It was FR-4


On Fri, Apr 4, 2014 at 6:32 PM, RussellMc <apptechnz@gmail.com> wrote:

> On 5 April 2014 12:54, David VanHorn <microbrix@gmail.com> wrote:
>
>
> *> I saw a PCB which was entirely UL-94V0 go up in flames while connected
> to a *
> *> brick supply in "hiccup" mode, delivering only 1w average to the board=
..*
>
> Was it FR4 material or something like paper-phenolic (rated to UL-94 V0).
>
>
>
> > I've mentioned it here before, but a web search on "Low voltage, the
> > incompetent ignition source" will turn up a very interesting article.
> >
> >
>
> The full title tells you what it's about (although Dave's citing it is a =
ra
> ther
> strong clue).
>
> LOW VOLTAGE
> THE *IN*COMPETENT IGNITION SOURCE
> DISPELLING THE MYTH
>
> from:
>
> http://www.kodiakconsulting.com/page19/assets/Low%20Voltage_The%20Incompe=
tent%20Ignition%20Source_Final.pdf
>
> ABSTRACT
>
>  The present, widely held belief is that products powered by "low voltage=
"
> (typically less than
> 24V) electrical energy are incapable of starting fires since there exists
> an insufficient level of energy to
> produce sufficient heat and ignition. By analyzing commonly implemented
> electronic circuits found in a
> variety if household electronic devices, manufactured using standard wave
> solder or surface mount
> technology (SMT) processes, single point failures will be discussed and
> induced that demonstrate ignition
> at low voltages, or more precisely, low power levels. Through the
> application of a thoughtfully designed
> series of experiments, this paper will demonstrate that voltages as low a=
s
> 3VDC and power levels in the 3W
> range or less, are entirely capable of igniting proximate fuel packages
> sufficient to produce sustained fire in
> a variety of electronic assemblies.
>
> __________
>
> UL 94 V-x requirements
>
>            http://web.rtpcompany.com/info/ul/ul94v012.htm
>
> UL 94 - Wikipedia:   http://en.wikipedia.org/wiki/UL_94
>
> Digikey - 3 pages.Notes that UL 94 V0 starts on page 2. Page 1 is the muc=
h
> less demanding UL94-HB. Not actually stated there !!!!  but  contains a
> section that reads ~~=3D "allows flaming incendiary arrows to rain down o=
n
> hapless crowd below".
>
> _____________________
>
> I dislike PCB materials which are cited as UL94-V0 as an effective MATERI=
AL
> spec, rather than as a safety spec.
> eg a device may be said to use FR4 and UL94V0 PCBs. The FR4 will be for t=
he
> main PCB(s) latter is usually for small assemblies such as switches or
> sensors. This may well be a material made of paper laminated with class B
> clarified Yak's butter, or perhaps Phenolic material. This is usually use=
d
> instead of FR$ either due to lower cost or (more likely) due to ability t=
o
> be punched. FR$ tends to blunt punching dies in under 1000 operations.
> Such materials may fracture due to relatively mild stresses or just becau=
se
> they want to. If the fracture line is crossed by a PCB track or tracks it
> is liable to be broken. (Ask me how I know).
>
> Some manufacturers offer only FR4 or equivalent and use more expensive
> routing instead of punching.
>
>
>
>
>       Russell
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