Printed Circuit Board

Important Points

• Provides mechanical support

• Electrically connects electronic components using conductive pathways

• Also referred as PWB-Printed wiring Board

• PCB populated with components is called PCA or PCBA-Printed Circuit Board Assembly

      Materials

• Conductive path - copper foil

• Insulated layer - epoxy resin prepreg

• Dielectric - Teflon, FR4, FR5, FR6, CEM1, CEM3, CEM4, CEM5, G10 etc. 

                              ( FR4 is the most common )   

                               

      Trace

                     :- The conductive Cu path is called TRACE.

      Etching
                     :- Removing undesired Cu leaving only desired Cu traces is called 
                        Etching process.

     

      Production

• Silk screen printing       

• Photoengraving

• PCB Milling   

• Addictive process  

      Drilling

                    Drill bit - made of solid tungsten carbide.

                    Holes are filled with angular rings.

                        

       PTH - Plated Through Hole    

        Via :-        The electrically conductive plated holes in the PCB is called via.

        Types of via

• Standard via

• Bind via :- from one side of the board to one or two of the inner layer,                                         but it do not protrude through the other side                              

• Buried via :- connects one or more inner layers

    Multilayer  

• Silkscreen layer :- component overlay/ component layer ( top/ bottom )
• A multilayer PCB is made up of individual boards separated by pre-impregnated bonding of layers, also known as "prepreg" 

       Electrical testing :-

•  Flying probe test machine 
•  Bed of nails test machine 

       Board thickness :-  
       
       1.6 mm standard ( 0.8, 2.4 mm are also available )

       Surface finish :- 

       SMOBC-Solder Mask Over Bare Copper, HAL-Hot Air Leveling, Goldflash

       Notes :-

• 100 thou - 2.54 mm; 100 thou basic measuring point

• via:-  0.5 - 0.7 mm 

• R, C, D round pad and IC oval pad  

• High frequency traces are short

• Minimum 8 mm gap between 230 and isolated signal traces 

• Pad size should be at least 1.8 times the size of hole