For young and mature mature designers alike, I’d like to offer a word to the wise: Talk to your board house before you start on the new design. We spend a lot of time helping designers to bring their pride and joy to a state of manufacturability after the fact. It would always be much better to have had a chance to avoid the mess rather than to clean it up.
I am speaking to two groups with this advice. For the young designer, you need to learn to understand the board manufacturing process and its limitations. For the mature designer, you need to adjust to shrinking parts and expanding complexity. In whatever stage of career you find yourself, the comments below will apply.
The best designs have bee made with thought all the way through to the completion process. Getting it right in the first place saves a lot of time, money, and headaches. Take these four steps to stay on track:
- Pre-select a board fabricator based, not just on cost and competence, but on their willingness and ability to communicate with you about your design needs. Pick someone who will answer your phone call or respond quickly to your messages. Lay your questions out in a logical way that will allow you to set or re-set your computer aided design (CAD) rules. Times are a changing and what was good enough last time, can potentially be improved. Don’t be afraid to get into a frank disucussion about cost trade offs. A good partner will usually respond with its own questions to help narrow down the best solution. Most of the questions have more than one possible answer and usually that will drive cost.
- Teach yourself enough about how modern PCBs are constructed to visualize the solutions proposed. We have a tutorial on our web site called PCB Explained under the banner “Helpful Design Stuff” that can walk you through the basics. The better fabrication houses will have similar information available on line to bring you into the fabricator’s processes. When we are talking about stack ups and process limitations, this type of information will help you communicate effectively with a fabricator.
- Make that phone call as you are developing your plan for the layout. Think of it as an early design review. Walk us through your plan and concerns. The first questions should be: What are your line and space rules and what are your smallest via and ring dimensions? Answers to these questions will drive the rest of the discussion. Other helpful bits of information for the fabricator are about desired chip architecture and packaging options, any heat concerns, and the desired size of passives (A tip: always use the largest parts you can squeeze in.) Ask for a standard stack-up for the layer count you anticipate. Another big topic to discuss is via fill or not fill and why. Talk about total tool count for efficiency. Most designs should not go above 10 different tool sizes.
- Don't neglect to provide fabrication drawing. Just getting ODB++ or Gerbers format to us is not enough. Your partner, to be successful, will need instructions on board material, soldermask, thickness, stackup if a default stackup will not work, surface finish, and any unique needs (such as press fit connector tolerances). All of this should be in your fab drawing. Panelization instructions are another important item to include if possible. Our web site has templates you can use for the Fab drawing. It can be either in Gerber format as part of the file package, or a separate PDF.
Follow these steps and you will avoid days lost and money wasted on re-dos.