Commercial Reflow ovens for Hobbyists

blakec1:
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 :wink: ). 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)

:x If someone stll happens to come here in searching for information about reflow ovens and especially T-962, here is my first impression.

I bought a Puhuit T-962. When it came, there were transportation damages. I mailed to the seller, but they did not comment.

There were two spare bulbs with the oven. In both bulbs the heads are not parallel to the tube. In one of them there is in one end written 220V 150W and in the other end 220V 100W. Which one is correct? I measure the current the oven took during heating, it was 1,37A, this means 300W. According to the specification and the label in the back it should be 800W.

I made a test reflow without a board. All seemed to go fine. There is in the display drawn the selected curve and a cursor is showing, how the reflow is moving on. The cursor seems to follow the curve very well. I measured the time with my clock and the whole sequence took 12 minutes. The clock in the display showed 7,5 minutes, that is right according to the curve. I made another test with the same results. During the heating phase the display clock is slowed down noticeably. This means that to give the user a picture that the oven makes the reflow according to specification for the paste, the computer calculates the horizontal axis time from the temperature using the curve “backwards”.

So the oven is not 800W as promised, it is only 300W. Based on this low power the heating period is a lot too slow. To “compensate” the low power the internal clock, which is used to show the horizontal axis values, is slowed down so that the cursor follows the curve and the clock shows the “correct” reflow time when the process ends. This all seems good, but obviously will not result in any amazing boards.

Believe it or not, a simple toaster oven does a great job. When we first started assembling surface mount boards we used a simple toaster oven that we bought from Sears. It did a great job. Once you notice everything has melted, you just open the door and have a small fan blow over the board to cool it off quickly. For simple prototypes it works great.

Today we use a $90,000 reflow oven. But the concept is the same. It’s just heating up the air around the circuit board. IR reflow was abandoned in the 80’s and hot plates have very uneven heating. Trust me. Use a toaster oven.