Characterization of Printed Circuit Board Material & Manufacturing Technology for High Frequency AT & S Leoben , Austria

Today ́s Electronic Industry is changing at a high pace. The root causes are manifold. So world population is growing up to eight billions and gives new challenges in terms of urbanization, mobility and connectivity. Consequently, there will raise up a lot of new business models for the electronic industry. Connectivity will take a large influence on our lives. Concepts like Industry 4.0, internet of things, M2M communication, smart homes or communication in or to cars are growing up. All these applications are based on the same demanding requirement – a high amount of data and increased data transfer rate. These arguments bring up large challenges to the Printed Circuit Board (PCB) design and manufacturing. This paper investigates the impact of different PCB manufacturing technologies and their relation to their high frequency behavior. In the course of the paper a brief overview of PCB manufacturing capabilities is be presented. Moreover, signal losses in terms of frequency, design, manufacturing processes, and substrate materials are investigated. The aim of this paper is, to develop a concept to use materials in combination with optimized PCB manufacturing processes, which allows a significant reduction of losses and increased signal quality. First analysis demonstrate, that for increased signal frequency, demanded by growing data transfer rate, the capabilities to manufacture high frequency PCBs become a key factor in terms of losses. Base materials with particularly high speed properties like very low dielectric constants are used for efficient design of high speed data link lines. Furthermore, copper foils with very low treatment are to be used to minimize loss caused by the skin effect. In addition to the materials composition, the design of high speed circuits is optimized with the help of comprehensive simulations studies. The work on this paper focuses on requirements and main questions arising during the PCB manufacturing process in order to improve the system in terms of losses. For that matter, there are several approaches that can be used. For example, the optimization of the structuring process, the use of efficient interconnection capabilities, and dedicated surface finishing can be used to reduce losses and preserve signal integrity. In this study, a comparison of different PCB manufacturing processes by using measurement results of demonstrators that imitate real PCB applications will be discussed. Special attention has be drawn to the manufacturing capabilities which are optimized for high frequency requirements and focused to avoid signal loss. Different line structures like microstrip lines, coplanar waveguides, and surface integrated waveguides are used for this assessment. This research was carried out by Austria Technologie & Systemtechnik AG (AT&S AG), in cooperation with Vienna University of Technology, Institute of Electrodynamics, Microwave and Circuit Engineering.  Several commercially available PCB fabrication processes exist for manufacturing PCBs. In this paper two methods, pattern plating and panel plating, were utilized for manufacturing the test samples. The first step in both described manufacturing processes is drilling, which allows connections in between different copper layers. The second step for pattern plating  is the flash copper plating process, wherein only a thin copper skin (flash copper) is plated into the drilled holes and over the entire surface. On top of the plated copper a layer of photosensitive etch resist is laminated which is imaged subsequently by ultraviolet (UV) light with a negative film. Negative film imaging is exposing the gaps in between the traces to the UV light. In developing process the non-exposed dry film is removed with a sodium solution. After that, the whole surrounding space is plated with copper and is eventually covered by tin. The tin layer protects the actual circuit pattern during etching. The pattern plating process shows typically a smaller line width tolerance, compared to panel plating, because of a lower copper thickness before etching. The overall process tolerance for narrow dimensions in the order of several tenths of μm is approximately ± 10%. As originally published in the IPC APEX EXPO Conference Proceedings.