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86 SMT Magazine • November 2015 wards of 35 million purchasable part numbers. To date, there has not been a single instance of a PCB-mountable electronic component that cannot be modeled in the library for DFA pur- poses. Second requirement The second major requirement to enable por- tability of the DFA process is to establish a stan- dardized package- and pin-classification system in which the DFA analysis rules can be managed. The main challenge arises from the need for rel- evant spacing measurements between pairs of components of different classification. For ex- ample, the acceptable spacing between a small chip-resistor and an adjacent BGA will probably be different to the acceptable spacing between the BGA and a connector. Thus, the number of component-to-component rules can be propor- tional to the square of the number of different types of components in the library. Obviously, while it is necessary for the sake of DFA mea- surement accuracy to have available a number of unique component models on the order of 100,000 (as described in the previous section), to have 100,000 x 100,000 separate DFA rules to manage is obviously impracticable. The approach we took was to consult people who are using DFA technology to determine the maximum granularity of component package types and lead form types needed to ensure that the DFA analysis measurements are appropri- ate to the combinations of components on the PCB. After many years of gathering feedback, we have 17 different package types and 23 dif- ferent lead-form classifications, which result in a range of DFA rules measured in the hundreds, not the billions that would result from using the library-level classifications to define the dis- tinction between DFA rules. Figure 7 shows an example of a component model defined in the library as DAT-R16/M- L38W16T5_CPN081. This is the same syntax for unique definitions of the component mod- els from the library definitions explained in the previous section. From this component model classification, the DFA software is able to auto- matically derive the package type as "chip" and the lead form as "c-bend-wrap." The rules for defining these two type assignments are also shown in Figure 7. The advantage of deriving the type assign- ments within the DFA software is that as the DFA requirements of the industry evolve, the STreAmLINING PCb ASSembLy AND TeST NPI WITH SHAreD ComPoNeNT LIbrArIeS arTIcLe figure 6: cloud-based library structure linking purchasable parts to fixed-syntax graphical models.