Sensors are the backbone of a digitized society, measuring a broad range of physical characteristics in every type of application from everyday consumer products to mission critical systems in aerospace, automotive, industrial, medical, optical and every other application that relies on smart, sensor-based devices. Sensors can measure every type of fundamental physical quantities like temperature and pressure, as well as dynamic characteristics like acceleration and rotation.

This one component, low viscosity epoxy can be used for bonding and underfill applications in very tight spaces.

For each type of measurement, product developers can find sensors with the required dynamic range, sensitivity, and accuracy. Combined in single packages and modules, highly integrated solutions incorporate multiple sensors with signal conditioning chains, processors, and even optical subsystems to support more complex measurement modalities, such as biometrics, inertial measurement, and diverse monitoring capabilities. Active chemical biosensors go even further, embedding molecules in a matrix or membrane composed of epoxy resin that immobilizes the molecule without degrading its ability to interact with molecules of interest. In fact, epoxy and silicone compounds play a vital role in sensors of all types.

Whether based on simple junction devices, advanced microelectromechanical systems (MEMS) devices, or even biosensing membranes, sensors are expected to deliver accurate data reliably despite rough handling, harsh environments, and continued stress from thermal, chemical, or mechanical factors through any combination of adverse operating conditions. Their performance and longevity depend critically on advanced manufacturing methods that combine multiple materials into precision assemblies.

Within these assemblies, epoxy and silicone compounds serve a critical role as adhesives, underfill encapsulants, potting compounds, or conformal coatings needed to stabilize, bond, and protect sensor components during fabrication and continued use in their target applications. By bonding and protecting sensor components, these compounds help simplify sensor fabrication and ensure continued performance of these devices. In fulfilling their role, these compounds need to support a combination of strict requirements that is unique to every application.

Meeting Diverse Requirements

Design engineers and manufacturers can find epoxy and silicone adhesive systems formulated to match nearly any performance and handling requirement.

Despite the diverse characteristics needed to support fabrication and deployment of different sensing devices, design engineers and manufacturers can find off-the-shelf or readily customized epoxy and silicone systems designed to match nearly any performance and handling requirement. For devices intended for temperature sensing applications, manufacturers can take advantage of available compounds that exhibit the high thermal conductivity needed to avoid compromising measurements.

Thermal Conductivity and Cryogenic Serviceability: While an essential requirement for temperature sensor assemblies, high thermal conductivity can play a vital role in other types of sensor systems. In aerospace and astrophysics applications, both thermal conductivity and cryogenic serviceability can be critical requirements. Engineers at GL Scientific needed to develop a module to house infrared sensor chip arrays to be used in an adaptive optics imager instrument for a telescope. [1]

Among design objectives, the ability to control temperature of the module baseplate and imager focal plane within 0.1 kelvin (K) using a combination of cryogenic and heat cycling to achieve thermal stability. In this design, temperature sensors and heaters would be bonded to the focal plane and baseplate to monitor and control thermal cycling. Consequently, the design required an electrically insulating bonding compound with high thermal conductivity, and ability to withstand thermal cycling down to cryogenic temperatures while maintaining bonding strength as well as thermal and structural stability.

Furthermore, the bonding compound needed to reliably form strong bonds with dissimilar materials. In this case, the focal plane was constructed from titanium-zirconium-molybdenum and molybdenum and finally plated with gold; the baseplate was constructed from aluminum and nickel plated. For this application, the GL Scientific engineering team selected Master Bond EP37-3FLFA0 — an epoxy system with high thermal conductivity, excellent electrical insulation properties, and good physical strength while retaining mechanical flexibility across temperatures ranging from 4K to 250 °C.

Electrical Insulation and Handling: The specific performance and handling characteristics of a bonding compound can vary dramatically from application to application. Few applications demonstrate the wide range of requirements facing bonding compounds that are found in biochemical or biophysical applications. In a series of experiments, researchers at Carnegie Mellon University used photolithographic techniques to create microscopic electrode arrays designed to measure changes in impedance of cells exposed to various drugs. [2] Because this method can be readily automated, it can help laboratories dramatically speed the throughput of drug screening, providing a critical capability for healthcare.

