Semiconductor packaging

The packaging process directly affects the yield of lead frame chip products, and the biggest source of problems in the whole packaging process is the particulate pollutants, oxides and epoxy resins on the chip and lead frame. In view of the different links of these different pollutants, different plasma cleaning processes can be added before different processes, and their applications are generally distributed before dispensing, before wire bonding, before plastic packaging, etc.

Plasma Clean for pre-wire bonding

At present, the most commonly used and most effective process technology for the connection between chip and lead frame or substrate is wire bonding. According to failure statistical analysis, wire bonding failure mode accounts for more than 70 % of all failure modes of products. The main reason for the decrease of solderability and reliability of wire bonding is that there are pollutants on the surface of the pad or the surface of the lead frame, and various factors such as the surface of the chip, the bonding cutter and the bonding wire may be attached to the pollutants. If the wire is bonded directly without plasma cleaning, it will lead to wire quality problems, such as virtual welding, de-welding or low wire bonding strength. Using a mixture of argon and hydrogen in an appropriate ratio for rapid plasma cleaning, chemical reduction reaction occurs, which can promote the reaction of pollutants to produce non-polluting carbon dioxide and water. In addition, the cleaning time is short, and the surface of the passivation film outside the bonding zone will not be damaged. Before the wire bonding process, the residual pollutants in the previous process can be effectively removed by equal cleaning, which greatly improves the yield of the wire bonding process and effectively reduces the failure probability.

Plasma Clean for die-attach

Usually, there are many oxides or organic pollutants on the surface of the product to be cleaned. If the chip is stuck directly, it will lead to incomplete bonding of the chip, resulting in poor voids ( Void fail ), and the heat dissipation capacity of the product after packaging will also be reduced, which seriously affects the reliability of the chip packaging. Therefore, before the chip is bonded, a mixture of oxygen, argon or hydrogen gas is used for rapid plasma cleaning. The purpose is to remove organic matter and other pollutants on the surface of the chip, which can effectively enhance the surface activity and bonding ability of the product, reduce the poor voids, and thus improve the reliability and stability of the bonding process.

Plasma clean for pre-molding

The raw materials selected for the lead frame must have the characteristics of high conductivity, good thermal conductivity, high hardness, good heat resistance and corrosion resistance, good bonding performance and low cost, and the requirements are extremely harsh. Among the commonly used materials, the lead frame made of copper alloy material is the most suitable for use and is suitable as the main lead frame material. As the main raw material for plastic packaging, copper lead frame accounts for more than 80 % of all materials in chip packaging from the beginning of packaging process to the end of plastic packaging, and is used to connect the internal contacts of the chip with the metal frame of the external welding wire. However, copper alloy materials have the following disadvantages : strong oxygen affinity, easy to be oxidized, and the generated oxides will again pollute the surface of copper alloy products. If the oxide film is too thick, it will lead to the bonding strength of the lead frame and the packaging plastic packaging material is greatly reduced, the packaging chip is prone to delamination or even cracking, and the packaging yield will be greatly reduced. Therefore, by using argon and hydrogen mixed gas for rapid plasma cleaning technology to solve the oxidation problem of copper lead frame, the oxides and organic pollutants on the copper lead frame can be removed, the surface roughness and adhesion of the product can be improved, and the reliability of bonding, laminating and plastic packaging processes can be improved.

Plasma clean for pre-underfill

Flip chip packaging technology is one of the mainstream packaging technologies with high speed and high density, which uses the bump of flip chip as the connection medium, and uses reflow soldering, hot pressure soldering and other methods to realize the circuit interconnection between chip and substrate. In the flip chip packaging process, due to the mismatch of the thermal expansion coefficient between the chip and the substrate, there will be a large thermal stress when the temperature changes, so it is often necessary to fill the bottom filling glue between the chip and the substrate to play a reinforcing role. 

The main purpose of plasma cleaning is to remove the pollutants on the surface of the ceramic substrate and provide a clean environment for the dispensing process. In addition, plasma cleaning can directly change the surface state of the substrate, improve the wettability of the substrate surface, promote the flow of the underfill adhesive between the chip and the ceramic substrate, reduce the flow time, improve the filling efficiency, thereby improving the engineering production efficiency and reducing the production cost.