Milled circuit board with SMD components.

I've had another try at improving circuit boards to use surface mount components. As an experiment I tried using some Chinese 0.2mm 30 degree carbide cutters - the results are excellent, clean edges to the cuts when milled 0.12mm deep. Best of all they are as cheap as chips, around £6 for a pack of 6.

Previous efforts at mounting SMD's have always looked scruffy, even though electrically sound. The problem was always getting an appropriately small amount of solder on the joint even though using solder paste.

My breakthrough was to thin down the solder paste with an alcohol based flux to such an extent that a small drop could be picked up on the end of a cocktail stick and transferred to a component pad. It is surprising how little is needed to form a good looking joint!! Once both pads are treated with paste, the component can be placed and positioned - again using a cocktail stick, and finally held in place and soldered. I use a 0.8mm 370 degree C pencil bit to solder with no additional flux or solder necessary.

When mounting IC's, I firstly solder one corner pin to get the positioning exact, followed by an opposite corner pin to ensure all the remaining pins line up with their respective pads. Lastly a drop of thinned solder paste is placed on all the remaining pins and the soldering completed. Finally the board is washed in IPA to remove any remaining solder paste and flux (probably unnecessary, but I'm super cautious).

Picture below shows a completed board - some of the components have excessive solder before I found the right amount od thinned solder paste to apply.