Solder Reflow Oven & Control
Our project consists of making a reflow soldering device using a normal toaster oven with a graphical LCD display for control and GUI. Soldering is an important and difficult task for custom printed circuit board design especially for integrated circuits that come as chip packages that are impossible to solder by hand. This is particularly true for ball grid arrays (BGA) and small-pitch quad flat packs. If one chooses to design a custom printed circuit board around these chips, then the designer may wish to also purchase a stencil of the designed board that would allow him to squeegee solderpaste precisely on the SMD pads. The designer would then carefully place the components on the board, and heat the solderpaste with a heat gun or a reflow soldering oven. The problem with soldering ovens is that they are expensive and cost thousands of dollars. We have decided to come up with a cheap and working solution to the problem by using a normal toaster oven and controlling it through a microcontroller along with an LCD display that guides the user through the soldering process and constantly provides feedback on the state of the system while reflow soldering. The input to the system would be via a conventional keypad and would consist of target temperature point at specific times that the user would enter based on the solderpaste's recommended tempearture profile. The system would interpolate the temperatures for the in-between time intervals and follow the curve generated by the input. The system would also fulfill the appropriate safety requirements and have the capability of aborting the process in case of a mishap.
High Level Design
Rationale and source:
The source of the project was one of the team members Ko Ihara who as part of his M.Eng. project worked on designing a circuit board and came up with the idea of using a toaster oven for reflow soldering. The project idea fully complies with the requirements of the course and the challenging part is coming up with a workable PID feedback control to make the toaster oven follow the temperature curve and heat up or cool down at appropriate times. The Atmel mega32 chip is sufficient for this project as the speed of the chip and the number of I/O pins suffices our needs. Another thing about the project is that it would benefit future students in the course since they would be able to solder boards with less pain and high efficiency and safety.
We are happy with the performance of our system. One of the problems we faced was cooling the system i.e. if the future target points show a decrease in temperature at a steep gradient, then the actual curve would be slightly off. This is due to the inertia of the oven. The heating coil retains the heat for a while even though the oven is off. This causes a slower decay in temperature. Similarly, a steep rise in temperature is also not readily achievable due to the heating limitation of the toaster oven. One of our future advancement would be to add a cooling system to the project. We can add fans that are triggered if the current temperature is higher then the target temperature. Another idea is to use a fan to blow hot air in the oven instead of using the heating coil. This way the same blower can be used to heat and cool the system by changing the temperature of the air blown in. The toaster oven used was an old one and had an inaccurate temperature controller inside which caused it to shutdown sometime even though the temperature was below the specification on the oven. This hindered our project a little particularly in heating up the oven. But this can be resolved by using a better quality oven.
Link: http://instruct1.cit.cornell.edu/courses/e...page/index.html
Our project consists of making a reflow soldering device using a normal toaster oven with a graphical LCD display for control and GUI. Soldering is an important and difficult task for custom printed circuit board design especially for integrated circuits that come as chip packages that are impossible to solder by hand. This is particularly true for ball grid arrays (BGA) and small-pitch quad flat packs. If one chooses to design a custom printed circuit board around these chips, then the designer may wish to also purchase a stencil of the designed board that would allow him to squeegee solderpaste precisely on the SMD pads. The designer would then carefully place the components on the board, and heat the solderpaste with a heat gun or a reflow soldering oven. The problem with soldering ovens is that they are expensive and cost thousands of dollars. We have decided to come up with a cheap and working solution to the problem by using a normal toaster oven and controlling it through a microcontroller along with an LCD display that guides the user through the soldering process and constantly provides feedback on the state of the system while reflow soldering. The input to the system would be via a conventional keypad and would consist of target temperature point at specific times that the user would enter based on the solderpaste's recommended tempearture profile. The system would interpolate the temperatures for the in-between time intervals and follow the curve generated by the input. The system would also fulfill the appropriate safety requirements and have the capability of aborting the process in case of a mishap.
High Level Design
Rationale and source:
The source of the project was one of the team members Ko Ihara who as part of his M.Eng. project worked on designing a circuit board and came up with the idea of using a toaster oven for reflow soldering. The project idea fully complies with the requirements of the course and the challenging part is coming up with a workable PID feedback control to make the toaster oven follow the temperature curve and heat up or cool down at appropriate times. The Atmel mega32 chip is sufficient for this project as the speed of the chip and the number of I/O pins suffices our needs. Another thing about the project is that it would benefit future students in the course since they would be able to solder boards with less pain and high efficiency and safety.
We are happy with the performance of our system. One of the problems we faced was cooling the system i.e. if the future target points show a decrease in temperature at a steep gradient, then the actual curve would be slightly off. This is due to the inertia of the oven. The heating coil retains the heat for a while even though the oven is off. This causes a slower decay in temperature. Similarly, a steep rise in temperature is also not readily achievable due to the heating limitation of the toaster oven. One of our future advancement would be to add a cooling system to the project. We can add fans that are triggered if the current temperature is higher then the target temperature. Another idea is to use a fan to blow hot air in the oven instead of using the heating coil. This way the same blower can be used to heat and cool the system by changing the temperature of the air blown in. The toaster oven used was an old one and had an inaccurate temperature controller inside which caused it to shutdown sometime even though the temperature was below the specification on the oven. This hindered our project a little particularly in heating up the oven. But this can be resolved by using a better quality oven.
Link: http://instruct1.cit.cornell.edu/courses/e...page/index.html