Due to the sensitivity of this approach, the research team needed to ensure that the measurement signal chain remained free of artifacts that could alter the results. In this case, the team needed a compound able to coat exposed portions of the electrode array to reduce parasitic capacitance that could significantly alter the measurements. At the same time, the compound needed to remain neutral to the biochemical environment to avoid affecting the biological target. For this application, the researchers chose Master Bond EP30HT — an epoxy system with strong electrical insulation characteristics and chemical resistance. Here, the research team used Master Bond EP30HT to coat interconnect about 150 pm away from the electrodes, successfully reducing parasites between the interconnect and liquid medium bathing the living cells used for this impedance-based bioassay method.

Meeting Broad Performance and Processing Needs

Suitable adhesive systems are readily available with characteristics fine-tuned using filler materials that are combined with the base compound in different loading factors. Using different fillers, manufacturers can create adhesive compounds that are optimized for specific combinations of performance characteristics like electrical or thermal conductivity, chemical resistance, and stability as well as processing characteristics like viscosity, work time, and cure time.

Other types of specialized epoxy and silicone compounds are designed to ensure compatibility with key standards in medical, aerospace, and other industries. Engineers developing more sophisticated sensors designed for implant or placement on the skin have already taken full advantage of biocompatible adhesives compounds to provide a protective interface between instruments and bone tissue, [3] enable measurement of dissolved oxygen, [4] encapsulate a fully implantable biosensor array, [5] and more. These specialized compounds not only provide the necessary thermal and electrical conductivity characteristics, but also meet requirements for biocompatibility specified in USP Class VI and ISO10993-5 standards.

Similarly, engineers working on assemblies for aerospace systems or other applications with sensitive electronics can find adhesive compounds that meet ASTM E595 and NASA requirements for low outgassing. Using these compounds helps ensure that optical systems, sensitive electronics, or other surfaces remain free from contamination from volatile compounds sometimes exuded by adhesives even after cure.

New Materials and Methods

Sensor technology continues to advance rapidly, keeping pace with advances in material science and manufacturing engineering. Advanced strain sensors based on single-walled carbon tube nanocomposites or highly sensitive heat detectors using the pyroelectric properties of emerging gallium nitride (GaN) devices promise to drive novel applications using these nanosensors to detect subtle phenomena.

Other sensor technologies bring similar benefits to a wide range of sensing modalities. Destined to be woven into textiles, painted on surfaces, or fabricated with 3D-printing methods, new types of sensors will enable development of smart products able to access more comprehensive measurement data. More than ever, these emerging sensors will require adhesive compounds able to meet specific requirements for conductivity, biocompatibility, and manufacturing. As with sensors, new compounds will continue to emerge, using new materials and methods for fillers based on advanced materials such as graphene, carbon nanotubes, nanosilicates, and more.

This article was written by Rohit Ramnath, Senior Product Engineer, Master Bond (Hackensack, NJ). For more information, visit here .


  1. Luppino, G. (2003). GSAOI H2RG 4Kx4K Detector Mosaic Module Design Description. GL Scientific Technical Report. GLSTR-0301.
  2. Nguyen, D., Domach, M. Huang, X., Greve, D. Impedance Array Studies of Mammalian Cell Growth.
  3. To, G, et al. (2008). Multi-channels wireless strain mapping instrument for total knee arthoplasty with 30 microcantilevers and ASIC technology. IEEE SENSORS 2008 Conference.
  4. Wittkampf, M., et al. (1997). Silicon thin film sensor for measurement of dissolved oxygen. Sensors and Actuators B: Chemical, Vol. 43, doi:10.1016/S0925-4005(97)00138-X.
  5. Baj-Rossi, C. et al. (2013). Fabrication and packaging of a fully implantable biosensor array. 2013 IEEE Biomedical Circuits and Systems Conference, BioCAS 2013. 166-169. doi:10.1109/BioCAS.2013.6679665.