Semiconductor Package Buffer Layer for Thermal Stress Relief
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Solution Overview
Problem
The integration of smaller semiconductor components into compact packages leads to thermal stress and reliability issues due to mismatched coefficients of thermal expansion, resulting in cracks and delamination.
Innovation Solution
A buffer layer made of a polymer material with specific properties is applied to cover and protect the semiconductor dies, reducing thermal stress by having a lower Young's modulus and higher elasticity than the encapsulant, thereby enhancing adhesion and preventing cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If smaller semiconductor components are integrated into compact packages, then integration density is improved, but thermal stress and reliability deteriorate due to mismatched coefficients of thermal expansion
Solution Approach 1:
A buffer layer is introduced as an intermediary between the semiconductor die and the encapsulant. This buffer layer has a coefficient of thermal expansion that is lower than the encapsulant but higher than the semiconductor die, creating a gradient that reduces thermal stress. The buffer layer acts as a stress-absorbing intermediary that prevents direct stress transmission from the encapsulant to the die, thereby maintaining reliability while enabling compact packaging.
Solution Approach 2:
The patent changes the physical parameters of the package structure by introducing a layer with specific mechanical properties (Young's modulus and coefficient of thermal expansion) that differ from both the die and encapsulant. The buffer layer's Young's modulus is lower than the encapsulant's, providing elasticity to absorb thermal stress. This parameter optimization allows the package to withstand thermal cycling without delamination or cracking.
2Area of stationary object
If compact packages are used, then area is reduced, but thermal stress increases leading to cracks and delamination
Solution Approach 1:
The buffer layer is positioned beforehand between the die and encapsulant to cushion against thermal stress before it can cause damage. This preventive measure absorbs and distributes the thermal stress that arises during temperature cycling, preventing stress concentration at the die-encapsulant interface that would lead to cracks or delamination in compact packages.
3Stress or pressure
If buffer layer with lower Young's modulus is used, then thermal stress is reduced, but adhesion must be maintained
Solution Approach 1:
The buffer layer is designed with optimized material parameters: a Young's modulus lower than the encapsulant to provide stress-absorbing elasticity, while maintaining sufficient adhesion strength to both the die and encapsulant. The coefficient of thermal expansion is specifically selected to be between that of the die and encapsulant, creating a stress-gradient structure that reduces overall thermal stress while maintaining interfacial adhesion.
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 buffer layer effectively reduces thermal stress and improves the reliability of the package structure by maintaining adhesion and preventing delamination, increasing yield and reliability.
Implementation Method 1
The buffer layer has a Young's modulus less than a Young's modulus of the first encapsulant and a Young's modulus of the second encapsulant. The buffer layer is able to release or reduce a thermal stress resulted from a coefficient of thermal expansion (CTE) mismatch.
Data Source
AI summary
A package structure and a method of forming the same are provided. The package structure includes a first die, a second die, a first encapsulant, and a buffer layer. The first die and the second die are disposed side by side. The first encapsulant encapsulates the first die and the second die. The second die includes a die stack encapsulated by a second encapsulant encapsulating a die stack. The buffer layer is disposed between the first encapsulant and the second encapsulant and covers at least a sidewall of the second die and disposed between the first encapsulant and the second encapsulant. The buffer layer has a Young's modulus less than a Young's modulus of the first encapsulant and a Young's modulus of the second encapsulant.