed with proximal and distal portions, then solder profile control is improved, but manufacturing precision requirements increase
Solution Approach 1:
The copper pillar is designed with asymmetric geometry, featuring a proximal portion with a first cross-sectional area and a distal portion with a second cross-sectional area that is smaller than the first. This asymmetric design allows the pillar to accommodate varying solder volumes and control the solder reflow profile effectively, as the smaller distal area naturally constrains solder flow while the larger proximal area provides structural support and manufacturing tolerance buffer
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 solution enables reliable and stress-free conductive connections with minimal solder bulging, ensuring superior structural integrity and reliability in fine-pitch arrangements.
Implementation Method 1
The distal portion of each copper pillar is subjected to a surface treatment configured to roughen the sidewall surface of the distal portion
Implementation Method 2
The roughened sidewall surfaces are configured to promote solder wetting
Implementation Method 3
Copper pillars are formed on seed layer portions over each UBM structure
Data Source
AI summary
A method of manufacturing a semiconductor device interconnect structure is provided. The method includes forming a copper pillar on a semiconductor die by way of a plating process. A proximal portion of the copper pillar has a first width dimension, and a distal portion of the copper pillar has a second width dimension. The second width dimension of the distal portion of the copper pillar is configured to be smaller than the first width dimension of the proximal portion of the copper pillar. Sidewalls of the distal portion of the copper pillar are selectively roughened. The roughened sidewalls of the distal portion of the copper pillar are configured to promote solder wetting.