Advanced Low Loss Dielectric Material Reliability and Filter Characteristics at High Frequency for mmWave Applications

In this paper, we report an advanced low-loss dry film build-up material applicable to high-frequency transmission, and evaluation of filter characteristics and dielectric characteristics in the mmWave band. The wireless communication standard is evolving from 5G to beyond 5G, and accordingly, it is critical to lower the loss tangent (Df) of build-up materials to enable high-speed transmission in signal paths. However, for high frequency filter applications, conventional materials such as epoxy and polyimide type build-up materials induce high insertion loss in the passband. This paper therefore introduces a lower-Df dry film build-up material (Material A) and investigates transmission characteristics of the same. To evaluate the insulation reliability and electrical performance of the material, test vehicles with precise copper patterns are designed and fabricated with a semi-additive patterning process (SAP) using the Material A. Each test board was fabricated to evaluate the insulation reliability and electrical performance of the material. By applying the Material A for SAP, over 5N/cm high peeling strength is achieved despite of the smooth surface. The material demonstrates an excellent insulation reliability between copper lines and between copper layers, specifically 300 hours of bHAST attributed to its low chlorine impurities. The dielectric property Df of the material is 0.0025 at 10 GHz. The electrical performance of lowpass filters and bandpass filters are measured by electrical analysis using microwave network analyzers system. These test boards demonstrate to achieve a low transmission loss of less than 1 dB at 28 GHz as a lowpass filter, and 1.05 dB at 28 GHz and 1.18 dB at 39 GHz as a bandpass filter. As a result of this excellent low transmission loss, this material has promising application potential for millimeter wave applications.