Flexible Interconnect Layer for Thermal Stress in Semiconductor Packages
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Solution Overview
Problem
Cavity-type semiconductor packages face issues with package failure due to mismatched coefficients of thermal expansion between the lid, substrate, and adhesive, leading to cracking and separation, especially in larger packages where increased material volume exacerbates expansion and contraction stresses.
Innovation Solution
Incorporating a layer of flexible material between the cap and substrate, which absorbs thermal expansion stresses by deforming to maintain electrical connections and prevent separation, while allowing the second die to be exposed for ambient environment sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single semiconductor die is coupled to a substrate in a cavity-type package, then the package structure is simple, but the functionality is insufficient for modern system requirements
Solution Approach 1:
The patent divides the semiconductor functionality into multiple separate dies (first die, second die, third die) that are coupled to different surfaces of the substrate. This segmentation allows each die to perform specific functions while maintaining a compact package footprint, resolving the contradiction between enhanced functionality and limited package size.
Solution Approach 2:
The patent utilizes three-dimensional space by coupling dies to both the top surface and bottom surface of the substrate, as well as coupling dies to each other in vertical arrangements. This multi-dimensional configuration maximizes functionality within a small package volume.
2Stability of the object's composition
If the lid, substrate, and adhesive are bonded together, then the package structure is stable, but the mismatched coefficients of thermal expansion cause cracking and separation during operation cycles
Solution Approach 1:
The patent introduces a compliant layer with specific mechanical properties (different modulus of elasticity than the substrate and lid) between the lid and substrate. This layer changes the stress distribution parameters during thermal cycling, absorbing expansion mismatches and preventing adhesive failure while maintaining overall structural stability.
Solution Approach 2:
The patent creates a composite structure by bonding the compliant layer to both the substrate and lid, forming a multi-material assembly. This composite construction combines the structural integrity of rigid materials with the stress-absorbing properties of the compliant material, resolving the contradiction between stability and reliability.
3Reliability
If the compliant layer is bonded to both the substrate and lid, then thermal expansion stress is absorbed, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies adhesive to specific regions of the substrate and lid before bonding the compliant layer, and uses alignment features to pre-position components. These preliminary actions simplify the subsequent assembly process and ensure proper positioning, reducing manufacturing complexity while maintaining reliable stress absorption.
Solution Approach 2:
The compliant layer serves as an intermediary component that simplifies the overall manufacturing process by providing a buffer zone that tolerates dimensional variations during assembly. This intermediary element makes the bonding process more forgiving and easier to control, improving ease of manufacture while ensuring reliable stress absorption.
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 flexible material reduces stress at connections, enhancing package reliability and extending service life by preventing cracking and separation between the cap and substrate during operation cycles.
Implementation Method 1
the substrate, the layer of flexible material, and the cap each have their own coefficient of thermal expansion. During operation, heat produced by operation of the package will expand each of these components a different amount because of the different coefficients of thermal expansion
Implementation Method 2
the layer of flexible material absorbs the stress produced within the package by the difference in the coefficient of thermal expansion between the substrate and the cap. In other words, during operation, the layer of flexible material deforms such that expansion and contraction of the cap and the substrate does not result in the cap separating from the substrate
Data Source
AI summary
A cavity type semiconductor package with a substrate and a cap is disclosed. The semiconductor package includes a first semiconductor die coupled to the substrate and a layer of flexible material on a surface of the cap. A trace is on the layer of flexible material. The cap is coupled to the substrate with the layer of flexible material and the trace between the cap and the substrate. A second semiconductor die is coupled to the layer of flexible material and the trace on the cap. The cap further includes an aperture to expose the second semiconductor die to the ambient environment. The layer of flexible material absorbs stress during operation cycles of the package induced by the different coefficient of thermal expansions of the cap and the substrate to reduce the likelihood of separation of the cap from the substrate.