Hello Brian. Yes you're right of course, and in previous incarnations I also have spent
lots of time measuring such as CO2 gulps and pondering the significance or otherwise of
such things, but I was trying to avoid getting into the theology of these machines. The
point I was trying to make, - maybe I could have spelled it out more clearly - was that
the results from these machines (IMHO) do not make absolute measurements of anything very
much for the type of reasons you give, they are useful in process control as they provide
numbers in real time which can be related to reliability. When measuring differences like
this errors tend to be become part of the base line / subtracted out.

----- Original Message -----
From: Brian Ellis <[log in to unmask]>
To: <[log in to unmask]>
Sent: 28 January 2000 07:42
Subject: Re: [TN] Omega meter v.s. Zero-ion(ZI-100A)


> Mike
>
> As an ex-manufacturer of instruments, please allow me to add another 2 cents worth. The
> Ionograph and Zero-Ion are so-called dynamic instruments which measure the conductivity
of the
> solution leaving the test tank, deionise it and then return it to the tank. This means
that
> the solution conductivity must return to the initial base line. The dissolved
contamination is
> integrated mathematically from the resultant curve. This idea is theoretically sound but
> depends on a) working the solution for long times at conductivities where the extraneous
CO2
> absorption from the air is at its highest and unpredictable; b) that the DI columns
remove all
> the ions in one passage and c) that the differentiation is instantaneous. These factors
result
> in necessary approximations which tend to give a too-high reading. Another problem is
that,
> because it can be set up with a very low conductivity baseline with very long test
times, it
> can detect ions from substrate materials, which are irrelevant to what is wanted.
>
> The Omega Meter, Contaminometer (one exception - see below) and some others are the
so-called
> static types. These depend on auto-integration by the accumulation of the ions in the
> solution. Because of their nature, they were less sensitive to CO2 absorption and were
> generally more accurate, except that - if the volume of solution was too small - there
was a
> small risk of saturation, in which case the reading would be slightly too low. Tests we
did
> showed that this would occur only at massive doses of ionic contaminants, especially
some
> organic lead salts and that the contamination would be extremely high, anyway. I shall
risk
> the ire of the dynamic fans by saying that the static type is inherently more precise.
Despite
> what was said in another post, some instruments of this type can stop the test
automatically
> when there is no further significant rise in conductivity and therefore are not working
for a
> fixed time. Another advantage of this type is that, if a test is stopped at, say, 15
minutes
> but the conductivity is still rising, it is easy to mathematically extrapolate with a
> reasonable accuracy to the end point, so that test times are shorter - this is done
> automatically by the software.
>
> One instrument we developed could be run in either static or dynamic mode by simply
loading a
> different software. Commercially, this was a flop as nearly all the customers opted for
the
> static mode because it was faster and more precise with easier number-crunching.
>
> Hope this helps.
>
> Brian
>
> Michael Fenner wrote:
>
> > These instruments are designed to wash ionic material from a specimen. The difference
is
> > that the Omegameter processes for a fixed time. The Zero Ion [and the Ionograpgh]
> > allegedly extract till there is nothing left. So in theory you can use an Omegameter
like
> > a Zero Ion by simply continuously replacing your sample back in the machine until the
> > reading doesn't change and then adding all the readings up, or you can do the opposite
and
> > take your work out after a fixed time from the other two. Consideration of the above
shows
> > that readings taken on one machine type can't be equated to readings from another, the
> > quality of correlation will obviously depend on the rate at which the ionic material
> > dissolves into the system.
> >
> > The amount of ionic material collected by the machine is then manipulated
mathematically
> > into a number which is called the amount of contamination per unit area of PCB.
> > Keep in mind that this is an average number only and is not qualitative:
> > You don't really know what the ionic contamination is, nor do you know its
distribution on
> > your work. You assume it comes only from your prior processing and is even
distributed.
> >
> > These machines are  good for process control and measuring the effect of process
changes
> > as results are obtained quickly enough to respond to in real world time.
> > In an ideal world to use them as a shopfloor method  for determination of reliability
you
> > would first need to plot their readings against time to fail in say SIR testing  or
> > accelerated ageing trials for the specific process they are to be used on.
> > In this real world you may have to adopt a more pragmatic method , like trying to find
out
> > what other similar companies to yours do, industry sector practice  and so on.
> >
> > Mike Fenner
> >
> > ----- Original Message -----
> > From: Collins, Graham <[log in to unmask]>
> > To: <[log in to unmask]>
> > Sent: 18 January 2000 13:36
> > Subject: Re: [TN] Omega meter v.s. Zero-ion(ZI-100A)
> >
> > > Ramsey, Fumiaki-San
> > > The Omegameter was sold in several different models, ours does the full
> > > calculations and prints the results on a small slip of paper (like a cash
> > > register), as well as .  So no calculators are used in our case.
> > > We have both an Omegameter and an Ionograph.  The operators prefer the
> > > Omegameter as being a bit easier to use, the main difference being that our
> > > Ionograph is an early model where the top of the tank is about 6 feet off
> > > the ground, and about 3 feet deep - so some tricks have to be used to get
> > > product in and out of the thing.
> > > The Ionograph is said to be more accurate than the Omegameter, the main
> > > difference (as I understand it anyway) is that the Ionograph uses heated
> > > solution, so it does a better job of removing the residue from the CCA.  The
> > > Ionograph is controlled by a separate PC and offers more "bells and
> > > whistles".  As well, the unit they currently sell does not have the elevated
> > > tank, so is much easier to use.
> > >
> > > Never having seen a Zero-Ion, I can't comment on those.
> > >
> > > regards,
> > >
> > > Graham Collins
> > > Process Engineer,
> > > Litton Systems Canada, Atlantic Facility
> > > (902) 873-2000 ext 6215
> > >
> > >
> ......

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