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

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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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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