Lead-Free Soldering Metallization for Brittle Substrates
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Solution Overview
Problem
Current lead-free soldering methods, particularly using tin-silver alloys, face challenges in achieving reliable bonding to thin films on brittle substrates like ceramics due to high reflow temperatures and mechanical stress issues, which require thicker films and are complex and costly to produce.
Innovation Solution
A method involving metallization steps including a tie layer of chromium or titanium, a diffusion barrier layer of platinum or palladium, and a wetting layer of gold, allowing for the direct deposition of a tin-silver or tin-silver-copper alloy solder, resulting in a thin-film trilayer with reduced thickness and enhanced adhesion and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free soldering is performed using tin-silver alloy at high reflow temperature, then soldering reliability is improved, but mechanical stress increases and dissolves thin films
Solution Approach 1:
The patent applies preliminary action by depositing a diffusion barrier layer and a wetting layer on the substrate before applying the solder. The diffusion barrier layer (e.g., ruthenium, rhodium, or iridium) prevents dissolution of the thin film during high-temperature reflow, while the wetting layer (e.g., gold or copper) ensures proper solder adhesion. This preparatory structure allows the thin film to withstand the mechanical stress of lead-free soldering without dissolving.
2Strength
If film thickness is increased to prevent dissolution during soldering, then film strength is improved, but device complexity and production cost increase
Solution Approach 1:
The patent uses an intermediary approach by introducing a diffusion barrier layer between the thin film and the solder. This intermediate layer has high resistance to solder dissolution, allowing the thin film to remain thin while still protecting against dissolution. The wetting layer serves as another intermediary that facilitates solder adhesion without requiring the film itself to be thick, thus maintaining film strength while avoiding increased production complexity.
3Stability of the object's composition
If multiple layers are deposited to prevent dissolution, then film stability is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies local quality by making the protective structure localized only where the solder contacts the substrate. The diffusion barrier layer and wetting layer are deposited only in the solder joint area, not across the entire substrate. This localized approach provides the necessary film stability at the critical interface while minimizing the overall material cost and manufacturing complexity compared to coating the entire surface.
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
This approach enables reliable lead-free soldering of thin films on brittle substrates with reduced mechanical stress, increased impact strength, and stable electrical continuity, while maintaining a low outgassing profile suitable for high-vacuum applications.
Implementation Method 1
an adhesion layer comprising Platinium or Titanium
Implementation Method 2
a barrier layer comprising Palladium or Platinium
Implementation Method 3
depositing a wetting layer comprising gold
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method of soldering a conducting body to a substrate using an alloy chosen from a tin-silver alloy and a tin-silver-copper alloy, characterized in that the method comprises the following steps: - metallization of the substrate, said metallization step comprising a step (6) of depositing a tie layer on the substrate and a step (10) of depositing a diffusion barrier layer, said tie layer having any one of the chemical components chosen from chromium, titanium and a titanium alloy, said diffusion barrier layer comprising a material chosen from platinum and palladium; and - depositing a wetting layer comprising gold; - application (18) of a solder between the conducting body and the metallized substrate, said solder comprising an alloy chosen from a tin-silver alloy and a tin-silver-copper alloy.