Epoxy casting used as nonhermetic encapsulation technique for implantable electronic devices

Area of Science:

• Biomaterials Science
• Materials Engineering
• Medical Device Technology

Background:

• Implantable medical devices require robust packaging to shield electronics from the body's corrosive environment.
• Current packaging options are limited, primarily to hermetic sealing, with nonhermetic encapsulation being a less explored alternative.
• Previous research indicated epoxy resins as potential encapsulants, necessitating further investigation into their material properties and long-term performance.

Purpose of the Study:

• To evaluate the water uptake and diffusion characteristics of three EPO-TEK (ET) epoxy resins.
• To assess the functional longevity of microcontrollers encapsulated in selected epoxy resins under simulated physiological conditions.
• To determine the suitability of nonhermetic epoxy encapsulation for implantable medical electronic applications.

Main Methods:

• Water uptake measurements were conducted on three EPO-TEK epoxies (ET 301, ET 301-2, ET 302-3M) following ISO 294-3 standards.
• Diffusion constants were calculated based on water uptake data.
• Eight microcontrollers were encapsulated in two selected epoxy types and immersed in phosphate-buffered saline (PBS) at 37°C for 78 days.

Main Results:

• Average water uptake percentages were 3.18% (ET 301), 1.81% (ET 301-2), and 2.34% (ET 302-3M).
• Calculated diffusion constants (D) were 3.61E-13 m²/s (ET 301), 3.63E-13 m²/s (ET 301-2), and 1.98E-13 m²/s (ET 302-3M).
• All encapsulated microcontrollers operated without malfunction for the entire 78-day test period.

Conclusions:

• The evaluated EPO-TEK epoxy resins exhibit favorable low water uptake and diffusion properties for potential use in nonhermetic encapsulation.
• Nonhermetic encapsulation using these epoxies provides adequate protection for microelectronic components in simulated physiological environments.
• These findings support the feasibility of using epoxy resins as an alternative packaging strategy for implantable medical electronics.