I have contacts that are so close together I'm either bridging them, or melting the neighboring one. What am I missing?
Flux. You're missing flux, and lots of experience. I regularly solder with a tip that easily covers 10 or more pins at a time, but by carefully controlling how much solder is on the tip and using lots of flux I can get perfect solder joints. When soldering a TQFP or TSSOP package here's what I do:
- If the pads on the PCB are not super flat, then use some solder braid and suck up some of the solder on the pads to make them flat.
- Put the part on the PCB and carefully align the part. Don't rush this step, because if you mess this one up then nothing else will work correctly.
- Put a drop or two of liquid flux on the part. I use water soluble liquid flux, but others are successful with other liquid fluxes.
- Clean the iron tip and put a little bit of solder on it.
- Carefully touch a corner pad (NOT the pin itself) and let the solder wick up and tack down that pin.
- Repeat 4 & 5 for 2 to 4 corner pins. Reapply flux as required.
- Put some solder on the tip and run the tip down one complete side of the chip. Ideally you won't have bridges, but if the last 2 or 3 pins are bridged then you did good. Ignore the bridges.
- Add more flux (you can never have too much flux).
- Repeat 7 and 8 for all sides of the chip.
- Add flux, clean the tip on the sponge, and touch the tip to the bridge. Solder should stick to the tip. Repeat until bridges are gone.
- In bad cases, careful use of a solder wick can help. But be careful because it is easy to bend the pins and then you're, um, hosed.
- Clean the flux off. Some flux can be conductive, like the water soluble flux, so make sure it's clean (and dry) before powering up.
I should mention that my soldering iron has a straight, but angled tip. It's often called a chisel tip. This tip makes it easy to do everything from 1206's, 0402's, TQFP's, TSSOP's, etc. It just doesn't work for BGA's, QFN's, and some of the weirder things.
Use less solder, lots of flux, and practice.
Consider pre-soldering the pads on the PCB. Cover the area with some flux, and use your iron to push a bead of solder over the necessary pads. It is surprising (or was to me) how little solder was necessary. After the small amount of extra solder you have added to the pads have cooled, add a little more flux, place your device, and use just your iron to attach.
It takes practice, and it seems everybody prefers something a little different. I learned by watching and reading some of the superb sparkfun tutorials and other random youtube videos. I think watching other people in action is the best way to learn.
To solder an item like that you need to:
- Use flux
- Make sure your iron is clean and tinned
- Have your soldering iron hot enough that your solder will melt as soon as you touch it to it
- Use a solder diameter that is rather narrow
- Heat up your trace and pad and then slide the solder into it
I think I have everything covered, am I missing anything?
Besides flux (to prevent a short in the first place): solder wick! (to remove excess solder after the fact)
You can try to wrap some steel wire around the shaft of your iron, and use that as a makeshift extension. Clamping a sewing needle to the shaft worked for me, too.
You need lots of flux, less solder.
If even that fails, and you need to solder some really tricky stuff like BGAs, I have some other tricks in the box, like stove-soldering, etc. Those tricks are likely to break your hardware, so I'm not gonna advice them before suggesting the needle-trick.