Palladium Layer Fills Bond Pad Gap for Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wire bond structures in semiconductors fail reliability tests at high temperatures due to intermetallic reactions and corrosion, leading to electrical failures, especially in automotive applications where extended reliability is crucial.
Innovation Solution
A bond pad structure is developed using a nickel layer with a palladium layer that fills the gap between the nickel and passivation layer, followed by a gold layer, which enhances adhesion and prevents corrosion, allowing for compact and reliable bond pads even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If copper bond pads are used to reduce resistivity, then electrical resistance is reduced, but corrosion susceptibility increases
Solution Approach 1:
The patent employs a composite bond pad structure consisting of multiple metal layers (copper, nickel, palladium, aluminum) with distinct functions. The copper core provides low resistivity, while the palladium and nickel layers provide corrosion resistance and adhesion, resolving the contradiction between electrical performance and environmental durability.
Solution Approach 2:
The patent introduces intermediate metal layers (palladium, nickel) between the copper bond pad and the external environment. These intermediary layers act as protective barriers that prevent direct exposure of copper to corrosive elements while maintaining electrical conductivity, thus resolving the corrosion susceptibility issue.
2Reliability
If aluminum cap is added to copper bond pad to prevent corrosion, then corrosion resistance is improved, but intermetallic reactions occur at high temperature
Solution Approach 1:
The patent positions the palladium layer as an intermediary between copper and aluminum, preventing direct contact between these two metals. This intermediary layer blocks intermetallic reaction pathways while maintaining the protective corrosion-resistant function of the aluminum cap, thus resolving the high-temperature stability issue.
Solution Approach 2:
The multi-layer composite structure (copper-nickel-palladium-aluminum) is designed to prevent harmful intermetallic reactions between adjacent layers. Each layer is selected for its specific properties, and the overall composite provides both corrosion resistance and thermal stability by eliminating direct metal-to-metal contact between reactive pairs.
3Ease of manufacture
If conventional wire bond structures are used, then manufacturing is simple, but reliability fails at high temperature
Solution Approach 1:
The patent replaces simple single-metal bond pads with a multi-layer composite structure. While the manufacturing process becomes more complex, the use of standard deposition and patterning techniques keeps the added complexity manageable, while the reliability benefits at high temperature are substantial.
4Area of moving object
If bond pad size is reduced for miniaturization, then device size is reduced, but adhesion to passivation layer becomes insufficient
Solution Approach 1:
The patent uses a composite structure with palladium and nickel layers specifically selected for their excellent adhesion properties to passivation materials. This allows the bond pad to maintain strong adhesion even when the overall area is reduced for miniaturization, as the adhesion-critical layers are optimized for bonding strength per unit area.
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 significantly reduces the distance between bond pads while maintaining reliability, preventing corrosion and electrical failures, and allowing for miniaturization of semiconductor devices without increased leakage current or bridging.
Implementation Method 1
A palladium layer is then deposited over the nickel layer so as to fill the space between the nickel layer and the passivation layer
Data Source
AI summary
A semiconductor device structure has a semiconductor die that has a bond pad with a passivation layer surrounding a portion of the bond pad. A nickel layer, which is deposited, is on the inner portion. A space is between a sidewall of the nickel layer and the passivation layer and extends to the bond pad. A palladium layer is over the nickel layer and fills the space. The space is initially quite small but is widened by an isotropic etch so that when the palladium layer is deposited, the space is sufficiently large so that the deposition of palladium is able to fill the space. Filling the space results in a structure in which the palladium contacts the nickel layer, the passivation layer and the bond pad.