CAD

Printed Circuit Boards (PCBs) (a work in progress)

A basic PCB is a flat board made of an insulating material (usually epoxy-fiberglass) with at least one layer of copper laminated to it. To implement a circuit, the un-needed portions of the copper are removed with the remainder providing the interconnections for the components in the circuit. For circuits that require too many connections for one layer of copper, wire jumpers can be used on the component side of the board to make the additional connections. At a slightly higher expense and complexity, a double-sided PCB could be used. Double-sided PCBs have copper on both the top/component and bottom/solder sides. Very complex circuits, such as computers, are implemented on multi-layer PCBs that have not only top and bottom layers but also layers of copper circuits sandwiched between thin layers of the epoxy-glass substrate.

If you're just experimenting with electronic circuits, solderless breadboards, prototyping perfboards and wirewrap methods are all fine. But for the highest quality, reliability and reproducability, you might be interesting in making a PCB. And yes, you can make inexpensive PCBs for one-off prototypes at home too.

How to design/layout a PCB

The pattern of lines, circles and other shapes that define the circuit of copper on a PCB is called the 'artwork'. There can be a bit of 'art' involved with it, with some layouts being pleasing to the eye and others being as ugly as my handwriting. There is, of course, a dose of science involved in creating a functional and reliable design.

Follow these simple rules for best results:

• Try to avoid right angles on small traces. When etching a PCB yourself, right angle turns are subject to etching through, leaving an open or poor quality connection.
• Pads (the copper circle or square that a component pin/lead will go through and be soldered to) must be sized properly to assure that it's easy to solder well and adheres well enough to the board that it won't pop off with heat or stress. If necessary, pads can have a smaller outside dimension (OD) on double-sided, manufactured PCBs because the holes will be plated-through, providing more area for solder and strength.
• Be certain that you make your traces the right size (width) for the current it will carry. I have seen at least 2 PCB designs with onboard fuses that didn't blow when a short circuit occurred because the copper traces feeding the fuse were too small and melted first. See 'Tips and tricks' below for more information.
• Be aware of what size of drill (tool) will be necessary for pads, vias and other holes, especially if you will have someone manufacture the board for you from your artwork. Specifying odd or non-standard tools can increase the board cost.

  Layout by hand

  The simplest, quickest way to layout a PCB is to draw the circuit directly on a copper-clad blank, using an indelible (permanent) ink marker. This might be the best choice for fairly simple circuits. Dry transfers are predefined patterns that you press on to the blank PCB. With these, you will probably still need a permanent marker to fix small errors.

  [mention photosensitive PCB blanks and 1:1 and 2:1 exposure, artwork on clear plastic, contrast to directly application]

  CAD software (commercial and free, from-scratch layout or from schematic netlist)

  A note about autorouting

How to make a PCB at home

types of PCB blanks (photosensitive, plain, double-sided)

sources for PCB blanks

transferring the layout to the board (laser printed transfer, indelible marker, dry transfers, etc).

etching (ferric chloride, chemical handling, agitation, fish tank aerator)

Farming out the manufacture of your PCB

cost drivers (size, number of layers, number of holes, complex cutouts, odd tool sizes)

Submitting your artwork

Getting quotes.

Design tips, tricks and insights

Sizing traces, pads and vias

Minimum feature size and spacing.

Keep-out zones (for heatsinks, mounting holes, etc)

Using traces as shunt resistors to measure current

Component position, placement and spacing (top and bottom layers should be routed perpendicularly, leaving room for heat sinks, minimizing trace lengths, decoupling cap placement in digital circuits, etc).

Standard apertures (tools)

Solder mask and silkscreen

Copper weight (1 oz standard, others available)

Final Assembly

link to soldering

delamination due to overheating (either by improper soldering or hot components)

Mounting standoffs (screws with plastic, ceramic or metalic standoffs, swage type standoffs)