We were tasked with checking the high end of the industrial temperature range (85 C) for some of the components we used. Left over from some prior temperature testing was a cheap toaster oven picked up a WalMart became the platform of choice.
These ovens now use quartz elements which can quickly heat the oven to well over 450 F or 230 C, beyond the operating range of most electronics, in fact at those temps solder melts and many people have modified these ovens to do simple reflow.
The quartz elements emit a great deal of infrared and can heat quickly. The goal though is to keep the ambient temperature close to the target range. To do that you should shield the electronics from direct radiation from these elements. We used the base panel to shield the bottom and a copper clad circuit board sitting on top as the shield. A stack of 4 boards held up the top shield as pictured below.
Also integral to the test was a meat thermometer that we could place near the components being tested. So by changing the temperature setting slowly good testing at various temperatures were possible.
With this setup we could verify proper operation at 85 C for extended periods, in fact the boards ran up to 105 C, showing a lot of margin.
We did have a startup glitch in the testing with the original USB serial connection being used. All boards were failing at around 70 C, which was totally unexpected, but also repeatable. Turns out the first USB serial adapter being used had a PTC resetable fuse to protect from over current. At the 175 mA at 70 C it was tripping. Once that was replaced with the USB serial connection from SparkFun mentioned a few blog posts ago, testing at temperature was successful.