Wearable PCB Design requirements focus on basic Materials (2)

                     Wearable PCB Design requirements focus on basic Materials (2)

          Manufacturing problem

          Wearable PCB requires stricter impedance control, an important factor for wearable devices, where impedance matching can produce cleaner signal transmissions. The standard tolerance of the signal carrying line is ±10. This parameter is obviously not good enough for today's high frequency and high speed circuits. The current requirement is ±7, and in some cases even ±5% or less. This parameter and other variables will have a serious impact. These impedance controls are particularly stringent in the manufacture of wearable PCB, This in turn limits the number of businesses that can make them.

          The permittivity tolerance of laminated layers made of Rogers UHF materials is generally kept at ±2, and some products can even reach ±1. By contrast, the permittivity tolerance of FR4 laminates is as high as 10, so, Comparing these two kinds of materials, we can find that the insertion loss of Rogers is very low. Compared with the traditional FR4 material, the transmission loss and insertion loss of Rogers stack are lower by half.

          In most cases, cost is the most important. However, Rogers can offer relatively low loss high frequency laminated properties at an acceptable price. For commercial applications, FR4 can be mixed with epoxy based FR4, some of which are made of Rogers materials. Other layers are FR4.

         When choosing the Rogers stack, the frequency is the primary consideration. When the frequency exceeds 500MHz, the designers tend to choose the Rogers material, especially for RF / microwave circuits, because the upper wiring is strictly controlled by impedance. These materials can provide higher performance.

         Compared with the FR4 material, the FR4 material can provide lower dielectric loss, and its dielectric constant is stable in a wide frequency range. In addition, the Rogers material can provide the ideal low insertion loss performance required for high frequency operation.

         The thermal expansion coefficient of Rogers 4000 series materials has excellent dimensional stability. This means that when PCB goes through cold, hot and very hot reflow soldering cycles compared with FR4, The thermal expansion and contraction of the circuit board can be maintained at a stable limit at higher frequencies and higher temperature cycles.

         In the case of hybrid lamination, Rogers and high performance FR4 can be easily mixed with common manufacturing technology, so it is relatively easy to achieve high manufacturing yield. Rogers lamination does not require a special perforation preparation process.

       Ordinary FR4 can't achieve very reliable electrical properties, but high performance FR4 materials do have good reliability properties, such as higher TG, still have relatively low cost and can be used in a wide range of applications. From simple audio design to complex microwave applications.