Advantage of non-etching adhesion promoter on high frequency signal loss

In the age where demands for mobile electronic devices are ever increasing, the propensity for an exponential growth of wireless data transfer is inevitable. The massive data exchange is driven by rise in the signal frequency and the trend having high frequency applications is imminent. The prolific examples of high frequency applications include the next generation 4G mobile phones, satellite communications, Wi-Fi LAN, milliwave radars on automotives, CPUs and GPUs. As the frequency signals carried by electronic devices continue to elevate, there is a greater risk of compromising the signal integrity. The main contributors of high frequency signal loss are the dielectric material and conductor which signals travel on. In order to minimize signal loss, material suppliers have been developing reliable high speed dielectrics with low dissipation factors and dielectric constants. On the other hand, the conductor loss of high frequency signals is largely dependent on the surface profile and roughness of the tracks. Uneven conductor surface profile and track roughness is a product of using conventional etch-based adhesion promoter. While the conventional etch-based adhesion promoters cause no major functionality issues to the manufacturing of commodity PCBs, the impact on the signal integrity for high frequency applications can be an issue. As signal frequency escalates, a phenomenon known as the "skin effect" propagates the signals on the track surface. The coupled impact of the "skin effect" and conductor roughness is an upsurge in resistance that results in signal loss. Contrary to the etch-based adhesion promoter, non-etching adhesion promoter (NEAP) can offer a flat conductor surface and a controlled track width. This can in turn reduce the high frequency signal loss significantly. The paper makes use of a commercially available non-etching adhesion promoters and copper foils in order to investigate the influence of surface roughness on high frequency signal loss. The characterization is carried out through the use of computer simulation as well as actual sample measurement in order to determine those factors which dominate the overall loss performance.