Electrical Performance of Microvia PCB Materials for WLAN and RF Module Applications

Conventional PCB processing of organic dielectrics has been proven to be a very economical interconnect solution for a variety of PCB, module, and packaging applications in the telecommunications and computing markets. Organic microvia dielectrics are well suited for mobile wireless as well as telecom and computing infrastructure products where the latest fabrication techniques, such as high-speed laser microvia drilling, are used to create the cost effective high density circuit boards found in these systems. For high speed/high frequency designs, epoxy resin coated copper foil often cannot meet electrical performance requirements while traditional high speed materials are often too expensive. However, substrates based on FR4 core constructions utilizing low loss microvia dielectrics can offer low cost, high performance solutions for these applications. This paper presents experimental results of electrical testing conducted on typical microstrip PCB and module constructions. The following quantitative, measured electrical data is presented. 1. Digital signal integrity of microstrip transmission lines 2. RF insertion loss of microstrip lines 3. RF performance of integrated passive, band-pass filter elements 4. Simulation of RF band-pass filter elements based on the measured data The effects of surface finish (Ni/Au with and without), microvia dielectric (RCC, FR4 and low loss), and solder mask (with and without) are examined.