Laser Assisted Frit Sealing for High Thermal Expansion Glasses

Analysis of laser assisted frit sealing processes for high CTE > 5x10/°C (coefficient of thermal expansion) glasses was done. The method is based on the thermal fusion of two glasses with a low melting point glass frit. This method is used when thermal sensitive materials such as OLED (organic light emissive device) are present in the glass package. The frit is selected to be highly absorbent at the sealing laser wavelength, while the glasses are transparent at the sealing wavelength. It was found that laser sealing of a high CTE glass with sealing conditions optimized for a low CTE (< 5x10/°C) glass, such as glass suitable for display devices, produces very poor results. The issue with sealing glasses with high CTE is high transient stress formed during heating and cooling the glass to the sealing temperatures. The sealing yield of high CTE glasses could be significantly improved by increasing “residential heating time” by reducing sealing speed or increasing laser spot size. This results in lower cooling rate of the glass and helps to reduce the residual stress. This was confirmed by stress analysis showing a reduction of the stress for soda lime glass with increasing residential heating time.