Trenches in Wafer Level Package Underfill for Warpage Control
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Solution Overview
Problem
Composite dies experience significant warpage due to high coefficient of thermal expansion (CTE) underfill materials, leading to assembly and reliability issues, with existing solutions offering limited improvements in warpage reduction and compromising adhesion strength or requiring frequent wafer flattening.
Innovation Solution
Incorporating trenches in the underfill between dies, filled with a mold layer of lower CTE and higher thermal conductivity, to reduce mechanical stress and enhance thermal performance, thereby improving warpage and thermal-mechanical reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If underfill material with high CTE is used to package composite dies, then thermal expansion matching is improved, but warpage increases significantly
Solution Approach 1:
The patent divides the underfill material into two distinct regions: a first underfill material filling trenches that provides structural support and warpage control, and a second underfill material in the spaces between trenches that provides thermal expansion matching. This segmentation allows each material to perform its specialized function without compromise.
Solution Approach 2:
The patent applies different material properties to different locations within the underfill structure. The first underfill material with specific mechanical properties is placed in trenches where warpage control is needed, while the second underfill material with matching CTE is placed in regions where thermal expansion compatibility is critical.
2Shape
If material reformulation to underfill is performed to reduce warpage, then warpage improvement is achieved, but adhesion strength decreases
Solution Approach 1:
The patent segments the underfill function into two materials: the first underfill material optimized for mechanical support and warpage control, and the second underfill material optimized for adhesion and thermal expansion matching. This eliminates the need to compromise adhesion strength when reformulating for warpage reduction.
3Shape
If wafer flattening processes are used to improve warpage, then warpage is reduced, but manufacturing complexity increases due to frequent re-flattening
Solution Approach 1:
The patent performs warpage control through the trench structure and dual underfill material configuration during the initial packaging process. This preliminary structural design eliminates the need for repeated wafer flattening operations during subsequent assembly steps, reducing manufacturing complexity.
4Shape
If mold layer additives are added to reduce warpage, then warpage improvement is achieved, but adhesion strength and toughness of mold layer decrease
Solution Approach 1:
The patent moves the warpage control function from the mold layer to the underfill structure through trenches and dual materials. This segmentation allows the mold layer to maintain its adhesion strength and toughness without requiring warpage-reducing additives, while the underfill structure independently handles warpage control.
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 trenches significantly reduce warpage in composite dies, enhance thermal performance by providing a low thermal resistance path, and mitigate delamination and cracking failures, resulting in improved assembly yield and reliability.
Implementation Method 1
Warpage is significant in part due to the high coefficient of thermal expansion (CTE) of the underfill. The trenches are filled with a lower CTE material.
Implementation Method 2
the trenches are filled with a lower CTE material and higher thermal conductivity, to reduce mechanical stress and enhance thermal performance
Data Source
AI summary
Embodiments disclosed herein include composite dies and methods of forming such composite dies. In an embodiment, a composite die comprises a base substrate, a first die over the base substrate, and a second die over the base substrate and adjacent to the first die. In an embodiment an underfill layer is between the first die and the base substrate, between the second die and the base substrate, and between the first die and the second die. In an embodiment, a trench into the underfill layer is between the first die and the second die. In an embodiment the composite die further comprises, a mold layer over the first die and the second die, wherein the mold layer fills the trench.