NextGen Camera Module adhesives: IR Filter bonding

Our electronic devices and automobiles have seen a dramatic increase in the number of Compact Camera Modules (CCMs) integrated into their assembly. For our mobile devices, the continuous integration of CCMs has resulted in exceptional clarity over a wide range of distances. The emergence of Advanced Driver Assistance Systems (ADAS) in the automotive industry has also increased demand for CCMs worldwide.

Depending on the type of CCM device, either fixed or autofocus, these CCMs can use between 5 to 10 different adhesives in their construction. The specification of the suitable adhesive is critical to the device’s performance and reliability. Depending on the specific bonding application, each bond will have very different performance requirements.

Fig 1: A typical IR filter and lens assembly

IR filters are one portion of the construction of CCM devices. Unfiltered or poorly filtered digital cameras can detect infrared waves reflected from an object that it is focusing on. This reflection can then negatively impact the quality of the captured image. The utilization of the IF filter ensures more vibrant imaging and display of more natural colors. The IR filter is attached to the VCM (Voice Coil Motor) module in auto-focus CCMs or the lens holder in fixed-focus CCMs.

The IR filter component is usually manufactured from specialized optical glass and contains an additive coating to filter target wavelengths in the infrared range of light. This range is typically 700-1000nm. Ensuring reliable bonding of the IR filter is critical to providing a robust CCM. There are several challenging requirements that any adhesive solution must meet to ensure reliable adhesion.

A Reflective Index (RI) determines how much the light path is bent or refracted when entering a material. To ensure that the photos taken are not of poor quality or distorted, the refractive index or material used in CCMs must not be too high or too low. Cameras are frequently exposed to an extensive range of harsh environments, and they will experience excess humidity, moisture, and elevated temperatures. A camera is also expected to last several years. Its adhesive component, alongside the other CCM components, must be developed to withstand such harsh conditions to ensure the camera’s lifespan.

Fig 2: Cross section of a IR Filter and lens assembly with a typical adhesive bond line

Accelerated environmental aging will be performed on the CCM assembly to ensure optical stability. Transmittance with yellow and blue colors is measured at different pre-determined intervals to ensure the CCM assembly is optically stable.
Aside from the harsh environmental and optical performance requirements demanded of the adhesive, CCM design must be optimized for high-volume manufacturing. Other requirements also include good adhesion to difficult-to-bond plastic compounds such as LCP. This material is sometimes the other portion of the assembly alongside the IR filter.

Krylex’s KU5146 has been developed explicitly for bonding IR filters to ensure excellent optical performance and environmental reliability. KU5146 offers the following features to a CCM manufacturer while maintaining excellent optical clarity:

• Exceptional depth of cure
• Good adhesion to a variety of plastics and glass
• Outstanding strength retention after harsh environmental testing
• Excellent ability to withstand thermal shock

October 20, 2021