Open (beggars version) reflow soldering

Introduction

Far-infrared heating, placed above the PCB, with a fan below to dissipate heat, can achieve two-sided (twice) patch welding; three thermocouples, real-time monitoring of the temperature of the heating plate, the temperature of the upper surface and lower surface of the PCB; the stepper motor automatically Lift and lower, cooling down faster after welding

characteristic

• Using 500W far-infrared ceramic heating plate, PWM + thyristor to achieve temperature adjustment, PCB heating area <120X120mm
• Heating is performed from the top of the PCB and the fan below dissipates heat. By controlling the temperature difference between the upper and lower surfaces of the PCB, it is ensured that the lower components do not fall out when the upper layer is welded.
• Use 3 thermocouples to monitor the heating plate temperature, PCB upper surface and lower surface temperature in real time
• A stepper motor is used to automatically lift the working platform. When placing the board, the platform is lowered to the lowest level so that there is enough space for manual placement. It automatically rises to the appropriate position during heating; after the welding is completed, it is lowered to the lowest level and cooperates with the fan for heat dissipation, which can achieve rapid cool down
• Use high temperature resistant magnets to quickly fix the PCB
• Touch screen operation, one-button start, real-time temperature curve can be viewed

structure

• The upper and lower multi-layer structure, the upper and lower bases are made of wooden boards (ready at home, CNC processing is also convenient), connected and fixed through four 6mm diameter optical axes
• The upper layer of the working platform is made of high-temperature-resistant mica board, and the lower layer is made of bakelite board. A fan, optical axis slider and screw nut are installed in the middle. The working platform is lifted and lowered by a stepper motor.
• The heating plate is fixed on the upper base plate through bayonet
• 3 circuit boards: power board, control board and display board, installed on the upper base board; using a 42 stepper motor with its own drive board

Circuit diagram

Known issues:

1. The two chip selects of the MAX6675 chip are connected to the IO with only input function. Since the output IO is not enough, the stepper motor enable pin IO and the buzzer IO can only be used.

2. The figure 8 socket package is inconsistent with the actual size

3. The heating plate and the upper base wooden board are not insulated, and the upper base wooden board is deformed after being heated, causing the center of the optical axis of the upper and lower base to be misaligned, and the lifting of the working platform is blocked.

4. The temperature of the heating plate is high and there is no protection around it. There is a risk of burns due to accidental touching of the hand.

Structural optimization:

1. The upper and lower base plates are made of bakelite boards

2. Surround the heating plate with mica boards to reduce heat loss and avoid accidental burns.

3. Design a touch display housing

4. Add lighting

5. Choose a smaller stepper motor

Software optimization

1. Heating PID parameter optimization, support parameter modification

2. Add PID control to the fan and support parameter modification

3. Interface optimization

Accessories purchase link

• Far infrared ceramic heating plate (120X120MM)
• High temperature mica plate (thickness 5MM)
• Bakelite board (thickness 5MM)
• touch display
• 42 stepper motor with driver board
• Screw and other accessories (length 200MM)
• High temperature magnet (diameter 8MM, thickness 5MM)

The notch on the right side of the control panel is the location of the power switch, which has not yet been installed.

Touch display panel temporarily fixed

Two iron plates are placed under the mica board to use high-temperature magnets to quickly fix the PCB board.

For the upper and lower K-type thermocouples, several small plates were made from epoxy boards and stuck on high-temperature magnets to quickly fix the PCB board. Because high-temperature magnets are expensive, only 2 have been made so far.

Welding effect, I found a random board and only put a few components on it