George,
Clause 2.9.4.3 of UL 1950 addresses PWB insulation as follows:
"Supplementary or Reinforced insulation between conductor layers
in single-layer and multi-layer printed boards shall meet one of
the following requirements. Either:
- the insulation shall have a minimum distance through insulation
of 0.4mm, or
- the insulation shall comprise two or more layers of prepreg or
other thin sheet insulating material. There is no requirement
for distance through insulation of individual layers nor the
overall insulation. The overall insulation in the finished
printed board shall pass the appropriate electric strength test
of 5.3.2.
Printed boards having supplementary or reinforced insulation comprising
of fewer than three layers of prepreg or other thin sheet insulating
material shall be subjected to routine testing for electric strength.
Printed boards employing thin sheet insulating material other than
prepreg shall pass the thermal ageing and thermal cycling tests of 2.9.5."
If you pass a hipot test between the layers you should be okay.
Patty Elliot
Qualcomm, Inc.
p...@qualcomm.com
At 12:51 PM 4/13/99 -0400, Sparacino,George wrote:
>Hello Group,
>
>Along this line, I was asked, if placing power and ground traces on
>separate (PCB) layers would be an acceptable way of reducing clearance
>requirements between (gnd&pwr) traces. Is there anyway to anticipate
>clearance between PCB layers of a multi layered board? Is there a need to
>as far as 950 is concerned? I haven't been able to find anything that
>mentions this.
>
>I would appreciate any input on this issue.
>
>Thanks,
>George
>
>> -----Original Message-----
>> From: jrbar...@lexmark.com [SMTP:jrbar...@lexmark.com]
>> Sent: Monday, April 12, 1999 2:14 PM
>> To: emc-p...@majordomo.ieee.org
>> Subject: Re: IEC 950 Insulation Requirements
>>
>> Donald,
>> The numeric suffixes key Table 0.1 to Figure 5A:
>> * OP1 through OP6 are all OPERATIONAL INSULATION (clause 1.2.9.1) which
>> does
>> not provide protection from electric shock.
>> * B1 through B8 are all BASIC INSULATION (clause 1.2.9.2) which provides
>> one
>> level of protection from electric shock.
>> * S1 and S2 are both SUPPLEMENTARY INSULATION (clause 1.2.9.3) which
>> provides a
>> second level of protection from electric shock.
>> * R1 through R4 are all REINFORCED INSULATION (clause 1.2.9.5), which is
>> equivalent to DOUBLE INSULATION (clause 1.2.9.4),
>> which consists of BASIC plus SUPPLEMENTARY INSULATION.
>> * S/R is SUPPLEMENTARY or REINFORCED INSULATION that meets Table 0.1
>> notes 3 &
>> 4.
>>
>> The insulation requirements cover not only the expected peak voltages, but
>> also
>> the transient voltages that may appear on the different circuits. They
>> also
>> cover the possibility of a pinhole or insufficient overlap of the
>> insulation
>> permitting an arc to occur. Insulation requirements are mainly covered by
>> IEC
>> 950:
>> * Section 2.9 Clearances, creepage distances and distances through
>> insulation.
>> * Section 5.3 Electric strength.
>> * Section 5.4 Abnormal operating and fault conditions.
>> * Annex F (normative) Measurement of creepage distances and clearances.
>>
>> Clearance is distance through the air. If an arc occurs, and then stops,
>> the
>> air is assumed to completely return to normal. Creepage is distance over
>> the
>> surface of an insulator. If an arc occurs and then stops there can be
>> damage
>> that leaves the surface conductive or otherwise more prone to arc again.
>> The
>> required creepage distances are a function of:
>> * Transient voltages.
>> * Pollution class-- how much crud can build up on a surface & its
>> likelihood of
>> getting wet.
>> * Comparative Tracking Index (CTI)-- how badly insulator gets damaged by
>> an
>> arc.
>> John Barnes
>> Advisory
>> Engineer
>> Lexmark
>> International
>>
>>
>>
>>
>> donald%hq.rossvideo....@interlock.lexmark.com on 04/12/99 11:11:56 AM
>>
>> Please respond to donald%hq.rossvideo....@interlock.lexmark.com
>>
>> To: emc-pstc%majordomo.ieee....@interlock.lexmark.com
>> cc: (bcc: John Barnes/Lex/Lexmark)
>> Subject: IEC 950 Insulation Requirements
>>
>>
>>
>>
>>
>> I have just received a copy of the IEC 950 standard and after
>> reviewing the insulation requirements outlined in section 2.2.6 I
>> have a question that the group maybe able to shed some light on.
>> The question relates to the two table 0.1 and Table 5 which is
>> intended to give examples for the application of the various
>> insulation requirements.
>>
>> In the two table it appears there are numerical reference to the
>> different categories of insulation, for example OP1, OP2, B1, B2
>> etc. I have reviewed the entire standard and I can not find any other
>> reference other then these tables to these numerical references of
>> the different categories of insulation.
>>
>> Could some one provide some insight in the the intent and use of
>> these tables? Are the numerical references simply to identify
>> various circuits to circuit situations and which of the five categories
>> of insulation applies?
>>
>> Thanks before hand
>>
>> Donald McElheran
>> Product Engineering
>> Ross Video Ltd.
>>
>>
>>
>>
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>>
>>
>>
>>
>>
>>
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