Synova's success
Swiss engineer re-invents the laser
By Delphine Perrottet, Synova
Imagine a laser cutting tool that sliced through silicon without thermal damage, or that removed debris without an assist gas. Imagine a water tool strong enough to cut through silicon without cracking the material. Over a decade ago, Bernold Richerzhagen, an engineer studying at the Federal Institute of Technology (EPFL) in Lausanne, Switzerland, decided to combine the two cutting methods. In 1996 after a lot of hard work, he revolutionized the micromachining industry with his invention, the water-jet guided laser. Until then, water-jet and dry laser cutting were well-established methods of cutting myriad materials, and Richerzhagen thought about combining those two methods as a means of overcoming the limitations of each individual technique.
Traditional water cutting is possible when the material breaks under the pressure of a high-powered water jet. Soft materials such as wood, cardboard, and food stuffs are well-suited for water-jet cutting; adding microscopic particles to the jet stream widens the range of materials to include metal, stone, ceramics, and glass. While water jets require less investment capital, and do not emit gas when cutting, water-jet cutting imposes a drying step on the manufacturing process, and can mechanically damage the material.
Dry laser cutting is possible when the material absorbs the energy of the laser and melts or vaporizes. Any residual material left from the cut is expelled by an assist gas. The two drawbacks of laser cutting are thermal damage to the material and contamination when the assist gas does not sufficiently remove the ablated material. In the latter case a protective coating can be applied to the surface prior to cutting, but this increases costs. Although lasers fit quite well into today's manufacturing processes, they incur higher initial costs than water-jet cutting equipment.
Clearly, cutting techniques could benefit from another method. The engineers at the EPFL focused the laser beam into a water nozzle while simultaneously passing the beam through a pressurized water chamber. The low-pressure water jet (lower pressure than the standard water-cutting jet) that is emitted from the nozzle guides the laser beam by means of total internal reflection at the water/air interface.
The purpose behind the water-jet-guided laser's development was to overcome the drawbacks of lasers with water, particularly for dental applications such as the removal of dental caries before filling. After the promising results of the first prototype, Dr. Richerzhagen began concentrating on industrial applications, and founded Synova SA in 1997. By 1998 the first precision cutting machines were on the market. Today, the semiconductor field is the primary beneficiary of this innovative technology. However, the water jet-guided laser is also used in an increasing number of other fields, including medical, tooling and energy.
Synova's Laser-Microjet
Variations on a theme by Synova is one way to describe the company's line of cutting systems. The machines on offer use the water-jet-guided laser technology (also called Laser-Microjet) for various micro-machining operations such as wafer dicing and edge grinding for the semiconductor industry, and cutting of hard materials such as CBN and PCD, PV solar cells, and thin metal masks for the electronics industries. The systems are called: the Laser Cutting System (LCS), the Laser Dicing System (LDS), the Laser Grinding System (LGS) and the Laser Stencil System (LSS).
Each machine features Sony cameras (a XC-HR70 and a XC-ES30) connected to a Matrox Meteor-II frame grabber for visual recognition of the work pieces. Depending on the system, the image data is processed and analyzed with the Matrox Imaging Library to calculate the required location for the laser. The Laser Dicing System for example, requires coordinates for the space between the chips, referred to as the street. Image processing techniques such as blob analysis allow the Laser Stencil System to detect the openings in metal masks, while geometric pattern recognition determines the cutting path for the laser.
Synova chose Matrox Imaging components for their reliability and high quality. Indeed, "we were able to develop the pattern recognition modules we use on our machines far more quickly than without," affirms Delphine Perrottet, Public Relations Manager. "The Matrox products perfectly correspond to our needs. [The Matrox Imaging] library accompanying the card is very useful. It is a flexible and complete tool, and the engineers found it easy to use. We also received excellent support from Matrox's distributor," she adds.
Best of both worlds
The Laser Micro-Jet technology has a number of advantages over the two traditional methods. In conventional laser cutting, the laser beam is divergent and the working distance is short; focus-distance control is required. Furthermore, conventional lasers generate a large amount of debris that adheres to the surface of the work piece. This debris is hard to remove and may be damaging. Adding a protective coating on the material avoids contamination but significantly increases costs. Dry lasers also create a significant heat-affected zone which generates micro-cracks that can decrease the die fracture strength.
When a water jet guides the laser beam, the working distance - corresponding to the area where the jet is cylindrical and constant - can be up to several centimetres long, resulting in constant kerf width (the cut between chips in a wafer) and no need for focus-distance control. The water jet expels the molten material; as a water film is generated on the material surface during cutting, the particles, already cooled by the water jet, remain in suspension and cannot adhere to the material. The water jet also prevents heat damage to the material by cooling the cut edges between the laser pulses; the heat-affected zone is negligible compared to conventional lasers.
Compared to abrasive sawing, the water-jet-guided laser is more flexible - almost any shape can be created. In addition, the running costs are much reduced as there is no tool wear leading to blade replacement and as the water consumption is significantly lower. Another advantage of the process over sawing is the absence of mechanical damage. Indeed, the force applied by the water jet is negligible (less than 0,1 N) due to the low pressure and small diameter of the jet.
Making the connections
During ScanWorks'® infancy, the engineering team at Perceptron focused on the most important design objective: to create portable equipment that could be calibrated quickly with minimal additional tools; customers need to transport it to the job site with a minimum of delay. As a result, Edwards says the engineers faced many challenges in the integration domain. "We had to get the laser, camera, lens and mounts to work together to meet our performance goals." And meeting the accuracy specifications for the micrometer category was no small engineering challenge. Edwards says the engineers persevered, and developed not one, but a family of ScanWorks® products that address the varying situations Perceptron's customers encounter. "This resulted in more choices for our customers, fewer overall parts, and a more robust solution for everyone," he says.
Synova's laser in the future
Experiments are currently underway, not only to determine the Laser Micro-Jet's effectiveness with a smaller jet diameter, but also with new application areas such as free-shape cutting of silicon sensors, metal masks for the FPD industry, and HDD parts and to inkjet printer heads. Synova has about 40 machines in operation worldwide, and sales are roughly equal across the US, Europe, and Asia. Synova expects to enjoy its current success with the semiconductors and electronics, as these sectors typically have a demand for thin wafers, thin and large stencils/masks, as well as flat panel displays.
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