Adhesives for optoelectronics

16 Apr 2013

DELO has developed a range of light- curing and light-/heat-curing epoxy adhesives, called DELO-KATIOBOND OB and DELO-DUALBOND OB. Light-curing ideally satisfy the needs of the optoelectronic industry as they allow manufacturers to reliably and quickly join their tiny components made of dissimilar materials without significant heat input.

Low outgassing

Nearly every cured adhesive shows mass loss under the influence of temperatures. This effect is called outgassing. The consequences of outgassing are usually not relevant for the user. The situation in optoelectronics, however, is different. Outgassing products may condense on lenses of LED packages, and thus change the emission characteristics. They may also directly interact with the LED surface and reduce the light yield.

When evaluating adhesives, the absolute outgassing volume plays a role. However, it is also important whether outgassing occurs only for a short time during heating or permanently, whether the outgassing products are volatile or re-condensable, and whether damaging interactions take place with active components.

DELO-OB adhesives show very low outgassing in the magnitude of 0.1 mass% at 120 °C. Outgassing stops shortly after heating, while most light-curing acrylates already durably outgas at 120 °C. The outstanding compatibility of DELO-OB adhesives with LEDs could be proven in comprehensive, application-related tests.

Optical stability

Bonded connections are often designed in such a way that the adhesive layer lies in the beam path of the optical component. Therefore, it is essential that the adhesive is highly transparent for the relevant wavelengths, and also largely retains this transparency upon temperature stress, when exposed to UV radiation, or during soldering processes. DELO-OB adhesives are transparent and stabilized against thermal aging. Therefore, they become significantly less yellow than other UV- or heat-curing products do.

Fast build-up of adhesion / active assembly

With DELO-KATIOBOND OB products, DELO succeeded in starting the polymerization of light-curing so fast that sufficient functional strength is already achieved at the end of irradiation.

Therefore, higher output rates can be achieved in series production, and the materials ideally meet the requirements of active alignment.

The entire adhesive volume can be cured in another step by light or heat. In doing so, it is very beneficial for optical components that dual-curing types can be cured at just 80 °C.

Low-temperature curing

Light-curing adhesives can be cured at room temperatures. This is an ideal answer to the requirements of optical components in terms of positioning accuracy and thermal loading capacity. As the DELO-KATIOBOND OB products cure very fast, the irradiation time can be kept short. As a result, the temperature increase remains low. With respect to the control of the temperature increase, the use of LED curing lamps is ideal.

Reliability

Especially when bonding optoelectronic components for consumer applications, such as smartphones, there are absolutely no compromises when it comes to the reliability of the connection as the image and reputation manufacturer would be severely damaged as a consequence of frequent component failures. Accordingly, adhesives are subjected to harsh reliability tests in order to ensure the durability of the bonded connection. DELO-KATIOBOND OB adhesive prove extremely stable in the corresponding tests.