Microfluidic Device Attachment With Indium-Silver Solder for Hermetic Sealing
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Solution Overview
Problem
Silicon and titanium materials cannot be directly soldered together due to mismatch in thermal expansion coefficients, leading to weak or fractured joints in MEMS pumps used in implantable medical devices, which require a hermetic seal to prevent water diffusion and fluid leakage.
Innovation Solution
A method involving surface preparation of silicon and titanium components with hydrofluoric acid to remove oxide coatings, followed by sputtering with Ti-W, Nickel, and Gold layers, and soldering with indium silver in forming gas to create a soft solder joint that accommodates thermal expansion mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon and titanium are directly soldered together, then the manufacturing process is simple, but the joint strength is weak or the joint fractures due to CTE mismatch
Solution Approach 1:
The patent applies multiple intermediary layers (Ti-W adhesion layer, nickel layer, and gold layer) between silicon and titanium to enable successful soldering. These intermediary layers resolve the CTE mismatch and material incompatibility, allowing the joint to withstand thermal stress while maintaining manufacturing simplicity through standardized deposition processes.
2Ease of manufacture
If silicon and titanium are directly soldered together, then the manufacturing process is simple, but the hermetic seal is compromised leading to water diffusion and fluid leakage
Solution Approach 1:
The multi-layer metallization structure (Ti-W, nickel, gold) serves as an intermediary system that ensures hermetic sealing. Each layer contributes to the seal integrity: Ti-W provides adhesion, nickel provides barrier properties, and gold provides corrosion resistance and solderability, collectively preventing water diffusion and fluid leakage while maintaining a reliable hermetic seal.
3Strength
If a hard solder joint is used, then the joint is rigid, but the joint fractures under thermal stress from CTE mismatch
Solution Approach 1:
The patent changes the material parameters of the solder joint by using a soft solder (indium-silver alloy) instead of hard solder. This parameter change allows the joint to accommodate thermal expansion mismatch through material compliance, preventing fracture under thermal stress while maintaining adequate mechanical strength through the controlled metallization layers.
4Ease of manufacture
If the temperature excursion is large, then the soldering process is effective, but the strain between silicon and titanium surfaces increases
Solution Approach 1:
The patent changes the thermal parameters by using a low-melting-point indium-silver solder alloy, which enables effective soldering at reduced temperatures. This parameter change limits the temperature excursion during soldering, thereby reducing the thermal strain between silicon and titanium surfaces while still achieving reliable joint formation through the intermediary metallization layers.
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 method provides a hermetic bond that withstands thermal stress, ensuring reliable sealing and preventing fluid leakage in MEMS pumps, suitable for implantable medical devices.
Implementation Method 1
The silicon micropump surface may be treated with hydrofluoric acid to remove its silicon oxide coating
Implementation Method 2
then Ti—W, Nickel, and gold layers successively sputtered onto it
Implementation Method 3
The manifold may be ground flat, and plated with electroless nickel
Implementation Method 4
The nickel plated manifold may then be baked, so as to create a transition from pure Ti to Ni—Ti alloy to pure Ni at the surface of the manifold
Implementation Method 5
silicon and titanium may be soldered together with a soft solder joint using indium silver
Data Source
AI summary
In embodiments, a silicon part and a titanium part may be soldered together without breakage or instability. In embodiments, silicon and titanium may be soldered together with a soft solder joint including indium silver, where the temperature excursion between solder solidus and use temperature limits the strain between the two surfaces. In embodiments a silicon micropump surface may be treated to remove its silicon oxide coating, and then Ti—W, Nickel, and gold layers successively sputtered onto it. A corresponding titanium manifold may be ground flat, and plated with electroless nickel. The nickel plated manifold may then be baked, so as to create a transition from pure Ti to Ni—Ti alloy to pure Ni at the surface of the manifold, and for protection of the upper Ni surface, a layer of gold may be added. The two surfaces may then be soldered in forming gas.