For one of my projects i had to use the LTC3526 Boost Switching regulator chip from Linear. It is a great chip. One downside being an extremely small 2mmx2mm DFN package
I never soldered a chip with this fine pitch. But i thought i’d give it a try. Got couple of LTC3526 as samples and the PCB from OSH-Park. Result shown below. Not bad for hand soldering
I usually stayed away from chips with this kind of footprint because i was not sure i could solder them. This gives me a bit more confidence.
One reason the soldering here worked is because the sides of the chip do expose a tiny amount of the pad, albeit flush with the package.
If there are tips to hand solder these packages, I feel that these are important.
- Get yourself some really fine point soldering tips. Definitely a temperate controlled soldering station. I used the Hakko-936
- The pads on the PCB have to project at-least 8~10mils outside of the IC package. This way your soldering iron tip can solder the pads and the solder will reach the IC package due to capillary action.
- Use Flux. Lots of it. Don’t use the no-clean variety. These flux are acid based and cause resistance shorts. Always use rosin flux (liquid or gel)
- Always clean your solder joints after soldering using rubbing alcohol. I use Q-tips for cleaning the solder. Then inspect the joints using a magnifier.
- Always keep your soldering tip clean and without oxidation. Use a wet sponge to clean the tip often.
- Try to use the thinnest soldering wire you can get. That way the solder tip will not pick up much solder. Else you will end up solder bridges.
- First apply flux to the PCB pads using a toothpick. Place the IC over the pads using a tweezer. I used a toothpick to first correctly orient the IC over the pads. I used a 40x jewelers loupe to confirm that. Then use the toothpick to press down on the package with one hand. Solder with the other. Use rubbing alcohol and Q-tips to clean up the flux residue. Use the loupe to confirm good solder joint. If not, repeat flux and solder.
- Lots of good lighting around the soldering area.