New adhesive for closed-cavity packaging in CMOS image sensors

DELO has created a new, reliable sealant adhesive for CMOS image sensors, which are often employed in driver monitoring systems. Glass filters can be bonded directly to the semiconductor chip using DELO DUALBOND EG6290. The electronics-specified adhesive can be dispensed in narrow, high bondlines, can compensate for temperature-dependent pressure changes, and satisfies routine automotive standards.

The adhesive was specially developed for the glass-on-die assembly method. The glass filter is fixed directly onto the chip, as is typical with iBGA image sensor packaging.

Compared to previous products, the new adhesive has a remarkably higher Young's modulus of 2,350MPa and significantly higher adhesion value. Due to a glass transition temperature (Tg) of over +130C, the adhesive displays mechanically consistent behaviour – even at high application temperatures, for example, during the moulding process – and can compensate for temperature-dependent pressure changes. The adhesive fulfils the requirements of the AEC-Q100 Grade 2 automotive industry standard.

The adhesive is applied via needle dispensing. Thanks to its very high thixotropy index, narrow and high bondlines can be precisely dispensed, onto which the glass filter is then joined.

Curing takes place in two successive process steps: First, the adhesive is exposed to light with a wavelength of 365nm or 400nm. Then, as a result, the glass filter is fixed within a few seconds. The adhesive typically fully cures in 15 minutes at +130C. Due to the rapid curing reaction, the matrix in the adhesive builds up quickly, which ensures the image sensor package is reliably sealed.

Both the dual curing process and the comparatively low curing temperature help to minimise the pressure that often occurs when bonding glass filters.

CMOS image sensors are crucial components in modern vehicles and are installed, for example, in LiDAR and driver monitoring systems. They must be completely sealed to keep out dust and moisture and maintain their safety functions over their complete service life.