Embarking on a new PCB design is akin to preparing for an opening night performance. No matter how many eyes are on the production, and regardless of its length, it’s challenging to escape an initial run entirely without issue. Interdepartmental notes can be lost in translation — or lost altogether. Meticulously placed features and designs can get moved around due to an operator trying to work best with the limitations of their tools. Unfortunately for PCB design, mistakes can prove much more complex to work around, if at all feasible. Rework can only go so far, and it doesn’t take much before once-promising boards get designated as scrap. For mid- or high-volume production runs, this is a dollar and time loss most businesses can’t afford, especially when trying to meet strict dates to reach the market.
Thankfully, electronic CAD tools have numerous standard features to create redundancies that minimize errors during all stages of PCB design. These integrated suites help streamline design flow from schematic capture to documentation to fabrication and assembly through many clever and common functions. The following features will form part of the indispensable aid that electronic CAD applications offer designers to ensure designs meet their intended specifications at the outset.
Annotation: Keeping All Steps of Electronic CAD in Lock-step
Any design suite with both schematic and layout capabilities must coordinate updates between the schematic and board files. Depending on the initial design document, annotations can flow in one of two directions. The schematic file will serve as the reference for the project in active revisions and new designs. There are some notable benefits to this over operating from the board level.
First, any updates to components in a new BOM will be implemented into the appropriate parts library in the case of new or altered land patterns. Though the exact design flow will change from electronic CAD toolset to toolset, updating part information into the schematic such as the MPN and the associated land pattern will synchronize the schematic to the new BOM revision. At this point, any changes to the schematic, like the addition of filters for signal conditioning or capacitors for a shorter current loop to a power plane, can easily be output to a new BOM file or netlisted and passed forward to the board file for layout and simulation.
Though less common at the start of the design process, backward annotation – updating the schematic from the board file – is sometimes necessary. This could result from a revision to an older project where files have been lost, misplaced, or otherwise had their integrity in the design flow compromised. The best option, in this case, would be to work from the most recent board file provided for manufacture, whether that be prototyping or production.
The schematic is updated from the board file (hence the backward in backward annotation, as this runs counter to the natural design progression). Any updates to the BOM or land patterns to the schematic file can continue as normal. Alternatively, a backward annotation may arise naturally during revisions as test engineers debug and finetune various circuit characteristics and parameters to more closely match idealized values. Regardless of which annotation direction the design is undergoing, care should be taken to establish a “primary” document; recklessly alternating between forward and backward annotations can result in a muddled project without a clear line of update succession.
All-in-one File Generation for Fabrication and Assembly
Fabrication and assembly are where the rubber meets the road for PCB design. While an immense amount of thought and work goes into designing the circuit and translating the thermal and electrical constraints into component placement and copper features, manufacturing is the literal make-or-break point of the design. There is a significant element of symbiosis, as DFM practices will influence the layout designer’s approach to designing the board and its associated elements, such as the stackup, design of vias, trace width, etc. However, once it comes time to manufacture, the design falls into the hands of sophisticated machinery and skilled operators. Although not unique to the PCB fabrication and assembly, the chance for communication error increases drastically in this industrial form of the schoolyard telephone game.
Electronic CAD tools rectify this issue in multiple ways. Toolsets will generate manufacturing files and drawings directly from the board file and the necessary layers. For instance, the Gerber or ODB++ files will be imaged 1:1 from the associated copper, silk, or solder mask layers. This step provides CAM operators with the exact design intent of the layout designer (with the client’s approval) with no room for interpretation.
Layout designers can go further with callouts on the appropriate layers for board cutouts and other similar features that may otherwise be open to interpretation. Drawings will include any additional notes for operators along each manufacturing step. They will serve to inform clients and operators of the tolerance for particular features, the processes the board or board material will undergo to reach specifications, and any regulatory statements or governance that must be adhered to.
Once more, the layout designer can reduce ambiguity and improve the likelihood of the final product fulfilling the original design intent with conscientious and forward-thinking choices. Take the drill drawings: simple, clean choices for drill symbols for the different hole sizes will provide operators with an easy reference document and reduce the chance of time lost communicating back-and-forth between departments. As in all things, the best results come from designers providing specific intent throughout the entirety of the manufacturing process.
VSE Covers Your Design and Manufacturing Needs from Beginning to End
Electronic CAD tools can be daunting, but having professionals handle the toolsets can greatly reduce errors and the time duration of schematic capture to initial manufacturing. The layout is only a single piece of the PCB puzzle, and your design may require an engineer’s expertise for an enclosure, for example. Whatever your concerns, VSE offers various services for all stages of PCB design, from schematic to finished product. VSE prides itself on building electronics for customers by our team of engineers. We’ll take the difficulty out of manufacturing and provide you with an exceptional product.
