surface mount threaded insert

Philips were doing mid-air splices from the 1930s onwards; they had a system known jokingly as a "Mitcham tagstrip"* where the component wires were shoved into a 'spring' (which looked as though it was made by winding tinned copper wire around a 3mm drill, then they flooding it with solder. (I have used it many times when I needed to join a lot of wires together and didn't have a convenient solder tag).

• The UK Philips plant was at Mitcham

Be very careful, large soldered mounting points can cool at the centre due to the component extracting the heat - and at the edge due to the cooler surroundings. This leaves a circle of solder which cools slower and under contraction to give a ring of dry joint. Eventually the board develops mysterious open-circuits because the centre of the tag is no longer connected to the track.

I know it can happen because I have fault-found it on several occasions.

I think the problem was made worse by some board-soldering machines that vibrated the boards after soldering, to remove any loose bits. The large pads hadn't quite completed solidifying and the ring of pasty solder became a dry joint. It was quite instructive to tap the board and see a ring of little sparks appearing in (what appeared to be) a perfectly good solder blob.

..

I trust the flange for mechanical support, but for the next board I could do a few test holes and pry them off and measure the required force.

-- mikko

We have some samples coming to abuse.

Worst case, we could add more solder to fill the barrel space. That would be a manual soldering operation, but not bad.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics