We have to use non lead solder by law over here, and due to the size of our shop, everything is done by hand.
There is a science of soldering, but some of the indicators we use for lead solder don't work for non lead solder.
Firstly, you'll never get a shiny joint: non lead gives a dull grainy look, but if you understand the science, the joints are as good.
So here's the facts:
1) Non lead melts at a higher temperature. This means that youve got to put more power into the joint, as you have to raise the PCB trace, the solder and the component temperature up by about 20 degrees. We use 80W solder stations set to 320 to 380 degrees C for this. The actual temperature at the tip while heating everything on the board goes to about 250 degrees C
2) The activity level of the flux is vital to soldering, especially to re-work of old, more corroded boards. Because lead solder flows better, the flux (which de-oxides the parts and allows the sodler to "stick") tends to be less agressive. We use a L0 category flux ( the US equivalent is RMA?) which is a medium activity flux. You need a more agressive flux to de-oxidise, and keep the parts clean while exposing them to higher temperatures. You can use higher agression fluxes, but they require very good cleaning after soldering, or they keep etching away ( fluxes are acids).
3) The amount of flux in the solder wire is important. We use a 2% by volume flux. Normal solders have a 1% flux. The extra flux wets and de-oxideses the joints better for a given volume of solder on the joint.
4) 2-3 seconds of heat per joint. You need to make sure that once the solder has started to melt that it flows properly around the joint and PCB trace. Now if soldering an IC, the time needs to be short, as ultimately you'll melt (or partially melt) the solder inside the IC. This is a factor of actual temperature on the solder tip ( not what the temperature guage on the soldering iron says) and the time applied. As a tip, apply the solder first, and heat the solder, not the joint. The latent heat needed to melt the solder reduces the actual temperature of the tip. You'll usually hear the opposite in older manuals - heat the joint and apply the solder. With modern ICs this is a factor in reducing their working life. Solder the other way around.
5) Gravity. With through hole soldering, solder the pins from the end side (component down), and let gravity suck the solder down the through hole towards the component ( also aids #4 above).
6) Amount of solder. As it melts, apply it until the joint starts to go concave as the solder flows up the leg of the component. Do not apply too much, or too little ( too little is better than too much though)
7) Inspection. Do this imediately after each joint, as it's impossible to focus on an entire board. All you can check is that the solder joint looks concave. This is the best indication that you have applied the right amount of solder, at the right heat. It doesn't actually guarantee that the joint is good - no visual inspection can do this, but it erradicates the common errors
8) Component leg cropping. Ideally, the legs should be cropped to the right height before insertion and soldering. This is because a bigger leg acts as a heat sink, so the solder doesn't flow as well, and because cutting the lead afterwards stresses the solder joint. When cropping, cut each leg, one at a time with sharp cutters, just above the solder joint.
9) Cleaning the board. Don't do it! Use rosin and halide free "no clean" flux( rosin & halide free = fumes don't mess with your lungs). It leaves a white waxy residue on the board which is ugly but harmless. Cleaning a board (unless done rigourously)actually just spreads impurities and possibly still active flux across the entire board. Customers often demand clean boards however - re-education required?
10) Avoid re-work. Get it right first time. Every time you re-work, you potentially damage parts.
Sounds easy? No you're right it's not. Leaded solder is very much more forgiving. It's taken us 3 years to get this right - if you can legally get away with leaded soldler, do so.