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Electronic Schematics, Layout and Printed Circuit Board (PCB) Production

The Process / Workflow for creating PCB's

http://electronicdesign.com/embedded/engineer-s-guide-high-quality-pcb-design - A brief guide to the overall process

Making Schematics

There are many videos teaching the various tools, but the main goal for a schematic (like a mechanical CAD model/drawing) is to communicate "intent" of your design.

Look at published schematics, especially for commercial products. They are generally very clear even though they may be very complicated. While commercial schematics often require multiple sheets, we generally encourage students to keep everything to a single sheet as its usually easier to follow.

Some tips:
  1. Avoid crossing wires.
  2. Use net names to avoid running long wires across / around the schematic. For example
    1. add as many ground points as needed rather than running long lines around the diagram
    2. use a net name for power then use that instead
  3. keep flow from left to right, then top to bottom
  4. ground should be on the bottom of the schematic, power source at the top. This is a common convention
  5. orient components in their common way, i.e. Op Amps are triangles that (usually) point to the right. It's a connection that makes it easier for others to follow intent
  6. use the standard graphic for parts.
    1. Using a triangle indicates the component is an Op Amp while using a rectangle does not
    2. Avoid rectangles for resistors. Use the zig zag line graphic
    3. make sure polarity of electrolytic capacitors / outside shield of regular ones is properly oriented when that matters. Shield side on non-polarized caps usually goes to ground if one side is grounded.

Tools

There are a number of tools used for electronics CAD including:

On Linux you can use EagleCAD or a number of Spice related packages including Oregano and Gschem. Oregano includes a small number of device models needed to run simulations. Gschem lets you run simulations using ng-spice or GNUCAP but does not include the models.

There are MANY (other) tutorials for all of these as well as videos posted to YouTube. Do a little searching to find these!

Which is best? Much web searching indicates that NONE of these are the "best". All work and can be used to create a schematic which can then be turned into a PCB. Some Open Source applications may require a little more work to get running or to get used to them - but that are inherently available to all!

Production

There are MANY PCB makers that can be found online. The following are a few that we have had some experience with in the Lab or that faculty / staff / students have used. You will need to search for them online to get more details and current information like price / delivery time. For some BMED projects (and some others) you might want to make sure they do ROHS processing.

  • Dfrobot : used by one of the faculty a lot for quantity 10-150 boards - very affordable.
  • elefreaks (overseas) can get them from 11 days standard down to about 7 for a price - this is for multiple boards
  • 4PCB (US) has fast turnaround, usually small quantity, may be costly but good results
  • BayAreaCircuits : http://instantdfm.bayareacircuits.com - very professional service, fast service (down to 1 day turnaround at a price!), or to mass produce a particular board. Suggest using DIPTRACE CAD software, as you get a better deal than going to them directly. Through DIPTRACE, there is a $35 dollar minimum (5/8/14), and the following specs apply:
    • 0.062 thick
    • FR4 (standard temp for 2 layers, high temp for 4-6 layers)
    • 5/5 min trace and space
    • HASL finish
    • 0.010 smallest finished hole size
    • green solder mask - You can choose your own color solder mask by going directly to the company, but you will pay dearly for this
    • They have student deals but they aren't that great. They can do up to 40 layers--doubt that will be of interest--and fancy routing if you require it.
  • OSH park: https://oshpark.com - There is a minimum order of 3 boards but of any size and you don't have to pay for more than you need. OSH waits until they have enough different designs on a panel and then send off to the fab. They save a lot of money this way and pass that on to the consumer. Of course the turnaround time is usually 2-3 weeks. For 2-layer board, $5 per square inch, and for 4-layer $10 per square inch. They may not go beyond 4-layers.
    • ENIG gold finish (very nice but you will need more solder)
    • 0.063 thick
    • ALL boards have purple solder mask; i'm not crazy about this because it's dark
    • 2-layer boards 6/6 trace and space, 13 mil drills; 4-layer, 5/5 and 10mil drills
    • plated slots are not supported
    • internal cutouts allowed
  • Advanced circuits : http://www.4pcb.com - Approved vendor, but standard service is expensive. Barebones (credit card only is cheaper and faster, one board per order, but can be combined shipping if you call immediately after placing the orders.)
    • http://www.4pcb.com/pcb-prototype-2-4-layer-boards-specials.html
    • 2-layer, FR-4, 0.062" thick
    • Plated or Non-plated holes (if no specifications provided, holes will be plated)
    • 6-mil line/gap minimum
    • Tin finish over 1-oz Copper
    • No internal routing (cutouts) and no scoring, tab rout, or drilled hole board separations.
    • Cut to rectangle shape only
    • No mask
    • No legend
    • Min size 1.0" X 1.0"
    • Max size 12" X 16" (192 sq. in.)
    • Gerber 274X preferred
    • Excellon drill (English Units)
    • Minimum hole size 0.015
    • Maximum 35 drilled holes per sq. inch
  • Sunstone Circuits : https://www.sunstone.com - Approved vendor