the PCB editor is preferably set to mil = 1/1000 inch,
while the boardhouse calculates with micrometers and millimeters.
1000 mil = 25.4 mm
50 mil = 1.28mm
40 mil approx 1.00 mm
10 mil approx 0.25 mm
4 mil approx 0.10 mm
35 um approx 1.4 mil
35 um is said to be 1 ounce copper per square foot
70 um is said to be 2 ounce copper per square foot
a few constraints
A standard pcb is 35 um (1 ounce/sqrfoot) copper. The following values are valid for that.
Other available thicknesses are 18 um, 70 um, 105 um, 200 um and 300 um.
A standard FR4 pcb is 1.6 mm. Other available thicknesses are 1.0 mm, 0.8 mm,
0.6 mm, 0.4 mm ...
One board house (preciprint) gave me the following numbers :
Another one (zbinden) operates with :
- minimum track width and min track distance 6 mil, better 8 mil
- minimum hole size 12mil, copper ring width 10mil each
- copper in the hole is 25 to 30 um at 35um-pcb.
Another one (db : oneshot) operates with :
- minimum track width and min track distance 4 mil, preferred 6 mil
This means check these numbers first. I found that smaller numbers lead to
a higher price as they have to be more careful, spend more drills and so on.
- minimum hole size 24mil, copper ring width 10mil each
high current considerations
Be the pcb a 35 um copper pcb. The resistance of copper is 17 mOhm for a
wire of 1m length and 1 mm^2 crossection. This means a track of 100mil
width has approx
Another aspect is the heat dissipation in a track.
- 4.86 mOhm per inch length.
- 191 mOhm per meter, with 39.37 inches to the meter
Utracad with dozends of articles.
Utracad's paper on current
high voltage considerations
To be continued
Recommended is Appcad, a tool downloadable from Agilent.
It is located somewhere on their pages, the internal search machine is able
to locate it. Last time I looked, it was under educatorscorner ,
Teacher's tools, References, RF corner, RF cool links a site somehow connected to Agilent/HP.
To be continued ...
last updated: 12.june.03, or perhaps later
Copyright (2003) Ing.Büro R.Tschaggelar