Help!
I am designing flexible circuits that seem to be over the IPC-D-275 charts.
Or any of the current capacity charts being that they are all the same. I
have circuits that utilize a ARINC 600 size 3 connector with insert A,D
having 150 x #22 AWG, B,E  60 x #20 AWG, and C,F 100 x #22 AWG.
My problem is with the "Input Current", The 22 AWG circuits are to carry
a current of 3 AMPS and the 20 AWG are to carry 5 AMPS. The hole
pattern for the 22 AWG is on 0.100" centers with a .035" hole and a
.065" pad, leaving .035" spacing. The 20 AWG pattern is on 0.150"
centers with a .043" hole and .073" pad, leaving a .077" spacing.  First, a
question with the charts, is a rigid flex considered an internal layer?
Are any flexes considered internal becouse of a kapton cover coat,
and/or a stiffener material? If considered internal, and I use a high TG
material (Polyimide), could I not go higher than the 45 deg C rise above
ambient? How? Also, in IPC-D-275 pg.10, note 5 states that for "groups
of similar parallel..." isn't that really the same as note 4? I do NOT know
how many of these circuits will be "on" at the same time and for how
long in time. I would think that if I put even 3 amps into parallel circuits
acording to the internal chart: 3 amp at 45 deg C rise, with 2 oz copper
equals a .030" trace (I have room for a .020" trace) that my flex would
heat up past that point. Now the 5 amp lines! Am I missing the boat?  Is
there another way?
Dan

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