Underfill Anchor Structures in Chip Packages for Stress Relief
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The underfill material between an interposer and a semiconductor die is prone to mechanical and thermal stress, leading to potential cracks and package failure due to inadequate stress absorption.
Innovation Solution
Forming recesses on the surface of the interconnect-containing structures, such as interposers or packaging substrates, which are filled with downward-protruding anchor portions of the underfill material, thereby reducing thermal and mechanical stress and preventing delamination or cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If underfill material is used between interposer and semiconductor die, then mechanical stress absorption is improved, but cracks may still form in the underfill material leading to package failure
Solution Approach 1:
The underfill material is segmented into multiple discrete anchor portions that protrude downward into recesses formed in the interposer. These segmented anchor portions are distributed at different locations rather than forming a continuous mass, allowing stress to be distributed across multiple discrete stress absorption points rather than concentrating in a single location, thereby preventing crack propagation through the entire underfill structure
Solution Approach 2:
The underfill material is configured with different local properties: the anchor portions have a first cross-sectional area and are positioned to absorb stress at critical locations near the interposer interface, while the body portion has a different cross-sectional area and provides overall structural support. This local differentiation allows optimal stress absorption at the interface without compromising the overall structural integrity
2Reliability
If recesses are formed in interposer and filled with anchor portions, then stress absorption is improved, but device structure and manufacturing complexity increase
Solution Approach 1:
The recesses are formed in the interposer before the underfill material is applied. This preliminary action allows the anchor portions to be precisely positioned and shaped to match the recess geometry, ensuring optimal stress absorption while maintaining a relatively simple overall structure. The pre-formed recesses guide the formation of anchor portions with controlled cross-sectional areas at specific locations
3Stress or pressure
If anchor portions protrude into recesses, then mechanical stress is reduced, but thermal stress management becomes more complex
Solution Approach 1:
The underfill material composition is modified by incorporating materials with different coefficients of thermal expansion (CTE) in different regions. The anchor portions may contain materials with CTE matched to the interposer to reduce thermal stress at the interface, while the body portion may contain materials optimized for overall thermal management. This parameter differentiation allows simultaneous optimization of mechanical stress absorption and thermal stress management
Data Source
AI summary
A bonded assembly includes an interposer including redistribution wiring interconnects and redistribution insulating layers and including recesses in corner regions. The recesses include surfaces that are recessed relative to a horizontal plane including a horizontal surface of the interposer. A least one semiconductor die is attached to the interposer through a respective array of solder material portions. An underfill material portion is located between the interposer and the at least one semiconductor die. The underfill material includes downward-protruding anchor portions that protrude downward from a horizontally-extending portion of the underfill material portion that laterally surrounds each array of solder material portions into the recesses.