Fabrication Drawings and Electrical Test— Reading the Fine Print

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When a new PCB design is born, designers envision what the product will provide when completed. Whether the product is for the consumer, aerospace, military, medical or countless other markets, the designers—or more likely, the customers—expect certain deliverables on the commodity they wish to purchase. To provide the desired functionality of the product design, engineers specify these deliverables on blueprints (prints) or fabrication drawings (fab drawings). These documents are the recipe for the manufacturing requirements of the given product.

A multitude of information is provided in these documents. In most cases the designers do not know the specific processes involved that satisfy their requirements, nor do they have to. They specify their requirements on the fab drawing and allow the PCB manufacturer to use the necessary processes to supply the final product, and herein lies the problem. Some complex designs could have fabrication drawings exceeding 20 pages, and may include requirements ranging from which raw materials are to be used to what type of anti-static packaging is required for shipping.

For this discussion, we will focus on how these documents pertain to electrical test (ET). In most fabrication drawings, many pages are graphical in nature and depict special dimensional or mechanical attributes, while others show drill/cutter requirements, plating requirements, special layup instructions, and almost always a note(s) page. Should ET read the entire package? Yes. Why? Because many times there can be mechanical attributes that will influence how the final product can be tested.

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Editor’s Note: This article originally appeared in the January 2016 issue of The PCB Magazine.