What are Footprints and Land Patterns

2. Plated Through Holes

Plated through-holes are little more than large-diameter vias, but they do require a small amount of design.  They have to be drilled large enough to allow the part to pass through after electroplating and have a pad large enough to allow a proper fillet to form.  You don't want to make them too large or they'll allow your part to become misaligned.

Three examples of plated through-hole parts.

The cheapest and most accurately located holes are created with drills.  So, where possible, drill rather than helically bore the holes on your PCB.  (This comment is primarily aimed at the makers.)

Just so you know -- the smallest cutters used in PCB fab shops are approximately 1 mm in diameter, so for holes smaller than 1mm, you have no choice but to drill.

Calculating Hole Size

To determine the size of the hole you need, look at the diameter of the pin you expect to insert into the board.  For rectangular parts, measure across the diagonal to determine the diameter.

For a drilled hole, IPC splits the recommended hole and pad diameters based on component density.  As density increases, so does the manufacturing difficulty.  Use the largest options wherever possible to keep your manufacturing yield as high as possible.  You should also remember that you will need an anti-pad (copper-free area) that surrounds the pad to prevent short circuits.  This number is determined by the weight of your copper.  Use your copper weight trace & space measurements to determine the anti-pad.  And if you are designing a high-voltage board, you should also look at your creepage and clearance numbers.


Density
Level

Diameter
Hole Pad
 A - Least   Lead + 0.25 mm   Hole + 0.7 mm 
 B - Moderate   Lead + 0.20 mm   Hole + 0.6 mm 
 C - Most   Lead + 0.15 mm   Hole + 0.5 mm 

Hard Way Hughes

We haven't discussed trace & space yet.  Until we do, for this design, assume you need at least 6 mils of copper to conduct current and 6 mils of air between adjacent bits of copper to prevent short-circuits.  I'll explain the actual minimum values and how to arrive at them in a few weeks.