Copper Pillar

A typical solder bump is used to connect a silicon die to its package and form an electrical path on the between the two. With passing time, however, the use of conventional or traditional solder bumps is being replaced by more advanced bumps such as the copper pillar.

The use of copper pillar technology began in 2001 by IBM and has spread since then to a wide array of applications, particularly adopted by outsourced semiconductor assembly and test providers, or OSAT providers. In fact, it is predicted to become the single most dominant form of interconnect used in the flip chip industry in the near future with 75% of flip chip companies using this tech.

What is a Copper Pillar?

A thermal copper pillar bump is a thermoelectric device that enables forming the first level interconnects between the die and the substrate. Typically, when using the conventional solder bumps, the solder melts during reflow and the interconnects that are formed as a result are in a roughly spherical shape. You do not have much control over the height, diameter, or any other dimension of the interconnect. With copper pillar technology, you gain a much better control over the dimensions of the connections between the die and the substrate. This allows finer pitch and further bump density across the silicon die.

The copper pillar bump operates on the concept of the thermoelectric effect which happens when a difference in temperature is converted directly into voltage or if a voltage difference is converted into a temperature. As such, this effect can be used to either produce electric voltage from heat or produce heat through the application of electricity.

Why Use Copper Pillar?

There are multiple reasons behind the increasing popularity in use of thermal copper pillar technology. As mentioned before, one of the main advantages of copper pillars over traditional solder is the finer fitch that makes this technology idea for high pin count or smaller size packaging. Not only that, but it also reduces the risk of shorts by increasing the reliability of the joints as well as the standoff height thanks to the higher pitch limit.

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