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Non-hermetic encapsulation for implantable electronic devices based on epoxy.
Summary
This study evaluated non-hermetic epoxy encapsulation for implantable electronics. The best performance for standard FR4 substrates was ET 301-2 epoxy, offering low water vapor transmission rate and minimal adhesion loss in moist conditions.
Area of Science:
- Biomaterials Engineering
- Electronic Packaging
- Implantable Devices
Background:
- Protecting implantable electronics from the body's humid environment is crucial for device longevity.
- Hermetic and non-hermetic packaging are primary strategies, with non-hermetic approaches offering potential cost and design advantages.
- Epoxy-based encapsulation is explored for its processability and protective qualities.
Purpose of the Study:
- To characterize material combinations for non-hermetic, high-reliability epoxy-based encapsulation.
- To evaluate processability, water vapor transmission rate (WVTR), and adhesion of epoxy encapsulants.
- To identify optimal epoxy and substrate combinations for implantable electronic protection.
Main Methods:
- Twelve epoxy-based material combinations were tested, including four epoxy types (three EPO-TEK, one budget) and three substrate types (two ceramic, one FR4).
- Encapsulation properties were analyzed over 30 days using aging tests in moist environments.
- Water vapor transmission rate (WVTR) and adhesion drop were measured.
- Commercially available USB flash drives were encapsulated and tested for 256 days in phosphate buffered saline (PBS) at 37°C.
Main Results:
- The combination of standard FR4 substrate and ET 301-2 epoxy demonstrated the best encapsulation properties, with a WVTR of 0.0278 g/day/m² and a 24.59% adhesion drop after 30 days in PBS.
- For ceramic-based systems, the alumina substrate with ET 302-3M epoxy showed promising results (WVTR: 0.0588 g/day/m², adhesion drop: 49.58%).
- Encapsulated USB flash drives showed no failures after 256 days of testing in PBS at 37°C.
Conclusions:
- Non-hermetic epoxy encapsulation is a viable strategy for protecting implantable electronics.
- ET 301-2 epoxy on FR4 substrates offers superior performance for non-hermetic packaging.
- Alumina substrates with ET 302-3M epoxy are a promising alternative for ceramic-based implantable electronic systems.
