In high voltage power equipment, potting processes are widely adopted to fill the gaps between internal components with encapsulants such as silicone gel, so as to guarantee electrical insulation performance and thermal management capability. Common substrate or structural materials for internal components include FR4 (flame retardant epoxy fiberglass board), silicone rubber, ceramics, polytetrafluoroethylene (PTFE) and epoxy resin. While these materials feature excellent dielectric strength, chemical resistance and good machinability, their surfaces generally exhibit low surface energy properties, weak polarity, poor hydrophilicity and chemical inertness. Especially at the nanoscale, the relatively smooth surface leads to poor wettability and insufficient interfacial adhesion between the substrates and silicone potting gel.

Consequently, in practical service, particularly under harsh operating conditions such as temperature cycling and thermal vacuum environments, interfacial debonding and delamination tend to occur between potting substrates and encapsulants. Moreover, such interfacial defects trigger local electric field concentration under high voltage electric fields (typically below 10 kV), giving rise to surface flashover. Meanwhile, interfacial voids increase thermal resistance and cause local overheating, which accelerates material ageing and failure.

To improve the interfacial bonding performance between low surface energy materials and potting compounds, wet chemical methods such as alkaline etching are conventionally used to enhance surface roughness and activity. Nevertheless, wet treatment suffers from obvious drawbacks. For one thing, strong alkaline solutions are liable to corrode sensitive structures including metal pads and circuit traces. For another, ionic residues may be introduced during treatment and impair the electrical performance of devices. In addition, wet processes are usually time consuming with strict processing conditions, and are unsuitable for post treatment after component mounting. Therefore, they can hardly satisfy the demands of modern high voltage power products for high integration, high reliability and mass production manufacturing.

Plasma Activation Treatment Technology

Plasma is a fully or partially ionized gaseous substance with high energy, which readily undergoes physical or chemical reactions with other materials. Plasma treatment under an appropriate gas atmosphere can raise the oxygen content on material surfaces and introduce polar groups such as hydroxyl and carboxyl groups. Meanwhile, high energy ions and free radicals bombard the material surface during plasma processing, breaking surface molecular chains and removing or volatilizing low molecular weight fragments. This etching effect increases surface roughness. Furthermore, plasma treatment only affects a thin surface insulation layer of approximately 5 10 μm, a depth far thinner than the overall insulation thickness inside high voltage power assemblies, so conductive materials embedded inside dielectrics will not be damaged.

Plasma activation on potting structure substrates simultaneously introduces oxygen containing polar functional groups (OH, C=O, etc.) and generates nano micro rough structures on material surfaces. It greatly improves the wettability of substrates towards silicone gel and intermolecular interaction forces, thereby remarkably enhancing interfacial adhesion and electrical insulation performance between potting substrates and silicone encapsulants, and improving the long term reliability of equipment under high voltage conditions. Compared with untreated substrates, plasma treated potting substrates achieve an adhesion strength improvement of over 50 %, and the surface flashover voltage reaches no less than 20 kV at electrode gaps of 5 15 mm.

The plasma treatment solution is capable of efficiently processing various low surface energy materials ranging from polymers and metals to ceramics. It delivers dual improvements in interfacial bonding strength and surface withstand voltage performance for multimaterial substrates bonded with silicone potting gel. This resolves the engineering challenge of integrated interfacial treatment for multi component and heterogeneous material potting inside high voltage power supplies, and can be easily integrated inline with existing vacuum potting production lines. Besides, plasma treatment is a dry physical process requiring no hazardous chemical reagents or harmful waste discharge. It eliminates potential corrosion and damage to precision electronic components caused by wet chemical treatment, featuring superior environmental friendliness and operational safety.