Must be capable of high-temperature lead-free reflow (240°C) as well as leaded reflow
Must be capable of reflowing a 8" x 10" board:
- Must not burn the components or the board
- Must reflow the entire board and not leave parts unsoldered
Must following industry-standard profiles for pre-soak, soak and reflow phases
The challenges of building a reflow oven
Lead-free solder requires higher temperatures than leaded solder. Leaded solder is dangerous and socially irresponsible so you shouldn't be using it! Take a look at a typical reflow curve for lead-free solder:
It is easy to think that the most important part of the reflow curve is the maximum temperature of 255°C (480°F). Yes, it is important to build an oven that is capable of reaching those temperatures. However, another important number is the rate-of-rise of temperature at the higher temperatures. At higher temperatures it becomes increasingly difficult to increase the temperature. You run the risk of damaging sensitive components if the reflow takes too long, and you can create hot spots (damaged components) and cold spots (no solder reflow) if you run the elements full blast.
There are a lot of other problems that can occur if the reflow profile isn't followed. Components can be damaged from thermal shock or cracking, solder paste can splatter which can lead to voiding in array type packages, and the solder paste could oxidate or the flux not fully activate. If the maximum allowable temperature of IC's is exceeded, it can damage the internal dies of components and foster intermetallic growth leading to shortened MTBF (mean time before failure) numbers. The time-above-liquidus and cooling rate also affect the quality of the resulting solder joint.
What makes ControLeo2 the best reflow oven controller?
The ControLeo2 controller and the oven built in the build guide should be considered top-of-the-line. A lot of engineering and experience has gone into making the ControLeo2 reflow oven, and there are currently more than 500 customers world-wide using ControLeo2.
If you are only doing small boards and using leaded solder paste (tut, tut!) you can get away with a less-capable controller and a poorly insulated oven. But how much is your time worth? What is the value of the components you plan to use? What is the turn-around time to order new boards or components when they get heat-damaged? Do yourself a favor and build yourself a great reflow oven. Do it once, and do it right!
Four outputs Control convection fans and heater elements individually.
Better heat distribution Having control over individual heating elements allows you to keep heat away from sensitive components.
Hot-spot elimination Intelligent software manages element on-time, reducing hot and cold spots in the oven.
Better heat direction Intelligent software controls whether heat comes from the top or bottom, depending on the reflow phase
Better current management Elements are turned on and off independently eliminating the current spikes common in single-relay controllers
Ready-to-run No programming needed. Just configure the fans/elements your oven has and the reflow wizard will do the rest. No need to connect ControLeo2 to a computer or write any software!
Proven hardware ControLeo2 is based on the original ControLeo, which has been field tested for more than a year. ControLeo was based on the Arduino Leonardo - another proven design.
Open-source ControLeo2 is fully compatible with the Arduino programming environment, and runs Arduino Leonardo sketches. A library and 15 sample programs for ControLeo2 has been posted to GitHub.
Reflow Wizard Intelligent software makes it easy to get your oven up and running. Ensures consistent results, run after run.
Reflow feedback If you connect ControLeo2 to a computer you can track the reflow progress and get data to plot a reflow temperature graph.
Servo support Supports industry-standard servos, so the oven door is automatically opened at the end of the reflow cycle to start the cooling process.
Build guide Our comprehensive build guide take you step-by step through building your own oven.
J-STD-020 compliance The Reflow Wizard is aware of the standards governing reflow ovens, and will auto-tune your oven so that it conforms to them.
Cheap China reflow oven (T962/T962A)
This oven has 4 infrared elements located directly above the boards. There are no heating elements below the boards.
Infrared is absorbed at different rates, so expect darker components to heat up much quicker than lighter ones.
The oven does not conform to the J-STD-020 reflow standard. Specifically, it fails to meet requirement 3.2.2: "It is required that this equipment use IR to heat only the air and not directly impinge upon the SMD Packages/ devices under test."
All the heat comes from the top. Imagine trying to reflow a microcontroller - the black microcontroller will absorb a lot of the infrared heat while shading the PCB underneath it. This creates a huge temperature differential!
