Toaster Oven Hotspots

[tweecer]

Hey Everyone,

We have been manufacturing our product ourselves since June 2012, with great success. I have been using a $50 toaster oven that uses the older thin elements, which were slow to heat. It worked well enough with lead free solder paste, but at the behest of my wife (and business partner), we switched to lead free. What a cluster f*ck that stuff is. I scrapped 1 entire panel (10 units) and another half panel, trying to get the reflow profile right.

I purchased a smaller unit that has the quartz elements and it heats much quicker, but does not have convection fan like the older unit which was to 2.5 times the volume. The new unit is just large enough to fit a 10x10" panel. It has over heated the panels twice and I need to do some more testing while moving the temperature sensor around to see how uniform the temp is.

I cut and bent the metal wire grill to support the panel in 3 locations. Could that metal to panel contact be causing the panel to overheat?

There is an element at the top and one on the bottom, I have thought about moving the bottom one to the top and seperating them. They are both center mounted on the sides. I have a PID controller, but have been manually controllling the off on times.

Any thoughts or suggestions would be welcomed. This is a 2 sided panel with both sides populated. I can post pics of the the panel and/or oven...

 

[BradtheRad]

To show up hot spots, there is a trendy science experiment which involves melting marshmallows in the microwave oven. Standing waves are created, causing rapid browning of the sugary stuff at spots which form a grid pattern.

There are several Youtube videos, which explain how you can measure the size of the grid pattern, and thence calculate the speed of light.

 

[tweecer]

Hey Brad,

I have not been back on in a while, but your suggestion sounds like a great method. I am also looking at replacing my temp sensor, as it may be reporting lower than actual temp or may be in a cooler spot. I will let you know what I find, thanks!!!

 

[dick_freebird]

I have a toaster oven which proclaims "EvenToast Technology"
proudly on the glass.

As near as I can tell, this "technology" resides in the cover plate
above the quartz element which has a peculiar arrangement of
holes punched in it, less dense in the center, more densely
at the edges.

You probably want more convection and less radiant heating,
perhaps some similar baffle-plate would help things. Maybe a
cheapo countertop convection oven (rather than toaster oven)
would suit you better?