Example Fabrication Drawing (Part 1)
There is an old saying, “A picture speaks a thousand words.” To help understand what a fabrication drawing is, I have posted several views along with brief explanations. The first view is a full size view of a fabrication drawing
The outside boarder contains a series of numbers and letters. These are triangulation points that define the various zones of the drawing. Zones are often referred to in revision changes to help locate items being changed on the drawing. The document title block is in the lower right corner in zones A-1 and A-2. The revision block is in the upper right corner in zones D-1 and D-2.
The title block containing identification and approval information. Ownership is identified by the company name and FSCM number. The name block can also include the company’s address of operation. The FSCM number is the Federal Supply Code for Manufacturer issued by the government. Identifying the part number and revision (REV) level of the drawing is important. This ensures that your pcb manufacturer has the correct design information that matches the submitted order. The block also identified how many sheets make up the drawing set. This is sheet 1 of 2. Anyone that looks at this document shall understand that there is a second drawing that compliments this one. The second drawing may contain information that is critical to the design. The title block also identifies all those individuals directly responsible for the document.
The revision block provides a brief description on what has changed in the design over time. It is common practice to document all changes in a formal document identified with a unique number. Documents of this type are sometimes referred to as either an ECO (Engineering Change Order) or DCN (Design Change Notice). It is easier to refer to the document number in the block’s description line rather than try to fit some cryptic reference. The ECO/DCN can contain detailed information and can be made available to contracted manufacturers if required. Centralizing changes in this type of format can come in handy if a second party needs to determine if older designs can be manually modified to meet the current design.
Drill and mechanical details are commonly combined into one view. Each drill size is represented by a unique symbol indicating the approximate location of the hole. The pcb profile is displayed and provided with dimensioning indicating part size and the location of critical features. The view the pcb is being viewed from is commonly done in this view. In the case of the image above we are viewing the Component Side View.
The Drill Legend provides the cross reference between the symbols in the drill detail and the actual hole sizes. In the example above the hole sizes are identified in mils. The holes are identified as being plated or non-plated. The number of holes for each size is listed. Hole tolerances are also identified for all hole sizes.
To ensure parts are properly manufactured it is a good idea to use side details to provide more detailed information. Sometimes the Drill and Mechanical details can become congested. Identifying points in the drill and mechanical detail and then elaborating upon the information in a side detail alleviates this problem. Detail views are typically drawn at a larger scale.
Some designers plan for specific insulation between conductive layers. These requirements may be identified in a detail view. It is common practice to include the copper weights as well.