Low cost solder paste dispenser

Easy to build but very capable and handy DIY solder paste dispenser built mostly from cheap Ebay components and modules.

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Already finished and nicely working solder paste dispenser. Powered with cheap ebay mini DC motor with gearbox (100RPM) and long M3 shaft secured by two axial bearings also from ebay. Body of both control box and dispenser is fully 3D printed. Accepts standard ebay 3ml luer lock syringes. Firmware supports dispensing speed configuration and also retraction to prevent leaks. Push button is available on the control box as well as on the handheld unit to be able to control the dispensing according to personal preferences.

Schematic is as simple as it gets. Power supply with basic protection, motor driver with voltage and current sensing and MCU to control the functionality.

MCU module with 3V3 regulator is bought from ebay, H-bridge and supply protection circuitry is hand soldered on piece of prototype PCB. Layout has not been created.Mechanically the dispenser has two parts. Handheld dispenser and stationary control box. Handheld dispenser is 3D printed chassis with motor mounted inside and slot for 3cc syringe with luer lock.

Control box contains main switch button, display, three control buttons, XLR4 connector to connect to handheld unit and banana sockets to power it. Control buttons are created from the standard cheapest standard micro switches and some simple mechanics. It is all 3D printed, very easily from PLA, without any supports. STL files are provided.

RevAC - Firmware and CubeMX.7z

Microcontroller pin mapping (aka hardware-firmware interface) using STM32 CubeMX and complete firmware for AC6 system workbench. Includes display driver. Tested during real PCB assembly and works like a charm.

7-Zip - 823.35 kB - 08/30/2020 at 15:10


RevAB - Electrical, KiCad.7z

Kicad electrical drawing, pdf included.

7-Zip - 245.44 kB - 01/31/2020 at 20:49


RevAB - Mechanical, Freecad.7z

Freecad 3D models for all the components (control box and handheld dispenser).

7-Zip - 5.40 MB - 01/31/2020 at 20:46


  • 1 × IIC I2C 0.91"128x32 Blue OLED LCD Display Module Source: ebay, approx 2 €
  • 1 × STM32F030F4P6 Mini System Board Source: ebay, approx 1 €
  • 1 × DC 6v 100RPM long shaft Mini Micro Metal Gear Motor Source: ebay, approx 3 €
  • 2 × 2pcs Axial Ball Thrust Bearing F3-8M 3 mm*8 mm*3.5 mm 3× 8× 3.5mm For RC Model Source: ebay, approx 1 €
  • 4 × 20PCS 6x6x5mm DIP Through-Hole 4pin Tactile Push Button Switch Momentary Source: ebay, approx 1 € for 20 pcs

View all 7 components

  • Tested during real PCB assembly and works like a charm !!!

    kevarek08/30/2020 at 15:27 0 comments

     So the solder paste dispenser is finally ready for daily use and tested.

    In normal mode:
    - middle button pulls (retracts) the paste with maximum speed while the button is pressed
    - right button pushes the paste (first with maximum speed for retract duration and after that with user defined speed), when released it immediately retracts (pulls) the paste for user defined time.

    Other modes are just configuration of speed and retraction time.

    Configuration of push speed
    and configuration of retraction duration:

    And here is the first result (PCB milled with my CNC3018PRO, isolated current sensor 50A)

    Im very satisfied with the result - the whole process of soldering with solder paste needs a bit of practice but it makes the PCB assembly much more efficient than with solder wire.

View project log

  • 1
    Prepare syringe holder and piston assembly
  • 2
    Assemble piston
  • 3
    Assemble syringe holder

View all 12 instructions

Enjoy this project?



Valentin Kirov wrote 07/03/2020 at 10:26 point

How can I load the firmware onto the STM32?

  Are you sure? yes | no

kevarek wrote 07/03/2020 at 21:07 point

Check "stlink v2" for instance on ebay... like 2$

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Ryan wrote 02/17/2020 at 04:54 point

This is awesome! I can imagine being able to input the type of pad you are dispensing on (SOIC8, 0603, etc) and having a precise amount dispensed onto the pad. Precision!!!

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kevarek wrote 02/17/2020 at 15:46 point

It would be possible to change the motor to same size stepper with gearbox. This would allow you to control the dispensed amount. But the biggest enemy is the elasticity of the system (syringe mostly) and a bit the hysteresis of the drive.

Trust me after testing this many times, the best is visual feedback and manual control. You can easily dispense solder paste on 0603 pads. SOIC or LQFP pads are typically dispensed all pins in one line and this works as well with this dispenser.

  Are you sure? yes | no

kevarek wrote 02/03/2020 at 18:48 point

Hi, thanks for comment. I dont have dispensing amount sensing or control. You can set dispensing speed [%] and retraction duration after dispensing [ms].

So you press and hold the push button (on the syringe or on the control box), piston pushes forward for specified retraction duration in order to preload the solder paste and continues with predefined dispensing speed. In any time when you release the push button, the piston is moved back with maximum speed for predefined retraction duration to reduce internal pressure (elastic strain of plastic syringe etc) which causes the unwanted leakage. This whole retraction behavior is nicely described in context of 3D printers - check google.

Anyway I have tried it many times already and it works perfectly for hand assembly and reflow of SMD components ranging from 1210 or SMC packages to fine pitch packages like LQFP100.

I plan to shoot and upload demonstration video after I will receive the display module from China.

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Dan Maloney wrote 02/03/2020 at 16:09 point

Nice! Do you have control of the drop size for each actuation? Or do you just control it by the amount of time you press the switch?

  Are you sure? yes | no

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