Introduction: Making a SMD Reflow Oven

About: technology hobbyist...

I have been an electronics hobbyist for many years and have always stuck with through-hole components when making a project. However as time goes by, not only are more and more components are becoming available only in SMD (surface mount device) but also more interesting projects are also SMD based.

There are several options for doing your own SMD soldering:

Hand Soldering - Using a fine-tipped soldering iron and small-diameter solder you can work with the larger of the SMD devices. However it can be pretty tedious and take a long time if you have lots of parts.

Electric Frying Pan - This can work for smaller boards but the temperature control is pretty difficult so it can be hit and miss.

Toaster Oven - This seems the most promising for the hobbyist and while you can just wing it with the manual controls there are also a range of control options for automation and temperature control. This essentially mimics a commercial reflow oven.

I decided to put together a toaster oven and wanted something that could handle large boards and possibly do small production runs. Doing a web search, you will find many options for toaster oven reflow controllers. They range from one-off designs to DIY boards to full kits. A large number of them are Arduino based. Some controllers just allow the oven to plug in (so you don't need to take the oven apart) while others integrate completely inside the oven (more work but a much better product in the end).

Looking at various options I decided on the Whizoo Controleo2 Reflow Controller. It offers a decent GUI and a self-calibration function that I felt was important to get decent results. It also has full PWM (pulse width modulation) control of the heaters to give you a more accurate temperature profile which is very important in reflow soldering. While I had wanted a kit, the Whizoo is fully assembled but you still have a lot of work to integrate it with your toaster oven. They also offer some extras in the kit including various insulation types (allows the oven to heat up quickly and evenly) and a booster heater (ensures the unit heats up at the correct rate). There is even a servo to crack the door open after the cycle is complete to allow the board to cool correctly. I bought my kit before the servo was available so I rigged up my own servo door opening mechanism. You can see the various purchasing options Here.

Whizoo also has a great Build Guide which details each step. I recommend you read completely through their guide and this Instructable before you start your own oven as there are a few caveats you will run into along the way. You can also find various examples of user made ovens Here.

I also found that the person behind Whizoo (Peter Easton) answers email questions very quickly and at all hours of the night. It is nice to know you get very good support when you purchase a product.

DISCLAIMER!! - This project deals with high voltages and high temperatures. You can easily electrocute yourself and/or burn your house down if you are not careful. Do not attempt this project if you are not competent in the various tasks required and able to do them safely. You will need to make various design decisions during a project of this nature and you need to be able to evaluate the various potential safety issues involved.

Don't say I didn't warn you...

If you are interested in an Instructable on setting up a solder paste dispenser for SMD projects check out this one I just recently published

Step 1: Find a Toaster Oven

You have many toaster oven options. While you can use something you find in the trash or "borrowed" from the kitchen, I decided to get something new. I didn't want any chance of contamination from previous food stuff nor did I want to work on something old and nasty. Ideally you want an oven with quartz style heaters as they heat up faster than the old rod style heaters. I went with the same model that Whizoo used in their example: a Black & Decker TO1322SBD. It has quartz heaters (one above and one below) and is rated at 1150 Watts. It will handle a board up to approx. 6" x 9" (large enough for anything I expect to do). You can get larger ovens and ovens with convection fans (the Whizoo controller also has a output to control the fan).

Step 2: Take Apart the Toaster Oven

At this point you want to take the oven apart and remove all unneeded parts. You also need to make some design decisions. You can re-use some of the oven parts and cabling (saving yourself some money) or opt to replace everything, depending on your budget and your needs.

I decided to replace pretty much everything. So I opened up the case and basically removed all the guts. The Whizoo kit comes with some high temperature reflective insulation that you line the oven chamber with. I decided to remove the heating elements to make it easier to install this tape. This meant I essentially took the unit completely apart. You may not decide to go this far.

One thing you will notice as you strip the unit down is how cheaply these ovens are made. Some of the screws barely hold in the thin sheet metal. Be careful you don't tighten the screws too much (or too often) or you may strip them. When putting the oven chamber back together I decided to use high-temperature RTV silicone on some of the wall seams to make it more rigid. This actually helped a lot.

Unfortunately, I don't have pictures of what the oven looked like when I first opened it but I do have pictures of what I stripped it down to. Make sure you save all the parts, wires and insulation sleeving as you may need them later.

