Okay, now don't everyone write to my layout guys, but I never bothered
to tell them they could change the constraint files for closer routing on inner
layers, so they do apply the spacings. I have try to keep an eye for it causing
us extra layers or any real grief and it hasn't.
Gary
-----Original Message-----
From: T.Sato [mailto:[email protected]]
Sent: Wednesday, August 14, 2002 6:41 PM
To: [email protected]
Subject: RE: Creepage on PCB Internal Layers
On Wed, 14 Aug 2002 15:22:21 -0400,
John Juhasz <[email protected]> wrote:
> While a different standard was originally referenced in this thread,
> I'd like to consider for a moment Chris Maxwell's question
> "...there should be some minimum distance... on an inner layer of the
> board"L
> The 950-based standards have guidelines in this regard.
>
> In section 2.9.6 'Enclosed or Sealed Parts'
> "For components or sub-assemblies which are enclosed or hermetically
> sealed against ingress of dirt or moisture, and which satisfy the following
> compliance requirements, the minimum internal CREEPAGE DISTANCES and
> CLEARANCES can be the values for Pollution Degree 1."
I think the clause wouldn't be applied in this situation.
In 60950, applicable clauses are 2.10.5.3 and 2.10.5.1 (I'm not
reading genuine IEC/EN 60950, and I'm sorry if I'm wrong) -
the former states that distance through insulation would be applied
in such situation, and the latter set minimum thickness of 0.4mm
for supplementary and reinforced insulation for peak working voltage
greater than 71V.
However, I think applying minimum distance for pollution degree 1 or
that for coated PCBs (clause 2.10.6) for inner layers when designing
PCBs are not bad idea, although both of them wouldn't be applied here.
The latter set, for example, minimum distance of 1.2mm for reinforced
insulation for working volgage up to 250V on coated PCBs.
Regards,
Tom
--------------------------------------------------
Tomonori Sato <[email protected]>
URL: http://member.nifty.ne.jp/tsato/
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