It’s tax time again, and that means I need to plan my annual trip to see my tax preparer. As usual, I have a box full of receipts, statements, and other assorted financial records that need to be gone through, organized, and converted to official tax documentation. I could save myself a lot of money if I would simply take the time to prepare my records before they are worked on by the tax preparer. But as history has shown, I’ll probably once again take the easy way out and just pay extra for someone else to figure it all out.
I can justify paying extra to my tax preparer because I really do have better things to do with my time. But when I’m preparing my schematic for PCB layout there is no excuse. No one is going to know better than me the details that need to be included in order for my design to be a success. If I’m going to do the layout myself, being prepared will help me to organize and remember important design details. If my design is going to be sent to someone else for layout, however, the lack of preparation on my part could result in disaster for the finished design and I certainly don’t want that.
If you yourself have ever wondered How do I convert PCB layout, let’s take a look at some of the things that you should consider doing in your schematic to ensure its success.
How Do I Convert PCB Layout? The First Rule: Neat Documentation
Circuit design may have come from a history of scribbled notes on a lunch napkin, or rushed schematics on a chalkboard or whiteboard, but those are certainly not the hallmarks of good documentation. There’s a reason that medical offices are now forcing doctors to write out their instructions electronically instead of using a pen and paper: so we the patients can read them.
And just as being able to accurately read your prescription is important, so too is reading the details and instructions in your schematic. Do yourself a favor and take the time to make sure that your schematic is legible. Here are some tips on how you can do that:
Use a grid to align symbols, draw straight lines, and organize text.
Use a text font and line width that is large enough to be readable, while not so large that it clutters up the schematic.
Don’t pack symbols and text tightly together, give them some space so that they can be accurately read.
Compose your schematic with a logic flow that makes sense. There’s no reason to jam components into an area just because it’s blank if they really don’t belong there.
Don’t be afraid to use additional pages in your schematic if it will help to create a more readable document.
If you give yourself enough time to create a document that is easy to work with, you will reap the benefits of that extra effort many times over during layout.
Ensure your schematic is in top order before attempting any conversion
Library Parts are Crucial in Converting a PCB Layout
Another important part of successfully converting your schematic to PCB layout is in making sure that your library parts are up-to-date and correct. Your symbols must be correct for the part that they are representing. This includes pins, text, shapes, and attributes. Sometimes people will use an existing symbol as a template for building a new symbol, and then neglect to add, delete, or modify portions of the original information. At best this can cause a lot of confusion when the part number on the schematic sheet doesn’t match what is being reported in a report. At worst is when symbol information is completely wrong and causes connectivity errors in the schematic or downstream tools such as simulators. Be careful to completely finish what you start when you are building a “make-from” symbol.
When you are building new symbols for your design, make sure that you include all of the relevant component information as well. This would include the physical footprint name for the layout tools, company part numbers, vendor part numbers, cost information and simulation data. Each company will have their own standards for what should or shouldn’t be included in a library part, but it is better to have too much information than too little. Once completed, make sure that your new parts get populated into the appropriate component library and that the parts on your schematic are updated to reference the correct library as well.
Collection of parts leading to the production of a circuit board
Detailed and Complete Schematic Information is Your Friend
Just as you can’t have too much information in your library parts, the same principle holds true for your schematic as well. You need to be careful that you don’t add so much data that the schematic becomes unreadable, but you should add as much information as you possibly can to help those people downstream doing layout, test, and re-work. Here are some examples of information that would be useful to include:
Identity of functional areas of the schematic (“Power Supply,” “Fan Control,” etc.).
Test locations for power, ground, or specific signals.
Layout placement locations for fixed components such as connectors and plugs.
Component groupings to identify high speed or sensitive areas of placement.
Sensitive circuitry that might require special attention such as RF shielding.
Areas of thermal concern.
High speed circuitry requirements such as measured trace lengths or controlled impedance routing.
In addition to functional information as listed above, don’t forget to also include all of the regular schematic documentation data as well. This will include items in the title block such as company names, part numbers, revisions, circuit board name, date, and copyright information. By making sure that you have all of the required information on your schematic and as much additional data as possible, you will help to ensure the successful conversion of your schematic to PCB layout.
Another way to help ensure that your schematic is ready to be converted into layout is to use the most advanced PCB design software as possible. PCB design tools like OrCAD have a long history of successfully converting their schematic data into layout with minimal effort. OrCAD has all the functionality that you need to make sure that your schematic is complete and 100% ready to go into layout with all of the library and design constraint information that it needs.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.