Step 3: Insulate the Oven

Although the Whizoo kit comes with reflective insulating tape and an insulating pad, I added extra insulation around the outside of the oven chamber. This both increases the heating performance of the oven and helps keep the exterior of the oven from getting too hot. Again these ovens are made as cheaply as possible so they have no insulation inside them.

The best and cheapest option is to use welding blanket. Essentially woven fibreglass, it's not too thick (less than 1/8") but does provide decent insulation. I obtained some Welders Blanket at Princess Auto (a local discount auto shop). I'm in Canada but you can probably get the same thing at Harbour Freight in the US.

I cut the blanket with a pair of scissors but found the edges tended to fry and the piece would start to fall apart once you handled it a bit. The cut piece of blanket also tended to lose its shape as it doesn't have much sheer strength as it was dependent on the stitched edges of the blanket. To stop it from coming apart and to to make it more physically stable I wrapped 1/2" wide high-temperature Kapton tape around each cut edge of the blanket. The tape also covered up the cut edges of the fibreglass which can be really itchy.

I insulated the oven in 3 steps:

  1. Bottom - The Whizoo kit comes with an insulting pad for the bottom but I decide to add more. The oven I had came with a removable bottom pan (crumb tray I guess). I took this out, added a piece of the welders blanket on the bottom and then put the tray on top of it. This sandwiched the insulation in place. I then pop-riveted the bottom tray in place to hold it all together.
  2. Back - The oven just has a single thin sheet metal wall for the rear. To avoid it burning whatever may be behind the oven they have a plastic knob affixed to the rear to ensure it doesn't touch anything directly. I wanted something better than this so I cut a piece of aluminum sheet to fit the oven's inside rear wall. Similar to the bottom, I also cut a piece of the welders blanket to fit the back wall. I then laid in the welders blanket and placed the piece of aluminum over it. I then pop-riveted the inner panel to the existing rear panel through the welders blanket.
  3. Sides & Top - Since both the sides and the top have an irregular shape I found the best solution was to cut a piece of the welders blanket that just drapes over the oven chamber. Again, I taped the edges so it kept its shape and then simply used pop rivets and washers to hold it in place. I also used some high-temperature RTV silicone to tack it in place. You will need to cut holes in this piece of the blanket to allow for the heating elements to get installed again.

Step 4: Install Bottom Panel & Heater Mount

The Whizoo kit comes with a metal-clad insulating plate and a booster heater. The booster heater ensures the oven heats up at the required rate for a proper reflow temperature profile. While I had already added the welder blanket insulation on the bottom I also added this pad figuring more insulation would be good. The kit also includes two eye bolts to mount the booster heater. You will need to determine the location for these and drill holes through the bottom of the oven. The eye bolts need to be at each end of the booster heater (about 5" apart). The middle portion of the heater gets red hot so make sure the eyes are just at the end. You may also need to use a pair of pliers to make the eye bolts the right size to fit the heater tube firmly. I mounted the booster heater centered in the width of the oven (from side to side) and about 2" forward of the quartz heater. I simply centred the insulation pad on the bottom (it's smaller than the oven) and drilled the holes through both the insulating pad and oven bottom. Then I used the eye bolts, washers, lock washers and nuts to hold the assembly together.

I kept the booster heater as high up off the bottom of the oven as the length of the eye bolts would allow.

Step 5: Mount the Power Switch

While you can leave the existing oven controller in place as a switch, I wanted to make the front panel look a bit nicer. I found a rocker switch that lit up when the power was on (figured it would be good to know if the oven is powered up or not). I decided to cut up a piece of aluminum sheet to make a new front panel. In order to fit the new rocker switch I had to remove some of the existing panel.

I somewhat butchered the old panel to make room but since it will all be covered with the new panel it didn't matter. I cut a square hole in the new pan and snapped the new rocker switch in place. Unfortunately my hole was a bit too big and the switch seemed a bit loose (especially when I flexed the new panel to match the curve of the old panel).

I used to regular RTV silicone to glue the switch in place and then pop riveted the new panel over the old one. I think it looks much better than leaving the old oven controls in place.

