Liquid Ejection Head Substrate Gold Diffusion Prevention
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Solution Overview
Problem
In ink jet print head manufacturing, thin gold films are desirable for cost reduction and surface uniformity, but they are prone to diffusion into the conductor layer during bonding, leading to reduced conductivity and reliability due to heat and pressure applied during external connection, which can be mitigated by altering bonding conditions but at the cost of adhesion.
Innovation Solution
A liquid ejection head substrate design featuring a conductor layer with an opening region and a gold layer above it, where the external connection is made on top of the gold, preventing diffusion by absorbing heat and pressure without the need for a lower conductor layer, thus maintaining high reliability and precision in nozzle processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a thin gold film is used, then cost is reduced and surface uniformity is improved, but heat or pressure during bonding causes gold to diffuse into the conductor layer, reducing reliability
Solution Approach 1:
The conductor layer is segmented by creating an opening region, separating the area where gold diffusion could occur from the area where electrical connection is needed. This allows the gold layer to be thin for cost savings while preventing diffusion into the conductor layer by providing a physical gap through the opening.
Solution Approach 2:
The opening region acts as an intermediary space between the gold layer and the conductor layer, preventing direct contact and thus preventing gold diffusion into the conductor layer during bonding while still allowing electrical connection through the opening.
2Reliability
If bonding conditions are lowered to prevent gold diffusion, then reliability is improved, but adhesion of the external connection portion to the gold bump decreases
Solution Approach 1:
The opening region serves as an intermediary structure that enables reliable bonding at standard conditions. By providing a configured interface through the opening, it allows adequate adhesion strength while the structure itself prevents gold diffusion into the conductor layer, eliminating the need to lower bonding conditions.
3Reliability
If a thick gold bump is formed, then conductivity is maintained, but it causes decrease in uniformity within the substrate surface for laminating organic materials
Solution Approach 1:
The conductor layer is segmented with an opening region that allows the gold layer to be thin in the bonding area while maintaining electrical connection. This segmentation enables the use of thinner gold films that provide sufficient conductivity for the connection function while reducing surface height variations for better laminating uniformity.
Data Source
AI summary
A liquid ejection head substrate includes an electrode pad for receiving driving power for liquid ejection from an outside, the electrode pad including at least a conductor layer and a layer of gold. A portion of the conductor layer has an opening region, and an upper layer portion in a laminating direction above the conductor layer including the opening region has at least the layer of gold. An external connection portion connected to the outside is provided on top of the layer of gold corresponding to the opening region of the conductor layer.