Reflow using two hot plates? - Page 1
Forum section: electronics / general

author: Peabody
author_rank: Super Contributor
timestamp: November 19, 2018, 03:18:48 am
content: I've been looking at using a hot plate for reflow, but the usual suspects have burners made with cast iron, which I think means they would be slow to change temperature. But then it occurred to me that at $20 each, it might make sense to get two of them. One would be set at a fixed temperature of 180C, and the other at 230C (for leaded solder paste). To reflow a board, you would place it on the first hot plate until it has soaked, then move it to the other plate until it reflows, then move it back to the first plate for a little while, then move it to something near room temperature until it has fully cooled down.There would be no need for a controller. The proper temperature settings for the hot plates would be confirmed with a thermocouple, and the same thermocouple could tell you when the board has reached soak temperature. And in this setup, the cast iron would be an advantage, allowing you to do multiple boards in succession.This setup would very roughly approximate the high-cost commercial ovens with multiple heating zones.What do you think?

author: Ian.M
author_rank: Super Contributor
timestamp: November 19, 2018, 04:59:46 am
content: Moving the board is asking for trouble with tombstoning and components getting jarred out of place unless you can devise a support mechanism for it with very smooth acting glides or ballbearing rails that moves it across the hotplates a very small distance above their surfaces. OTOH, that would make it easy to automate - just add a motor to drive the mechanism and a few position sensors for the two hotplate locations, and the cooldown and loading/unloading zone. You may want a blackened metal tray under the board to limit the rate it heats up and cools down to get the desired profile. The cooldown zone could have a fan that comes on once the temperature drops below say 115 deg C to speed up the final cooling to a safe to handle temperature.

author: Peabody
author_rank: Super Contributor
timestamp: November 19, 2018, 02:04:55 pm
content: If boards are that touchy, then I guess this wouldn't work. Having to build drive mechanisms would defeat the main idea of easy and simple. But from Youtube videos, I don't get the impression that people using hot plates leave them on the burner until everything is solid. My impression is the cooldown would take too long that way.

author: Ian.M
author_rank: Super Contributor
timestamp: November 19, 2018, 03:38:49 pm
content: People *do* manage to reflow on hotplates, and for simpler, coarser pitch boards you are probably going to get away with manually moving the board while the solder's still molten, if you can lift it off very smoothly and gently, and don't put it down again to finish cooling off till the solder has solidified. If you have shaky hands, your odds of success are much lower.

author: ar__systems
author_rank: Frequent Contributor
timestamp: November 20, 2018, 11:19:31 am
content: It is such inaccurate heating device that using two is just waste of effort. Why bother? For hobby you can be reasonably successful reflowing boards in an open fire fireplace, especially after a bit of practice.If you want to be sophisticated about using your hotplates, you can preheat at an edge, then move the boards to the center.