blakec1 wrote:I have never been happy with the skillet / hotplate. As an ME I just can't reconcile how heat will travel through a fiberglass board with multiple heat contuctors (via's and traces) and not have hot/cold spots. Many times I will put exposed copper on both sides of the board for heatsinking - and I can just feel that hotplate roasting the Power IC's due to the better thermals of the heatsink with numerous vias.
I have used hotplates on aluminum backed boards (for LED's) with some success.
I would not be comfortable using a hotplate on complex boards especially with small SMT connectors and electrolytics. Electrolytic caps can and are damaged by temperature spikes and are giving people fits as the ramifications of temp spikes during reflow may not show up for 6 months to a year. Basically they can get their lifespan cut significantly. Think of all the Mitsubishi TV's or Escort Radar detectors that have died due to dead Electrolytics. CM's will tell you that RoHS has significantly increased the problem due to the higher reflow temps.
All that being said I have tried it and it "works" but again - my comfort level is low.
In the engineering world, "Perfect" is often the enemy of "Good Enough"
Hot-plating works really well, and despite the non-perfect heating of a PCB, the difference is generally negligible for hobby and prototype production. The likelihood of frying a component or significantly reducing it's life-span is pretty low and that sort of thing would be indicative of a greater problem in the way you're going about the reflow (Too much heat, not enough patience is the enemy of both cooking food and making electronics
). Would I have used hot-plating in mass production? No, the temperature controlled ovens we used in MP are useful because better control means less fall-out when you're doing runs of 10,000 PCBs at a time. But there's a huge difference between MP and small runs.
We used hot plating extensively in my last job for prototyping, including very small, complicated circuits with SMT electrolytic, various 0.3-0.5mm pitch SMT connectors and ICs (some with ground slugs, some without on the same board), and never had serious problems because of re-flowing. On occasion we'd rework components if the connections didn't take, but those were more indicative of a non-uniform paste application than a problem with the reflow method. (Again, in MP there are machines that do that precisely for you, but in the prototype/hobby world it's generally done by hand with stencils).
Not to knock the toaster-oven reflow, I'm thinking about setting one up for my hobby stuff because I do double sided PCBs almost exclusively, and am tired of always putting the leadless packages on one side, and doing the other side by hand.. That's one area where hot-plating is less convenient than an oven.
(As reference, my last job was double hatting as a design engineer and manager of production engineering in an electronics company)