Solder bumping is a type of flip chip bumping that involves placing underbump metallization over the bond pad through a method of sputtering, plating, or another similar process. It is performed at the wafer level and thus involves very small components in the process. It is one of many different types of flip chip bumping and is a preferred form of bumping.
Flip chip bumping itself is the process of forming a bump on the bond pad of the die. By creating these bumps it serves a variety of purposes. First and foremost, flip chip bumping provides an electrical connection between the die and the board or substrate involved, allowing for it to control the substrate with various processes. Another reason for flip chip bumping is in order to provide thermal conduction from the chip to the substrate. This helps to dissipate the heat so that the flip chip does not over heat and cause problems. A third use for bumping is to use the bump to act as a spacer and prevent electrical shortage between the chip circuit and the substrate circuit. The last purpose for bumping is providing mechanical support to the flip chip itself.
The process of specifically solder bumping is separated from other types of flip chip bumping because, as stated before, it uses underbump metallization. Also known as UBM, by performing underbump metallization it removes the passivating oxide layer from the bond pad as well as defines the solder-wetted area. The solder may then be deposited over the UBM as a means of maintaining electrical stability. This can be done through a number of different processes, such as evaporation, electroplating, screen-printing, and many other types of depositing techniques.
Solder bumping is of course done on a microscopic level. The solder-bumped wafers are sawn into each individual flip-chip that are then mounted on the substrate through subjecting the assembly to a temperature high enough to melt the solder in order to form the interconnection of parts.