Ceramic Substrate Terminal Corrosion Resistance via Interlayer Design
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Solution Overview
Problem
Ceramic substrates for LED packages face corrosion issues at the connecting terminal portions when used in high-temperature and high-humidity environments, leading to open failures and reduced connection reliability.
Innovation Solution
Incorporating a titanium or chromium contact layer and an intermediate layer, such as a titanium-tungsten alloy, nickel-chromium alloy, tungsten, palladium, or molybdenum, between the ceramic substrate and the copper layer, with the contact and intermediate layers set back from the copper layer's side surface, and using a nickel or gold coating to enhance adhesion and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper layer is used in the connecting terminal portion, then electrical conductivity is improved, but adhesion to the ceramic layer deteriorates and corrosion resistance in harsh environments worsens
Solution Approach 1:
The patent introduces a contact layer of titanium or chromium as an intermediary between the copper layer and the ceramic substrate. This contact layer serves as a mediator that provides both adhesion to the ceramic and compatibility with the copper layer, preventing direct contact between copper and ceramic that would lead to corrosion in high-temperature and high-humidity environments.
Solution Approach 2:
The patent employs a composite multi-layer structure consisting of copper layer, contact layer (titanium or chromium), and ceramic substrate. This composite structure combines the advantages of each material: copper for electrical conductivity, titanium/chromium for adhesion and corrosion resistance, and ceramic for thermal and mechanical stability, thereby resolving the contradiction between conductivity and corrosion resistance.
2Strength
If a contact layer of titanium is formed to improve adhesion, then adhesion property is improved, but corrosion resistance in high-temperature and high-humidity environments deteriorates
Solution Approach 1:
The patent introduces an intermediate layer as a mediator between the titanium contact layer and the copper layer. This intermediate layer protects the titanium from direct exposure to corrosive environments while maintaining the adhesion benefits, thus resolving the contradiction between adhesion improvement and corrosion resistance deterioration.
Solution Approach 2:
The patent creates a composite three-layer structure (copper layer + contact layer + intermediate layer) where each layer contributes specific properties. The titanium contact layer provides adhesion to ceramic, while the intermediate layer provides corrosion resistance, and the copper layer provides electrical conductivity. This composite approach allows simultaneous achievement of adhesion and corrosion resistance.
3Area of stationary object
If the contact layer and intermediate layer are extended to the side surface of the copper layer, then coverage is improved, but manufacturing complexity increases due to additional masking and etching steps
Solution Approach 1:
The patent applies partial action by extending the contact and intermediate layers only to the necessary extent (set back from the side surface) rather than covering the entire side surface. This partial coverage achieves sufficient protection and adhesion functions while avoiding the need for complex masking and etching processes that would be required for full side surface coverage.
Data Source
AI summary
A ceramic substrate is provided that includes a ceramic substrate main body including a principal surface, a connecting terminal portion disposed on the principal surface of the ceramic substrate main body that is capable of being connected to another component via solder, the connecting terminal portion including a copper layer and a coating metal layer covering a surface of the copper layer; a contact layer of titanium or chromium disposed between the ceramic substrate main body and the connecting terminal portion; and an intermediate layer disposed between the copper layer of the connecting terminal portion and the contact layer, the intermediate layer including one of a titanium-tungsten alloy, a nickel-chromium alloy, tungsten, palladium, and molybdenum. The contact layer and the intermediate layer are set back from a side surface of the copper layer in a substrate plane direction.