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Zulki's PCB Nuggets: ECOs Reviewed - The Importance of Accuracy

Engineering change orders (ECOs) have been part of the product development and PCB landscapes for as far back as one can remember. Particularly, when it comes to ECOs for PCBs, there are varying and endless reasons for these changes.

Certainly, PCB designers can perfectly layout a design and, in theory, follow written specifications to the letter and to the best of their abilities. But when you factor in the practicality of that design, virtually everything associated with it has its limitations, ranging from the material used to make the circuit board to assembly, machine tolerances, process limitations, and the list goes on.

But, before we continue, let’s start at the beginning. First, the design is completed; the board is then manufactured and tested. However, once it’s tested, the expected results aren’t there, at least theoretically. Next, it is either re-spun and all necessary adjustments incorporated in the next revision design before it gets tested post-assembly. Or, the other option is to keep the design as is and create an ECO to make the project work without re-spinning the design. ECOs are normally generated during the engineering debugging and bring-up phase of the board, when issues are found.  Figure 1 shows an example of an ECO with the description of the changes along with a figure, an approval signature, and a date and time stamp on it.Read the full column here.Editor's Note: This column originally appeared in the August 2013 issue of SMT Magazine.