At present, plastic packaging devices have great advantages in size, quality, cost, performance and life, so the plastic packaging process has become the key process in the whole chip packaging process. However, there are many deficiencies in plastic packaging materials. The non-airtightness of the packaging resin can easily lead to moisture corrosion and even ' popcorn ' effect in the device, causing abnormal quality such as interface fracture or delamination, affecting the performance of the internal circuit of the device and reducing its reliability. Therefore, improving the bonding force of the plastic packaging contact surface is an important way to reduce the hidden danger of device delamination.

Bonding strength of plastic sealing material and lead frame

Usually, the bonding strength is used as an important index to evaluate the bonding ability between the plastic packaging material and the lead frame. The bonding strength depends on many factors, such as the choice of adhesive, the treatment of the surface of the bonded material, the bonding operation process and the curing process. In the chip packaging process, as the lead frame of the bonded material, the surface cleaning process plays a vital role in improving the bonding strength.

In the process of combining the plastic sealing material with the surface of the lead frame, improving the wettability of the surface of the lead frame is beneficial to improve the degree of infiltration and diffusion of the plastic sealing material on the surface of the frame, so that the plastic sealing material can fully contact with the surface of the lead frame, so as to enhance the bonding force, as shown in Fig.1 and Fig.2.

Plasma cleaning improves the adhesion of plastic seals

The surface treatment or modification of the lead frame before plastic packaging is a common technical means in the chip packaging process. The purpose is to obtain high bonding strength and improve the resistance to medium corrosion of the bonding surface. Plasma cleaning technology is the most excellent and effective surface treatment and modification technology at present. It can effectively micro-treat the surface of the lead frame, improve the micro-roughness and wettability of the surface, and promote the covalent bonding between the plastic sealing material and the surface of the lead frame. The plasma cleaning process can increase the contact surface area of the plastic sealing material and the lead frame, increase the density of the contact point, and increase the degree of meshing between the plastic sealing material and the lead frame, so as to improve the bonding strength, as shown in Figure 3.

Comparison of water droplet angle before and after plasma cleaning of lead frame

Before plasma cleaning, the angle of water droplets on the surface of the lead frame is about 70, and the angle of water droplets is reduced to about 10 degrees by plasma cleaning. Plasma cleaning can effectively remove the oxide layer, organic matter, activate the surface of the frame, and enhance the wettability of the lead frame.

The sealing of the product is determined by the binding capacity of the plastic packaging material and the substrate. The bonding between the two interfaces must ensure that the interface is clean. In the packaging production process, the surface of the substrate will be contaminated, impurities and other foreign objects, which will affect the combination of the plastic packaging material and the substrate. Therefore, before the plastic packaging, the plasma cleaning process is used to clean the surface of the substrate, remove the contamination and impurities, ensure that the two materials can be well combined during the plastic packaging, and effectively solve the stratification of the product after the plastic packaging.