Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Bought a GOOD lab hot plate to do solder reflow. Half inch thick aluminum top, temp setting dial.

When I first fired it up I very carefully found the settings on the dial that corresponded to 160C and 230C, the two temps I was interested in, for Toner Transfer, and for solder paste reflow.

The IR thermometer said the dial was WAY off. By a factor of like 1.5.
But this is OK, I just marked the spots on the dial and went about my
business.

Just did some toner transfer with the plate on the bottom and the normal iron on the top. I.E, the board and paper sandwiched between the hot plate and the iron. Set the hot plate for where the IR thermometer had found the setting for 160C

After being on the hot plate for like 15 seconds the paper started to
turn brown and smoke.

WTF?

I took the temp again. Yep, says right at 160C. But paper doesn't burn
at that low a temp... ????

I turned it down to the setting on the dial for 160, and tried again.

I after it had cooled off I put a piece of paper on top of the hot plate and took ∗it's∗ temperature. Just about exactly 160C.

After cleaning the board up and scraping off the burnt paper I ran it
through again and it worked fine a the dial setting of 160C.

Odd, no? IR non-emission coating on the plate or something?