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Capacitors survive extreme down-hole drilling conditions

Posted: 20 May 2015 ?? ?Print Version ?Bookmark and Share

Keywords:electronic controllers? capacitors? MLCCs? X7R? Highly Accelerated Life Testing?

At the forefront of engineering and technology, electronic controllers are being deployed in increasingly harsh environments, particularly in applications such as extracting offshore oil and gas, and also in sectors like aerospace, defence and automotive. New generations of components, including capacitors, are needed to withstand today's highest extremes of temperature, pressure, mechanical shock and vibration.

Extreme down-hole, and more
Today's oil exploration and production industry perfectly illustrates the increasing demands placed on high-tech equipment, and electronic components in particular. As easily accessible oilfields are exhausted, activities are moving into more extreme and challenging environments; drilling deeper, further, and often far offshore. With operating costs in the order of millions of dollars per day, any downtime caused by equipment failure can quickly become very expensive. Yet the conditions under which drilling and extraction equipment must operate have become extremely demanding.

One of today's deepest oil wells, the BP Tiber well discovered in 2009, lies in over 4000 feet of water off the Gulf of Mexico, and has been drilled to a depth of more than 35,000 feet. Projects like these are causing the industry to redefine the terms used to describe drilling conditions. The UK Energy Institute's Model Code Of Safe Practice originally standardized a definition for High-Pressure/High-Temperature (HPHT) wells, as having undisturbed bottom-well temperatures above 149C and needing pressure-control equipment with a rated working pressure of over 69MPa (10,000 psi). These limits are no longer adequate to distinguish today's most extreme wells, and new definitions are emerging. Although yet to become widely standardised, the ultra High-Pressure/High-Temperature (uHPHT) category now covers temperatures from 204C to 260C and pressure from 139MPa to 241MPa, while extremely High-Pressure/High-Temperature (xHPHT) refers to temperatures above 260C and pressures above 241MPa.

In addition, the use of new processes such as hydraulic fracturing (fracking) and horizontal drilling introduce hazards such as high vibration and shock, which can challenge the electrical interconnections of electronic controllers and data loggers. At the same time, the control of equipment operating at very low depths is becoming more complex, requiring greater quantities of data to be monitored. As a result, electronic equipment must not only be more physically robust and highly reliable, but must also support extra data channels and functionality within tight space constraints. As demand for more sophisticated instrumentation increases, component size has become an important consideration.

Extreme down-hole drilling is just one example among many applications that expose electronic devices to extremely harsh environmental conditions. Geophysical probes, controls mounted in aircraft engine compartments, automotive hybrid and electric-vehicle power controllers, and modern defense systems are also subjected to increasingly harsh temperatures, mechanical shock, and vibration.

Designed for harsh environment
For some types of components, screening or characterization at high temperature is often adequate to verify suitable performance in the target environment. With other components, such as Multilayer Ceramic Capacitors (MLCCs) that are widely used for duties such as timing or tuning, pulse generation, decoupling, filtering, transient voltage suppression, blocking or energy storage, enhanced materials and construction can produce a better performing device.

MLCCs built using X7R dielectric materials provide an attractive combination of performance and economy for general-purpose applications. Devices with C0G dielectric, on the other hand, can maintain significantly more stable capacitance over a wide temperature range. To ensure the desired capacitance at the intended operating temperature, the designer can save valuable PCB real-estate by using a relatively small C0G MLCC rather than a physically larger X7R device that has higher capacitance.

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