Floating Die Package Cavity Structure for Thermo-Mechanical Stress Relief
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Solution Overview
Problem
Conventional semiconductor packaging technologies suffer from post-assembly thermo-mechanical stresses that cause parametric shifting and temperature drift due to the use of materials with high thermal expansion coefficients, leading to performance issues and reliability concerns.
Innovation Solution
A semiconductor package design that incorporates a partially sublimated or delaminated die attach material, allowing the die to be suspended in a cavity formed by sublimation of a sacrificial encapsulant, with pinhole vents for gas escape, reducing mechanical stress through a 'floating die' configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional packaging materials are used, then mechanical support and protection are provided, but thermo-mechanical stresses cause parametric shifting and temperature drift
Solution Approach 1:
The package is divided into distinct functional regions: a rigid support structure (substrate/leadframe) for mechanical support, and a floating die cavity with low-modulus material for stress isolation. This segmentation allows each region to perform its specialized function without compromising the other.
Solution Approach 2:
The package uses composite construction combining rigid materials (substrate, leadframe) with low-modulus materials (encapsulant, underfill) to create a structure that provides both mechanical support and stress relief. The composite design enables the package to maintain structural integrity while minimizing thermo-mechanical stresses on the die.
2Object-affected harmful factors
If materials with low modulus of elasticity are used to improve stress immunity, then stress resistance improves, but coefficient of thermal expansion remains high
Solution Approach 1:
Different regions of the package have different material properties optimized for their specific functions: the substrate and leadframe use rigid materials with controlled CTE for structural stability, while the encapsulant and underfill use low-modulus materials for stress relief. This local quality differentiation resolves the contradiction between stress resistance and thermal expansion control.
Solution Approach 2:
The package employs a composite material system where rigid structural components are combined with compliant low-modulus materials. This composite approach allows the package to achieve both stress immunity through the low-modulus materials and thermal expansion control through the rigid components with matched CTE.
3Object-affected harmful factors
If a floating die configuration is implemented, then thermo-mechanical stresses are reduced, but manufacturing complexity increases
Solution Approach 1:
The die is attached to the substrate using die attach materials (underfill/encapsulant) before final encapsulation. This preliminary attachment establishes the floating die configuration early in the manufacturing process, allowing subsequent encapsulation to complete the stress-isolated structure without additional complex steps.
Solution Approach 2:
Die attach materials (underfill and encapsulant) serve as intermediary substances between the die and substrate, creating the floating die configuration. These intermediary materials provide both mechanical attachment and stress isolation, achieving the desired stress reduction while using well-established packaging materials and processes.
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 floating die package significantly reduces thermo-mechanical stresses, minimizing parametric drift and enhancing performance and reliability while maintaining cost-effectiveness.
Implementation Method 1
a cavity formed through sublimation of a sacrificial die encapsulant
Data Source
Figure 1A
Figure 1B
Figure 2A-1~2A-2
AI summary
Described examples include a floating die package (200B-1) including a cavity (252) formed through sublimation of a sacrificial die encapsulant and sublimation or separation of die attach materials after molding (216) assembly. A pinhole vent (218) in the molding structure is provided as a sublimation path to allow gases to escape, wherein the die (206) or die stack is released from the substrate (202) and suspended in the cavity (252) by the bond wires (210) only.