Oven with single ON/OFF control
It is possible to build an oven with a single ON/OFF relay controlling power to the oven, but having control over individual heating elements has its benefits:
Better heat distribution. Keep heat away from sensitive components as much as possible.
Better control for hot-spot elimination.
Better control over heat direction.
Pre-soak = rapid rise in temperature. The lower elements are on full-blast. The upper elements are on half of the time.
Soak = stabilize temperature of PCB and components. The lower elements are on 3/4 of the time. The upper elements are on 1/4 of the time
Reflow = heat the solder and pads rapidly. The lower elements are on full-blast. The upper elements are on most of the time.
Better control over current draw. Instead of all-on/all-off, you can keep current draw at a more consistent level.
Here all the heat comes from the bottom, which is great for keeping heat away from sensitive components. Unfortunately:
Lead-free reflow is not possible. You'll burn the PCB long before the solder reflows.
No good automation means you need to keep a close eye on the reflow.
How do you follow the recommended reflow profile?
Reflow Wizard software
ControLeo2 ships with the "Reflow Wizard" software installed. The software is open-source and has 3 parts:
Test the outputs - helps you verify that the heater elements and convection fan (if applicable) work.
Oven setup - this part allows you to configure what each output controls. You can also set the maximum reflow temperature and door servo positions.
Reflow - This is where the magic happens!
The Reflow Wizard starts off in "learning mode". It looks at the configured hardware and maximum temperature, then takes an educated guess at how to achieve the correct reflow profile. It takes a few test runs to tune the duty cycle settings for each phase of the reflow cycle. Once it conforms to the J-STD-020 reflow standard, it exits learning mode. From then on, you'll get consistent runs time after time. The Wizard will continuously monitor the runs and make tiny adjustments if necessary.
You can follow the Wizard's performance and commentary by connecting ControLeo2 to a computer using USB.
The firmware running on ControLeo2 can be easily updated, following these instructions.
Step-by-step build instructions
Complete step-by-step instructions for building your own reflow oven can be found here.
ControLeo2 Test and Setup menu
ControLeo2 in action
ControLeo2 is open
There is no need to program ControLeo2 at all, but if you're a software guru you can tinker to your heart's content. We've open-sourced all the software we've written for ControLeo2, including the Reflow Wizard. The software consists of a single Arduino library that controls all of ControLeo2's functions, as well as 15 sample programs. You can find everything on GitHub (https://github.com/engineertype/ControLeo2)
ControLeo2 uses the standard Arduino environment. The library should be installed into your Arduino environment using the instructions found here: http://arduino.cc/en/Guide/Libraries. The single ControLeo2 library gives you access to all of ControLeo2's functionality. Installing the library also installs all the sample code we've written for it.
In Arduino, select the board as "Arduino Leonardo". Your sketches can then be sent to ControLeo2 using its micro-USB port.
ControLeo2 is expandable
ControLeo2 provides both 5V and 3.3V (max 80mA) to power additional components. There are 3 pins available for digital I/O (D3 is used for the servo).
ControLeo2 uses a quality off-the-shelf flame-retardant ABS plastic enclosure with a textured finish. The holes are CNC machined to perfectly fit ControLeo2. The result is a high quality, tight fitting case that looks very good. We are thrilled with this enclosure. Only the lid has holes; you'll need to make a hole to route your wires through the case.
ControLeo2 specifications and features
ATmega32u4 microcontroller with Arduino Leonardo boot loader
32Kb Flash memory
LCD display - 2 lines x 16 characters.
4 relay outputs - relays are connected using screw terminals or the 6-pin relay header (4 outputs, +5V, GND). The outputs provide up to 220mA at 5V. The outputs support connections to solid-state relays (SSRs) or mechanical relays
Buzzer - 80db at 10cm
2 momentary switches - for user input.
ABS plastic case - custom fit, flame-retardant (UL94-5VA)
MAX31855KASA thermocouple - capable of reading temperatures from -200°C to 1350°C using a k-type thermocouple.
Input voltage: 5V (USB or screw terminals) - For reliability and longevity, the screw terminals should be used to power ControLeo2. For solid-state relays, the 500mA provided by USB is sufficient to power ControLeo2 and the relays. For mechanical relays please use a 1000mA 5V power supply connected to the screw terminals.