SMD Soldering Reflow Oven

SMD Soldering Reflow Oven

 

I’m sure you’ve seen a ton of these by now. If you are a maker then this is one tool that you MUST have. Its convenient fast and you can even do a small production batch with these. If you are completely new to SMD soldering then search for reflow soldering and you’ll get tons of information.

This particular instructable is based on the ControLeo2 reflow oven controller by Peter Easton. This is by far the best I’ve come across and the software is fully open source. It can control up to 4 solid state relays (SSRs), a servo motor (to open the door for cooling at the end of reflow process) and a buzzer. Most impressive is that it is self-learning. That means, it can adapt to your oven heating elements and their behavior. Thanks Peter for putting this out there! The electronics hardware design is based off Brian Barrett’s design. He is super helpful and I suggest reading his build guide (multiple times). Thanks Brian! 🙂

Before we start a word of caution: We are dealing with 240V AC mains supply here. Please be careful. These are fatal and can really cause massive bodily harm. Turn off all power before you start working on these. I cannot be held responsible for any erroneous steps you take while building/modifying this oven.

Now lets get building! This i’ble is broken up into sections, namely: the mechanics, the electronics, the wiring and and powering up and testing.

Lets get started with the mechanicals. On to step 1!
Step 1: The mechanicals
Picture of The mechanicals

The oven selection is one of the most steps here. Here are some points to keep in mind:

Choose an oven with quartz heater elements. They heat and cool rapidly and are cost effective.
Choose an oven with approx. 1200W to 1500W preferably with 4 heater elements. Mine has two on the top and two on the bottom. These are essentially two pairs in series.
Look for a simple oven without fancy controls and such stuff. Mine has just a temperature knob along with a timer.

Apart from the oven, here is a basic parts list (does not include the electronics which is listed in the next section):

M3x10mm screws, nuts and washers – about 10-12 of them
1 sq. mm electrical wire – about 3m in length if you go for a single color. I had 4 different colors lying around the house which was very convenient.
Fork terminals and straight lugs – about 20 odd
Fiberglass wool – for insulating the oven so that heat remains inside the chamber
Silicone gel sealant – These are very commonly available. I chose the white one cause its easier to see where you are applying it and more importantly if there are any gaps.
A caulking gun – for applying the silicone gel
Aluminum foil tape – to be applied inside the oven such that the heat reflects well and also for covering spots from where heat could leak and affect the heating of the chamber. The ControLeo2 build guide uses reflect-a-gold which unfortunately was not available in my part of the world.
Fiberglass sleeves – for the wires inside the oven. Dont get the acrylic coated ones. Get the normal white braided ones.
Heatshrink tubes that would fit the 1 sq. mm and 22 AWG wires when shrunk. I used 2mm and 4mm tubes. I also used a larger 5mm one to encase the connections for the neutral wire of the AC mains.
A small aluminum plate – about 12 in x 12 in – this acts as a the support structure for the SSRs as well as their heatsink.
Thermal transfer compound – for attaching the relays to the aluminum plate which acts as a heatsink for the SSRs. I used the ones that are used in attaching desktop CPUs to their heatsinks. A great example is the Arctic Silver or the Noctua NT-H1.

Open up the oven and you’ll see the wiring. A quick note on the heating elements wiring: Usually you’ll either have two elements or two pairs of elements. I had two pairs of them with one pair for the top and another for the bottom. Each pair was connected in series. This usually means they are rated for half your AC mains supply voltage. Since I’m using 220V AC, this meant each element is rated for 110V AC. I verified this the hard way. Initially I connected all four heaters individually but they heated up really fast (like within seconds).

Now, you’ll need to disconnect all the wiring and remove the temperature controller and timer.

Next, you’ll need to use the silicone gel to seal off any areas that are open and where heat might escape from.

Now comes the tough part – applying the foil tape to the insides of the oven chamber including the glass door. You must cover any open seams, hinges gaps etc. to prevent heat loss.

Now you will need to disconnect some of the wiring attached to the heater elements. In my case they were welded and had to be removed with something like a Dremel. Remember not to saw off the element endpoints. Those are needed. Its a tricky job so take your time with it. Most ovens in the US come with screw connections.

I also drilled a small hole in the side to insert the thermocouple.

Mounting the SSRs in the oven enclosure

I also made a small mounting assembly for attaching the SSRs and the mounting this aluminum plate to the oven. I chose a 1.5mm thick aluminum sheet but choose something a little thinner. It was really painful to cut this even with the Dremel. A 1mm sheet should give the same rigidity and would be more easier to work with.

This step took some time since the space inside for this was very small and I had to think through how to assemble it. I made an outline in Sketchup and then made a paper mockup. I then checked if everything fit right and then eventually replicated it in aluminum. I took plenty of measurements and eventually had to drill a few holes near the bottom side edge to mount the plate. I also used the existing holes where the original control circuitry was mounted. This made sure that the plate was not wobbly and wouldn’t touch any of the oven sides.

Moving on to the electronics.
Step 2: The electronics and the wiring
Picture of The electronics and the wiring

The electronics combined with the software, control the solid state relays which in turn control the heating elements. Think of the relays as replacements for physical switches. Except they are electronic and can switch on and off very rapidly since there are no mechanical contacts based on inputs from the software.

 

For More Details: SMD Soldering Reflow Oven

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