Miniature Implant Hermetic Seal Design

In the medical device industry, miniature implants can provide real-time monitoring that enhance patient outcomes, tracks physiological parameters, and manages chronic conditions. One of the current developments in this field is miniature implant hermetic seal designs, which ensure device biocompatibility and longevity at an ultra-miniature scale. Micromachining has accelerated the miniaturization of medical implants by enabling higher precision, micron-scale feedthroughs, and tighter tolerances. In this article, we examine the major types of hermetic seals, their applications in medical devices, and key design principles to support your next innovation.

Types of Miniature Implant Hermetic Seal Designs

1. Ceramic-to-Metal Hermetic Seals:

Manufacturers create ceramic-to-metal seals by brazing high-strength ceramic materials to metal components. Alumina (Al₂O₃) and Zirconia ceramics are typically used due to their electrical insulation and mechanical strength. To form a strong bond, gold alloys (Au-Ni-Ag) are used in a brazing process. Stainless steel, platinum iridium, and titanium alloys serve as the standard metal materials.
Why Choose Ceramic-to-Metal Seals?
  • Provides superior mechanical strength and thermal stability compared to glass-to-metal seals.
Where Are They Used?
  • High-density electrical feedthroughs requiring exceptional biocompatibility and durability, such as neurostimulators and cardiac implants (e.g., LVADs, artificial hearts).
Key Features of Ceramic Feedthroughs:
  • Via Hole Size: ~25–100 µm (0.025–0.1 mm) for Alumina feedthroughs
  • Ceramic Barriers: ~50 µm for ultra-thin ceramic films
  • Pin Diameter: 25–50 µm for micro-feedthroughs
Brazing Process Details:
  • Brazing Gap: 0.05 mm to 0.1 mm
  • Gold Alloy Brazing Layer Thickness: 10-50 µm
Miniature Feedthrough Design
Micro hermetic devices
Ceramic hermetic implants

2. Fiber Laser-Welded Hermetic Seals:

For fiber laser-welded hermetic seals, a highly focused laser beam creates high-precision, non-contact welds between metal materials. Titanium alloys (Ti-6Al-4V), platinum iridium alloys, and stainless steel (316L, 17-4 PH) are common choices due to their excellent biocompatibility and corrosion resistance.

What Makes Fiber Laser-Welding Effective?

  • Prevents contamination and heat damage by avoiding direct metal contact.
  • Ensures strong, precise bonds with micron-scale welds.
Where Is It Applied?
  • Medical implants such as pacemakers and implantable cardioverter-defibrillators (ICDs) benefit from this technique’s precision and corrosion resistance.
Smallest Laser Weld Spot Size:
  • Micromachined parts enable weld spot sizes as small as ~10 µm or even sub-micron levels.
  • Gap tolerances of <20 microns.
  • Shallow welds of 0.05 mm to 0.3 mm depth (1:1 width-to-depth ratio).
Ideal Joint Types:
  • Butt Joints: Preferred for precise alignment and continuous welds on flat surfaces.
  • Keyhole Joints: Less preferred but useful for complex geometries in thicker parts.
  • V-Joints: Ideal for deeper welds in thicker components.

3. Glass-to-Metal Hermetic Seals:

Glass-to-metal seals form by bonding melted glass materials to metal components. Common glass choices include borosilicate (e.g., Pyrex), aluminosilicate, lead glass, and glass-ceramics. To ensure compatibility, the glass must match the thermal expansion coefficients of metals such as titanium alloys, and stainless steels.
Why Use Glass-to-Metal Seals?
  • Offer excellent thermal and chemical resistance along with electrical insulation.
  • Provide a cost-effective and well-established manufacturing process.
Where Are They Used?
  • Ideal for devices needing lower voltage electrical insulation and minimal mechanical stress, such as micro-sensors (e.g., glucose and pressure sensors), cochlear and retinal implants, and battery enclosures.
Common Joint Designs:
  • Flat Interface Joint: The most common method, ensuring a flat metal surface for bonding.
  • Beveled/Angled Edge: Helps minimize mechanical stress and maximize seal strength.
Manufacturing Tolerances:
  • Glass Molding Tolerances: ±0.05 mm for diameter and ±0.1 mm for thickness.
  • Metal Surface Roughness (Ra): ≤ 0.1 µm to ensure strong bonding.
  • Gap Tolerances: ≤ 0.5 mm; feedthrough diameter ranges from 1-10 mm.

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