| | | | I need to setup an oven to run with a nitrogen atmosphere for | | boards with BGA's, but our ovens do not have the optional atmosphere monitor and controller. Is there a good way to sample and control the atmosphere without the optional built-in atmospehre monitor and controller ? The only adjustments I have are the main control valves on air and N2 lines ? | | | John: Nitrogen is hard to measure. You might consider an oxygen monitor (or lack of oxygen monitor). A popular supplier used by at least one major oven manufacturer follows. TTYL Dave F | | PBI-Dansensor America 139 Harristown Rd Glen Rock, NJ 07452 201 251 6490 Fax 6491 Jim Margiotta | John I ran Nitrogen reflow in my previous job for several years. When we first put it in we were keen to determine at what level you could run it to get maximum benefit. Hence we spec'd the furnace with sample ports and bought an oxygen analyser. This was a chemical cell type as opposed to a zirconia type sensor. The theory being that people were looking at Nitrogen/Hydrogen mixes for reflow at the time and zirconia would not read under those circumstances. We rapidly came to a few fairly obvious conclusions. 1. The Oxygen contentent in your process area is a function of the oven design, this will give you a background O2 level in the oven. 2. The largest effect on this was from the product itself. Even reflowing one board was enough to drive the O2 level from 30ppm up to approx 300-500ppm as it passed through the "reflow spike" . 3. The only way to maintain the level lower was to chuck Nitrogen at the machine. Too much N2 and the profile would become unstable, too little and the O2 level would not drop back between boards.
Unfortunately due to the design of the oven I was not able to process boards with air flowing instead of N2. ( the supply was sealed in order to guarentee O2 levels supplied to the machine) I was however able to process single boards with not gas flowing at all. These were definately worse looking that N2 flowed boards but that may have been a function of the profile change brought about by no gas flowing.
I listened to a lot of people claiming that single figure ppm levels of O2 would give the best results. I never managed to get anyone to demonstrate this with real production equipment, my feeling is that you would never have been able to keep those levels when the boards were actually in the oven. If you cannot get a probe into the oven to measure the levels. Try running as much gas as you can without disturbing the profile. Set it up using air and then confirm your profiles with N2.
For the last 4 years I have been running a plant using infra red reflow in air. I am still not sure if Nitrogen truly did anything for me.
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I need to setup an oven to run with a nitrogen atmospher...
- Mar 04, 1999
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