Electrical – Reflow oven vs even hot plate

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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.

Best Answer

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.