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October 2002

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From:
Mel Parrish <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 1 Oct 2002 07:50:29 -0500
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Good input!
From an historical perspective, Ionograph testing was intended to support
rosin base fluxes closely controlled by flux qualification specifications
which is certainly not the case today. Given the consistent contamination
resource as well as cleaning chemistries the correlation to cleanliness to
performance was a valid consideration. Good application for the time and
common processes allowed.
Today we must rely more heavily upon SIR/MIR types of testing however IC
testing resources can add a degree of confidence as it can identify and
quantify the contamination type. Unfortunately these tests are not inline
process tests as were the quick and simple Ionic tests when life was
simpler.


Mel Parrish
Director, Training Materials Resources
Soldering Technology International
102 Tribble Drive
Madison, AL 35758
256 705 5530
256 705 5538 Fax
[log in to unmask]
www.solderingtech.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Tegehall Per-Erik
Sent: Tuesday, October 01, 2002 1:56 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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