Chip Resistor Electrode with Silver-Palladium Layering
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Solution Overview
Problem
Conventional resistive elements formed using wire bonding face challenges in achieving dense and strong electrical connections between electrodes and bonding wires, leading to potential damage and reduced contact strength during the bonding process.
Innovation Solution
A method involving the formation of electrodes with a first layer containing high silver content and a second layer containing silver and palladium, where silver diffuses from the first layer to fill voids in the second layer during heat treatment, creating a dense and thick conductive film, and palladium prevents silver migration and sulfuration, enhancing adhesion and connection strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-layer electrode structures are used, then manufacturing is simpler, but the electrode density and connection strength are insufficient for reliable wire bonding
Solution Approach 1:
The electrode is divided into two distinct layers: a first electrode layer with high silver content (≥95 wt%) and a second electrode layer with silver-palladium composition (70-90 wt% Ag, 10-30 wt% Pd). This segmentation allows each layer to perform its specific function - the first layer provides density and conductivity while the second layer prevents sulfuration and migration, collectively achieving reliable wire bonding connections
Solution Approach 2:
The electrode structure employs composite materials with different compositions in each layer. The first layer uses silver-rich paste for optimal conductivity and density, while the second layer uses silver-palladium paste for chemical stability and protection against sulfuration. This composite approach combines the advantages of different material systems to achieve both high connection strength and reliability
2Strength
If the electrode layer is made thicker to improve connection strength, then wire bonding reliability improves, but manufacturing precision and density control become more difficult
Solution Approach 1:
Different regions of the electrode structure are assigned different material compositions optimized for their specific functions. The first layer (thicker, 5-15 μm) is designed with high silver content for density and conductivity where mechanical connection is needed, while the second layer (thinner, 2-10 μm) contains palladium for chemical protection at the surface exposed to sulfur-containing atmospheres during wire bonding
Solution Approach 2:
The invention controls specific compositional parameters - the first layer contains ≥95 wt% silver while the second layer contains 70-90 wt% silver with 10-30 wt% palladium. These parameter specifications ensure optimal diffusion behavior during heat treatment, where silver from the first layer fills voids in the second layer to create a dense structure with controlled thickness and improved connection strength
3Reliability
If silver content is increased to improve conductivity and density, then electrode performance improves, but silver migration and sulfuration become more problematic
Solution Approach 1:
The second electrode layer acts as an intermediary barrier between the high-silver first layer and the external environment. The palladium-rich composition (10-30 wt% Pd) in this layer prevents direct contact between sulfur in the atmosphere and silver, blocking sulfuration reactions. It also serves as a diffusion barrier that prevents silver migration while allowing the beneficial silver diffusion from the first layer to fill voids during controlled heat treatment
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 approach results in reduced damage during wire bonding and increased contact strength, allowing for more reliable electrical connections and improved resistance to temperature extremes, while preventing silver migration and sulfuration.
Implementation Method 1
diffusion of silver to the second electrode layer, which is the upper layer, becomes dominant when Ag mutually diffuses during heat treatment (baking) and the like
Implementation Method 2
when Ag mutually diffuses during heat treatment (baking) and the like
Data Source
AI summary
A method for manufacturing a chip resistive element including a substrate, a resistor formed on the substrate, and electrodes connected to opposite ends of the resistor, the method including an electrode forming step of forming the electrodes on the substrate. The electrode forming step includes a step of forming a first electrode layer on the substrate using a first electrode material containing silver, and a step of forming a second electrode layer on the first electrode layer using a second electrode material containing silver and palladium. The first electrode material has a higher silver content than the second electrode material.