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Clean vs No Clean PCB assembly process

johnmaetta

#7342

Clean vs No Clean PCB assembly process | 23 July, 2001

We are currently re-thinking our policy of no-clean and would like more information from users of both process'.

Our assemblies exhibit residue and other 'contaminates' and this raises questions at our customer sites.

Thanks,

John

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#7346

Clean vs No Clean PCB assembly process | 23 July, 2001

We run both NC and OA flux, although the majority of our product is run on OA. For application not requiring uBGA, we find the benefits of NC elusive, at best.

What? .... Your customer recognizes that initially the NC res in non-ionic, but sticky. Over time, they think the sticky surface will collect dirt, dust, and ionic materials that threaten the LT reliability of their product, eh?

Oooo, that's my question. What's your question?

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johnmaetta

#7363

Clean vs No Clean PCB assembly process | 24 July, 2001

Thanks Dave.

We develop high-speed telecom PCB assemblies that use uBGA and other fine pitch components. Our policy has been to use an NC process at our CM.

Our engineering group, who is also a customer, and uses these assemblies for development, has noted an increase in failures, for whatever reason. Upon inspection of the assemblies they have spotted residue on suspected components or areas of the assembly.

I must state, as I have to our engineers that until we can clean this 'residue' and confirm that this is the cause of failure, we will continue to use the NC process. Whether the residue has caused the component to fail completely has still not been determined.

But, I want to learn more about using OA. If anything, just to get the engineers 'off my back'. A pretty board is a good board...

Sounds like I don't care, but I do...

Your comment leads my to believe that applications using uBGA technology benefit by using NC?

They 'don't think the sticky stuff will collect dirt', we can see it does.

John

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#7367

Clean vs No Clean PCB assembly process | 24 July, 2001

We don't believe that water is thin enough to clean a uBGA.

Given your telecom biz, what cleanliness standard do you use? How do you measure it? And how often do you check it? What are your in-bound materials cleanliness standards? [Oooo, I guess that doesn't count, since you contract-out your assembly.]

Continuing, what level of involvement would you have with OA, given that you subout your work?

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CAL

#7368

Clean vs No Clean PCB assembly process | 25 July, 2001

Our July 2000 empfasis article has a residue topic available for down load. http://www.empf.org (look under empfasis). Also, there are tons of Tech Pubs information available for down load via our web site as well.

Caldon W. Driscoll ACI USA 610-362-1200 cdriscoll@aciusa.org

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Steve

#7374

Clean vs No Clean PCB assembly process | 25 July, 2001

Most of the problems that you will find with NC is visual. I have not found or heard of any real evidence that NC causes component or board failures. The residue has extremely high resistance, which actually gets higher as time goes on. It's a paradigm shift that some people have a hard time dealing with.

I agree with your stance; until your engineers find the "real" cause, don't change your process.

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Hussman

#7410

Clean vs No Clean PCB assembly process | 26 July, 2001

John,

Are these spots the result of repair? I notice a lot of repair people love to squirt flux onto the board when they repair it.

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johnmaetta

#7412

Clean vs No Clean PCB assembly process | 26 July, 2001

That's a good question. On some of the assemblies that our engineers test, appear to have been reworked in these suspect locations. I have requested rework data from our CM by providing them with assembly and serial numbers. Their data shows that these assemblies did not have post reflow rework, but appearances of the component solder joints tell a different story. There are still residues on the assemblies in other locations which don't appear to be reworked.

I believe it's lack of data entry by the rework personnel at the CM. A 'repair it and get it off my bench' attitude.

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johnmaetta

#7414

Clean vs No Clean PCB assembly process | 26 July, 2001

That's a good question. On some of the assemblies that our engineers test, appear to have been reworked in these suspect locations. I have requested rework data from our CM by providing them with assembly and serial numbers. Their data shows that these assemblies did not have post reflow rework, but appearances of the component solder joints tell a different story. There are still residues on the assemblies in other locations which don't appear to be reworked.

I believe it's lack of data entry by the rework personnel at the CM. A 'repair it and get it off my bench' attitude.

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#7427

Clean vs No Clean PCB assembly process | 26 July, 2001

GT 8 years ago every board saw "touchup". Touch was done to fix boards to conform to A-610. Now A-610 allows less than complete hole fill.

Our operators were totally freaking nuts about touching boards. They touched each others touch and on and on. It was beezerk!!!

Obviously, now, everytime you put at 750�F iron to a board and melt the solder, you put a beaucoup amount of theremal stress on the plating of through holes, vias, and pads. Most of this came from an idea that barrel cracking alone caused less than complete fill. Certainly, barrel cracking does limit hole fill, but it's not the only reason holes don't fill. Now less than complete hole fill is thought of as an opportunity to understand why the hole hasn't filled, rather than a reason to reject boards.

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Yngwie

#7441

Clean vs No Clean PCB assembly process | 28 July, 2001

I'm curious over what would happen if we continue to use the WS paste when dealing with uBGA. Definitely the cured flux under uBGA package couldn't be cleaned/reached and as I understand correctly they are corrosive. if that so, how long do you guys think this corossion will be developed ( eletro migatrion ? dendrite formation ?...I'm not sure ), until they can cause reliability problem or failure onto the finished product ?

cheers...

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#7446

Clean vs No Clean PCB assembly process | 29 July, 2001

Tough to say. The residues from fluxes vary according to the suppliers' forulations.

Consider: * Talking to your supplier. * Running life cycle tests.

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