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Pushing the envelope with microelectronics

For many years, the omnipresent hybrid microcircuit or ceramic multi chip module (mcm) has proven its outstanding pedigree for harsh environment applications against conventional pcbs with soldered, surface mount components.

The aerospace, automotive and more recently the oil and gas industries have in depth experience with the application of mcm technology and have long since endorsed it as the gold standard for the critical electronic functions within their systems. The scientific reasons for this are extensive with features including: robust/hermetic enclosures, reduced interconnections, 'free space' unstressed wire bonds, welded seals, closely matched temperature coefficients of expansion (tce) and many more.

British companies such as C-MAC MicroTechnology have been focusing on mcm technology; with products such as the optical transceiver used on the Eurofighter Typhoon aircraft. This module performs the optoelectronic interface for a significant number of subsystems within the airframe, including avionics, communications and munitions management. Working at extremely low optical signal levels and high mechanical stress, the transceiver is designed and manufactured for reliable operation for the lifetime of the aircraft.

This module, as with many others, operates reliably over what is universally classified as the 'military temperature range' of –55 to 125°C. However, increasingly we now see that this maximum temperature of 125°C is no longer adequate. So, with a combination of higher data rates, increased electronic packing density and the handling and switching of higher power levels the junction temperature within semiconductor components is being pushed to 200°C and beyond. This high temperature challenge is further accentuated by increased integration and miniaturisation, reduced mass and more importantly the desire for sensing and control in remote and high temperature environments.

Opportunities
Currently, the biggest opportunities for high operating temperature electronics lies where there is greatest gain, and this certainly includes applications such as jet engines, turbines, turbochargers, electric vehicles and in deep well subterranean drilling. Specialist microtechnology companies have quickly and effectively engaged in these new requirements and are able to leverage their extensive experience with ceramic mcms and established capability, materials and processes to develop and manufacture high operating temperature electronic modules. For example, C-MAC MicroTechnology has launched a voltage step down, DC-DC converter module with a high aspect ratio footprint suited to the drill tubes for deep well drilling in the oil and gas industry.

The circuit is housed in a welded hermetic metal package with a cross sectional width of 25.4mm. The choice of materials and the development of interconnect processes are key to the long term reliability of the product operating continuously at high temperatures and high dynamic mechanical loads.

Key challenges in transitioning the original pcba design to an mcm format included assessment of the smallest space envelope in which the circuit could be reliably housed, tce management of different elements of the construction and finally, the electrical and environmental testing to ensure the resultant product would fully satisfy the environmental requirements down hole. While this realisation of the DC-DC converter is targeted specifically at the oil and gas drilling market, the physical envelope may be modified for applications in the aerospace and defence markets.

Clearly, this is an exciting and changing time for electronics used in harsh environments, and the Defence Systems & Equipment International Trade show held in London next month will showcase how leading electronics companies are designing and manufacturing systems for some of the most extreme conditions in the world.

Author
Chris Andrews, product marketing manager, C-MAC

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