Primary Plasma Surface Treatment for Electronics

Nordson Electronics Solutions

Jump To Blog Content

What Is Primary Plasma?

The primary plasma mode employs an energy source to ionize and dissociate a source gas, creating a gas plasma consisting of physically and chemically active components. A majority of gas plasma equipment manufacturers for the semiconductor packaging industry rely on a primary plasma mode for generating active plasma species.

Samples to be plasma-treated are placed directly in the gas discharge, on or near the electrode plates of the system, with full exposure to the working species of the plasma (i.e., ions, free radicals, and byproducts). An added benefit to capacitively coupled (radiofrequency) RF-based plasma systems is the generation of a negative direct-current (DC) bias on the powered electrode. The self-DC bias is useful for applications that require more aggressive, anisotropic etching.

There Are Two Variations of Primary Plasma:

Direct primary plasma and Reactive Ion Etch Plasma (RIE) primary plasma. When considering these two modes, an appreciation of the system's electrode configuration is crucial. The powered electrode is inherently more aggressive and operates at a higher temperature than the alternating grounded electrode in the process.

Both the powered and grounded electrodes offer benefits for any given application. One must consider the sample's location within the direct plasma, its chemical or physical characteristics, and the required throughput for process justifications.

Since the powered electrode is more aggressive than the grounded electrode, cleaning, surface activation, and etching processes are accomplished at an accelerated rate when parts are placed directly on the powered electrode. RIE processing further exploits the powered-electrode benefit by minimizing the spacing between the two electrodes to increase the high RF electric field and DC bias levels for true material etching. This is evidenced by failure analysis or MEMS applications where the creation of deep features in the sample with anisotropy and aggressive ion bombardment is desired.

Typical applications for direct primary plasma include all packages that are not sensitive to direct plasma exposure, given the integrated circuit technology or material selection.

Applications for Advanced Electronics Manufacturing

Employ plasma for substrate pretreatment and package processing before die attach, wire bond, underfill, mold, or encapsulation. Plasma improves wire bond pull strength and CpK through contamination removal and surface activation processes; it increases wicking speed and filet height and minimizes voids in underfill via surface modification processes; and it maximizes fluid adhesion in mold/encapsulation through surface activation mechanisms. The use of plasma for these applications greatly increases the yield and reliability of the microelectronic package.