Reflow oven project.

[elcomtel]

I've been lamenting recently how I was going to design and build some reflow equipment for SMT work.
A reflow oven and a preheating hotplate has been the focus of my recent thoughts.

I was going to set up some proof of concept tests, but that is a pointless exercise as we all know that people are using toaster ovens and kitchen hotplates very successfully.

As most people here don't have the luxury to spend enormous amounts of money on equipment and the need to be resourceful is a high priority. As most technocrats on this forum I always resort to eBay, Aliexpress, Deal Extreme and so on to find affordable solutions for my needs.

I've been wanting to put together a reflow oven for under $100-$150 that will give professional results. Most people here would be familiar with the temperature profile curves that are required for baking PCBs.

I've finally found an affordable PID temperature controller that has the ability to store up to 16 temperature settings that can be sequence controlled to provide a suitable temperature reflow curve for SMT soldering for very little money ($67 USD on Aliexpress).

I came across a gentleman in China by the name of Li Long who has done exactly this (http://atommann.com/learn/toaster-reflow/ for your convenience I have with the help of Google Translate translated the website into English and attached a PDF).

The temperature controller is an ALTEC PC410 (http://www.altec.cc/) The family is PC900/PC400/PC410 which all seem very similar. In addition they can be controlled/programmed via RS232 opening up the possibilities of computer control if required.

I later discovered by Googling with >>>ALTEC PC410<<< that this ALTEC PC410 PID temperature controller is very popular with SMT homebrew projects such as reflow ovens and homebrew BGA reflow machines.

So get yourself a $70 ALTEC PC410 temperature controller and a toaster oven and you possibly have the foundations for a very capable SMT reflow oven. I've placed an order for an ALTEC PC410 and have to patiently wait four weeks for the slow boat from China to make it's way to Australia.

[Kremmen]

I did a similar project early last year with good results.
Two points you may want to consider.

1. Air circulation. You probably will have 1 thermocouple probe in contact with a "typical" point of a PCB being soldered. That may or may not provide a good average value of the temp over the whole PCB. Circulating air around will tend to even out the temp differences somewhat and thereby improve the result. Or that is the hypothesis anyway.

2. Heating the PCBs from the bottom probably serves little or no purpose, and can actually be counterproductive. I modified my oven by placing the bottom heaters to top so that i have 4 on top and none in the bottom. The heat radiation  to the topside of the PCB is relatively uniform now. Not heating the bottom side allows me to do double sided loads by alternately baking the bottom and top sides. The components on the non-heated side do not reach anything close to liquidus during the cycle. Also, the extra power on the top side allows a quick ramp from pre-soak to liquidus thereby being a bit gentler on the more sensitive components.

The controller is also a sequence programmable PID which i have tuned to correspond the Altera temp profile recommendation. The system has worked surprisingly well. Actually, not a single failed solder joint in all of the times i have used it.