Multi-Trench IC Package Substrate Underfill Reliability
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Solution Overview
Problem
Conventional flip-chip packaging of integrated circuits often results in underfill material cracking and delamination due to shear and peeling stresses between the flipped substrate and package substrate, which existing methods fail to adequately address.
Innovation Solution
A multi-trench structure is formed on the flipped substrate, proximate to each corner, to increase the contact surface area with the underfill material and alter the crack-tip phase angle from mode I to mode II, reducing stress intensity and enhancing interface fracture toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If underfill material is applied in liquid form from a dispenser, then the gap between flipped substrate and package substrate is filled through capillary action, but the underfill material is subject to shear and peeling stress resulting in cracking and delamination
Solution Approach 1:
The patent applies local quality by creating trenches at specific locations (corners and edges) of the substrate where stress concentration occurs. These trenches modify the local structure to reduce stress intensity factors at critical points, thereby preventing delamination while maintaining the overall simplicity of the underfill application process.
Solution Approach 2:
The patent segments the continuous substrate surface by introducing trenches that divide the underfill interface into distinct regions. This segmentation reduces the continuous stress path and creates stress relief zones, preventing the propagation of delamination cracks while maintaining effective capillary flow of underfill material.
2Reliability
If solder bumps are used to couple the flipped substrate to the package substrate, then electrical connection is achieved, but stress concentration occurs at the corners of the substrate leading to underfill failure
Solution Approach 1:
The patent addresses stress concentration at corners by introducing trenches specifically at these high-stress locations. The trenches modify the local stress distribution by creating stress relief zones that reduce the stress intensity factor, thereby preventing underfill delamination at the most vulnerable points without affecting the overall electrical connection functionality.
3Manufacturing precision
If the underfill material flows into the narrow gap due to capillary action, then complete gap filling is achieved, but the underfill material spreads across the flipped substrate creating large surface area exposure to stress
Solution Approach 1:
The patent segments the underfill interface by introducing trenches that divide the continuous underfill layer into separate regions. This segmentation reduces the effective surface area exposed to stress by creating barriers that prevent stress propagation across the entire substrate surface, while still allowing complete gap filling through capillary action in each segmented region.
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 multi-trench structure effectively mitigates underfill delamination and cracking by increasing adhesion and reducing stress intensity at the crack tip, thereby improving the reliability of the IC package.
Implementation Method 1
The underfill then flows into the narrow gap due to capillary action and spreads across the flipped substrate until the gap is filled
Data Source
AI summary
In an example, an integrated circuit (IC) package includes a package substrate, an IC die, solder bumps, a first plurality of trenches, and underfill material. The IC die includes a front surface and a back surface, the front surface facing the package substrate and including a conductive interface. The solder bumps couple the conductive interface to the package substrate. The first plurality of trenches includes at least one trench proximate each corner of the IC die formed in the front surface of the IC die in an area between the conductive interface and a perimeter of the IC die. The underfill material is disposed between the front surface of the IC die and the package substrate, the underfill material being in contact with the first plurality of trenches.