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Controlled Impedance Requirements

Impedance, generally measured in Ohms is a characteristic of the circuit that has to be taken care of during design of the pcb. Resistance and reactance of an electrical circuit have a major impact on functionality, as certain processes must be completed before others to ensure proper operation. This chain of command disrupts a system and leads to a complete failure when these actions aren’t performed as planned. Printed circuit boards with impedance requirements will nullify the changes in voltage occurring and lead to an appliance or gadget that operates as expected.
The use of differential impedance PCB components provide the control needed for a range of products. We can recommend software programs designed to detect resistance and reactance flow, providing you with the specs you require. MCL will use this data to create custom PCBs. The resulting circuitry is cost effective and provides heightened reliability.

The pcb design factor’s affecting impedance are: Trace width, copper thickness, dielectric thickness, dielectric constant.

How Does PCB Impedance Control Work?

Before you can decide what kind of impedance control service you need for your printed circuit boards, you need to understand impedance control basics. What is impedance control, exactly, and how does it work? There are three basic levels of service when it comes to PCB impedance control. They are:

  • No Impedance Control: This is a situation where you do not need any extra design elements to ensure correct impedance because you have very loose impedance tolerance. Naturally, this will result in a faster-completed, less expensive board because the manufacturer does not have to include any special measures.
  • Controlled Dielectric:  This is a situation where the designer will determine the impedance of the desired trace and specify a controlled dielectric. The manufacturer does not have to run an impedance calculator on the traces because the designer already ran the impedance calculations and specified a specific controlled dielectric.
  • Impedance Control: Actual impedance control is something you will request when you want the manufacture to use a program (typically polar instruments) to determine the stack up needed for a specified

What Is Impedance Control on a  Microstrip?

There are four parameters to consider when it comes to impedance for a microstrip:

  1. Dielectric height, or H, which you can adjust incrementally (e.g. +1mil =+2 Ohms)
  2. Material Dielectric, or Er, which will be fixed once you choose your material
  3. Trace Thickness, or T
  4. Trace Width, or W

Standard final impedance tolerance is about +/- 10 percent.

Here’s How We Do It

As a circuit is created, the elements in place impact impedance and the schedule on which a circuit completes its functions. The flow of energy is changed by modifying the physical characteristics of flexible circuit boards. The thickness of the copper used and proximity of circuits to one another lower or increase impedance, which in turn will impact the timing – and integrity – of critical processes.
Provide us with the specs you need, and MCL will create the most robust circuitry available with all the benefits of flexible applications using our state of the art systems. PCBs are more cost effective, easier to use, allow for greater amounts of circuits to be utilized in small spaces. Take advantage of these benefits while retaining the ability to fine-tune your processing times. Get in touch with MCL today to discuss our controlled impedance capabilities.

PCB Glossary

  • FR4

    The UL-designated rating for a laminate composed of glass and epoxy that meets a specific standard for fire-retardance. FR-4 is the most common dielectric material used in the construction of PCBs.