I use a 4 element oven, 2 top & 2 bottom, 1500W, observations with k-type thermocouple to digitlal multimeter are that it heats up fast enough.
skyjumper found the same a while ago - 3 elements not quite enough.
CrossRoads:
I use a 4 element oven, 2 top & 2 bottom, 1500W, observations with k-type thermocouple to digitlal multimeter are that it heats up fast enough.
skyjumper found the same a while ago - 3 elements not quite enough.
+1. I agree.
Using 1500 watts here too.
4yi, here is the temperature curve of my reflow oven (850 W with 2 elements, k-type thermocouple; PID )
reflow curve.pdf (38.7 KB)
My cool-down curve is achieved by:
1 switch off
2 open the door
3 carefully slide the wire mesh shelf out as far as I can (don't want to disturb
components while solder still molten)
4 waft a piece of card gently to produce a draught over the board for a while.
Takes about 1 minute for the board to be cool enough to handle (just).
If using a fan it would need to blow otherwise it will melt itself, and will need to be
quite small (to prevent components being blown about. A short steel tube to keep it
mounted remotely from the heat might be wise.
Simply opening the door is probably causing a faster cooldown than 6°C/second, which is a excellent way to damage components. Especially ceramic caps. And the nice thing about cracked ceramics, they rarely show signs of failure right away.
You really need to allow the board to come down from the peak soldering temperature before exposing it to room temperature air.
I doubt it, the oven stays hot for a long time, its walls are radiating heat efficiently and
until the board is outside to some extent you won't get much cooling. The board itself holds a
lot of heat and limits the rate of cooling of the components. Even fanning a board for
a minute leaves it hot enough to burn fingers.
A couple of observations...
I happen to use a heavily-modified toaster oven with a rocket scream PID controller. As best as I can tell, the unit ramps up as desired, i.e. it follows the reflow pattern recommended for my Kester 'green' solder paste (i.e. no Lead). The only part that is likely 'non-compliant' so far is the cooldown phase, i.e. I have to figure out how far to open the door so that the temperature drops as intended, hopefully without cracking a ceramic cap. If you'd like to see some pictures, see this thread.
As for the construction process, I disassembled the oven and removed all controls. A ebay-sourced SCR (2x20A) is perfect for this formerly-'Black and Decker' $30 toaster oven since the four quartz-tubes are OEM-limited by a fat diode. The SCR achieves the same thing, but with control and I used the second channel for the convection fan. On the front face, I mounted a leftover plastic enclosure that I salvaged from a Neuton mower whose motor had gone bad. It holds the Arduino 2009 and the Rocketscream shield perfectly. I stuffed the (formerly empty) voids between the inner and outer oven cavity with 2000*F rated insulation.
Inside, I further reduced the mass 'visible' to the quartz lamps by stuffing the same insulation between the lamps, filling the rear of the cavity where no PCB would ever go, etc. The unit still gets hot during operation, but nowhere as hot as it would get without the benefit of insulation. I even insulated the door window, leaving just a little peep-hole to limit heat loss through the glass as well. I presume this is why the oven has no issues ramping up as needed - there is 'spare' capacity and the quartz elements are not on 100% of the time. At full power, it draws around 1340 Watts, IIRC.
If anyone in the Boston area is interested in looking at the thing or would like some leftover insulation, I'd be happy to share.
... and one more thing... does it necessarily make sense to go through all this effort when you can buy a certified reflow oven on Amazon/eBay for about $285, delivered? Consider that the materials alone (oven, insulation, heat sink, reflow shield, K-thermocouple, etc.) probably came out to about $125.
Sometimes the journey is just as much fun as the destination. 