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The water jet guided laser technology (laser Microjet®) has been developed since 10 years now and is used for several applications in the semiconductor industry. In this unique laser cutting technique, a thin stable water jet is used as a waveguide for a high-power Nd:YAG laser, that may be frequency doubled or tripled. This presentation gives an overview of the semiconductor machining applications of this technique and relates the different applications to alternative techniques and the different functions of the water jet. The water jet cools the sample when the laser is not emitting, it expels the melt very efficiently, and it avoids that the few generated particles can attach to the wafer surface. The strengths of Laser Microjet® machining are free shape cutting and cutting of thin wafers. In free shape cutting the system leads to much better results in terms of fracture strength and process simplicity than the classical laser cutting methods. In thin wafer cutting astonishing cutting speeds are obtained at very good cut quality (200 mm/s in 50 micron thick wafers). Due to the free shape cutting possibilities drilling and slotting with aspect ratios of up to 5 is also possible resulting in the same edge quality as standard cutting.

Cutting electronic packages that are produced in a matrix array fashion is an important process and deals with the ready-to-use devices. Thus an increase in the singulation yield is directly correlated to an increase in benefit. Due to the usage of different substrate materials, the saws encounter big problems in terms of lifetime and constancy of cut quality in these applications. Today’s equipment manufacturers are not yet in the position to propose an adequate solution for all types of packages. Compared to classical laser cutting, the water-jet guided laser technology minimizes the heat damages in any kind of sample. This new material processing method consists in guiding a laser beam inside a hair thin, lowpressure water-jet by total internal reflection, and is applied to package singulation since two years approximately. Using a frequency doubled Nd:YAG laser guided by a water jet, an LTCC-ceramics based package is singulated according to a scribe and break process. Speeds of 2-10 mm/s are reached in the LTTC and 40 mm/s in the mold compound. The process is wear-free and provides very good edge quality of the LTCC and the mold compound as well as reliable separation of the packages.

Each electronic chip is packaged in order to connect the integrated circuit and the printed circuit board. In consequence high-speed singulation of packages is an important step in the manufacturing process of electronic devices. The widely used technique of abrasive sawing encounters problems due to the combination of different materials used in packages such as copper and mold compound. The sawing blade rapidly blunts because of the copper adhering to the saw blade and covering the diamonds. In fact, the abrasive saw, well adapted to silicon wafer sawing, has problems to adapt to package materials. It has already been shown that the water jet guided laser can be used for efficient high quality singulation of leadframe based packages. In this technique a low-pressure water jet guides the laser beam like an optical fiber, providing efficient cooling of the cutting kerf at exactly the point that was heated during the laser pulse. We present new cutting results using a frequency doubled Nd:YAG laser with 100 W average power, and the combination setup for generating a 200 W green laser beam. The timing between the two lasers can be precisely controlled.

Cutting of thin material, c.f. stencils, stents and thin wafers, is an important market for laser machining. Traditionally this task is performed using flash-lamp pumped, free-running Nd:YAG lasers. Using the water-jet guided laser technology, we experienced that the use of Q-switched lasers leads to superior results while cutting a variety of thin materials. In this technique, the laser is conducted to the work piece by total internal reflection in a thin stable water-jet, comparable to the core of an optical fiber. Utilizing this system, we obtain burr-free, slightly tapered cuts at the same speed as the classical laser cutting and without distinguishable heat affected zone. The main difference is, except the water-jet usage, the pulse duration which is approximately 400 ns instead of 20 to 200 μs in the case of free running lasers. Up to 40'000 high quality apertures per hour can be achieved in stencil mask cutting with the new system. We will compare qualitatively the two possibilities: conventional laser cutting with free-running lasers and water-jet guided laser cutting with Q-switched lasers. The results will be discussed in terms of the different physical effects involved in the material removal upon both methods. In particular the importance of molten material expulsion by the water-jet will be pointed out and compared to the action of the assist-gas. The mentioned effects show that the combination of short pulse laser and water-jet will be beneficial for the production of a wide range of precision parts.

The incessantly growing demands for higher speed of the wireless telecommunications and more compact devices require using of thin compound semiconductor wafers. The dicing is the very last process of the wafer manufacturing. At this stage the IC pattern is completely built up and the wafer has the highest value. Therefore, the goal of the singulation process is to provide the highest possible throughput. The conventional saw techniques "struggle" at their speed limits, while the conventional laser is not an appropriate dicing tool due to the strong thermal effect and big heat affected zones. The water-jet guided laser technology provides cool laser dicing since the laser is coupled in a fine stable water-jet and conducted to the work piece by means of total internal reflection like through an optical fiber, as the relatively low water pressure (10 - 30 MPa) of the tiny jet with diameter 40 - 100 μm results in a negligible force on the sample. This technology provides higher cutting speeds and burr-free kerf quality. By means of the Laser MicroJet, wafers as thin as 25 μm could be diced in streets of 50 μm width, with almost 100% wafer throughput. Here we compare the water-jet guided laser cutting with conventional techniques for dicing of thin semiconductor wafers. The results for Silicon and GaAs/Ge wafers are discussed in terms of speed, kerf quality and die fracture strength.

Singulation of packages is an important step in the manufacturing of IC devices. Presently, the most widely used technique is abrasive sawing. Due to the combination of different materials used in packages such as copper and mold compound, the saw rapidly blunts and also conventional laser cutting by a water-jet with the high precision and speed of a laser cut and is now applied into electronic package singulation.