IONIC CLEANLINESS SPEC FOR BARE PWBs

Bare board cleanliness is still primarily measured by resistivity of solvent extract (ROSE) using instruments such as Omegameters and Zero Ions. What is considered as "acceptable" cleanliness varies between specification and from company to company.

For bare boards, the obsolete MIL-P-55110 allowed a level of 6.5 by the ROSE method. Companies use anything from 1 to 8 by ROSE.

Solvent extract tests are chemical characterization tests. The measure of board cleanliness by surface insulation resistance [SIR], such as for Bellcore, is another issue entirely. Bellcore GR-78, chapter 14.4 shows how clean a fabricators process need to be for telecommunications stuff.

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Mike wrote : "Personally, I would not accept an incoming board that measures more than 0.5 �g/in of NaCl."

Would your recommendation be valid for an IONOGRAPH tester ? Did you perform any reliability study that you can share that drove you your conclusion?

T

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The EMPF has published a paper/ study on this topic, one of there better pieces of work.

http://www.empf.org/html/empfset.htm www.empf.org Doccument number rroo13

Best regards, Cal

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Considering only Ionic residues is very dangerous, most heat transfer fluids that are extremely hygroscopic are also non ionic especially those used in HASL / Roller Tinning fluids. Also consider if the resist is cured or in fact porous which absorbs PWB chemistries and Assembly chemistries both ionic and non ionic. Huge problem here in Europe at present with Solder balling, SIR,bridging and electromigration and of course not forgetting peeling solder resist over wave soldering (MUST BE YA FLUX - yeh yeh yeh) Scope Labs in Chicago are good at this analysis work speak with Jim Hevel and ask for IR Extraction.

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Hi Mike

Why is there a difference in readings on the Omega meter and the Ionograph ? Is it because that the IONOGRAPH is a closed loop extraction mechanism while the Omegameter is not ? Can you explain

T

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> Military and most commercial standards requires > post-soldered boards to measure less than 10 > �g/in of NaCl (14 when using an Omegameter, 20 > on a Ionagraph, and 37 on a Zero-Ion). > > As Dave > stated, 6.5 �g/in of NaCl is called out in > Mil-P-55110 for bare boards. Obviously, 0.0 is > the best number. Although specifications allow > higher amounts of contamination, it is important > to understand how ionic contamination testers > work, before determining a pass/fail > number. > > All ionic contamination testers are > capable of determining the total volume of > contamination on a board, then, based on the > board�s area, calculating contamination per > square inch (or cm). Ionic contamination testers > are not capable of telling you where the > contamination is or what the contamination is. > Although a tester may indicate a contamination > level of 5.5 �g/in of NaCl, don�t assume that the > contamination is evenly spread throughout the > board. A result of 5.5 may actually be a result > of an extremely high amount of contamination in > small area of the board (which will cause > solderability problems) while the rest of the > board is clean. As a manufacturer of ionic > contamination testers, I recommend that our > customers NOT breathe a sigh of relief if the > cleanliness result is a few points under the > maximum allowed. Use a high test result as a > flag and conduct additional testing such as ion > chromatography (CSL Labs or American > Competitiveness Institute conduct such tests). > If an ionic contamination tester indicates a low > level of contamination (less than 2 �g/in of > NaCl) then odds are good that your board is > clean. > > Personally, I would not accept an > incoming board that measures more than 0.5 �g/in > of NaCl. It is perfectly acceptable to expect > incoming boards to be very clean. > > Mike 800) > 218-8128

Hello Gents, I learaned a lot by reading your treads.

I would ask you please to clarify better for me this point: ------------- Military and most commercial standards requires post-soldered boards to measure less than 10 �g/in of NaCl (14 when using an Omegameter, 20 on a Ionagraph, and 37 on a Zero-Ion). ---------- Does it mean when I read 10 ugr/in using ROSE (performed by LAB) I have to consider same as 14 ugr/in when using Omegameter (ie. 600SMD), 20 ugr/in when using Ionograph and 37ugr/in when using Zero-Ion ?

It seams the answer should be YES, but I have seen plenty of people in trouble comparing readings from different instruments used, an mainly all of them where looking all for 1,56 ugr/cm2 even if using different instruments like ove mentionned.

Other question please: when using ie: Omegameter to detect ionic presence on PWA (double sided SMT plus TH, what area (surface) is better to consider ? Top Side Plus Bottom Side? or just a Sigle Side the most populated one ? And what about when large Components (BGA, TQFP, Connectors) are located on the PWA (all of the togheter means a considerable surface ) ? do I have to extimate also the total surface of componenst to put into the formula ?

Thank you very much in advance for your answer

Best Regards Gabriele

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Ionic cleanliness is pretty much meaningless, when discussing nc flux residues. If you do the good solder routine and measure the boards, you'll be in the out-house, because the water in your resistivity of solvent extract tester will turn the res on the boards white.

As an alternative, which still maintaining the good solder routine, check with your customer to see if you can either: * Sacrifice a board * Ship a board with white flux res * Test a scrap board without components

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