SMT007 Magazine

SMT-July2016

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July 2016 • SMT Magazine 99 (or rest) times between passes thereby allowing the surface to remain cooler. Figure 17 shows that with shorter cooling times a slightly higher amount of carbon and oxygen are present. For probes 5 and 6 the cutting speed was changed significantly, which means that with the slower speed a complete cut is obtained with fewer repetitions. With the higher cutting speed more carbon and less oxygen remains present. All the tests were compared to a routed side wall where in each case more carbon was pres- ent there while the amount of oxygen did not vary significantly. The chemical element that would raise most concern is carbon, yet in all these laser cut cas- es, the presence of this element is lower or at most similar to that in the routed board. Conclusions Using a laser for depaneling can have sig- nificant economic advantages because more boards can be placed on the same panel. But also one can expect better long-term reliability as the board's edges are not exposed to bending strain when breaking the last connecting points to the panel. In addition, the board edges are not seeing high levels of compression when they are be- ing cut. The panels retain their original rigidity during assembly which may make it possible to work without pallets. During the laser cutting, process tempera- tures near the edges are lower than temperatures encountered during soldering and therefore no negative impacts are detected. When the cut- ting is well controlled by the system operator, no carbonization occurs, which other wise might reduce the surface resistance of the cut edge. Finally, the high precision of locating the outline of the board insures that the cuts do not encroach into the areas of the board where runs or even components are located and also assure a proper fit in a tight and well-designed enclosure. Figure 18: Inspecting surface of glass fibers. Figure 19: EDX analysis on glass area. MATERIAL EFFECTS OF LASER ENERGY

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