PCB-TIPS

Controlled Dielectric vs. Controlled Impedance

In many different applications, managing the impedance of certain traces on the PCB are absolutely critical to proper function of the device, usually to reduce signal reflections and distortions in high speed designs, or to achieve maximum power transfer to a load. Controlled Dielectric and Controlled Impedance are industry terms which both refer to the achievement of a specific trace impedance on a board. PCB Transtek can accommodate either method as a part of our PCB Fabrication service.

 
Controlled Dielectric

The term Controlled Dielectric is used when the PCB layout designer chooses to take care of the impedance calculations. In this case, you would specify exact copper weights and dielectric thicknesses for each layer of the PCB in a custom Multi-Layer Stack-Up. The image below shows PCB Transtek’s standard 8-layer PCB stack-up, which can be used as a starting point, to give you an idea of what sort of information should be included in your description. You should send your custom stack-up along with your other Design Files when you request a PCB quotation from PCB Transtek so that our engineering team can get started on their analysis right away.

 

8 Layer Stack-up

Layer Order Layer Name Material Type Material Description Dielectric Constant Thickness Copper Weight
1 Top Copper Signal 0.0014” 1 oz
1080 (2 sheets) Prepreg 4.2 0.0059“
2 Inner1 Copper Plane 0.0014” 1 oz
Core Core 4.2 0.009”
3 Inner2 Copper Plane 0.0014” 1 oz
7628 Prepreg 4.2 0.0073”
4 Inner3 Copper Plane 0.0014” 1 oz
Core Core 4.2 0.0051”
5 Inner4 Copper Plane 0.0014” 1 oz
7628 Prepreg 4.2 0.0073”
6 Inner5 Copper Plane 0.0014” 1 oz
Core Core 4.2 0.009”
7 Inner6 Copper Plane 0.0014” 1 oz
1080(2 sheets) Prepreg 4.2 0.0059”
8 Bottom Copper Signal 0.0014” 1 oz
Final board thickness: 0.062” ± 10%
 
Controlled Impedance

PCB Transtek has many years of experience in providing PCB Fabrication services, and we are very familiar with the calculations and considerations required for impedance control in a PCB design. As such, you can always choose our Impedance Controlled PCB service to have PCB Transtek’s engineering team handle this part of the process for you. Controlled Impedance generally describes the case where the client simply marks the traces that require specific impedance values, and the manufacturer takes responsibility for impedance management.

 

When we handle the impedance for you, we can provide the stack-ups and impedance calculations we used for your reference. We also include the manufacturing of TDR coupons in our Quality Management strategy for impedance controlled designs, so you can always rest assured that the impedance on your board is exactly what you intended.