Reflow oven vs even hot plate

I've recently been searching for a simple, easy yet cheap way to reflow SMDs on a PCB board as I have never tried it before and always wanted to create a small and compact circuit. I then found a crowd funding campaign (whom I will not currently name because my point isn't to advertise) of a product where instead of a soldering oven, it was a hot plate. However in general, hot plates aren't the best for reflowing as the heating is uneven unlike this one where it claims to have an even heating surface (also because it's quite small).

If such product exists being a hot plate that evenly heats up the PCB, how would that be anyway advantageous over a soldering oven? One way I can think of is being able to re-shift the components if they move during the reflow. Any problems or disadvantages?

In addition, Is it safe to put components at 219 degrees Celsius when their max storage temperature is 150 degrees celsius? Looking at the reflow process, for 75 seconds, the oven or the PCB reach over the max (and the hot plate crowd funding product follows this exact same profile). And when looking for a PCB, what aspects should I be looking for to ensure it is reflow friendly? I'm guessing most PCBs are designed for this.

• Soldering technology for surface-mounted components is pretty competitive, with equipment pricing north of $10,000-$20,000. This equipment employs all types of heating techniques, and a hot plate function is a must for usual boards. The equipment uses sophisticated computer controls designed by seasoned engineers, and the price tag has its reasons. How many manufacturers did your research? What makes you think that you can do a cheap reflow station and have any successful results? Nov 17 '16 at 6:47
• Ali, there are huge number of reasons he could do this for less than 10k. I'll just list a few: he doesn't need 24/7 reliability, he doesn't need high throughput, his required tolerances are probably lower, he doesn't have engineering and administrative overhead to pay for, he can use consumer grade parts instead of industrial. Etc, etc.
– Drew
Aug 1 '18 at 20:13

DISCLAIMER: I have backed the campaign in question, but have no other affiliation with the campaign or its creator.

The biggest issue with the r***R, as with all surface reflow tools, is that double-sided loads are essentially impossible to create. Flipping the board over means that it will be held away from the heating surface, resulting in at best uneven heating of the board.

A reflow oven uses either infrared radiation or air convection to heat the board instead, which means that suspending the board by its edges does not impede the reflow process (and in some cases may be required), making double-sided loads possible. It also allows for a mixture of SMT and TH devices to be reflowed (insomuch as TH devices can be).

The flip side is that with a surface reflow tool heat can be transferred to and from the board much more quickly than via air convection, which allows tighter adherence to JEDEC reflow profiles.

In addition, the exposed nature of a surface reflow tool means that not only can parts be manipulated during reflow as you note, but also during rework after the board may have been in service for some time. This of course requires tighter thermal control than has previously been available using more... primitive tools.

As for storage, this refers to long-term thermal profiles, a month or longer. The few minutes during reflow or even rework have been factored into the construction of most devices from reputable suppliers.

• Ohohoh you know it. I honestly don't care about double sided SMD PCBs, I could just get a half-as-thin pcb, stick two either side and screw them together. That would work, right? Nov 17 '16 at 6:55
• I would be concerned about physical stresses with that method. What I might do for double-sided loads is to get the second thermocouple and then convert it into a makeshift oven by putting some sort of glass or crystal cover over the tool surface, letting convection act instead. Nov 17 '16 at 6:58
• Physical stresses? maybe a soft pad in between will help? I'm not going to be compressing any components. The other side of the PCB is completely flat. Something I'm missing? And I'm confused about your idea. Nov 17 '16 at 7:02
• The best method is to follow the 300 second ramp profile with hot air convection at controlled humidity 40% -50% using thermocouple profiles on a bare board with large part samples placed for shadow and heatsink effects. if adequate heat source is not possible a hotplate preheated can assist with adequate separation. But the oven insulation and energy requirements of many quartz halogen heaters can be large. Nov 17 '16 at 7:03
• The epoxy is applied once both halves have been reflowed separately. As for the other method, double-sided SMT loads are done all the time using conventional tools. Smaller components will be held by the surface tension of the solder while larger components usually have a tiny dab of glue holding them to the board. Nov 17 '16 at 7:13

I use an old Sears Kenmore 4-element toaster oven for reflow, with a thermocouple probe into a digital multimeter for temperature monitoring. Heat to 150C to activate the solder paste flux (Kester EP256), heat to 190-195 for 90 seconds for solder reflow, turn off heat and let it cool down slow with the door cracked a little until below 180C, then open the door more.

We do double sided also, using a couple of bare boards to hold the components off the tray for the 2nd cycle, sometimes with kapton tape if we're worried about them falling off.

We can do two 100mm x 100mm boards at a time, and more if the boards are smaller.

Regarding the temperature, thats certainly not a problem. The components are made for that. Of course you cannot reflow solder plastic headers (there might be some that can withstand that).

Plate vs. oven, I would recommend to go for the oven because the heat comes from all sides and if you need to rework something you can still do it with a solder iron. You probably dont want to work on such a heating plate while it is hot (in full operation). Maybe the advantage of the plate is that it is more conveniently storable. Furthermore the oven can probably more precisely follow a heating pattern than the plate can.

Would be nice to see the specs of the plate and compare it to an oven.

What comes also to my mind are double side populated pcbs. On a plate I can only imagine that they get too hot on one side in order to get them hot enough on the other side. Or you have to do the process twice, once for each side.

• Look at the other answer. You can guess the name. Nov 17 '16 at 6:56
• Why there is such a secrecy? WTF? Can you just give the link, so we all can learn alternative technologies and compare notes? Nov 17 '16 at 6:59
• Ok then. If the mods get mad at me, not my fault. indiegogo.com/projects/… Nov 17 '16 at 7:01
• Thanks for the link. Id rather buy an oven than investing in this project. The oven is just more versatile and the plate looks tiny (didnt find any measures). The only advantage is that its better storable and maybe the price, but I wouldnt save a couple of bucks, because in the end you will be using the oven for years. Nov 17 '16 at 22:29
• @Ueberflieger 150x80mm for smart and 200x150mm for large. yea an oven would be more professional but i just dont have the money to buy one. Nov 18 '16 at 3:26