Ben:
The charts in IPC-D-275 are based on research conducted by Charles
Jannings at Sandia National Labs.
Jannings' report describes a series of trest to establish electrical
properties. The results includes voltage holdoff, current carrying
capacity and insulation resistance for 2-sided bare, coated, and
encapsulated boards.
Average breakdown voltage (V) followed the relationship
V = 3.1 S(superscript)0.51,
where separation (S) ranged from 0.25 to 1.5 mm.
(This is for bare boards at ambient conditions.)
Current carrying capacity of conductors was evaluated by temperature
rise between conductors generated with step increases in current.
Variations in temperature rise between conductors with the same nominal
or design width were correlated with meaured differences in conductor
cross-sectional areas. Resistances calculated from conductor lengths and
cross sectional areas were within 10 percent of the measured values.
The boards tested were fabricated using a panel plate and solder dip or
plate and liquid level process. A few measurements were made on boards
fabricated using a pattern plating process with thin clad laminate.
Testing was "frequently" extended until functional failure to obtain a
better understanding of the failure mode.
IPC published the Jannings paper, "Electrical Properties of Printed
Wiring Boards," as IPC-TP-117 in September 1976.
The results of the study indicated that conductor spacing recommendations
in MIL-STD-275 were very conservative and could be reduced.
Copies are available from IPC's order dept., email: [log in to unmask]
Mike Buetow
IPC Technical Staff
2215 Sanders Road
Northbrook, IL 60062
P: 847-509-9700, ext. 335
F: 847-509-9798
[log in to unmask]
On Tue, 8 Oct 1996, Davis Benjamin L wrote:
> Does anyone have the mathmatical formulas to determine the current
> carrying capacity of traces. I know this information is available in
> charts (Fig. 3-4a,b,c in IPC-D-275), but I was wondering if someone has
> the mathematical formulas used to construct these charts.
>
> My plan is to try and write a short program to figure the current
> capabilities rather than search for my copy of the 275 and a
> ruler/staightedge each time I need the infomation. On the other hand,
> if anyone has a script and can share it, I'd love to have it and save
> myself some time.
>
> If I get something together I'll be happy to share it (if I can).
>
> thanks....ben
> Ben Davis
> Systems & Electronics, Inc.
> [log in to unmask]
>
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