While you can reuse the existing oven power cable I wanted a longer one with a heavy duty plug. I had some Cabtie (heavy duty rubber covered cable) so I used that. The existing hole for the cable connector was too small for the larger cable and too flimsy so I cut a small square of aluminum sheet and pop riveted it to the inside of the case. Then I drilled through both the case and aluminum sheet for a heavy-duty cable connector. Again these ovens are not very well built so adding strength where it is needed will hopefully allow it to handle being banged around a bit. In later pictures you will see I also added a strengthening panel where I had to drill for the control cabling.

Step 6: Install the SSR Mounting Plate

To control the two existing oven quartz heaters and the added booster heater the Whizoo kit comes with 3 SSR (solid state relays). The kit also includes a pre-formed aluminum plate for both mounting the relays and providing a heat sink for them.

I didn't like the amount of space the plate took when mounting horizontally so I changed things around a bit. First I cut off the bent section of the existing plate (I used a table saw). Then I turned the plate 90 degrees so the relays mounted vertically. I had to add some angle braces to the bottom to enable the plate to be mounted to the oven case. Due to the flimsiness of the oven case (and the location of some vents) I also needed to add some aluminum strips on the bottom of the case for the brackets to mount to. This gave me a bit more room in the case for wiring. You can see I also allowed for clearance behind the back of the mounting plate and the connections to the heater elements.

Step 7: Install the Space Age Reflecting Insulation Tape

The Whizoo kits also included some high-temperature reflective tape. This helps insulate the oven chamber and reflects the heat to where you need it.

It also makes the oven look like a friggin' Mars Rover and that's pretty cool.

However installing this tape is a pain. You won't get enough to completely line the inside of the oven (though newer kits come with a bit more so this may not be an issue anymore) but you can get most of it. I tried to get the back, most of the side, most of the top and the front panel (except for a viewing area). Since the bottom pad is already reflective I did not bother covering it.

Some hints:

  • Remove the door completely if you can or use bungee cords (or whatever you can rig up) to keep the door open while lining the oven with the tape.
  • I removed the heaters. This helped a lot (and I was afraid I may break them).
  • Make sure you first clean the inside of the cabinet with thinner or alcohol to get rid of any grease that would affect tape sticking. IMPORTANT: Do this outside (away from flames) and let it dry completely before applying tape.
  • I cut the tape to the exact length needed then carefully put in place while trying to avoid bubbles. I also burnished the tape completely after placing it to ensure good adhesion.

Step 8: Install the Booster Heater

I installed the eye bolts for the booster heater when we installed the bottom insulating pad. At this point the bottom pad should be secured in place with the reflective tape. So you can remove the eye bolts to allow you to install the booster heater. You need to drill a hole through the right side of the oven wall in line with the booster heater location for the heater power wires. Make this hole large enough so the wires don't risk chaffing or getting cut from the hole edges.

I had a piece of insulating sleeving left over from the tear down that I used to protect the wiring. You can also use some of the reflective insulating tape to wrap around the wires.

You will find that you probably need to adjust the eye bolts with a pair of pliers to get the booster heater to fit snuggly. Once done, you can secure the eye bolts again and the booster heater will be in place.

Step 9: Wire Up the Heating Elements

If you removed the heaters as I did, you will now need to re-install them. There are tabs you need to bend on the oven walls to lock them in place. Note that one of the heaters is 600 Watts and one is 550 Watts. The 600 Watt one should go at the top.

At this point I ran into a problem. Since I had a roll of high-temperature oven wire I wasn't concerned about reusing the existing high-temperature cabling. In my hurry of ripping things apart I assumed that everything was connected with normal crimp connectors that I could easily replace. So I didn't really leave any of the old wiring in place.

But I was wrong. The existing wiring was crimped directly to the heater terminals (rather than to a crimp terminal that then affiixed to the heater terminals). One choice would have been to try and pry the existing crimp open and attach my new wiring. I was concerned that this would either risk breaking the heater or that I'd not be able to get a decent crimp.

At this point I was a bit bummed out as I didn't want to get another oven and start all over again. I found some plastic terminal strips with a metal insert. Using a knife and chisel, I cut the plastic away to release the insert.

I then used this metal insert from the terminal strip to connect the new wire to the little bit of old wiring I had not hacked away. I then wrapped the whole thing with Kapton tape.

