Floating Die Package With Vented Cavity for Thermal Stress Drift
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Solution Overview
Problem
Conventional semiconductor packaging technologies suffer from post-assembly stresses and temperature drift, leading to parametric shifting in high precision ICs due to thermo-mechanical stresses from packaging materials, despite using materials with low modulus of elasticity and high Coefficient of Thermal Expansion (CTE).
Innovation Solution
A floating die package is created by sublimating a sacrificial die encapsulant and die attach materials, using pinhole vents to form a cavity, allowing the die to be suspended by bond wires, thereby reducing mechanical stress and temperature-induced drift. This involves a method of singulating semiconductor dies, attaching them to a substrate with sublimatable materials, wire-bonding, and applying a sacrificial encapsulant and molding material with pinhole vents to facilitate sublimation and delamination, resulting in a stress-free package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional packaging materials with low modulus of elasticity and high CTE are used, then stress immunity is improved, but parametric drift over temperature still occurs
Solution Approach 1:
The patent employs a sacrificial encapsulant material that undergoes phase transition from solid to gas through sublimation. This phase change creates a cavity that suspends the die, eliminating thermo-mechanical stress while maintaining parametric stability across temperature variations.
Solution Approach 2:
The invention extracts the source of stress by removing the sacrificial encapsulant material through sublimation. The extracted gas escapes through vent holes, leaving a void space that isolates the die from stress-inducing contact with the substrate and molding compound.
2Strength
If the die is rigidly attached to the substrate, then mechanical support is provided, but thermo-mechanical stresses cause parametric shifting
Solution Approach 1:
The patent transforms the static rigid attachment into a dynamic suspended configuration. The die is held in place only by bond wires, allowing it to float freely within the cavity and adapt to temperature changes without transmitting mechanical stress to the electrical characteristics.
Solution Approach 2:
The bond wires serve as intermediaries between the die and the substrate. These thin wires provide minimal mechanical support while electrically connecting the die, effectively decoupling the mechanical stress path from the electrical signal path.
3Reliability
If sublimatable materials are used for die attach and encapsulant, then stress-free suspension is achieved, but additional processing steps are required
Solution Approach 1:
The patent changes the physical-chemical parameters of the encapsulant and die attach materials by selecting substances with specific sublimation properties. These materials remain stable during assembly but transform into gas at elevated temperatures, automatically creating the stress-free cavity without additional machining or assembly steps.
Solution Approach 2:
The sacrificial encapsulant material is applied in advance during the standard packaging process. Its sublimation is triggered later during a thermal aging or burn-in process that is already part of the manufacturing workflow, integrating the cavity formation into existing process steps.
4Reliability
If the sacrificial encapsulant is completely removed by sublimation, then a cavity is formed for stress relief, but vent holes must be provided and sealed
Solution Approach 1:
The molding compound is designed with controlled porosity in the form of vent holes that allow gas escape during sublimation. These porous pathways are strategically positioned to facilitate complete removal of the sacrificial material while maintaining structural integrity of the package.
Solution Approach 2:
The vent holes serve as temporary features that fulfill their purpose during the sublimation process and can be sealed afterward. Their transient nature is acceptable since they enable the formation of the permanent stress-relief cavity, and sealing them restores the hermetic seal of the package.
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 solution effectively reduces thermo-mechanical stresses and parametric shifts, enhancing the reliability and performance of semiconductor devices by suspending the die in a cavity, minimizing stress and temperature-related issues, while maintaining mechanical support and environmental protection.
Implementation Method 1
A sublimation process is then effectuated to gasify the sublimatable sacrificial encapsulant material, thereby allowing the gasified encapsulant material to escape through the pinhole vent of the molding, thereby creating a cavity.
Implementation Method 2
The die or die stack is released from the substrate and suspended in the cavity by the bond wires only.
Data Source
AI summary
A floating die package including a cavity formed through sublimation of a sacrificial die encapsulant and sublimation or separation of die attach materials after molding assembly. A pinhole vent in the molding structure is provided as a sublimation path to allow gases to escape, whereby the die or die stack is released from the substrate and suspended in the cavity by the bond wires only.