After seeing the discussion on how to correctly setup QFN footprints, I thought I’d share how I hand soldered the new ATTiny816 20pin VQFN, which has a central pad and 0.45mm lead spacing, in a 3x3mm package.
The method I used was essentially to place a reasonable sized plated through hole in the centre of the pad of the PCB.
The soldering process is then to;
- Pre-tin the pad
- Clean the residue
- Apply flux
- Hold the board level in a fixture so that you have access to the underside
- Place the component
- Using wetted/tinned iron apply the iron tip to the underside of the through hole
- Once heated you will notice that slight up and down movement of the iron tip will raise and lower the chip. This slight movement will help to align it to the footprint.
- Carefully lower the iron and it will pull the chip down onto the pad
- Once cooled the leads can be soldered
This method is applicable to other small thermal pad components.
The image below shows the board with VQFN soldered in place and on the right the bare PCB, showing the central hole.
As a disclaimer, there will likely be a higher failure rate using this compared to the correct profile in a re-flow oven, but beggars cant be choosers.