What Is Plasma Surface Treatment?

Plasma surface treatment is a critical process in electronics manufacturing that uses a partially ionized gas to clean, activate, and modify material surfaces prior to bonding, coating, or encapsulation. Plasma is an electrically neutral mixture of physically and chemically active gas phase species capable of surface modification.

Surface modification results from the interaction between gas-phase active species and a solid surface. The active species in the plasma are capable of both physical work via ion-assisted sputtering and chemical work through radical or byproduct reactions. As a result, plasma can perform numerous surface modification processes, including surface activation, contamination removal, cross-linking, chemical reaction etching, and physical bombardment.

There Are Two Key Mechanisms in Plasma Processing:

Ions perform a physical mechanism, and free radicals and byproducts perform a chemical mechanism.

Physical Plasma Mechanisms

Physical plasma is a result of the charged ionic species gaining sufficient kinetic energy from the applied electric field to perform sputtering. Through energy transfer, partial molecules and atoms are sputtered from the surface, removing contaminants from the substrate. Physical bombardment also changes the surface topography, increases surface roughness at the molecular level, and can enhance interface adhesion.

Chemical Plasma Mechanisms

Chemical plasma relies on the chemically active free radicals and byproducts generated in the plasma to diffuse to the sample surface. These free radicals and byproducts decrease the activation energy in a chemical reaction, resulting in material removal. The volatile chemical reaction byproducts are removed from the sample surface and the process chamber by the vacuum system. Isolation of a particular plasma mechanism is determined by the plasma mode, with mechanism selection based on the packaging application.

Plasma Surface Treatment Applications

Package Level Applications

• Die attach – Improved adhesion and thermal performance
• Wire bond – Cleaner pads and higher bond strength
• Underfill (flip chip & advanced packaging) – Faster wicking and reduced voiding
• Molding & encapsulation – Stronger mold adhesion, reduced delamination
• Copper lead frame oxide removal – Improved bonding and reliability
• Wafer level packaging (WLP) – Cleaning, descum, etch, VIA prep, and bump adhesion
• MEMs manufacturing – Cleaning, descum, stripping, and etching

Board Level Applications

• PCBA surface preparation – Contamination removal and surface activation
• Pre conformal coating – Improved coating adhesion, coverage, and reliability

To explore the use of plasma for your process, please refer to the full articles in the Related Articles section or contact us at [email protected].