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Printed Circuit Board Assembly & PCB Design Forum

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No-clean solder paste

Steve

#5682

No-clean solder paste | 21 March, 2001

The design engineers I work with are blaming some circuit problems on what they think might be related to the no-clean flux residue. (It couldn't be the design.) Has any body else seen noise issues in high speed circuits related to no-clean flux residue?

Has any body switched from no-clean back to a cleanable type because of circuit performace issues?

Thanks for your responses.

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#5688

No-clean solder paste | 21 March, 2001

We have RF boards with ...

* No solder mask

* Strategically placed globs of solder

It's possible that your boards will not work with NC flux res on them. We generally don't see noise problems. We loose one of the edges [front I think, but don't quote me], because as frequencies increase the motion of electrons become more of a skin effect than a conductor effect.

Can someone clean your flux for you to determine the effect of the flux res?

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#5696

No-clean solder paste | 22 March, 2001

Interesting...the very reason we use water soluble paste on some of our boards is for that reason, although I've never been able to get anyone to show me something in print that supports it. It's just what engineering has told me.

We currently have a product that's just started failing miserably in PCB test, and now engineering wants to do an "extensive" audit of the reflow process. We don't have problems with any other product. Strange that such an out of control process would produce only one bad (but of course robustly designed) product. They're basing their comments on the fact that removing and replacing the SOICs that fail seems to occasionally solve the problem. I'm thinking it's either a funky part, or the nc flux residue. Time and testing will tell...........

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Steve

#5702

No-clean solder paste | 22 March, 2001

Deja vu! When I read your response I turned around to see if you standing behind me listening to our problem. We currently make about 50 different boards all using no-clean that have no problems, yet this newest boards has a couple of issues that engineering is blaming on the reflow process. Another "robust design" mishandled by manufacturing.

I am not going to change anything based on a couple opinions. I am going to start conducting ESS temperature cycle tests to determine the actual solder joint reliability.

So far, I haven't seen any sound evidence that no-clean flux residue is causing a good design to go bad.

Thanks.

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#5707

No-clean solder paste | 22 March, 2001

Hey!!! Watch it!!! I don�t want to get you believing too much of this stuff. But if you bought that, listen to this � some circuits are so critical with that skin effect stuff that they use silver as the top level solderability preservative. Turns-out that thin coat of Au has a lower resistivity, er sumpin, that really makes for a screamin�mama�jama, er sum such engineer mumbo jumbo.

As a additional point, I, like you, don�t buy the replace the SOIC and call for an audit of the reflow soldering machine story, if that makes you feel any better. [I just don�t see SOIC in too many high speed circuits, sorry.] Oh, one more final note. The Montreal Protocal sounded the death knell for RMA fluxes. BGA sounded the death knell for aqueous fluxed boards. Virtually every modern board is run NC. Smack those engineers and get them thinking RIGHT!!! [Oh, and enjoy the extensive audit of your reflow processing. Haaaaa!!! ;-)]

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#5708

No-clean solder paste | 22 March, 2001

OK, lemme take a different angle on this, �cuz I forgot to touch on this when I first responded. I mentioned a study ["Evaluation of Low Residue Soldering for Military and Commercial Applications: A Report from the Low-Residue Soldering Task Force" June 1995] a cuppla threads ago. [Actually, I tried to find it by using "search", wanting to review what I said, in hopes of not saying two different things about the same study and forever ruining my believability index. But, I must need a nap.]

To further confound my believability index, some momma bear has swiped my copy of the study. [Like that�s something that people around here would really care about!!!] [Or I�ve filed it some where "really intelligent". Or it�s in that pile of stuff under the Krispy Kream Donut box. Er, who knows???] So, we�re going on pure muscle here. [Scary, eh???]

They designed a common board to be used by all in the study. It had a power supply, a high voltage section, a digital section, a RF section, and maybe more. The design had machine soldered SMT and PTH components and hand soldered jumpers. [I�m workin� here!!!] The study used the board to compare coated and uncoated NC fluxed boards built at several [4?] plants [using different processes and NC fluxes] to the same board soldered with RMA flux and cleaned in both coated and uncoated versions. As I remember, they said some thing like � "Hey, [Yano, those government technical reports always start with "Hey".] we messed-up the board design a little and the production processing of the boards could have been better, but we don�t see much difference between the operation of these boards." Or words to that effect.

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