Reflow Oven System Ryan Kennedy ELT2720 Project 2008

Reflow soldering Reflow soldering is a process in which a solder paste is used to temporarily hold electrical components to their attachment pads on a PCB, after which the assembly is heated over a carefully controlled thermal profile inside an oven in order to solder the joint. For my project I built a small automated reflow oven system.

Reflow Soldering Thermal Profile Courtesy: Robert Lacoste (2004)

System Diagram MCU and control circuitry Heating status LEDs Control buttons and power switch Thermocouple Reflow Oven Solid State Relay Wall jack (temperature probe)

The brains of this system exist in the code which is programmed into the MCU. That program follows this flow diagram. Power On Start button pressed? Temp less than 100 o C? 120 seconds elapsed? Oven temp 220 o C? Turn oven on. Hold temp around 100 o C for 120 seconds. Bring oven temp up to 220 o C. Shut down oven and begin cooling. Yes No Yes No (temp must be 100) No

Circuit Board Schematic AD594 HCS12

Complete System Power Jack (8 to 25 VDC) Serial Port Control Board Solid State Relay Circuit Board Thermocouple

This system is ideal for the hobbyist that can’t afford to pay $5000 for the current reflow ovens that are on the market which are really only designed for industrial use. And if someone was only soldering a small project, using a large industrial reflow oven would be a huge waste of energy for a single small PCB. This system also saves energy because of it’s reprogram ability. One doesn’t need to construct a whole new system if a different type of solder is being used. Be it lead, tin or whatever, the user can upload whatever program is needed into the MCU to achieve reflow.

In the Future LCD showing current temperature inside oven. Solenoid to open oven door when heating is complete. Circulation system to ensure even temperature inside oven. Neater power cord harness.