Casimir: Let me expand on something that I said in my response to your thread on ionic testing. Generally, no-clean people don�t use ROSE testing as part of their process control, because the ROSE test is essentially washing your board in DI/IPA � a sure fire approach to turning your solder connections white on each board you test. And the assumption when using no-clean is the flux residues are non-ionic.
The issue you are struggling with is one I�d expect should be the struggle of every no-clean shop (actually every assembly shop for that matter, but non-no-clean people accept the issue, to a greater degree). If they�re not (and they aren�t because their soldering process is so far out of control that they�re limited to whining about solder balls), had better get in touch with this issue, because it surely will affect the long term reliability of their product. Can you spell electromigration and corrosion?
There, I got that out of my system.
Ooooh them�s some ugly "no-clean" boards. OK, let�s think about these corrosive, ionic salts on your board. They come from three sources. 1 What is the level of ionic contamination of the boards you receive from your fabricator? For instance: � Many fabricated boards are hot air solder leveled. Is that no-clean or some other type of solder? What level of ionics are left from this process, when you receive them? � The "F" in FR-4 stand for fire retardant. Bromine is used as a fire retardant. Br- is not far from Cl- on the periodic table. Both combine with things to make corrosive salts. � Solder masks are potential source of ionics. � Fabs wet process their product. What is the level of ionics in their rinse water? 2 What is the level of ionic contamination of the components you receive from your suppliers? Look at "Circuits Assembly" magazine, November 1999 for "Component Residues" by D. Pauls and T. Munson. The article discusses ionic residues on various in-bound components. 3 Your processes. As Gramham said, things like the amount of flux you put on the board contributes. But fluxing is not the only in-house process that can add ionics to your board.
Look at: "How to qualify the solder flux of a new vendor? - Gyver 00:59:33 11/17/1999" in the SMTnet archives.
Good luck
Dave F
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