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DFA: Design For Assembly or Design And Assembly

My blogs have talked about the advantages of running DFM analysis early in the design process where it is easier to address the issues that have been found. The Valor Division product, vSure, is the perfect solution to work in conjunction with Expedition Enterprise for example to provide that feedback. However, there is one area of DFM that can benefit from analysis that is performed with the assembly environment, and that relates to correct part selection.

For Contract Electronic Manufacturers (CEM) and even some Original Equipment Manufacturers (OEM) the parts that were used during the design process may not be the same that will be used in the assembly process. Here is it very important to validate the actual parts that will be used in assembly will actually fit on the board. I know this sounds crazy but it is a common scenario that the purchasing people try and get a cheap deal on a part without paying much attention to the actual package that is needed. So during the first article inspection a 1206 chip resistor is placed on the board’s 0805 landpattern with disastrous results. Production stops while this is sorted out costing significant amounts of time and money.

This is where the vPlan DFA capability of performing automated package to board analysis provides the solution. Using the accurate manufacturer specific part data from the VPL, each placement on the board can be validated against the actual part that will be placed there to be sure it is correct before the first board runs through the assembly process. Any discrepancies can then be discovered and corrected but production starts. These checks ensure that the correct clearance around the pin to the edge of the copper pad on to which it is associated with are all as needed. Not only does this highlight potential issues where one manufacturer sized part is sub-optimum for the design layout but it will highlight those more extreme examples that I mentioned above, namely the 0805 part on a 1206 landpattern.

So in summary, there are many reasons to run DFA analysis as early in the design process as possible but there are even some reasons to run DFA analysis in both Design And Assembly.

For more information on vPlan, please click on the following link:

http://www.mentor.com/pcb-manufacturing-assembly/

Mark Laing

Product Marketing Manager

Valor Division, Mentor Graphics Corporation

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