On a couple of the element connections there was not enough old wire left to connect to. I did manage to kinda squish down the existing crimp connector to be able to fit it into the terminal strip insert. Again I wrapped it with Kapton tape for protection.

I now had all the elements installed with new wiring connected to all of it. Having nice long length of wires allowed for a much neater wiring job. I like this much better than trying to make use of the original wiring.

Step 10: Heater Test (Or What Not to Do...)

At this point I was feeling good about the build but was getting restless about firing it up. Rather than wait till I got the controller installed I thought it would be a great idea to hook the elements up to power manually and at least see what temperatures I'd get. I set up the oven outside (figured there would be some outgassing from the tape and insulation), and put in a thermocouple connected to a temperature gauge to watch the temperature..

Initially, I kept the temperature low and just played around a bit. I was leery of the high temperature reflective tape but was amazed that the peel and stick glue held up to the high temperature (don't know why I was amazed as it is designed for this).

However I got a little too cocky and left the top element on for a bit too long. I heard a small puff and saw smoke and flame coming from the tape located near the top element. I quickly shut everything off and feared the worst. Not really sure how hot it got or what happened but a small section of the tape seemed to puff up and perhaps the adhesive behind it ignited? Anyways I used a rag and thinner to clean up the area. A small portion of the tape was damaged but I simply removed it and all was well again.

* Since I wasn't sure how hot things got, I feared the tape might have problems during normal operation. However, after several months of operation I have not had any issues, so not to worry.

Step 11: Wiring Everything Up

Now I was ready to install the control systems. I mounted the relays on the modified mounting panel. Remember to use the silicone pads supplied in the kit or use silicone heat sink compound (use the pads as the grease is really, really messy).

I labelled the relays to avoid getting confused. In my system I have control over all three heaters.

I could now see the end of the tunnel but then then had a thought about safety. The original oven controls probably had a high safety limit switch. This would cut off the power should the temperature get too high (say a fire in the oven or the controls failing with all elements powered on). This didn't sound too good so I looked around for a solution. I found some a few high-limit switches at Lees Electronics (a very decent local electronics shop). It was a bit of a guess to determine an appropriate temperature as the limit switch is in the cabinet not the oven chamber. The one I used is set at 125 C. So if the inside of the cabinet gets hotter than that the AC power shuts off. It hasn't triggered in normal operation so it seems like a decent setpoint.

Then Whizoo kit comes with a wall wart style +5VDC power supply. I modified this a bit by cutting down the prongs (wanted to make more room for wiring) and soldering wires to them. I then covered the prongs with glue filled heat shrinkable tubing. It looks a mess but the 120 VAC connections are protected.

I used a bit of RTV silicone and wire ties to secure the wall wart to the back of the case. Then everything else was wired up as required. I drilled a hole near the top of the back case to run the control cabling to the control unit.

I also installed the thermocouple at this time. While I don't show a good picture of it, I positioned it through a hole on the right side of the oven chamber. It is a bit above the shelf height and stuck in a few inches.

The thermocouple cable, +5 & GND from the power supply and the relay control wiring are all lead out the top hole through a grommet.

Don't forget to attach the power cord ground wire to the case and make sure all your heater and AC connections are tight and properly insulated. I used crimped connectors where ever possible and tried to keep the cabling neat and tidy.

At this point you can connect up the control box and should be able to do initial testing to confirm your cabling is correct and you have basic functionality. Make sure you get a temperature reading from the thermocouple.

Step 12: Control Unit & Servo Mounting

I did have some concerns about the oven cabinet and control box location. I often take the oven to our local maker space Vancouver Hack Space for workshops and such, so I wanted it to be able to hold up to being moved around. I also wanted a handle to be able to carry it. So I decide to mount it externally on top of the oven. This also gives a little protection to the control box if you tend to move your oven from place to place..

I ended up using some large aluminum angle and sheet aluminum to make a shelf-like additional top panel. This gave me a decent base to mount the controller and a decent spot to mount the handle. It also made it easier to rig up a mechanism to open the door with a servo. It also provides some heat shielding when the oven is working.

To mount the control box I cut some up some lengths of 1/8" x 3/4" aluminum stock and bent them at a 45 degree angle. This lets you see the LCD when the unit is working.

