Impedance Control PCB

Impedance is the sum of the resistance and reactance of an electrical circuit expressed in Ohms. The resistance being the opposition to current flow present in all materials. The reactance is the opposition to current flow resulting from the effect of the inherent capacitance and inductance of the conductor interacting with changes in voltage and current. There is no reactance and the resistance of copper conductors is typically insignificant. However in high speed AC circuits (those with sharp changes in voltage and/or current) the reactance and thus the impedance can become very significant. This can become critical to a design's functionality because of the effects that changes in the impedance along the signals path from transmitter to receiver will have on the efficiency of power transfer as well as signal integrity. While a circuit’s speed is often expressed as the frequency of the wave form: the critical concern is the speed at which the voltage and/or current is required to change.

Controlled Dielectric

The typical design considerations involved in the determination of the requirement for controlling the impedance are the strength of the signals involved, the susceptibility of the circuit to noise and signal distortion, the criticality of signal timing and the speed at which the signal’s source is attempting to force a change in voltage and/or current.

The design considerations for setting the value of the impedance for the conductor is typically the output impedance of the transmitter and the input impedance of the receiver. The impedance of other conductors (i.e. coaxial cables) in the circuit path will also need to be considered. The acceptable range (tolerance) for the impedance will need to be determined and taken into account during the design phase as well as when specifying the PCB parameters. In many cases merely by using software models to determine the anticipated impedance with particular dielectric materials and spacing, followed by requesting these parameters be followed when the PCB’s are fabricated will suffice. This is what we call “controlled dielectric”. For more critical applications you will need to specify “controlled impedance” and supply the actual impedance requirements for the conductors and we will fine tune the dielectrics and conductors to meet these requirements. The impedance requirements will have to be specified based on the layer and the conductor widths.

Impedance controlled PCB Built on FR-4 With 4 Layer Copper Example

1.1 General description

This is a type of multilayer PCB built on FR-4 substrate with Tg 150°C for the application of Heart monitors. It's 1.6 mm thick with white silkscreen(Taiyo) on green solder mask (Taiyo) and immersion gold on pads. The base material is from ITEQ supplying 8 up PCBs per panel. They're fabricated per IPC 6012 Class 2 using supplied Gerber data. Each 25 panels are packed for shipment.

1.2 Features and benifits

Outstanding thermal resistance and suitable for lead-free process

Excellent surface planarity, helpful for PCBs with BGA packages to reduce failure rate during assembly and soldering.

Improved the speed of signal transmission

Reliability test, insulation resistance test and ionic contamination test

Delivery on time. Higher than 98% on-time-delivery rate.

Small quantity order is accepted

Customer complaint rate: <1%

1.3 Application

Preamplifier, Navigation System, GPS Tracking Devices, GPS Device, AC Drives, Biometric Access Control, Mobile Broadband Router, Electronics Assembly, Memory Module, Weather analysis

1.4 Parameter and data sheet