Amendment: Potential heating problem with standard patch Cat5 panels
There have been a bunch of replies to my reported potential PCB problem.
Here is what I have since learned.
1) A PCB vendor told me that the epoxy glass (FR4) boards are good to
130 degree C
2) Others on the committee gave various estimates running from 90 to 140
3) Stirling Vaden pointed out that momentarily during wave soldering,
they go beyond 200 degree C
4) John Kee presented a paper to this group 3/7/2000. His paper was
conservative at 90 degree C
I could not get anybody to give a temperature where, under continuos
load, the board would not discolor. That said,
maybe my memory of discoloration proceed the advent of FR4. It may be
that FR4 does not have a problem.
But let me go back to original issue. I have looked at many patch panel
PC boards and for various reasons, the traces run from 10 to 18 mils.
1) Making pairs of traces 100 ohm. 2) Trying to get between the RJ45
pins. 3) Running a pair between the 110 punch down pins. 4) In general,
there is very little space for both compensation and wiring while
leaving margins between pairs of traces. 5) People are afraid of too
But it is important to recognize here is no general standard for patch
panel traces (as pointed out in one of the responses).
So with typical pitch and traces I asked the question. What is the
likely temperature rise. And for my assumptions (subject to critique) I
found a 12 degree rise.
So if discoloration is not an issue at high ambient (40 degree C) plus
12 then there is no issue. If we double the current density the
temperature rises only to 19 degree C and it is still not an issue.
Enough said on this problem.
Several people have mentioned normal copper thickness is 1.4 mil. While
correct, most boards are then overcoated with solder giving twice that
thickness Thus, I used 3 mils.