Q. Can I hand-mount fine-pitch lead devices?
With leads as small as 0.8 mm pitch, hand mounting gets very finicky. A colleague reckons he can mount one in five minutes having had some practice. He tacks a couple of leads to hold the chip in place, then blobs the leads with a solder specially designed for surface-mount devices. This has silver in it, and is better at wetting contacts than ordinary solder. It doesn't matter if the leads are all blobbed together, the surplus is then mopped up by solder wick. The silver solder is ten times more expensive, so it grates that most of it ends up in the solder wick, but ordinary solder just doesn't make joints reliably.
Q. My flatpack chips go through the surface mount machine but joints don't form on one side. Why?
As the chip passes the solder wave, the wave hits the leading edge and side edges, but the wave does not re-form on the trailing edge fast enough to hit the leads. It's like the wake of a moving boat. There's not much you can do at this stage apart from be aware of this problem and check after surface mounting.
The problem has to be avoided early, at the PCB layout stage. The solution is to place the chip rotated by 45 degrees. The solder wave flows round the edges much easier.
If you look at a lot of consumer electronics, you'll often see this technique used. But I notice not in my PC motherboard and PC cards. That's because they don't use a solder wave. Instead, solder paste is applied through a silk screen mask, and melted with infra-red or hot air jets. Solder wave is a cheaper process, which is why it gets used in less expensive products.
Q: Boards from the solder wave machine often have leads solder blobbed together. Why?
As the wave passes along, surface tension pulls the wave from one pin to the next. This is fine until the last pin or two in the row, and there are no more pins to pull at the solder wave. So solder blobs tend to accumulate there.
This problem again has to be avoided at the PCB layout stage. The solution is to put little copper pads after the last pins passing the solder wave. These are called "solder thieves", because they steal the surplus solder from the end pins to a pad where it can do no harm.