PCB Trace Width

[psycho]

I made a PCB with a USB host port. I am having trouble with the USB module and I think it micht be due to lack of current for writing to a flash drive. I can read the drive but I can't write. I used 7mil traces (even for the supply lines). I put some 30awg jumper wires in at all of the gnd/vcc lines to/from the usb port and still no-go.

So, what would you guess is the current through a 7mil trace and a 30awg wire? I looked at a web page before I had the board made and it says that a 7mil trace will handle over 500mA - is it wrong???

Thanks!
Kevin

[CeaSaR]

Kevin,

Did you use the previous thread (mid-May, 2009) on this to check yourself? There are links to calculators etc.
in that thread, along with hand calcs courtesy MrAl.

Only reason I remember the actual time frame is that a very similar question came up in the question section
of the Jan. 2010 issue of N&V. I sent the link to Russ so he could give the person more info.

Link to thread.

CeaSaR

[haklesup]

7 mil trace should be sufficient for most ICs' Even if it were slightly undersize, it would not cause sufficient voltage drop to make the device stop working. Easy enough to verify, just measure the voltage at the device pin and verify its in spec during the write operation (oscilloscope would be best but a DMM might be fast enough if the sag were severe). Did you use a decoupling cap near the device. Anything else I suggest would be a WAG

[Lenp]

I designed several board in the past that contained power switching relays. Because of the contact density and board clutter the trace width could not be increased. I simply oversoldered the traces. That solder layer really lowers the resistance of the thin trace and boosts its capacity.

Len

[psycho]

Hmmm. Well then with the 30awg jumpers there should be plenty of juice available. I will have to look elsewhere for a problem.

Thanks a lot!
Kevin

[Bygar]

PCB trace widths
1. Rule of thumb with 1oz. copper 1/16" trace at 5 amps will give 20 degree C. temperature rise,
adjust width/thickness to suit.
2. Overlay solder and or wire to increase current capacity,.
Bygar