My First StoryJamie Keener
Final Details: the Fabrication and Assembly Drawing



  • I'm definitely going to do it through the next week without my favorite pillow (although with a lot of whining and complaining), but if you neglect any of the details needed to make it, your circuit board will not do so well. With the different amounts of documentation needed to manufacture and assemble your PCB, one important detail can be easily forgotten.To make sure you don't forget anything, you should develop a routine along with a checklist for this reason. Here are some of those items you should keep in mind when creating your PCB manufacturing and assembly drawings.

    All is packed, and I'm ready to leave for my camping trip. In fact we'll be heading out of town as soon as I finish writing this. However, there is one thing that happens every time we go on a trip like this, when we set up camp tonight we will find out to our annoyance what items we have forgotten and left at home.Usually it's a simple thing like a toothbrush, which can be easily replaced by a trip to the store. But on those trips where important items–like my pillow–have been left behind, that's when it can get uncomfortable! You'd think I'd finally put in place a checklist after all these years to avoid this annual annoyance, but no, I'm a creature of habit.

    The Basics of the Fabrication and Assembly Drawing

    Your drawings of manufacture and assembly must convey the various information to the vendors for which they are intended. The fabrication drawing will include information on how to construct the raw printed circuit board, while specifics on how the components will be connected to that raw PCB will be included in the assembly drawing.However, in either case you will start with those drawings from the same place; in your PCB design tools. As such, there are a few generic items you'll want to make sure you include for both drawings:

    Drawing Format: While some CAD systems require you to use a library part drawing format, other systems will auto-generate the format for you. Whatever template your CAD system uses, the format will be combined with your PCB model to create your drawing.

    Board Outline: This is the outline from your layout database for your circuit board design. It will usually include slots and cutouts in it, which will be dimensioned on the drawing of the manufacture and referenced on the drawing of the assembly with components.

    Identification Information: Typically your drawing format should include one or more places for you to add the drawing identification number, revision stage, board name, corporate address and contact information, and date of production.

    These are the basic elements needed for any drawing. Now let’s take a look at the specific elements needed for each.

    Key Elements for Both Drawings

    Beginning with the drawing of the produce, here are some of the features you wish to include on your drawing:

    Drill Locations: This drawing needs to show every hole in your board for pieces or vias. Normally these are auto-generated by your CAD system with PCB design. Since your supplier will use the NC drill file you give them for the actual locations of the hole, the drill symbols are useful as a guide here.

    Hole Chart: This table, also called a "drill schedule," associates each finished hole size with a unique drill symbol and holes quantity.

    Board Layer Stackup: This is the board's cut-away view, which shows the layer structure. In general, pointers are used to describe the structure and width of the board's conductive layers and their corresponding prepreg and core layers.

    Dimensions and Notes: Dimensions display the board's overall size as well as the positioning of the various features around and within the board outline. The notes should give specific directions which are not available elsewhere to the manufacturer.

    First, let's look at what you need to include on your drawing for assembly:

    Component Outlines: You will want to show all the outlines of the components as well as their reference designators that will be soldered onto the plate. This will also include mechanical parts that with mounting hardware will be pressed fit in or attached.Such pieces may not be portrayed correctly in your footprint library often requiring a little extra drafting effort on your part to include them in drawing.

    Additional views: In addition to the front, double-sided boards would typically allow a view of the rear side of the board. You can include both of these views on one assembly drawing sheet if the board is small enough to allow for that, otherwise you'll need additional sheets in your drawing.Of clarification, you might also need to provide extended views to describe the attachment of mechanical parts on a larger scale.

    Delivery marks: Any packaging labels such as barcodes or assembly tags must be marked with a pointer and referenced in the notes.

    Configuration Notes: These are a set of production instructions that include descriptions of configuration, industry standards & specifications, and locations of special features. We can also include a list of parts if the supplier asks for that.

    Where necessary, any of these drawing elements can be changed or modified, and in some cases completely omitted, if appropriate. The important thing is to find out what they need from your contract manufacturer to build your board, and include those details on your drawings. Don't forget it's a smart idea to create a checklist so nothing gets left out too.

    How Your PCB Design Tools Can Help

    The older PCB design systems used to have little capacity in the way of drafting. Many of the things I have described above had to be manually developed every time you needed them. We used third party CAD drafting tools in some cases simply for convenience.Fortunately those days are over, and today's PCB design systems have the power and utilities to build any drawing you need with an amazing level of automation. If you still use an older PCB design system to create drawings that requires a lot of your time, do yourself a favor and check out the help you can get from today's powerful design tools.

    Cadence's PCB design systems can give you powerful utilities and automation to quickly and efficiently produce accurate fabrication and assembly drawings. OrCAD PCB Designer has the capabilities you are searching for, with its manufacturing drawing creation tools and other powerful utilities.

    If you are looking to find out more about how Cadence has the answer for you, talk to us and our expert team.



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