Mike

Agreed, except you had to be sure that the base line was always at the same level and that the
DI resins in the dynamic types were always at the same degree of activity each time, to obtain
consistent numbers for process control.

Brian

Michael Fenner wrote:

> 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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