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FR4/soldermask trace clearances

J

Jim

Jan 1, 1970
0
Hello all,

If FR4 and soldermask have a similar dielectric breakdown voltage
(~50kv per mil) then the trace clearances (trace to hole or trace to
trace) should be the same between inner and outer layers. Is this
approximately correct?

Related question: Are UL requrirements based on a non-masked PCB (or
related thru-hole parts)? (ie 6mm between AC Hot and neutral)

Thanks in advance.
 
L

legg

Jan 1, 1970
0
Hello all,

If FR4 and soldermask have a similar dielectric breakdown voltage
(~50kv per mil) then the trace clearances (trace to hole or trace to
trace) should be the same between inner and outer layers. Is this
approximately correct?

Related question: Are UL requrirements based on a non-masked PCB (or
related thru-hole parts)? (ie 6mm between AC Hot and neutral)

Thanks in advance.

Soldermask is not considered a construction material in PCB or
assembly safety evaluation, to my knowledge, save for it's suitability
in the flammability class of construction as listed for the specific
pcb vendor's process.

Evaluate as bare boards.

RL
 
T

Travis Hayes

Jan 1, 1970
0
Jim said:
Hello all,

If FR4 and soldermask have a similar dielectric breakdown voltage
(~50kv per mil) then the trace clearances (trace to hole or trace to
trace) should be the same between inner and outer layers. Is this
approximately correct?

Outer-layer traces which are completely covered with soldermask may have a
different breakdown voltage from two traces which are exposed with
soldermask between them, like you would see on IC pads. Surface
contamination, moisture, and atmospheric pressure will vary the voltage.
Higher frequency currents will have skin effects. Usually, soldermask is
not that thick, so your figure of ~50kV/mil will quickly be overwhelmed by
the lower breakdown voltage of the air above it.
 
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