Glass Laser Welding

Ultra-short pulse lasers combined with sophisticated self-focusing technology provide the quality and process reliability required to enable laser glass welding to be used in series production. The unique and excellent characteristics of glass make it widely used in various high-tech products in different fields such as biomedicine and microelectronics. We have previously described the challenges it presents to manufacturers, especially in the high-volume, precision glass-cutting field. It also presents difficulties in bonding, including welding individual glass components together and welding glass to other materials such as metals and semiconductors.

All traditional methods for welding glass struggle to provide the precision, bonding quality and production speed required for cost-effective mass production. For example, adhesive bonding is an economical method, but leaves adhesive material on the part and even requires degassing.

Dielectric welding involves placing a powder material at a contact point and then melting it to complete the bonding. Whether this melting is achieved through an oven or a laser, a lot of heat is pumped into the part. This is a problem for microelectronics and many medical devices.

Ionic bonding is an ingenious method that provides extremely high bonding strength. Two new, extremely flat surfaces of glass are pressed together and truly fused together by molecular bonds. However, it is not realistic to do this in a production environment.

So, what about laser welding? Glass has many very useful properties, such as extremely high melting point, transparency, brittleness and mechanical rigidity, but it also induses many difficulties for laser welding. Therefore, typical industrial lasers and methods used to weld metals and other materials are not suitable for glass.

Just like precision glass cutting, the secret lies in the use of infrared ultra-short wavelength pulse (USP) lasers. Glass is transparent in infrared, so a focused laser beam can pass directly through it until the focused beam Narrows and becomes so focused that it triggers "non-linear absorption." This "nonlinear absorption" only occurs in ultrashort pulsed lasers with peak power, and other types of lasers cannot be used to accomplish the same thing.

So, in a very small area around the focus of the laser beam (usually less than a few tens of microns in diameter), the glass absorbs the laser light and quickly melts. This focused beam is scanned along the desired welding path to complete the bonding, just like other forms of laser welding.

First, it creates a strong bond because both materials being welded partially melt and then solidify together to form a weld. Moreover, the process is also suitable for bonding glass to glass, glass to metal, and glass to semiconductors.

Second, in this process, very little heat enters the part, and this heat is generated in an area at most a few hundred microns wide. This allows welds to be placed very close to electronic circuits or other heat-sensitive components, which gives designers and manufacturers greater freedom and enables better product miniaturization.

Finally, if USP laser glass welding is implemented properly, there will be no micro-cracks around the weld. Microcracks reduce the mechanical strength of glass. In addition, after the temperature cycle changes (which are inevitable for everything), microcracks can be the source of the ultimate failure of the device.

The advantage of USP laser glass welding is that the glass is heated only in a small volume. But it also poses practical challenges. This means that even if the part moves, the laser focus position must be kept very precisely at the interface between the two welded components. Because the parts of the real world are not perfectly flat, this is difficult to achieve. In addition, the placement of the parts in the welding system may not fit perfectly.

One solution is to use an axially elongated focus. This "stretches" the size of the laser beam focus to address position sensitivity. However, the disadvantage of this method is that the elongated beam focus creates a molten pool in the glass with a non-circular cross-section. When the glass solidifies in the melting zone, the non-circular molten pool is more likely to form micro-cracks.

The other method can realize the welding effect without micro-cracks, and can adapt to the significant change of interface distance in the process. The secret is that, combined with high dynamic focusing technology, high numerical aperture (NA) optics are used to produce small focal spots.

In this way, the laser system achieves a high sphericity of the molten pool, thus avoiding micro-cracks. It also senses the interface distance and constantly adjusts the optics to always stay in perfect focus. The result is that high-quality welding is guaranteed on almost any shape of part, and the process is not affected by part tolerances and location.

Xi'an Guosheng Laser Technology Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing and sales of automatic laser cladding machine, high-speed laser cladding machine, laser quenching machine, laser welding machine and laser 3D printing equipment. Our products are cost-effective and sold domestically and abroad. If you're interested in our products, please contact us at bob@gshenglaser.com.