Rheometric Pump - Yes or No???

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Hi Folks, just wondering if anyone else agrees tha... - Jun 23, 2005 by

Paul, I'm quite frankly relieved, I thought I was the only ... - Jun 23, 2005 by

Hi Erik, looks like there's not much appetite for t... - Jun 27, 2005 by

We have a couple sites (out of over 150 lines) that use them... - Jun 27, 2005 by

Paul

#35109

Rheometric Pump - Yes or No??? | 23 June, 2005

Hi Folks, just wondering if anyone else agrees that Rheometric pumps do not work and are more trouble than they're worth. They do not circulate the solder paste properly. The only solder paste that is processed on a FIFO basis is the material directly under the supply points which means "dead spots" in the middle and the edges. Doesn't matter which solder paste you use, if you leave it in that environment for days without being used, then it's going to deteriorate.

On top of that, the number of parameters you need to control mean the process window is very small. With squeegees, assuming a sound mechanical setup, you just need to worry about force and speed. Rheopump has speed, force, pressure, PID and they all have a big impact on each other.

My opinon is based on 4yrs of hardship trying to get a stable process with this technology. We're now cleaning out the pumps every week which completely eliminates the argument that Rheopumps reduce waste drastically.

All opinion/suggestions welcome.

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Erik

#35132

Rheometric Pump - Yes or No??? | 23 June, 2005

Paul, I'm quite frankly relieved, I thought I was the only one with these thoughts! We have only had our Rheometric pumps since February, but since then our process has been difficult to control with fine pitch applications. And then there's always the question of how often to change the paste... I find that if I keep the pump covered when not in use and scoop out the first 1/2" before using it I can squeeze 2 weeks in before the paste noticably deteriorates.

The idea has also been tossed around to build a motor-powered 3-axis rotating stand for the pumps when not in use to try to keep the paste dynamic and from seperating quite so quickly. It would be interesting to see if that adds any life to the paste. Any thoughts on this?

The Rheo pump looks good on paper, but I think still leaves many problems that need attended to. Even with cleaning them once every 2 weeks, we still see moderate paste savings with all the changeovers we do.

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Paul

#35182

Rheometric Pump - Yes or No??? | 27 June, 2005

Hi Erik, looks like there's not much appetite for this debate on this forum. Possibly because not many use them and aren't in a position to confirm or deny what we know.

We use our pumps 6 days a week, 24hrs a day so it's a very dynamic process. The problem is that no solder paste is designed to remain in a pump for days on end and, as far as I know, no test or evaluation lasts long enough for the problem to show. I have tried various pastes to try and get around the issue but no joy. Typically the problem shows up around day 4. If you take your pump off after 6 days, remove the side dams and clean out about 4 inches of the chamber. Take a look in along the chamber at a cross section of the solder paste bead. The paste at the back of the chamber (furthest away from screen) will be noticeably drier. If any of this stuff gets pulled around to the blades then it cannot fill an aperture properly and will block QFP apertures. I suspect if you're waiting for 2 weeks, then it's already caused you problems. We're lucky in that we have AOI to provide instant feedback. Well, kind of, but that's for another thread!!!

This problem is something we're working on with Speedline and there may be a retrofit fix available soon.

I have some info available on some test results. Please contact me off-line if you'ld like to exchange some info. Maybe we can help each other out. - p.fahy@kostal.com

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Bob R.

#35188

Rheometric Pump - Yes or No??? | 27 June, 2005

We have a couple sites (out of over 150 lines) that use them. The site that picked them stands by them through thick and thin. Any time they have problems they blame it on the paste, even though paste from the same lot will be running great next door with squeegees. Another site that got stuck with the rheometric heads, but had no input in choosing them, hates them. What's aggravating for me is that they want us to allow changes to the solder pastes we use company wide to hopefully make them work better with the rheometric pump heads. I'm dead against it because my experience is that any time we think we're smart enough to monkey with paste formulations we get bit by unanticipated side effects.

As someone else mentioned, it's also hard to bring the issues out in a lab environment. We're doing our Pb free development in a lab and the first production use of Pb free in our company will use squeegees. I don't have a good way to know if the paste we've picked is going to work in the rheometric pump head - I just can't print boards for days on end in the lab and think I'm really simulating a production environment.

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