Electronics are becoming a ubiquitous part of our everyday lives, not only in our homes but also at commercial and industrial sites. The use of electronics at these sites is changing the way many companies are managing and averting risk, allowing them to measure and control risk in ways they’ve never been able to before. The oil and gas industry relies heavily on these advanced technologies to develop reliable and innovative ways to optimize businesses as advancements in offshore drilling and hydraulic fracturing are making it possible to recover gas from greater depths and in harsher environments.

The high price of oil and, in some regions, natural gas has helped fund research into extracting hydrocarbons from these more difficult places, both onshore and offshore. The challenge to electronics manufacturers and designers is to get these ever-shrinking, increasingly complex electronics to work at the high temperatures, vibration, and extreme pressures encountered in these environments. Instrumentation designed to work in this environment is constantly being challenged, and there has been a proliferation of electronic devices for some of these difficult environments, including the most challenging to date: downhole.

A drive for high levels of functionality in products designed to measure performance in downhole environments – such as sensors within drillheads that can measure depth, vibration, and temperature – has seen the electronics change from simple low-technology, “conservative” designs to ones using technology normally seen in mobile phones, such as 0.5-mm pitch ball grid arrays, small chip components measuring less than 1 mm, and high-performance silicon. But these complex designs still have to survive the high temperature and vibration commonly seen in a drilling operation. A typical example of this is the accurate vibration sensor that lives right behind the drillbit. This sensor has a high-specification digital signal processor, radio communications, and flash memory, which all fit into a metal tube 100 mm long and 40 mm in diameter. So the challenge is to develop technology that allows more information to be delivered in smaller devices in harsher environments, and the electronics industry is having to work hard to come up with a solution to this problem.

High melt-point solder techniques

Electronics manufacturers are accustomed to the use of different solder alloys to achieve strong joints at higher temperatures. In fact, high-temperature alloys were being used before EU legislation had moved the rest of the industry away from tin or lead. The performance of these alloys is sufficient between 150°C and 175°C (302°F and 347°F) operating temperatures, but above this range, different alloys are needed to provide the tensile strength required. Each of these has its own challenges – Pb85 has poor solderability, and Au80 is prohibitively expensive – but the alloy that is currently getting the most focus is high melt-point (HMP) Pb93.5,Sn5,Ag1.5. This alloy has great tensile strength at high temperatures and flows well when liquid. The main problem is that its melting point of 301°C (574°F) means that the processing temperature of current automated manufacturing methods is so hot that the silicon devices within the manufacturing process can get damaged. Currently, the only method of soldering these devices is by using skilled people, but even then it is not possible to solder some of the new miniaturized parts by hand. However, new manufacturing equipment that will help solve this problem is on the horizon, driven by the demand created by the industry.

Packaging technology

HMP can take the working temperatures of the electronics above 200°C (392°F), but soon after this the integrity of the component packages defines the limit of the working temperatures. Most electronics are only available in plastic packages. These are designed to withstand 260°C (500°F) for short periods, for example as part of the soldering process, but not for extended periods of time. Thus, many high-temperature tools used above 200°C have a very short life expectancy before the packaging deteriorates.

Hybrids

Hybrid technology is currently being investigated to get away from the packaging issue. This technology has been around for a long time; it involves bonding the bare silicon onto a ceramic substrate and wire-bonding the connections onto conductive paths printed onto the substrate. These can withstand much higher temperatures for much longer, but they have a few drawbacks. The hybrid circuits are more time-consuming and costly to prepare tooling for and are not easily modified. This means design changes are more difficult and expensive and take longer. Also, many of the parts that are used downhole are not available in bare die format, although increasingly vendors are responding to the need.

Silicon carbide

Silicon carbide (SiC) is getting a lot of attention and funding in the power electronics segment. It is a new higher performance replacement for silicon due to its high energy gap, good thermal conductivity, and high-temperature operation. These characteristics make it good for downhole applications, and it is now possible to drive more efficient motors and power supplies at higher temperatures. At present it is only available for power diodes and transistors, and unfortunately there is no sign yet that this development is going to extend into processor, sensor, and communication technology that would be required to get these products working at above 300°C (572°F).

More ruggedized products

Current electronics also need to go through a suitable ruggedization program to make sure they can physically survive the environment they are made to work in. This normally involves mechanical adhesive to support the joints and some kind of coating and potting to ensure physical separation from the elements. Care has to be taken to ensure that at the extremes of temperature and pressure, the coefficients of thermal expansion (CTEs) are matched throughout the product to ensure that no undue stress is put on the joints that might cause premature failure. In such critical devices this ruggedization is a necessity – one customer develops a drillhead control product that uses up to five different products for ruggedization. They include mechanical adhesive for big parts to aid vibration-proofing, a white ceramic product to help heat dissipation, a conformal coat for electronics protection, a potting compound to protect the hole assembly, and a foam to stop material going where it shouldn’t and causing a CTE mismatch.

Heat-sinking

Working electronics create heat, even when they are hot already. This problem will become more acute as the environment gets hotter. The initial solution is to make the electronics withstand the hotter temperatures again, but as the realistic working limit is reached, methods of heat-sinking the electronic assemblies need to be found. Initially this has been through traditional heat sinks, but now the use of thermally conductive adhesives is becoming common. Other methods such as banked thermoelectric coolers (a solid-state electric cooler) may need to be considered to keep the junction temperature of the silicon down to a level where its working life will be suitable.

How hot will we go?

While we can visualize the development path of electronics working at more than 300°C – and it’s not too much of a stretch to see 500°C (932°F) – the unknown quantity is how long it will take to get there. This depends on the market drive and investment availability, which in turn will depend ultimately on the price of oil. It also is uncertain whether a disruptive technology will change the expected development path using hybrids and SiC. This potentially could be high-temperature conductive adhesives, encapsulants, or polychlorinated biphenyl materials. The threat of this will stop investment in the technology until the market needs it imminently, and many assemblers won’t invest in hybrid technology until they can see the demand. The winners – as always – will be those who are bold enough to gamble on the right technology at the right time.