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Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C)

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#57332

Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C) | 19 November, 2008

Hi all,

I have been in the game for near on 15 years and finally something has stumped me! As this site has always provided a wealth of knowledge and at times some amusement I have decided to post it here.

Ok. My company uses a test method on an Omegameter SMD600 which we have some set pass/fail levels which are <0.3 ugNaCl/cm2 for bareboards and <0.8 ugNaCl/cm2 for Assemblies.

We have approached a subcontractor to complete these boards and they keep referring to MIL-P-28809A. Now under this piece of (outdated?) information it lists 'Equivalence factors' on table 8. I have in all my years never used any sort of calculations for eqivalence. Which according to them and thier process would mean that our UCL is <0.417 for <0.3 and UCL <1.112 for <0.8.

Now understand that I am not an expert in this field, but why such a difference? I understand this is based on calbration techniques to do with specific equipment, but i have never had to calculate the UCL like this before!?!

Should it be that we should not get them to use the MILSPEC and ask them to use IPC?

Any information would be much appriciated.

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#57337

Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C) | 19 November, 2008

Simon,

The equivalence factors were used to scale the values measured by ionic testing equipment to the values measured in the standard manual method.

There is a good write-up by Bill Kenyon in this Technet Post describing the creating of the factors:

http://listserv.ipc.org/scripts/wa.exe?A2=ind0510&L=technet&D=1&T=0&P=93119

You seem to be using your own corporate cleanliness standard of 0.8 ugNaCl/cm2 for assemblies rather than the 1.56 standard value. Coming from a cleaning equipment manufacturer, I like it when a customer has an internal standard because usually it means they have a good handle on the cleaning required for their assemblies and it makes everything else much easier. I am assuming that your value is based on the measurement you achieve in your Omegameter.

The values specified by your subcontractor seem to indicate that the equivalent cleanliness was calculated incorrectly.

The equivalence factor for the Omegameter was 1.39 and so the acceptable value acording to the manual extraction method, for example 1.56 ugNaCl/cm2, would be multiplied by the 1.39 to produce a 2.17 ugNaCl/cm2 acceptance level as measured in an Omegameter.

Using this process your 0.8 ugNaCl/cm2 in an Omegameter would equate to 0.58 ugNaCl/cm2 using the manual extraction method. It seems that value of 1.112 was produced by multiplying your supplied value by 1.39 instead of dividing.

Some of the confusion may have come from the fact that in previous revisions IPC-TM-650 (2.3.25) was only the manual method of extraction and the static method (Omegameter) was in (2.3.26.1). If your specification to the subcontractor said 0.8 ugNaCl acoring to 2.3.25C they may have interpreted that as meaning 0.8 according to the manual extraction which would give 1.112 in an Omegameter.

Hopefully this clears up the issue some.

You may want to also have a look at IPC-TR-583 for more information as to the inherent problems in converting test data from different types of testing equipment.

What type of ionic testing is your subcontractor using? Obviously the best would be for them to be using an Omegameter as well, because then you could just tell them to use your numbers and be done with it.

Stephen Pence Unit Design, Inc.

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#57342

Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C) | 19 November, 2008

First, it's GREAT to have a long-term lurker posting here on SMTnet. Maybe this will encourage other lurkers to join us. [We'll try to be on our best behavior.]

Second, while Stephen Pence's explanation of 'equivalence factors' is accurate, your contractor friends are just puffing-up a smoke screen by going on about equivalence factors. BIC (bulk ion contamination) testers are quality control tools. The value measured using BIC testers is not ment to be a standard or an absolute value. It's ment to be compared with the previous measurements to confirm whether the cleaning process is in-control or not.

Third, a "Note" to J-STD-001C, Section 8.3.6, Ionic Residues (Instrument Method) states, "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." We interpret this to mean: "Gage R&R for these methods suck."

Finally, in responding to to your fundamental question, "We agree. Yes, you should expect the your potential supplier is using current, rather than obsolete methods."

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#57347

Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C) | 20 November, 2008

Our sub-contractors will be using SMD600.

Thankyou all for your replies much appriciated.

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#57348

Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C) | 20 November, 2008

I'm not sure I completely agree with you regarding the smoke screen factor. I have found many times confusion around bulk ionic testing comes down to people not understanding your point about it not being a "standard or absolute value". Most people I talk to really want it to be as that would make things so much easier. No if you were saying they were throwing up a smoke screen because they didn't understand than I can definetly agree with that.

There are definite problems with attempting to convert from one method to another which is why it is good that Simon's contractor is using the same method as they are.

Since they are using the same methods and Simon has set a standard value based on their own testing I think it is fair to require the contractor to just use those values in their testing. Your thoughts?

And your right I went through all of that and didn't answer the question of expecting a potential supplier to use the current methods. On that topic I completely agree with you.

Stephen Pence Unit Design, Inc.

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#57364

Ionic - MIL-P-28809A vs IPC TM650 (2.3.25C) | 20 November, 2008

Steve

In response to your comments:

SP: I'm not sure I completely agree with you regarding the smoke screen factor. I have found many times confusion around bulk ionic testing comes down to people not understanding your point about it not being a "standard or absolute value". Most people I talk to really want it to be as that would make things so much easier. No if you were saying they were throwing up a smoke screen because they didn't understand than I can definetly agree with that. DF: We get your point. Maybe "smoke screen" gives an improper connotation, since it implies intent. It is possible that these folk are poorly informed, as you say.

SP: Since they are using the same methods and Simon has set a standard value based on their own testing I think it is fair to require the contractor to just use those values in their testing. Your thoughts? DF: Sure, as long as we agree that bulk ionic contamination testers: * Are strictly a quality control tool used to monitor process. * Have poor gage R&R.

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