Q.DIL? SIL?
DIP?
ADual In Line. Single In Line. Dual In-line
Package.
Q.What is a "Thou"? Is a "Thou"
the same as a "mil"?
A. A "Thou" is one thousandth of an Inch,
0.001". A "mil" is the same quantity, a milli-inch. I prefer the term thou
because it is less likely to be confused with millimeters. Since there are
25.4mm to the inch, 1mm = 39thou. All components originally used imperial
measurements, so the thou are a good unit to work with. For example the
pins on a normal DIL package are 100thou apart.
If you haven't
seen it used before, a single quote ' is an abbreviation for feet, and a
double quote " stands for inches. So I could write my height as 5'10".
If you are working in metric, just use millimeters for everything.
E.g., I am about 1800mm high. DON'T use cm!
Q. What size grid should I
use? How close can my tracks be?
A. Short answer - 12 thou
tracks on a 25 thou grid is preferred.
Long answer. Well the old
capabilities of most PCB manufacturers were 12 thou tracks with 12 thou
clearances (gap between tracks). These are called 12/12 design rules. If
you use 12 thou tracks on a 25 thou grid then you have a guaranteed 13thou
gap between adjacent tracks. You can run one track between the pads of a
DIP and meet the clearance rule if you use 62 thou diameter pads, or at
least 62 thou wide anyway. Almost everyone can manufacture to 10/10 rules
these days. Some can do 8/8, even 6/6, but you will start to pay for the
privilege. Stick to 12/12 rules unless you have a reason not to. With
10/10 rules you can run two 10thou tracks between 50thou wide DIP
pads on a 5thou grid.
Q. What clearances and track
widths should I use?
A. On a standard (1 Oz. Cu) PCB, a 0.010"
track will carry 0.8A with a 10 degree C rise. Plenty for you. But
remember to use thicker tracks anyway for power supply traces etc, just in
case you short them.
