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92 SMT Magazine • July 2016 steps. Like a router, the laser cuts completely through the board, so no bending or pressing on the edges of the board occurs, which means no stresses are exerted on the board material. With the use of a laser, cutting any board shape can be accommodated, and the changeover to different boards is very quick as the process is completely computer controlled. Laser System The three main parts of a laser cutting sys- tem are the laser, the X-Y table for panel move- ment and the scanner to move and locate the beam. To cut various materials, several types of la- sers are available. These have varied from CO2 at about 10 um wavelength available for well more than 20 years to UV lasers at about 350 nm wavelength showing up around 10 years ago. About 20 years ago the Nd:YAG lasers at 1054 nm wavelength were introduced to be used in stainless steel stencil cutting systems. As the wavelength gets shorter the lasers have been more difficult to be produced eco- nomically, which has led to the gradual time- wise availability of the different systems. Short- er wavelength lasers and those with very short pulse widths have typically been much more expensive, which is why it has taken time to get them deployed in the industry. do damage to the board edges because of signifi- cant pressure and/or bending forces potentially causing some delamination which may impact long-term reliability. All this means that dur- ing the board layout care must be exercised to keep fragile components and sometimes circuit traces away from board edges. And the waterjet method has hardly been explored. The most commonly used method is the routing where a kerf is cut around each board, regardless of board shape, by the panel manu- facturer. To keep the board in the panel during the assembly process in a few locations the kerf is interrupted. The routed kerf in the panel typi- cally is about 3 mm wide, which means that in a case with many small boards a significant amount of panel space is used for cutting slots. Sometimes, with many slots in the panel, the panel becomes less rigid and panel supports or a pallet is required during the assembly process. Typically, holes are being drilled in the connect- ed areas to make it easier to break the boards from the panel which means that during board layout these locations must be decided and frag- ile components must be kept away from them. Laser Cutting The latest method added is laser routing, which can be done after the last step in the board assembly process. This means the panel retains its rigidity throughout the previous assembly Figure 1: Combining various singulation methods in the one panel. Figure 2: Example of a laser depaneling system in an in-line setting for automatic loading and unloading. MATERIAL EFFECTS OF LASER ENERGY

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