One of the features of the Whizoo controller is support for a servo to open the door after the reflow is done. This allows for a proper cooling (again keeping a correct reflow temperature profile). I cobbled together an opening mechanism on my own but now Whizoo supplies a servo kit to make this easier.

I used some aluminum angle to make a bracket for the servo. Then I used some of the 3/4" stock to make a lever that allows the servo to push the door open. Hopefully the pictures make the operation clear to the reader. This Video shows it in operation. Its may be a bit overkill but it will work reliably and I used stuff I had in my shop.

In order to use the servo you need to make a few additions to the control board. First, I added a right angle header to pick up the +5, Gnd and D3 control line. This lines up with the standard servo pinouts so it became easy to just attach a servo (note in the picture I used a 3-pin cable extender for the servo and the wire colours are not standard). You also should install an extra electrolytic capacitor at the servo header to allow for the rush current of the servo motor. If you don't do this you may get your control unit resetting when the servo moves. I used a 16V 470uF electrolytic capacitor. Make sure you pay attention to the polarity.

Note that various servos tend to behave differently when powered up prior to a proper control signal being present (as happens during the boot process of the controller). Some servos are fine, but some (when initially powered up) will move to an incorrect or damaging position before the controller moves it to the configured startup position. This can be annoying so try connecting a 10K pull up resistor between the servo control line and the +5 rail. This cured the problem with my servo.

Once I got the servo door opening mechanism operational I completed the cabling from the servo and oven to the control box. I used some wire tie saddles and mesh sleeving to protect the wiring and make things look nicer. Remember to drill a hole in the side of the case to allow access to the USB port on the controller board. You`ll need access to this for firmware updates and if you feel particularly geeky you can monitor the oven during the baking.

Step 13: The Final Touches

You are almost done. You will also need a shelf for the PCBs. The oven comes with a perforated steel shelf but it is recommended that you replace this with a sheet of aluminum. You can also see the thermocouple location in the first two pictures. Ideally it should be as close to the board you are baking as possible but I don`t like it so close that you can knock parts off a board when you slide it in. It seems to work fine where it is.

Now you should also update the firmware on the controller. For this you need the Arduino IDE (runs on Windows, Mac OS, Linux) and the most recent firmware. The Whizoo site has Full Details on how to do this. As the code is open source you are free to make any changes you see fit. I doubt you will want to change the working part of the code but you may want to configure a customized startup screen.

Once the firmware is updated it's time to configure the unit, set the temperature and calibrate the unit.

For configuration refer to the Whizoo Build Guide Configuration section. Basically you setup up the outputs for what you have connected to them, set the max temp, setup the door servo open and closed positions. You then set the max Temperature for the solder you are using. For leaded solder you typically want it set for 183 C, for lead free its 240 C (though you should check your solder specs to make sure).

For calibration refer to the Whizoo Build Guide Calibration section. The calibration is quite simple but can take some time. Simply press the start button. The unit will start to heat up using the default settings. But it monitors the various heating cycles and will abort if the temperature doesn't match the required profile. At this point it adjusts the heating values for the next run. You then let it cool down for a bit (at least 20-30 minutes) and then start it again.

This typically takes 6 to 10 cycles until it dials itself in. Once it is happy it will tell you it has exited the learning mode and is ready to go. After this you are good. It monitors the profile for each run and will make small adjustments if needed. However if the run is too far off the profile it will abort the run and you will see this on the LCD screen. This way you know it has been a bad run.

While it may seem like common sense, make sure you do not use the oven for food as it will get contaminated with the solder and various compounds from the soldering process. You should label it also to make sure others that have access, don't decide to warm up their bagels in it.

And remember it is an oven, so it does get hot. The insulation and the extra top panel help keep the outside cool but you will burn yourself on some parts when the oven has done a few runs. Best to put some warning labels about that also.

Step 14: Cooking My First SMD Board

For the initial test of the SMD reflow oven I used a SMD Star Kit designed by a fellow member at VHS. I used a syringe to manually place the paste (way too much as you can see). But other than a couple of easy to fix solder bridges it came out fine!

I can now cook SMD boards to my heart's content...

Thanks for reading this Instructable. I hope it may help you when building your own oven.



If you are interested in an Instructable on setting up a solder paste dispenser for SMD projects check out this one I just recently published.

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