I can't stress this enough, don't buy a small Chinese made reflow oven
, it just isn't safe. More than one person in this thread
share my sentiments.Our story
In the course of business we reflow about 10 boards/day (obviously not just 10 every day, but say 100 once every two-weeks). Originally, we used a plain-jane toaster oven, a digital thermometer, a stop-watch, and a careful eye. This actually worked pretty well, assuming someone was willing to devote their attention to watching the thermometer, and we kept the panel size below say 6"x4". We did this since 2006.
In November, we had need to do single boards about 8"x8" with many power-transistors, something beyond the capacity of our lowly toaster oven. We purchased (from eBay) a "Small Factory" brand 1500W IR oven with a convection fan. It cost us $360 + $100 S&H. It had dials to set the soak temp and time, and a nice bell that told you when your boards were done. While it didn't do a perfect job (the corners of large boards had some discouloration) it did what we bought it to do. We put boards in, it whirred, it went ding, we took boards out.
Today (Feb 4th, 2010), it did something else: It caught fire!
I was sitting at the "assembly desk" (where the machine rests) placing new boards while a set of smaller boards ran through the machine. Realizing it was taking longer than normal, I looked up to see grey smoke seeping from the corners of the machine. I opened the door to check the problem (letting in fresh oxygen) and the machine's elements burst into flames. Thankfully by this point the smoke alarm had been activated and my intern jumped in with the fire extinguisher.
The root cause would appear to have been a shorted thermocouple causing the oven to run at full output, without even the timer activating. The thermocouple is routed to the back of the enclosure where it can be fastened to the board surface, it does so by escaping from a small hole behind the fan mounting, where (as a cost savings measure I assume), it runs through a raw hole punched through the sheet metal (but behind the insulation). Over time (two months!!), the metal had cut through the cable jacket and wires. After the oven was cool enough to examine, we found the "probe" end of the thermocouple came out with a small yank and the wires leading back to the controller stripped bare and pinned against the metal surface.
Unfortunately I don't have pictures of the oven, before or after it's excitement, but I do have a picture of the oven tray with what's left of the PCBs. (attached)
The predictable end to the story, is both the manufacturer, and the eBay seller are long gone. Hopefully, this will make someone think twice before trying a cheap Chinese reflow oven. Personally we'll be going back to the toaster oven, but maybe we'll add a PID to it now.