"Printed wiring material" Creepage puzzle from EN60664-1 (2007) - Page 1
Forum section: electronics / projects

author: jn
author_rank: Newbie
timestamp: March 25, 2014, 02:51:20 pm
content: Dear EE Wizards,would you please know, how to handle "printed wiring material" in EN60664-1 (2007), particularly table F.4?At the first glance, I'd just say, ok, "printed wiring material" just means PCB and I'm free to use much much lower creepage distances comparing to other structures. Honestly, I feel I'm terribly wrong with this assumption for many reasons.- First, from the creepage point of view, I don't see _any_ reason, why poor FR4 would be anyhow better in terms for tracking, bridging distances, etc., than any other material. In fact, I'd expect the PCB to be far _worse_ due to chemical residuals, uneven etching, etc...- Second, the distances are simply too small for my taste. Empirically I know, that applying DC 48V in pollution degree 2 environment over 40um distance is a road to hell in matter of days. In other words, the distance is absolutely inadequate.So for now I stick with the general columns of that table (e.g. 10V, pollution degree 2 => 0.4mm) and the fact, that I don't understand the meaning of these columns. In respect to the applications I'm involved in (automotive), I'd be sort of happy with that, even though the spacing is sometimes a limiting factor. But the factor of unknown is very irritating :-)I was just wondering, if anyone has a background for these two columns in the table and could explain the meaning and use of that?Many thanks,Jiri

author: nctnico
author_rank: Super Contributor
timestamp: March 25, 2014, 04:58:04 pm
content: Google for 'creepage distance' and you'll find several useful articles. It does take some reading to understand it though.

author: jn
author_rank: Newbie
timestamp: March 25, 2014, 05:53:21 pm
content: Would you be more specific, please?I've studied pile of papers on the topic, plus I had the uneviable honour to spend weeks with experiments on dendritic growth, caf, etc. Hence I dare to believe that I already know a few things about the topic, at least from the physical/electrochemical point of view. Still, no clue to decipher the meaning of the "printed wire material" column :-)Thanks.

author: rchapman
author_rank: Newbie
timestamp: May 05, 2014, 11:01:16 am
content: Hi Jiri et al...I have been puzzling over the same mystery. Why do they allow smaller creepages in EN60664-1-2007 for Printed Wiring Material than for other unspecified conditions - even under the same climate category and Material Class/ Comparative Tracking Index?I cannot speak authoritatively on the question - but the only clue I have found is a quote from this document:http://www.nen.nl/pdfpreview/preview_171161.pdf"NOTE 3 For clearances on printed wiring material, the following Note 3 in Table F.2 in 60664-1:2007 can be used:“For printed wiring material, the values for pollution degree 1 apply except that the value should not be less than0,04 mm, as specified in Table F.4.” For creepage distances on printed wiring material, distances in Table F.4 in60664-1:2007 can be used if protected with a coating meeting IEC 60664-3 requirements and tests."Maybe this is saying that the "Printed Wiring Columns" in table F4 apply only where the PCB is coated according to IEC60664-3. I only purchased 60664-1 and I am getting a bit tired of having to buy a new standard every time you find some small print at the bottom of a table somewhere.. Does anyone have any other thoughts on this issue?Richard.

author: Niklas
author_rank: Frequent Contributor
timestamp: May 05, 2014, 08:50:04 pm
content: Have you checked if there is a product group specific standard available? For household equipment there is EN60335, which references to EN60664 and other standards. If I remember correctly, there was at least one place in the 60335 that referenced to a table in 60664 and had a note similar to "take the value from table X in 60664 and then add 0.5 mm for mass production tolerances and possible shrinkage during the product's lifetime".I still have a copy of the EN60335-1, dated February 2007. In the Creepage tables for both functional and basic insulation, there are no columns for "Printed wiring material".Pollution degree 1: Same value for all material groupsPollution degree 2: Material groups I, II, IIIa and IIIb as separate columnsPollution degree 3: Material groups I, II, IIIa and IIIb as separate columnsIt might have been in one of the addendums, but I have a weak memory that I have read something about either adding or removing the "Printed wiring material" columns.