Stacked Package Structure With Air Gap for Thermal Stress Relief
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Solution Overview
Problem
The mismatched coefficients of thermal expansion (CTE) between substrates in package stacking structures lead to thermal stress during high-temperature processes, causing cracks in the conductive material and compromising package structure reliability.
Innovation Solution
Incorporating an air gap between the substrates and using a protective layer to surround the bonding pads, which are connected to through vias in both substrates, helps to mitigate thermal stress and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a bonding layer is coated entirely between two adjacent substrates to connect them, then the substrates are bonded together, but the mismatched coefficients of thermal expansion cause thermal stress during high-temperature processes, resulting in cracks in the conductive material embedded in the bonding layer
Solution Approach 1:
The bonding layer is segmented into discrete bonding pads rather than being a continuous layer. This segmentation allows different regions to independently accommodate thermal expansion differences, preventing stress concentration and crack propagation that would occur in a continuous bonding layer.
Solution Approach 2:
Air gaps are introduced between adjacent substrates before the bonding process to cushion against thermal expansion forces. These pre-positioned air gaps act as stress relief zones that accommodate dimensional changes during high-temperature processes, preventing cracks in the conductive material.
2Adaptability or versatility
If the wiring density, spacing, or size of the memory package does not match the logic package, then additional substrates are disposed between them to bridge the mismatch, but this increases the complexity of the package structure and introduces more bonding interfaces that are susceptible to thermal stress
Solution Approach 1:
The intermediate substrate is designed with universal bonding pad patterns that can accommodate different wiring densities and spacing requirements. By using standardized bonding pad geometries and arrangements, the same intermediate substrate structure can bridge multiple different package types without requiring custom designs for each pairing.
Solution Approach 2:
The intermediate substrate features locally optimized bonding pad regions with varying densities and spacing to match different adjacent substrates. Each bonding interface is locally tailored to its specific connection requirements while maintaining overall structural consistency.
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 air gap and protective layer configuration effectively reduce the risk of bonding pad cracking due to thermal expansion mismatch, thereby enhancing the reliability of the package structure by maintaining signal connections intact.
Implementation Method 1
the coefficient of thermal expansion (CTE) of the bonding layer coated entirely between two adjacent substrates does not match the materials used for the substrates. Consequently, during other subsequent packaging processes, the thermal stress generated in high-temperature processes such as the reflow process can cause cracks in the conductive material embedded in the bonding layer
Data Source
AI summary
Disclosed is a package structure, including a first substrate, a second substrate, a bonding pad, a protective layer, and an air gap. The first substrate has a first surface and a second surface opposite to each other, and includes a first via extending from the first surface to the second surface. The second substrate is disposed on the first surface of the first substrate, has a third surface facing the first surface and a fourth surface opposite to the third surface, and includes a second via extending from the third surface to the fourth surface. The bonding pad is disposed between the first and second substrates and connected to the first and second vias. The protective layer is disposed between the first and second substrates, and surrounds the bonding pad. The air gap is disposed between the first and second substrates.