Plasma cleaning is widely used in microelectronic packaging

Plasma cleaning is widely used in microelectronic packaging:

Abstract: With the development of microelectronic technology, wet cleaning is more and more limited, while dry cleaning can avoid the environmental pollution caused by wet cleaning, and the production rate is also greatly improved. Plasma cleaning has obvious advantages in dry cleaning. This paper mainly introduces the mechanism, type, process characteristics of plasma cleaning and its application in microelectronic packaging process.

1. the introduction

Cleaning in the microelectronics industry is a very broad concept that includes any process associated with the removal of contaminants. It usually refers to effectively remove the residual dust, metal ions and organic impurities on the premise of not destroying the material surface characteristics and electrical characteristics. At present, physical and chemical cleaning methods have been widely used, which can be roughly divided into two categories: wet cleaning and dry cleaning.

Wet cleaning is still dominant in the current microelectronic cleaning technology. However, from the perspective of environmental impact, raw material consumption and future development, dry cleaning is obviously superior to wet cleaning.

Plasma cleaning has been widely used in semiconductor manufacturing, microelectronic packaging, precision machinery and other industries.

2. Plasma cleaning mechanism

Plasma is a partially ionized gas, which is the fourth state of matter other than solid, liquid and gas. A plasma consists of electrons, ions, free radicals, photons, and other neutral particles. Because of the existence of active ions such as electrons, ions and free radicals in plasma, it is easy to react with the solid surface.

Plasma cleaning technology is characterized by both process base material type of object, can be processing, metal, semiconductor, oxides and most of the polymer materials, such as polypropylene, polyester, polyimide, poly (ethyl chloride, epoxy, and even can well with teflon etc, and can realize the overall and partial cleaning and complex structure.

Plasma cleaning also has the following characteristics: easy to adopt numerical control technology, high degree of automation; With high precision control device, the time control precision is very high; Correct plasma cleaning will not produce damage layer on the surface, and the surface quality is guaranteed. As it is carried out in a vacuum, it does not pollute the environment and ensures that the cleaning surface is not contaminated by secondary pollution.

3. Application in packaging process

In the production process of microelectronic packaging, due to fingerprinting, flux, various cross contamination, natural oxidation, etc., the surface of devices and materials will form a variety of stains, including organic matter, epoxy resin, photoresist, solder, metal salts, etc. These stains will obviously affect the quality of the packaging process. Using plasma cleaning can easily remove pollution produced in the process of production of the molecular level, ensure the workpiece surface atoms and the attachment materials close contact between atoms, thereby effectively improve the bonding strength, lead to improve chip bonding quality, reduce packaging leak rate, improve the performance of components, yield, and performance. The yield of aluminum wire was increased by 10% and the consistency of the bonding strength was also improved after the plasma cleaning was used in a domestic unit before the bonding.

In microelectronic packaging, the choice of plasma cleaning process depends on the subsequent process requirements on the material surface, the original characteristics of the material surface, chemical composition and the nature of pollutants. Gases commonly used in plasma cleaning include argon, oxygen, hydrogen, carbon tetrafluoride and their mixtures.

At present, it is widely used in: (1) plasma cleaning of aluminum bonding area (2) plasma cleaning of the substrate welding plate (3) plasma cleaning of copper lead frame (4) plasma cleaning of ceramic packaging before electroplating

4. the conclusion

Although wet cleaning plays a dominant role in the current microelectronic packaging production, the environmental and material consumption problems brought by wet cleaning cannot be ignored. As a dry cleaning plasma cleaning has the potential to develop, it can be cleaned regardless of the material type, the cleaning quality is good, and the environmental pollution is small. Plasma cleaning technology has a wide range of applications in microelectronic packaging, mainly used to remove surface pollutants and surface etching, etc. The choice of process depends on the requirements of subsequent process on the surface of the material, the original characteristics of the material surface, chemical composition and surface pollution properties. Introducing plasma cleaning into microelectronic packaging can significantly improve the packaging quality and plasticity. However, the influences of different processes on the bonding characteristics and the performance of the lead frame are quite different.

For example, after cleaning the aluminum bonding zone with argon hydrogen plasma for a period of time, the bonding performance of the bonding zone is obviously improved, but too long time will also cause damage to the passivation layer. The use of physical reaction mechanism for plasma cleaning of welding disc will cause "secondary pollution", but reduce the surface characteristics of welding disc; Plasma-cleaned copper lead frame with two different mechanisms, the tensile test results are very different. Therefore, it is very important to choose the right cleaning method and cleaning time to improve packaging quality and plasticity.