Hermetic package, electronic devices

In dry-heat sterilization, the parts are exposed for 2-3 hours at 165°C-170 °C. Dry-heat exposure is the least effective sterilization method and most likely to degrade materials and electronic devices. Although adhesives may have been cured at 165 °C prior to hermetic packaging, the additional temperature exposure within the sealed package can result in further outgassing of moisture and corrosive volatiles causing electrical failures. Outgassing is worse if the adhesive had been cured at a temperature below 165 °C. 

Implantable medical devices have been widely used to restore body functions, improve the quality of life, or save lives. Experts estimate that 8 to 10 percent of all Americans (some 20 million to 25 million people) [1], or about 1 in 17 people in industrialized countries [2], carry some form of implanted device. Many medical devices, such as the implantable cardiac defibrillator, cochlear implant, artificial vision prosthesis, neuromuscular microstimulator, and the like contain sophisticated electronic circuits. Such long-term implantable medical devices are susceptible to damage by body fluids over time. Hermetic packaging is required to protect the electronic circuitry of the implant from the harsh environment of the human body. 

Adhesives in both paste and film form have been used to attach and seal ceramic or metal lids to cavity packages that may also be ceramic or metal. These packages cannot be considered hermetic in the sense that seam-sealed, welded, or soldered fids are, but they are adequate for most commercial and consumer electronics where extreme moisture-temperature environments are not encountered. Packages sealed with Epo-Tek H77 epoxy adhesive are reported to provide near-hermetic sealing of hybrid microcircuits, integrated-circuit devices, and MEM packages withstand 100 hours of 95% relative humidity."... 

Electronic circuits must be protected from the harsh environment of the human body. The packaging of implantable electronics uses various materials, including polymers, metals, and ceramics. The encapsulation method depends somewhat on the electronic circuit technology. Older devices may still use discrete components in a classical form, such as leaded transistors and resistors. The newer designs, depending on the sophistication of the implanted device, may employ application-specific integrated circuits (ASICs) and thick film hybrid circuitry for their implementation. Such circuits place considerable requirements for hermeticity and protection on the implanted circuit packaging. 

X-ray imaging of electronic assemblies can check for voids in the die-attach material to the substrate or to substrate-attach material to the package. There is no need to apply power to the DUT nor measure any electrical parameter. Devices may be potted or hermetically sealed for this test. 

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