I've gone through IPC-2221A again considering key concepts you kindly advised.
Basically it seems like a job of designers who knows overall requirements from base materials to complete products. : )
Anyhow I've seen important relations of 'current to allowable temp rise' and 'voltage to min. spacing between conductors'.
In terms of current capacity, I should know allowable temp rise first before refering to the IPC-2221A Fig.6-4.
IPC-2152(final draft) seems to be useful to get more information.
And I guess UL recognition like min/max requirements for conductor and dielectric
is associated with the relations above in some extent.
Thanks a lot for your advise, Jack!
Have a good day.
jc
----- Original Message -----
From: Jack Olson
To: [log in to unmask]
Sent: Saturday, February 14, 2009 12:27 AM
Subject: Re: [TN] Permissible current and voltage in PCB
wow, I just realized that ipc.org doesn't work,
you have to use www.ipc.org
(someone should fix that)
onward thru the fog,
Jack
.
On Fri, Feb 13, 2009 at 8:55 AM, Jack Olson <[log in to unmask]> wrote:
> There is no such thing as "permissible current and voltage"
> in circuit board design, (except by safety regulations, and
> those requirements differ).
>
> There is a relationship between current, trace size and temperature
> (which is described by the curves in IPC-2221 Figure 6-4)
> so by increasing the current or decreasing the trace cross section,
> you increase the temperature.
>
> The curves will show the "temperature rise" above ambient for
> any given trace size and current. The key is in knowing what your
> "ambient temperature" is.
> ...and that's why we designers make the big bucks (just kidding!)
>
> The caution is that you don't want the temperature to affect
> the integrity of the board material, so for example if the Tg of
> a particular material is 170 degrees C, we may limit the maximum
> operating temperature to something like 135 degrees C
> (by adjusting the trace width or copper thickness, or by moving
> the trace from an internal to an external layer, or by pouring copper
> planes near it to dissipate the heat, etc.)
>
> also, clearances define maximum voltage, not trace size.
>
> You can get a better description of these concepts by downloading
> a draft of the new IPC-2152 (Current Carrying Capacity) at ipc.org
> under "Status of Standardization" in the Knowledge menu.
>
> hope that helps,
> Jack
>
>
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