the management of any CTE mismatch is critical to avoid tension and stress on the joint that can result in voids, separation between the glass and the metal, or a breakdown in the structural integrity of the glass. The glass-to-metal seal not only has to survive the melting process during manufacturing but also must withstand the thousands of thermal cycles under actual operating conditions. This requirement of matching the CTE of the metal and the glass limits the choice of metal material. Kovar has extensively been used for packaging in glass-to-metal seals because its linear thermal expansion coefficient value of 5.5 × 10–6/K from 20 to 200°C and 4.9 × 10–6/K at 400°C closely matches the CTE of borosilicate glass. Feedthrough pins composed of nickel alloys and stainless steel are similarly chosen for the necessary thermophysical properties. However, these materials involve significant compromises in electrical conductivity — the main purpose of an electrical connector.
allowing optimization of the electrical properties of the metal feedthrough pins. Without the constraint of matching thermal expansion coefficients, conductor materials can be chosen to fit the application rather than the method of manufacture. For example, beryllium copper (BeCu) can be utilized which provides lower electrical resistance compared to Inconel and stainless steel. The more efficient conductivity allows more current to pass through while generating less heat. That means more reliable power and signal transmission. With higher electrical conductivity, smaller pin diameters are possible, enabling significantly higher pin density and more flexibility in the pin pattern design, resulting in smaller overall connector size. Injection molding processes with plastics are also better suited to manufacturing very small parts than the glass melting process. The lighter thermoplastic material, combined with the smaller size of the pins and the overall connector, results in a significant reduction in weight compared to GTMS connectors. With applications in the aerospace, subsea, and energy industries, component weight and dimensional size are critical to the overall subsystem performance.
PEEK AND PEK ADDRESSES SHORTCOMINGS OF GLASS
The introduction of PEEK and PEK electrical connectors overcomes the inherent weaknesses of glass-to-metal connectors. The CTE of thermoplastic material does not need to be matched to the metal,
82
Powered by FlippingBook