Under-Bump Package Structure for Void-Resistant Semiconductor Interconnects
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Solution Overview
Problem
Existing semiconductor packages face challenges in reliability and yield due to issues such as void formation, cracking, and delamination of under-bumps and external connection terminals.
Innovation Solution
The semiconductor package incorporates a redistribution substrate with a dielectric layer having inclined holes, under-bumps with specific geometries, and a barrier/seed layer to prevent metal diffusion and void formation, along with a wetting layer to enhance bonding and prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional under-bump structures are used, then manufacturing is simpler, but void formation and delamination occur reducing reliability
Solution Approach 1:
The under-bump structure is divided into multiple functional layers: barrier layer, wetting layer, and under-bump metallization layer. This segmentation allows each layer to perform its specific function (preventing diffusion, enhancing bonding, providing electrical connection) independently, thereby improving reliability without creating a monolithic complex structure that is difficult to manufacture.
Solution Approach 2:
A wetting layer is introduced as an intermediary between the external connection terminal and the under-bump metallization. This wetting layer acts as a mediator that prevents oxidation of the under-bump metallization and enhances bonding between the terminal and the bump structure, directly addressing the reliability issue of delamination and void formation.
2Productivity
If vertical holes are used in dielectric layer, then manufacturing is easier, but voids and cracking occur reducing yield
Solution Approach 1:
The hole in the dielectric layer is designed with an asymmetric inclined shape rather than a vertical cylindrical shape. The inner sidewall is inclined at a specific angle (45° to 85°) relative to the bottom surface, which prevents void formation and cracking during the bonding process. This asymmetric geometry accommodates the bonding process better and improves yield, while the inclination angle can be controlled during manufacturing to balance complexity and performance.
3Reliability
If barrier/seed layer is added, then metal diffusion is prevented improving reliability, but manufacturing steps increase
Solution Approach 1:
The barrier/seed layer performs multiple functions simultaneously: it acts as a diffusion barrier to prevent metal atoms from diffusing into the dielectric layer, serves as a seed layer for subsequent metallization deposition, and provides a transition interface between different materials. This multi-functionality reduces the need for separate layers, thereby limiting the increase in manufacturing steps while maintaining reliability.
4Reliability
If wetting layer is applied, then oxidation is prevented and bonding is enhanced, but additional manufacturing steps are required
Solution Approach 1:
The wetting layer is applied in advance before the bonding process to pre-prevent oxidation of the under-bump metallization and to pre-establish good bonding characteristics. By performing this protective action beforehand, the actual bonding process becomes more reliable and may even be simplified, as the preliminary wetting layer application ensures optimal bonding conditions are already in place.
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
This configuration enhances the reliability of the semiconductor package by reducing voids, cracking, and delamination, thereby increasing yield and ensuring stable electrical connections.
Implementation Method 1
a wetting layer between the external connection terminal and the under-bump
Implementation Method 2
a first barrier/seed layer between the under-bump and the first dielectric layer and between the under-bump and the wetting layer
Data Source
AI summary
Disclosed are semiconductor packages and methods of fabricating the same. The semiconductor package comprises a first redistribution substrate and a first semiconductor device on the first redistribution substrate. The first redistribution substrate includes a first dielectric layer that includes a first hole, an under-bump that includes a first bump part in the first hole and a second bump part that protrudes from the first bump part onto the first dielectric layer, an external connection terminal on a bottom surface of the first dielectric layer and connected to the under-bump through the first hole, a wetting layer between the external connection terminal and the under-bump, and a first barrier/seed layer between the under-bump and the first dielectric layer and between the under-bump and the wetting layer.