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.
Dicing of semiconductor wafers is an example of an application requiring a processing quality superior to what can be achieved using classical laser techniques. For this reason, sawing the wafers with a diamond-edged blade has been developed into a high-tech process, that guarantees good and reliable cuts for Silicon wafers of more than 300 microns thickness. Today, wafer thickness is getting thinner; down to 50 microns and also more brittle III-V compound semiconductors are used more frequently. On these thin wafers; the laser begins again to compete with the diamond saw, because of laser cutting-quality and cutting-speed, are increasing with decreasing wafer thickness. Conventional laser cutting however has the disadvantages of debris deposition on the wafer surface, weak chip fracture strength because of heat induced micro cracks. An elegant way to overcome these problems is to opt for the water-jet guided laser technology. In this technique the laser is conducted to the work piece by total internal reflection in a 'hair-thin' stable water-jet, comparable to an optical fiber. The water jet guided laser technique was developed originally in order to reduce the heat affected zone near the cut, but in fact the absence of beam divergence and the efficient melt xpulsion are also important advantages. In this presentation we will give an overview on today’s state of the art in dicing thin wafers, especially compound semiconductor wafers, using the water-jet guided laser technology.
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.
Material laser cutting is well known and widely used in industrial processes, including micro fabrication. An increasing number of applications require nevertheless a superior machining quality than can be achieved using this method. A possibility to increase the cut quality is to opt for the water-jet guided laser technology. 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. The water jet guided laser technique was developed originally in order to reduce the heat damaged zone near the cut, but in fact many other advantages were observed due to the usage of a water-jet instead of an assist gas stream applied in conventional laser cutting. In brief, the advantages are three-fold: the absence of divergence due to light guiding, the efficient melt expulsion, and optimum work piece cooling. In this presentation we will give an overview on several industrial applications of the water-jet guided laser technique. These applications range from the cutting of CBN or ferrite cores to the dicing of thin wafers and the manufacturing of stencils, each illustrates the important impact of the water-jet usage.