In this tutorial we are going to learn about WHAT IS HIGH SPEED DIGITAL BOARD MATERIAL ?
There are 2 basic types of circuits that fall under the heading of High Frequency-RF/analog (RF or micro- wave) & high-speed digital. Each of these has its own unique requirements, spawning 2 distinct classes of materials. Radio Frequency /analog circuits usually process precision and/or low level signals. As a result, these circuits require much tighter control of parameters pertaining to signal losses. The 2 losses of greatest concern are losses caused by signal reflections, due to impedance mismatch or impedance changes and the loss of signal energy into the dielectric of the material. Some critical applications also must need to focus on losses due to “skin effect.” Impedance variations result from 2 things: material parameters that vary with changes in frequency or temperature, & variations in the processes at the fabricator. The signal lost into the dielectric is a function of the material’s characteristics. Skin effect can be separate controlled through choice of copper type in/on the PCB. Material choice can have a major impact on all these sources of energy loss. Generally, materials of RF/analog domain tightly control parameters such as dielectric thickness, dielectric constant , loss tangent (tan (d) and even copper type. In contrast, digital circuits can tolerate much greater signal loss & still function. Losses are still important in the digital domain, but because of very broad noise margins of digital ICs, lossses usually don’t affect circuit working until they become a very significant portion of the noise budget. This most often occurs at very high operating frequencies. Also, digital circuits are generally very complex & dense & often require very large, high-layer count boards. This tends to put the emphasis for digital materials on process capabilities & cost. These needs have spawned the II group of materials, one geared toward digital applications.