SMD Chips or ICs are not as easy to solder as SMD or through-hole components since alignment of SMD IC pins on PCB pads is extremely difficult because of the very fine pitch of these IC pins. Soldering process of SMD ICs is more difficult and differs from that of small SMD components.
1. The soldering process for an SMD IC should start by putting flux on all the IC pads on the PCB. Flux actually ensures even spreading of solder on a pad which eventually helps in stronger bonding of the pin on the pad because the flux itself gets burnt in a flux cored solder.
2. After putting flux on all pads, SMD IC is to be aligned over the pads with tweezers so that each pin settles on its pad and no PCB pad has two pins over it.
3. A small amount of solder is to be put on the tip of soldering iron to solder a single pin of the IC on the pad. Two different techniques can work well for soldering a single pin:
In case of very fine pitch ICs, Soldering iron can be dragged on the PCB towards the pin that has to be soldered, when soldering iron gets in touch with the pin, the solder quickly goes on to the pad because of the flux and the IC pin is soldered.
ICs with large pitched pins can be soldered by directly applying solder to each pad while the pin is placed over it.
4. Once a single pin has been soldered, its position and alignment on the PCB should be verified and corrected by melting the soldering again if required. Internal connections within the PCB can be damaged if a pin is heated for longer durations of time so it should be avoided.
If an IC has very fine pitched pins, a thin soldering wire can be placed on its pins and melted with a soldering iron so that the solder attaches the IC pics to the pads on the PCB.