How to dispense solder paste for small SMD pads as 0402 and 0201

How to manually assemble 0402 / 0201 SMD components

I prefer to always 0603 components, because they are very easy to assemble by hand. Assembling the smaller 0402 parts by hand is not that easy. You must be able to apply micro dots of solder paste, otherwise you will get short circuits. Spoty is a solder paste dispenser developed to address the challenge of applying extremely small amounts of solder paste:

Precision micro-dot solder paste dispenser for SMD pads as 0402 / 0201

This video demonstrates how to apply tin to the small 0402 parts with the Spoty solder paste dispenser:

Placing the SMD 0402 parts manually. If the components are close together you need very fine tweezers:

I always place all SMD components on the PCB first, without aligning them exactly. Alignment during assembling makes no sense because you always accidentally bump to another component. When all components are in place, I align them using a sewing needle:

More about solder paste

• Solder paste is thixotropic, to lower the viscosity, it may be needed to stir the paste.
• The paste must be at room temperature before use.
• Note that the volume of the soldered joint is about half that of the solder paste applied.
• There are special solder pastes for dispensing and stenciling.
• Chip Quik: shelf life refrigerated 3-8C (37-46F) > 6 months, unrefrigerated > 2 months.
• Chip Quik: allow 4 hours for solder paste to reach an operating temperature of 20-25C (68-77F) before use.

Solder pastes are classified based on the particle size, from type1 (160 µm) to type8 (11 µm), see Wikipedia.

Here you can see the solder paste with the solder ball particles very well here:

Solder paste with solder ball particles

Common solder paste that works fine for stencils doesn't work with a dispenser, it is too syrupy:

Precisely dispense the smallest amount of solder paste

The main thing that goes wrong with soldering surface-mounted devices is the excess of solder. On this extremely small PCB from an iPod touch, which contains 0201 size SMD, you can see how little solder paste is used:

iPod touch micro PCB with 0201 size SMD

Real size

After the components have been placed, you can solder the board as you like, with a reflow oven or hot air. I use the Atten AT858D to solder SMD parts, it is important that you can control both the temperature and the airflow.

Solder paste dispenser step 1Solder paste dispenser step 2SolderedSoldered