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70 SMT Magazine • December 2015 or laminate, effectively creating a trace, which can have very fine line definition (Figures 3 and 4). This method, while having engineering and set-up costs not present to near the degree of the more manual methods, has several benefits. There are several benefits to using this par- ticular approach. First, line definitions achieved by the laser are very tight with 0.5 mil traces and spaces well within the capability spectrum of most lasers. Second, very complex trace paths, which are very time consuming to hand fabricate, are easy to fabricate with a laser. A beam steering mechanism can make this hap- pen based on the pattern programmed into the machine. Finally, due to the processing speed and the ability to process "multiple-up" panels at the same time on the laser, the cost for re- work is greatly reduced versus other methods on a per-piece part basis. The cost per-piece part for rework is a fraction of the same work done manually, with the difference becoming more pronounced as the patterns get more complex and the volumes increase. conclusion There are several way to remove solder mask selectively from a PCB when required. The methods of scraping, chemical etching, micro abrasion and a directed laser ablation technique can have their positive and negative attributes. For a few boards the mechanical scraping or grinding off of the solder mask is a method that is well-suited for low-volume, non-high-preci- sion work while the laser ablation method is the right choice when ultra precision or high-vol- ume is required. Each of the methods to be con- sidered need to be weighed against the speed, accuracy and repeatability required for the work at hand. SmT references 1. IPC 7721 Rework, Modification and Re- pair of Electronic Assemblies, Method 2.3.5— Grinding and Scraping. 2. IPC 7721 Rework, Modification and Re- pair of Electronic Assemblies, Method 2.3.6— Micro Blasting Technique. 3. IPC 7721 Rework, Modification and Re- pair of Electronic Assemblies, Method 2.3.2— Solvent Technique. bob Wettermann is the principal of BEST inc., a contract rework and repair facility in Chicago. rice university researchers have developed a camera that is a little more than a thin sensor chip with a mask that replaces lenses in a traditional camera. invented by the rice labs of Electrical and computer engineers Richard Baraniuk and Ashok Veeraraghavan, FlatCam can be fabricated like microchips, with the precision, speed and the as - sociated reduction in costs. Without lenses, the most recent prototype is thinner than a dime. "as traditional cameras get smaller, their sen- sors also get smaller, and this means they collect very little light," Veeraraghavan said. "The low- light performance of a camera is tied to the surface area of the sensor. unfortunately, since all camera designs are basically cubes, surface area is tied to thickness. our design decouples the two param - eters, providing the ability to utilize the enhanced light-collection abilities of large sensors with a re- ally thin device." flatCam shares its heritage with lens-less pin- hole cameras, but instead of a single hole, it fea- tures a grid-like coded mask positioned very close to the sensor. Each aperture allows a slightly dif- ferent set of light data to reach the sensor. Raw data sent to the back-end processor is sorted into an image. like much larger light field cameras, the picture can be focused to different depths after the data is collected. rice's hand-built prototypes use off-the-shelf sensors and produce 512x512 images in seconds, but the researchers expect that resolution will im - prove as more advanced manufacturing techniques and reconstruction algorithms are developed. Flat Camera Looks into the Future no TIme For A boArD SPIn? SeLecTIVe SoLDer mASK remoVAL knoCking Down THe bone Pile

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