accelerating performance requirements are driving the demand for highspeed, multilayer PCBs. Traditional manufacturing methods for laminating these layered boards and removing residue from the vias are no longer effective. The use of radio frequency driven, low-pressure plasma provides an efficient, cost-effective and environmentally friendly method for surface treatment and cleaning of the boards. Specific applications of plasma technology to PCB manufacturing, critical parameters, and process examples will be discussed. Innovations in PCB material technology and the use of smaller geometries have led to an increased requirement for plasma processing at multiple steps in the manufacturing cycle. Multilayer PCBs with high-density interconnects require designs with finer pitch, smaller vias, and the use of new material technologies with high glass transition temperatures and low loss factors. While these materials solve coefficient of thermal expansion (CTE) and speed issues, difficulties arise during board manufacturing where the use of traditional processes is limited. Chemical processing with permanganate chemistry is limited due to the inability of the fluid to penetrate the small vias found in multilayer PCBs. In addition, permanganate does not effectively clean the very small via holes that are usually located at the inner layer level of laser-drilled via holes. Other wet chemistries, such as acid etch, have difficulties etching polyimide dielectric materials. Plasma processing overcomes these limitations due to the inherent penetrating nature of plasma and the ability to precisely control the process. Plasma can etch highaspect ratio vias, and is environmentally benign with a low cost of ownership. Complex and sophisticated boards with ever increasing layer counts and circuit densities need the benefits of plasma for descum, desmear/carbon removal, etchback, Teflon® activation, and surface preparation. Examples include: multilayer boards with 6 to 64 or more inner layers; boards with high-aspect ratio holes; PCBs with m i c r o v i a s , b u r i e d v i a s , blind vias, and laser formed vias; and those PCBs manufactured from new types of resin, Teflon®-based materials, and chemically inert materials. What is Plasma? Plasma is an electrically neutral mixture of physically and chemically active gas phase species including ions, radicals, and reaction by-products. These active gas phase species can perform numerous surface modification processes including surface activation, contamination removal, cross-linking, and etch (Ref. 1). The type of plasma process is determined by the PCB material type and post process requirements, and is controlled by the plasma conditions. Typical plasma equipment consists of four major components: the vacuum chamber, electrodes, vacuum pump and an RF power supply (see Figure 1). For PCB applications, the PCB panels are suspended between a pair Plasma Processes for Printed Circuit Board Manufacturing By Lou Fierro and James D. Getty Figure 1. Plasma Treatment System Diagram. A New technology, high-performance boards require the use of plasma in numerous manufacturing steps. of electrodes located within the vacuum chamber. A vacuum pumping system, such as a rotary vane pump and roots blower, is utilized to maintain a plasma process pressure in the low milliTorr range. Source gases are introduced through mass flow controllers at a specified flow rate. Once the desired process pressure is achieved, RF power is applied to the electrodes thereby initiating the plasma process. The process gas is ionized and dissociated through the application of RF energy. Typically the RF generators operate in the kHz to MHz range. The processes described later in this article utilized a 40 kHz power supply. Plasma-generated active species perform both physical and chemical processes through ion bombardm