Its probably worth recalling that the original Mil 28809 actually required
the ionics on a board to be extracted manually in a "classic lab" manner by
a someone in a white coat. The Ionograph, Omegameter and so on were
developed as means to simplify this process and make it possible for
non-chemists to carry out testing without a lab. This they did with varying
degrees of efficiency and that's where the equivalence numbers come from.
We need to keep in mind that there is a high degree of empiricism in them
and they are only quantitative - an amount. Qualitative aspects were looked
after by defining quite closely the flux type they were valid for. Also keep
in mind this was decades ago.

Current technology fluxes may or may not have the same relationship of
quantity of extractable ionics to reliability that was assumed in the MIL.
Today the Ionograph is just a dirt meter for ionics. It produces a number
which goes up and down same as a volt meter does for electricity. The
numbers it produces can be used as an approximate measure of process
control. Clearly a high number is bad, but how bad should preferably be
related to something more application specific founded on reliability
testing.

Regards

Mike Fenner

Applications Engineer, European Operations
Indium Corporation
 T: + 44 1908 580 400
M: + 44 7810 526 317
 F: + 44 1908 580 411
 E: [log in to unmask]
W: www.indium.com
Leadfree: www.Pb-Free.com



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of joyce
Sent: Wednesday, October 02, 2002 1:19 PM
To: [log in to unmask]
Subject: Re: [TN] Ionograph measurements


guys, I am bit confused here.  Are we talking about process development or
process control at assembly level?
(1) all the cleanliness establishment shall be done at development stage.
Ionograph is not a good tool.  Liquid chromatography might be the better way
to go to define what is the compatibility problem and what kind of
contamination is on the board.  If you get the right personnel, you might be
able to pin point what is the root cause if you exceeding the spec.
(2) Ionograph is good for process control after you defined your "process".
It give a lump sum of ionic reading without differentiate where it come from
and what it is.  If you got 6 sigma control of everything, you should not
see any difference between your process development stage and control.  If
you change vendor, as long as you know what to look for, you should be fine
after vendor qual.
(3) sure you can use Ionograph machine as cleaner (did that
before)...provide you know what are you doing and have enough money to
replace some of the parts in the Ionograph machine...(depend upon who is
going to do the replacement, if it is you, you most likely will have second
thought).
In theory, if the process development were done properly, the chances for
the exceeding spec is very very slim.  Normally, when it is start to drift
towards the limit, someone should start walk on the floor to play
detectives.  However, that does not give you any glory status of "problem
solver" or "team player".

jk

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Tegehall Per-Erik
>Sent: Tuesday, October 01, 2002 2:56 AM
>To: [log in to unmask]
>Subject: Re: [TN] Ionograph measurements
>
>
>Even if you could find a method to scientifically measure cleanliness of an
>assembly (which I doubt will ever happen since flux residues are absorbed
>into the epoxy resin) you would also need to be able to tell how the
>concentration of the various contaminants varies over the surface of the
>assembly in order to assess the impact on reliability. This means that you
>also must be able to transform contamination levels into reliability
>figures. You must then know which of the contaminants that are hygroscopic
>and which are hydrophobic, which are ionic and which are
>non-ionic, but also
>which contaminants that cause synergistic effects when mixed.
>
>Therefore, I think, a scintific approach for verifying quality ought to
>focus on methods for assessing the impact on reliability instead of methods
>for measuring the cleanliness. Surface Insulation Resistance (SIR)
>measurements is such a method (described in Appendix B in J-STD-001C) but,
>as it is used today, its scintific base including acceptance criterion is
>not what it ought to be.
>
>Per-Erik
>
>-----Ursprungligt meddelande-----
>Från: [log in to unmask] [mailto:[log in to unmask]]
>Skickat: den 1 oktober 2002 01:50
>Till: TechNet E-Mail Forum.; Tegehall Per-Erik
>Kopia: [log in to unmask]
>Ämne: Re: [TN] Ionograph measurements
>
>
>
>How does one, scientifically, measure cleanliness of an assembly? It's
>always struck me that if your cleanliness measuring equipment can extract
>enough salts, etc., to measure something, then your cleaning equipment
>isn't good enough, and maybe you should be cleaning with your measuring
>equipment instead.
>
>And how to tell that you're not extracting some vital ingredient of the
>board material and not just surface contaminaton, short of using some SEM
>and checking out the molecules?
>
>Just a thought (or not) (where have I heard that before?)
>
>Peter
>
>
>
>Tegehall Per-Erik <[log in to unmask]>    30/09/2002 10:04 PM
>Sent by: TechNet <[log in to unmask]>
>
>Please respond to "TechNet E-Mail Forum."; Please respond to Tegehall
>Per-Erik
>
>
>              To:  [log in to unmask]
>
>              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
>
>              Subject: Re: [TN] Ionograph measurements
>
>
>
>
>
>
>
>
>
>
>
>
>Daan,
>
>In a note to section 8.3.6 in I-STD-001C, it is written that "In comparing
>the sensitivity between methods, the solvent used to extract the residue,
>the method used to present the solvent to the assembly and the method of
>detecting the residue should all be considered. " I interpret that as you
>are allowed to and should do the correction. But if you use correction
>values, the figures given in the MIL standard are only valid for the models
>of cleanliness equipment that were used at that time. I guess Alpha
>Ionograph 500M is a later model, which means that it should have a
>different
>correction figure (probably higher since it likely has better cleaning
>efficiency).
>
>However, the use of equivalence factors has no scientific base. But on the
>other hand, neither has the method for cleanliness measurement. It
>shouldn´t
>be used as proof of the cleanliness of an assembly since it is no proof of
>assembly reliability. It is a good tool for process control, i.e. to
>control
>that the cleanliness of assemblies manufactured in certain line does not
>change with time. In my opinion, its use should be limited to that.
>
>Regards
>Per-Erik

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