RADAR

What adhesives contribute to RADAR technology

Over the last 25 years of automotive technological progress, no aspect has evolved quite as rapidly as Advanced Driver Assistance Systems, or ADAS. Throughout their deployment, these functions, such as adaptive cruise control and blind spot detection, have grown to become standard equipment on automobiles across most segments.

RADAR is the baseline of many of these features. After the introduction of RADAR-guided adaptive cruise control in the late 1990s, this feature evolved to include collision mitigation capabilities, eventually enabling the automobile to stop entirely.

But despite having been around much longer than other ADAS technologies, new RADAR-enabled systems are still becoming more complex, with many layers playing a role in their operation. And as with other ADAS technologies, adhesive bonding is fundamental to each. This technical article will go over these layers, what they do, how they are manufactured, and how adhesives are incorporated into their assembly.

RADAR application overview

RADAR sensors can be broken down into four basic layers: the radome, the antenna, the printed circuit board (PCB), and the housing. In each of these layers, oftentimes more than one bonding process is needed.

A multitude of tasks for high-tech adhesives

Below the top radome layer, antennas are fixed to the PCB by way of antenna bonding. Within certain antenna designs, layers can be bonded through thin bondlines. These adhesive layers can be featured with or without electrical contacting or EMI-shielding properties. Meanwhile, the PCB comes with its own functional applications through RADAR-absorbing or thermally conductive adhesives. Even more bonding tasks come with advanced packaging solutions on PCBs, such as encapsulation or pin sealing applications. The PCB is then bonded inside the housing, followed by bonding the housing and radome to create the final assembly.

Each one of these bonding tasks, despite all of them taking place within one assembly, comes with its own adhesive requirements, desired properties and curing methods for optimal results. Understanding these intricacies, DELO Industrial Adhesives offers tailored products for every one of these applications.

Antenna bonding

For antenna bonding, an ideal adhesive would leverage dual-initiator technology. In short, this process consists of light-preactivation and an additional UV-fixation method as a final process step after joining.

By exposing the adhesive to light directly after being dispensed onto the surface, preactivation allows the material to “activate” curing before joining, allowing end users to forego the limitations of heat curing. Instead, they can take advantage of low energy consumption, low thermal stress, and no need for a time-consuming cool-down phase.

With the second UV-fixation of the fillet taking place in a mere four seconds, thanks to this technology, joined components can continue processing immediately.

Antenna stacking

As the name of the process suggests, in antenna stacking, layers of the assembly are stacked atop one another, with either electrically conductive or non-conductive adhesive materials fixing each layer in place. Specific fillers inside of the adhesive offer the possibility to achieve a shielding effect against electromagnetic waves. This way the several channels within 3D antennas can be perfectly isolated from unwanted electromagnetic influence, ensuring optimal quality of transmitting and receiving signals.

Other important adhesive requirements include excellent peeling, temperature and humidity resistance, as well as narrow bondlines measuring below 20 µm.

EMI shielding

For electromagnetic interference or EMI shielding, using the right adhesives at various levels helps prevent the interaction of parasitic electromagnetic waves which can influence the accuracy of the sensor or even the functionality of the electronics themselves.

EMI shielding can be achieved in various ways; different filler materials can make the adhesive either reflect or absorb electromagnetic waves. This can either almost entirely block the wave from sensitive areas or absorb it whilst transferring it into heat. Adhesives can therefore offer multifunctional properties. For example, they can ensure a strong bond while absorbing electromagnetic waves and remaining thermally conductive.

Housing bonding and sealing

In bonding the RADAR housing, the task is simple; seal the housing and all of its contents, including the PCB and antenna, to the radome. Silicones are currently the most widely used materials for this. However, special light-activated adhesives are an interesting alternative, demonstrating advanced properties for high-tech applications.

Possessing properties such as ~500% elongation at tear while offering significantly higher bonding forces than silicones, these modified urethane polymers make housings extremely resistant to pressure or thermal changes. It also retains its flexibility and structure at temperatures as low as -40 °C.

They are first preactivated via LED light, with recommended wavelengths of 400 or 460 nm activating the adhesive to begin humidity curing. This leaves enough open time for the housing and radome to be joined, reaching functional strength within minutes and allowing for faster processing.

Conclusion

Adhesives are indispensable for modern radar technology

The examples given were merely some of the adhesive solutions that can be employed in RADAR sensor assembly. In antenna stacking and bonding, light preactivation reduces curing time and carbon emissions while maintaining high bonding strength and resistance. Heat curing can be foregone by way of dual-initiating adhesives. EMI shielding using DELO adhesives ensures optimal functionality of RADAR sensors and electronics while simultaneously offering multifunctional properties. DELO PHOTOBOND LA is used for RADAR housing bonding, offering strong mechanical properties, preactivation capabilities, and high environmental resilience. All of this goes to show that, even if different tasks come with different requirements, an adhesive solution always awaits to simplify and optimize each.