REFLOW SOLDERING
A reflow soldering oven and mobile applications for its managing are presented in the diploma thesis. The device is appropriate especially for making of prototype products.
The reflow oven is used for soldering of SMT circuits. A lot of SMT components are extremely small, some of them do not even include connections, which would enable soldering in a classical way, with a torch. Therefore, the only possible way is soldering in a reflow oven.
The reflow oven is actually an oven, where a circuit is exposed to controlled heating. The temperature has to be accurately set because too high deviation in temperature reflects in the quality of a joint and therefore possibility of a component failure if they are exposed to too high temperature for too long. To follow the temperature profile well, it is therefore essential to assure enough power of heating and cooling at the same time when necessary. For cooling, a trap has been installed, operated by a servomotor. The position of temperature sensor has presented the additional problem for the assurance of good results. IR-heaters have been used for heating. It is typical for infrared heating that it warms up the objects and not the air between.
The diploma thesis describes the main problems, which appear when spolding with reflow and solutions for them. There are phases described, which define the temperature profile. It is essential to assure that the actual temperature in the oven follows as musch as possible the temperature profile.
For basic reflow oven, a table oven has been used, where new components have been installed. The procedure of processing of the table oven and the used component has been described.
Heating in the oven has been done with a discrete PID-regulation. The used equations are presented and the setting rules, which have given the approximate parameter values. The indicators of quality with tracking regulation have helped with optimization of the parameters.
A program on microcontroller and Android application on a mobile phone have been described as well in the diploma thesis. The Android application connects with the oven with Bluetooth connection. We can change all key parameters, important for working of the oven with the application. It also enables a graphic presentation of actual and wanted temperature in the oven in the real time.
All the systems, which have been used in the reflow oven, have proved very efficient. Cooling with a ventilator and a trap enables much better cooling of the oven than opening the door of the oven in the phase of cooling. Discreet PID-regulation enables good following of the temperature profile. With reaction of graduate stirring, the flow of the stationary state does not exceed +⁄(-1 °C).
Following the temperature profile with time changing of reference value is very successful. The user interface has proved as very reliable and it enables changes of all key parameters, important for the working of the oven. It also enables graphic presentation of the wanted and actual temperature in the oven.
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