We are looking at several reflow ovens with intent to acquire one for both air and nitrogen reflow capability (i.e. have the capability to reflow in either air or nitrogen environment). Would be interested to know what I should look for in comparing the N2 capable ovens.
Do all the ovens feed N2 into the chambers/zones in essentially the same manner? On the outside panel of the ovens, I noticed several flow gauges (4-8) . . . are these the gauges which control the flow rate of N2 into each zone? In several semicon processes, I know that vacuum is created to suck out the mixed oxygen and nitrogen atmosphere (while the nitrogen purge is ongoing) so that over time O2 is in the desired <20ppm range. Is vacuum also the standard process in reflow ovens or is it that nitrogen is continuously purged into the chambers until the desaired O2 atmosphere is achieved; and then we feed the boards? If nitrogen is simply purged, on average how long would it take to reach an atmosphere of <20ppm O2 (I know it would vary by ovens but is it close to the 20 minute mark that we consider "warm-up" time or the 5 minute mark)?
Also, do reflow ovens come equipped with specific gauges or pre-installed analyzers to display a reading of O2 inside the zone?
Low-consumption Nitrogen configurations with an on-board O2 analyzer is the ideal way to go. I cannot speak for all oven manufacturers, but ours have N2 fed to the reflow zone only, which to me is really only where you need it. The gauges/flowmeters that you are referring to are more than likely just like you said; A flowmeter for the zone. I believe vacuum may have been used on older designs, but now I believe it is more a purging of the Oxygen by pushing Nitrogen into the tunnel. I think it will depend on the oven design itself that will dictate how long it will take before the O2 count is low enough to process boards.