Bev
I'll take, but this is going to take hours of Q & A, I fear. First of
all let us be quite clear what we mean by SIR. Rather, let us say what
SIR is NOT. SIR is not the formation of dendrites by biasing a
double-comb pattern. SIR is not a means of determining whether flux
residues are OK, under some conditions or not. Yes, I know some call
this SIR, but they are wrong. Unfortunately, it is not possible to
isolate SIR from some other phenomena, so there is one helluva lot of
confusion in the industry. This is partly because some other tests, such
as electrochemical migration resistance (ECMR), are conducted in a
similar, but not identical, manner and this is confusing. So confusing
that many guys are no longer able to separate the sheep from the goats,
because they have all become woolly through the use and misuse of woolly
terminology.
SIR is a purely physical measurement of the resistance along the surface
of an insulator. It's really as simple as that, like taking an ohmmeter
to measure it. Unfortunately, surface physics is an impossible science,
because, by definition, a suface has something below it (the substrate)
and something above it (contaminants and air). Just to make the equation
more complex, it is not even homogeneous, in its infinite thinness.
Microscopically, and smaller, it is usually Himalayan in nature in its
hills and vales, and also in its structure with different chemical
species (rocks). All this has an influence on resistance.
I'm strapped for time just now, so I'll have to hang up, but I'll
continue with some more answers tomorrow.
Brian
Bev Christian wrote:
>
> OK, let's see what I can stir up today. :)
>
> I am looking for a clear, succinct definition of surface insulation
> resistance. If I look in IPC-9201 "Surface Insulation Resistance Handbook",
> I don't find what I am looking for. (Sorry, Joe, Doug et al). What I find
> on page 2, section 2.1, Definitions is the following: "It represents the
> electrical resistance between two electrical conductors separated by some
> dielectric material(s). This property is loosely based on the concept of
> sheet resistance, (see ASTM-D-263), but also contains elements of bulk
> conductivity, leakage through electrolytic contaminants, multiple dielectric
> and metallization materials and air." Whew!
>
> Any takers? Hmmm?
>
> regards,
> Bev Christian
> Research in Motion
>
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