Bonding Pad Composite Layers for Corrosion and Delamination
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Solution Overview
Problem
Conventional semiconductor devices face issues with size reduction and durability due to the fragility of aluminum bonding pads and the detachment of protection layers, leading to corrosion and reduced reliability.
Innovation Solution
A semiconductor device design featuring a metal underlying layer with a bonding pad composed of multiple conductive layers with lower ionization tendencies, covered by an insulative protection layer, which prevents delamination and corrosion by maintaining close contact with the protection layer, thereby enhancing durability and allowing for a smaller form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection layer is formed to cover the periphery of the bonding pad, then the bonding pad is protected from corrosion, but the protection layer may detach from the metal layer leading to exposed portions that are susceptible to corrosion
Solution Approach 1:
The bonding pad uses a composite structure with multiple metal layers (Al base layer, Ti layer, Pd layer, Au layer) where each layer provides specific properties. The Ti and Pd layers form strong adhesive bonds with both the Al base layer and the protection layer, creating a composite structure that prevents protection layer detachment while maintaining corrosion resistance.
Solution Approach 2:
The Ti layer and Pd layer act as intermediary layers between the Al base layer and the protection layer. These intermediate layers have high adhesion to both the metal base and the protection layer, preventing direct contact between Al and the protection layer, thereby eliminating the detachment issue while maintaining protection.
2Strength
If the metal layer is formed over a larger region than the exposed bonding pad, then the bonding pad structure is more robust, but the semiconductor device size increases
Solution Approach 1:
The metal layers are selectively formed only in the region where the bonding pad is needed, with precise thickness control. The Ti and Pd layers are applied locally to the Al base layer only in the bonding pad area, not across the entire semiconductor device, thereby maintaining structural robustness where needed while minimizing overall device area.
Solution Approach 2:
Instead of expanding the metal layer area in the horizontal plane, the solution adds vertical dimensionality by stacking multiple thin metal layers (Al, Ti, Pd, Au) with controlled thicknesses. This provides robustness through layered structure rather than through increased surface area, allowing compact device footprint.
3Ease of manufacture
If ultrasonic vibration and pressure are applied during wire bonding, then the wire bonds successfully to the bonding pad, but the bonding pad may crack or fragment due to the softness of aluminum
Solution Approach 1:
The bonding pad uses a composite metal layer structure where the Al base layer provides electrical conductivity and cost-effectiveness, while the Ti and Pd overlaying layers provide high mechanical strength and crack resistance. During wire bonding, the harder Ti and Pd layers absorb the mechanical stress from ultrasonic vibration and pressure, preventing cracks in the softer Al layer while still allowing successful wire attachment.
Solution Approach 2:
The Ti and Pd layers are applied in advance to the Al base layer to create a protective cushioning layer that will absorb and distribute the mechanical stresses during subsequent wire bonding operations. This pre-applied layering prevents direct transmission of damaging forces to the Al layer, preventing cracks before they can occur.
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 prevents corrosion and delamination, improving the durability and reducing the size of the semiconductor device by ensuring the bonding pad's close contact with the protection layer, while withstanding the pressure applied during the wire bonding process without cracking.
Implementation Method 1
a first conductive layer covering the metal underlying layer and made of a metal having a lower ionization tendency than the metal underlying layer; and a second conductive layer covering the first conductive layer and made of a metal having a lower ionization tendency than the first conductive layer
Implementation Method 2
The first conductive layer and the second conductive layer have peripheries, respectively, that are in close contact with the protection layer and cover a part of the protection layer
Data Source
AI summary
A semiconductor device includes a semiconductor element having first and second main surfaces spaced apart in a thickness direction. The semiconductor element includes a metal underlying layer on the first main surface, a bonding pad on the metal underlying layer with a wire bonded to the pad, and an insulative protection layer formed on the first main surface and surrounding the bonding pad. The bonding pad includes first and second conductive layers. The first conductive layer covers the metal underlying layer and is made of a metal having a lower ionization tendency than the metal underlying layer. The second conductive layer covers the first conductive layer and is made of a metal having a lower ionization tendency than the first conductive layer. The first and second conductive layers have respective peripheries held in close contact with the protection layer and covering a part of the protection layer.