Wednesday December 13 , 2017

MultiLayer PCB Overview - PcbSchematics.com

Multilayer PCBs are printed circuit boards with more than one conductor layer mostly dedicated to power connections; power planes, these layers buried inside the PCB by a way that makes each conductor layer on the outside surface. These layers; Inner layers & the top layer, are connected to each other by plating through holes and vias; the inner holes connecting the inner layers. The number of layers needed for any printed circuit board depends on the desired application and vary from one application to another, these layers can be from 3 up to 50 or more in very complicated applications. Lamination for these layers is made by some composite fibers pre-impregnated with a resin system; this resin system must be accurately chosen to meet the needed requirements such as the resistance to chemicals, maintaining the dielectric constant and Bearing the expected temperature. Multilayer PCBs able to carry high speed devices, large complicated schematics and all applications required controlling the impedance.

 

The Processes of multilayer PCB manufacturing is divided into two parts: the outer layer PCB and the inner layers PCBs. The inner layers of any product usually seem to be typically standard and the manufacturing processes of these layers always contain several common steps such as:

  • Layer cleaning either mechanical or chemical cleaning
  • Photo-resist materials coating and photo-resist exposure
  • Etching the exposed copper
  • Stripping the remaining photo-resist
  • Lamination by oxide layer
  • Plus too many other steps

 

The outer layer processes in manufacturing contain too many steps such as:

  • Isolating the outer layer of the inner layers with the PrePreg; pre-impregnated fibers
  • Laminating with copper foil to create the copper surface of the outer layer
  • Drilling of the holes and vias between the outer layer and the inner layer
  • Copper plating in the holes and vias to maintain conductivity between layers
  • Coating the outer layer with a photo-resist material, and exposing
  • Stripping of the remaining photo-resist and etching useless remaining exposed copper
  • Solder masking, silk screening, gold plating, additional holes, mechanical components considerations and finalizing related steps
  • Plus too many other steps

 

What are Backplanes?

Backplanes in the printed circuit boards science are special cases of multilayer PCBs.

Contain large quantities of connectors that have been installed using press fit pins.

Used also to distribute large amounts of dc power to the circuit, this is accomplished by laminating the power planes inside backplanes and bolting bus bars onto the outside surfaces, some components need these active elements such as the surface mount ICs.

Backplanes make The Final PCB thicker than the original multilayer PCB; it makes the process of PCB manufacturing very hard as the press fit pins have to deal with the added thickness.

 

Six-layers or more PCBs usually built on the standard (18 in * 24 in) panels using the lamination technique mentioned above, also the four-layers PCBs laminated using a technique called mass lamination with a panel of (36 in * 48 in); i.e., 4*standard panel. The pricing of Multilayer PCBs are affected by several factors:

 

  • How many PCBs Can be Fitted in a standard panel using the lamination technique
  • The thickness of the inner copper layers and the outer layer
  • The accuracy of the copper layer thickness
  • The controlled impedance requirements
  • The minimum copper plating in vias
  • The diameter of traces and minimum spacing
  • The gold plating requirements
  • Testing to CAD Net-List
  • There are too many other factors that can affect the multilayer PCB pricing such as the solder mask, the silk screen and other factors depend on the client requirements

 We are now preparing a DIY; Do It Yourself tutorial for how to make a quality pcb at home with very simple tools? and how to print the complicated pcb schematics without loosing connection, dots and lines? Come back soon!

 

multilayer pcb examle, how the layers placed to form the multilayer pcb and how holes can connect through layers