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66 SMT Magazine • May 2015 In this month's installment in this series of columns aimed at helping buyers analyze and select SMT equipment for printed circuit board assembly, I will address features that affect deci- sions on the selection and purchase of an ap- propriate automatic pick-and-place machine. As with any complex machine, there will be tradeoffs between cost and capabilities, some of which specifically relate to production accuracy and yield. We will address: 1. Mechanical positioning methods 2. Machine construction 3. Solder paste fluid dispensing 4. Component feeders To review, when starting the evaluation pro- cess, there are two defining factors to keep in mind which determine what category fits your machine needs. The first principal factor is CPH (components per hour), and the secondary fac- tor is machine capability. While it's construc- tive to start by understanding how production rates affect the type and performance of a pick- and-place machine, please refer to the prior two installments, in the February and March issues, for those ranges. Machine capability is the second defining factor in helping choose the correct auto pick- and-place machine for your needs. In this in- stallment, we will address three aspects of ma- chine capability that have a direct impact on final board quality and production yield. accuracy and Repeatability For production machines, we typically rec- ommend looking for a machine with accuracy of +/- .001" and fine pitch capability, down to 12 mils, on a repeated basis. Be aware that less expensive machines rarely meet this spec. There are several types of positioning systems employed, differences in construction methods, and a variety of component feeders, all of which have an impact on quality and yield. Component Positioning Systems After each component is picked up and centered in the tool by one of the methods de- scribed in Part 2, it must then be positioned ac- by Robert Voigt DDM noVASTAr SmT QUICk TIPS Selecting an automatic Pick-and-Place machine, Part 3 ColuMn figure 1: underside view of a renishaw linear scale and encoder, one of the most accurate brands for mechanical positioning.

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