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Dirty Reflow owens.

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#53488

Dirty Reflow owens. | 31 January, 2008

Hello. We have currently a big problem with our Reflow owens getting very dirty very fast. It's like a thick layer of "dust" on all parts in the preheat and the beginning of the cooling zoon. We dont have that all the time and it's seems to be from boards we get from one specific supplier. We have discussed this problem with him but the only answer we get is that noone else is complaining. Do any of you know what can cause this "dust" (you can vacuum clean most of it) in the owens? We don't have the knowledge to get this suppier against the wall here and I wish it would be easy just to get another supplier but it's not. If anyone has an input here i would appreciate it much. Regards Jola.

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#53493

Dirty Reflow owens. | 31 January, 2008

My first thought is that your roof exhaust blower is dead and that these boards are the only no-clean boards you build but that's probably not the case.

To start from the beginning, though, are all of your blowers operating normally (in the oven and whatever fume exhaust system you are using, usually a blower on the roof), do you measure your vent airflow regularly, do you have filters that need to be cleaned, etc., etc.?

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#53507

Dirty Reflow owens. | 1 February, 2008

Hi. There is no problem with the exhaust system and the owen also has a sensor to messure the exhaust and would give an alarm if it stopped or went under a preset value. We have had our owens for one year now and the problem just started suddenly, were gone for a period of time and then came back again. That is the reson we can say it's probobly related to some specific boards when they are the only differens in our production mix during that period. We have two owens the same type on the same exhaust system but only one that have this problem.

Regards Jola

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#53509

Dirty Reflow owens. | 1 February, 2008

Hello,

If I do understand it correct, the dust in your oven are salt-crystals, comming from No-clean fluxes. We had them also once, it was a problem with one fan in the oven, I think you should check your fans inside the oven. Our extraction was OK, but we had some turbulance witch was incorrect and created these strange "dust lookalike" flux crystals. Check the fans who controle the zone deviation.

hope maybe this could help you. regards Bart

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#53521

Dirty Reflow owens. | 1 February, 2008

Its most likely flux residue from your paste. This is normal in my experience. Just clean it out.

Some paste fluxes are waaaay worse than others.

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#53543

Dirty Reflow owens. | 4 February, 2008

Thanks for your replys but I can't figure out why this problem is so much bigger in one owen when we run nearly the same mix in both our lines and we use in 99% of the production only the same 2 different pastes, lead and leadfree. The pastes we use are Senju OZ 2062 and M 705. So noone of you have had any problem that those low price boards make your owens dirty? If it's the flux that is causing this, do any of you have a bright idea what to do (change the paste is probobly not an option) to shorten this 4h dirt cleaning every week. I will attach a picture from the coolingzoon and I hope you can see the problem.

Regards Jola.

Attachments:

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#53548

Dirty Reflow owens. | 4 February, 2008

Sure looks like flux residue to me and I don't know how your bare boards could be causing that unless there's something on them when you get them, and that you would notice. I'd still be looking at my own system, blowers and exhaust lines. Do any of your ovens share an exhaust blower?

Do you profile regularly? Have you monitored your oven heater output to see if it's doing anything unusual? Some ovens will run merrily along with a dead element or blower if the profile and alarm points are set up just right. You have to watch outputs (or compare profiles) to catch it.

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#53886

Dirty Reflow owens. | 4 March, 2008

Recently I have been hearing and see this excess flux residue problem at several companies, US, Mexico, and Japan. It seems to have increased recently. In fact, it seems so common that it seems normal, but if everything is correct, a re-flow oven should run relatively clean.

Cleaning is the best option for right now. Cooking out the flux is not advised as it can produce overwhelming smoke.

There are hardware modifications coming. Check with your manufacturer. This is an industry issue.

My guess is that companies are removing inorganic VOC's which previously improved the evaporation process. VOC free fluxes need another component to effectively evaporate.

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#53887

Dirty Reflow owens. | 4 March, 2008

An industry issue??? Sounds more like another ROHS issue to me.

Experience tells us the LF flux leave much more residue inside the oven

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#53892

Dirty Reflow owens. | 4 March, 2008

Hi. Thanks for your replies and your inputs in this. Regarding the exhaust or airflow might cause the problem I have finally got the manufacture to bring some specialist to us to have a check on the system. The other possible thoughts about the flux in the paste I have to forward to the production technicans and hear what inputs they might have. If it is a ROHS problem, yea why not, it seemes to get worse the more lead free production we get...

Regards Jola.

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#53894

Dirty Reflow oVens. | 4 March, 2008

What are you profile temperatures? I wonder if you're not ramping up too soon in the first zones.

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#53895

Dirty Reflow oVens. | 4 March, 2008

Our profile tempatures in the owen is: Preheat 6 zoones 135,155,165,175,185,195. Peak 3 zoones 255,245,240. We do check our profiles with test probs and a "Surveier" temrature recorder every 3 month and we are within the paste supplyer recommendation 2-4 degrees celcius/second in preheat The board we have the biggest baches of at the moment and from wich I took the profiles is 0,85 mm thick and 200x300 mm in size.

Regards Jola.

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#53960

Dirty Reflow oVens. | 11 March, 2008

If your oven has the flux collection unit just like the Tamura oven, then you will not experience same as what you have shown on the picture. The only thing to do now is to clean and take out the flux. Also, please consider, flux accumolation depend on the flux contain on the solder paste being used on the production. flux will normally accumolate on colder area.

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#53985

Dirty Reflow oVens. | 12 March, 2008

Lead Free is probably worse as it contains something like 25% more flux by volume than Leaded. But is unusual as No Clean organics usually volatise off and rosins are non volatile so should not accumulate readily unless mixing with other gases in the oven and not volatising correctly. Have you checked the resist cure and made sure it is not plasticizers from this as this is much worse now Lead Free is upon us due to higher heats killing the PCB and the PCB manufacturers not curing at correct temperatures with Liquid Photoimageable resists. Wish I had a pound for very time this causes me problems. Could also be the reason why it is more board specific and therefore oven specific. Cheers Greg BLT Circuit Service Ltd

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#53986

Dirty Reflow oVens. | 12 March, 2008

Blimey just seen the picture that is bad.

You could try to dissolve some of the residue/gunge in IPA if it is flux residue it should readily dissolve if it is resist issue then only portions will dissolve leaving a white powder which is Talc If you get powder left then Solvent Wipe the Bare PCB and see if you get some resist discolouration off, clear indicator of poor curing Worth a go at it Cheers Greg BLT Circuit Services Ltd

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