Reflow Controller Shield

Up & Running

• When the Arduino board together with the shield is being powered up, you’ll notice a splash screen indicating the firmware revision will appear on the 8×2 alphanumeric LCD. The buzzer will also beep with red LED turn on for a duration of 2 seconds.
• Once the start up sequence is completed, the board will enter the idle state where it is ready to perform the reflow process. If a valid type K thermocouple wire is connected, the board will display it’s current temperature reading in Degree Celsius. You can check whether the temperature is increasing by rubbing your fingers on the tip of the thermocouple wires. If the temperature decreases when you do that, you might have connected the thermocouple wires in a reverse direction.
• When no thermocouple is connected to the board, a “TC Error” status will be displayed on the LCD. Any attempt to start the reflow process will not be executed. If you connect a thermocouple on the fly while the system is running, it will be able to detect the thermocouple wire and the error status will revert to the ready status.
• Now we are ready make the first run of the reflow oven. We advise not to put any real board for the reflow process first except the board used for temperature monitoring. In order to check the reflow curve output of the system, connect any terminal software at 57600 bps to get the real time temperature data in the oven during the reflow process. This data can be used to plot and verify the reflow curve later on. Once everything is ready, you can press the push button “SW1” to start the reflow process. This “SW1” push button acts as a start & stop reflow process button. You’ll also notice that the red LED will start blinking at 1 second rate. If you have a terminal software running, you’ll notice the current temperature in the oven together with few other useful parameters will be sent to the computer like the screenshot below. The time and input values can be used to plot the reflow curve.
• The whole reflow process will basically go through Preheat->Soak->Reflow->Cool sequence. All these stages is explained in the preceding sections.
• The first stage will be the preheat stage where the temperature will be increased from room temperature to 150 °C at 1-3 °C per second rate. You’ll also notice that the current set point sent to the terminal will be 150 °C. You are only allowed to start the reflow process if the current temperature is lower than 50°C. This is to ensure that the components does not experience thermal shock if it was at room temperature prior to the process. But, you can change this temperature value in the sketch itself.
• Once the preheat stage is completed, the process will enter the soaking stage where the temperature will be increased at a lower rate of 0.5-1.5 °C per second from 150-200 °C. You’ll notice that the set point will be increased at a 5 Degree Celcius step until it reaches 200 °C. This is to allow the temperature to rise at a less ramp compared to the preheat stage. This is an important stage which serve as a solder paste oxides removal process and to activate the fluxes.
• Once the soaking stage is completed, the process will enter the most crucial stage; reflow. Temperature will be increased from 200 °C to 245 °C at 1-3 °C per second rate. Once the peak temperature is achieved, the temperature in the oven is allowed to cool down to room temperature. You are free to open the oven door slowly to help the cooling process as long as the temperature does not decrease at a rate higher than 6 °C per second. This is important to avoid any thermal shock on the components. PID controlled oven door powered by servo motor anyone? The cooling process is deemed to be completed once it reaches 100 °C (yes, we are impatience). Once completed, a “Complete” status on the LCD will be displayed. The buzzer will also beep with the red LED on for 1 second.
• Now, you can retrieve the temperature data received on the terminal and plot them to get the reflow curve. If everything goes as plan, you’ll have something like the following curve. Please ensure that the reflow curve obey all the necessary temperature increment rate and duration of each stages discussed above.
• However, if your reflow curve does not look like the above curve, you’ll need to do some PID parameters adjustment and tuning to make it work.