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
-----Ursprungligt meddelande-----
Från: d. terstegge [mailto:[log in to unmask]]
Skickat: den 30 september 2002 15:03
Till: [log in to unmask]
Ämne: Re: [TN] Ionograph measurements
Thanks Ron, I'll have a look at these standards. Unfortunately so far
nobody could give me the evidence that I'm allowed to use an
"equivalence factor" when measuring ionic contamination.
The document that Per-Erik referred to comes very close (it mentions
how the "A" version of the Ansi J-std-001 had an appendix with a
statement about the equivalence factor), and I'm still expecting a
report from Graham.
Best regards,
Daan
>>> [log in to unmask] 09/30/02 01:06pm >>>
Daan, the info is shown in table VIII in MIL-P-28809. It probably is
also in
MIL-C-28809, but I cannot find my copy of "C" to verify that.
Ron Dieselberg
CMC ELECTRONICS
CINCINNATI
[log in to unmask]
-----Original Message-----
From: Graham Naisbitt [mailto:[log in to unmask]]
Sent: Friday, September 27, 2002 11:54 AM
To: [log in to unmask]
Subject: Re: [TN] Ionograph measurements
> Hi Technet,
>
> One of our customers is complaining that the upper limit for our
> ionograph test is set at 3.1 micrograms/cm2 instead of the 1.56
> micrograms/cm2 that the IPC/EIA J-STD-001C prescribes is section
8.3.6.
>
> I know there exists a document (probably an IPC or MIL-spec)
> explaining how the 1.56 limit should be corrected for the exact type
of
> machine. For the Alpha Ionograph 500M the conversion factor is 2,
> resulting in the 3.1 micrograms/cm2 limit.
> However I can't remember where exactly this information can be
found,
> and I don't even know if it's still valid. Does anyone has a clue for
me
> ?
>
> Daan Terstegge
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
>
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Daan
I have a copy that I shall dig out for you. If anyone else needs a copy
let
me know
--
Regards, Graham Naisbitt
[log in to unmask]
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