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Vapor phase versus forced convection


sly

#30042

Vapor phase versus forced convection | 16 August, 2004

Hi everybody, now that lead-free is coming, I'm looking forward to change the oven we own in company I work for.

Eternal question: what's the best oven technology on market. I allready know that we won't work with IR ovens, but I would like to have (in addition to several tests and measurements that we'll do) an objective comparison between forced convection and vapor phase ovens.

Does anybody knows something about?

Thanx

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Dreamsniper

#30046

Vapor phase versus forced convection | 16 August, 2004

I've worked with a Vapor Phase Oven a semi-automatic and a manual oven for evaluation. They worked fine and produce better grain of solder joints. The fluid that you need depends on the solder temperature that you require. I've used a 200'C fluid for our eutectic solder and it's just fine. And with regards to profile, I've used a slimkic2000 to measure the thermal profile and we have only 0.2'C delta between a BGA272 and 0603 chip capacitor. This is very adviseable if you are going Lead Free. The only problem we had during the initial stage of its introduction was TOMBSTONING. But we managed to fixed it when we reduced the aperture sizes of chip caps and resistors. Also we reduced our stencil thickness to 5 thou and we eliminated the tombstoning problem. VP ovens are guarnteed to provide you good results. We bought an in-line oven for future Lead free purposes and it took us 9 months for the oven to be delivered from Germany. And this is due to the shortage of supply die to its high demand from Europe and Japan. I will not mention the Brand that we bought but it's not cheap.

Check this Vapor Phase Oven Manufacturers:

Asscon and IBL

regards,

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sly

#30047

Vapor phase versus forced convection | 16 August, 2004

Thanx a lot for advice...

My only question is: did you had troubles with prehaeating of the boards? I heard it was the only critical point due to chosen technology, infrared preheat (if it's still IR).

I allready checked Vitronics Soltec and IBL, I'll see what are ASSCON products like.

Thanks again, brgrds

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Dreamsniper

#30050

Vapor phase versus forced convection | 16 August, 2004

We do not have problems with preheating. before we used to suspect that the cause of tombstone was that because the semi-auto and manual version do not have pre-heat stage. We had 1 with an IR heater and it is quite okay. you can use it too to cure adhesives. We do not have any problem with our VP with pre-heat stage. I can give you a contact or a reference for this VP process if you need to.

regards,

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Grant

#30060

Vapor phase versus forced convection | 16 August, 2004

Hi,

We have both Vapor Phase ASSCON semi auto as well as Soltec convection inline ovens. I must say we had no end of problems with Vapor Phase. We tried everything, and just could not totally eliminate tomb-stoning completely.

We would always get a more than 10 percent defect rate from the vapor phase, while we often get sub 1 percent from the convection reflow.

We have a lot of expensive boards that still need x-raying to see what's wrong, but they have large BGA parts and we think they either did not reflow correctly, or we got some other kind of component cracking due to overly fast heat up. We don't even use vapor phase for prototyping any longer.

When you study the vapor phase process, it's quite an amazing technology, or you think so at first. The sale guys love to share all the details about it, and they did mention tomb-stoning, as an easy to overcome problem, however we went through many stencil designs, and nothing worked. Funny how the sales guys then referred to it as a process problem that can be fixed, but had no further advice on how. We tried everything.

The solder quality of vapor phase is incredible, and the joints are amazing, but when using in in production in the real world it's these problems that killed the process for us.

Convection reflow with the Soltec is just so stable and reliable, that we use it for everything now. We even run first prototype boards through, unprofiled without problems. We just use a profile with similar component types.

So with experience with both, I would go convection any time. It's also much cheaper to do inline convection, while vapor phase is mostly a batch process, and inline vapor phase is very expensive.

Where I would consider vapor phase is if I had no money and needed to do only prototype boards only. I would then use the pasta cooker on the hot-plate approach using the vapor phase fluid. (The fluid is also expensive) But even in this case I would still get a batch convection oven, and try and mod it to get better airflow than go back to vapor now.

A little about our process. We are doing a few thousand boards a month, and for us vapor phase based faults were too much of a problem. Convection allowed us to go inline, and faults dropped off to almost nothing immediately.

I hope my experience helps. I remember asking the same question on this forum a while ago, and not many people knew much about vapor phase, apart from 1970's based equpment. At least I can share some experience now!

Regards,

Grant

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sly

#30065

Vapor phase versus forced convection | 17 August, 2004

thank you Grant and dreamsniper for these shared experiences; I think I'll still try some vapor phase just to have a look to this process, but will focus on a convection as long as it's the actually chosen technology in the company and that it's expensives investments to switch to VP.

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Grant

#30097

Vapor phase versus forced convection | 18 August, 2004

Hi,

I think you cannot go wrong with Convection. If you want to experiment with VP, just get some of the fluid and put it into a pasta cooker on a standard domestic hot plate. Have a basin full of cold water so after reflow you can lift the cooker and place it into the cold water to condense the vapor cloud.

You also need to hold it in the cold water to let the solder cool and set. A pasta cooker with a clear glass lid works ok, and I covered a vent hold with silicon.

Be careful not to burn the fluid, as it's really toxic if burnt. I used the smallest hot plate on high so it did not warm the edges of the cooker too much. Once the fluid starts to boil, you will actually see the vapor cloud coming up the side of the cooker. I placed the board on an egg ring to allow me to get my fingers under the board to take it out.

This should let you do some playing with VP at very little cost. You will like the solder joints, but the tomb-stoning could be an issue. Low volume of only a few will be hard to see though.

Regards,

Grant Blackmagic Design

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sly

#30099

Vapor phase versus forced convection | 18 August, 2004

Hi, cool news!

I'll try to cook some as soon as I get some experiment material.

Thank you for the test method.

Rgds

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