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Clean vs No-Clean

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#56384

Clean vs No-Clean | 8 September, 2008

Hi

We are designing a new pcb which contains sensitive analogue circuitry, where tiny leakage currents could dramatically affect product performance. Should I build this product Clean or a No-clean chemistry set ?

Thanks in advance

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#56388

Clean vs No-Clean | 8 September, 2008

Because of our high volume production, we use no clean flux. We have experienced leakage currents with leadless QFNs. One problem is the part isn't being utilized as it should, but another is the flux residue. There is ionic residue in no-clean flux and if the board is not coated, moisture, voltage, and ionics can create a leakage current.

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#56396

Clean vs No-Clean | 8 September, 2008

�Another direct measurement to determine resistivity values (i.e. of remaining no-clean residues) can be performed through impedance spectroscopy. The surface resistance underneath chip resistors and capacitors can be determined to show the improvements cleaning provides with respect to surface resistivity (Figure 3). For example, during studies, impedance was measured on identical components on five assemblies. These tests were repeated after the cleaning process. Measurements matched, indicating a high level of cleanliness across all assemblies.� [�Analyzing the Debate of Clean vs. No-clean� Umut Tosun, M.S., Ch.E, and Harald Wack, Ph.D.; Zestron America; SMT March, 2006]

From this type of analysis, you might be able to determine the acceptable impedance level of your circuit. From there, you might be able to determine the acceptability of specific no-clean flux residues.

Attachments:

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#56401

Clean vs No-Clean | 9 September, 2008

Try the "straw test" to test for ionic contamination. For reference, here it is from the fine SMTNet archives:

http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=496&#Message3044

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#56403

Clean vs No-Clean | 9 September, 2008

Oh that's GREAT. Now, we're encouraging engineers blow to saliva on boards.

The saliva is made 99.5 percent of water and 0.5 percent of dissolved inorganic compounds. One third of the 0.5 percent are dissolved metal-ions such as Ca2+, Na+, K+, Cl- and [PO4]3-. The remaining two thirds are organic substances, among which long and complicated molecules, proteins, dominate. These proteins tend to affect the viscosity of the saliva: the less the total amount of water, the higher the concentration of proteins. Thus, if there is a deficiency of water in the body, the saliva becomes 'thicker'.

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#56405

Clean vs No-Clean | 9 September, 2008

Wow, the anger grows deep within this one.

Why not build some with and without no cleans flux? Nothing like real life stuff versus all these experts.

Or start by cleaning and work your way out form there. I's rather clean and know i have good product at first then start experimenting form there.

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#56429

Clean vs No-Clean | 10 September, 2008

I guess sarcasm and quick wit flies over some peoples' heads. 8 years ago (wow, that's an old post), I was poking fun at the guy, and wanted to illustrate how ridiculous it was that he spat upon our printed circuit board assemblies to simulate moisture. BTW, if the boards failed, the boards that he "spit on" had to go through the in-line washer again, hence, washing away all the dangerous spit. Funny how google and wikipedia give some folks other-worldly knowledge. Anybody can quote (or cut and paste) scientific literature. Original thought is a different story altogether. I guess that's what separates "white-paper-consultant types" from guys who've been on the production floor for 15 years solving real-world problems. :-)

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