Manufacturing Processes for a 4 Layer Multi-layer PCB Section through PCB Via hole SMD Pad The following presentation covers the main processes during the production of a 4 layer or a multi-layer PCB. The diagrams which follow represent a section through a PCB, as indicated in red. Tracks under solder mask +44 (0)

Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) COPPER FOIL PRE-PREG INNER LAYER (CORE) CopperLaminate Typical Layer Construction - 4 Layer PCB 1.Multilayer PCBs have inner tracking layers which are individually processed layer pairs which require bonding and connecting to form the finished PCB. 4 Layer PCBs +44 (0)

Inner Layer Processing Layer 2 (Inner) Layer 3 (Inner) Core CopperLaminate (Dielectric) For Multilayer PCBs Inner layer Core materials are usually processed as Layer pairs Core materials can be typically 0.2mm thick which come pre coated with a ½ oz copper foil. +44 (0)

Layer 2 (Inner) Layer 3 (Inner) Core Laminating and Imaging of Internal Layers UV sensitive film is laminated over top and bottom surfaces of the Core Areas of the Core where no copper is required are left exposed Inner Layer Imaging The addition of the inner layer track patterns to layers 2 and (0)

Core The etch process produces an etch back or undercut of the tracks. This can be specified by the W / W1 parameters This means that tracks will end up approximately 0,025 mm (0.001) thinner than the original design. Inner Layer Etching Etch Process - Remove Exposed Copper Copper Removed Layer 2 (Inner) Layer 3 (Inner) +44 (0)

Core Remove Laminating Film Layer 2 (Inner) Layer 3 (Inner) Film Strip The laminated film is removed prior to AOI inspection. +44 (0)

Core Completed Inner Layer Core Layer 2 (Inner) Layer 3 (Inner) All inner layer Core materials are processed as Layer Pairs prior to Bonding At this stage the Cores are inspected visually (AOI) and defective Cores rejected Sometimes a surface treatment is applied to the Cores to aid with the Bonding process AOI Inspection Automatic Optical Inspection (AOI). Inner layers are scanned and compared to Gerber data for errors. +44 (0)

Layer stackup Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) FOIL PRE-PREG INNER LAYER Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER Layer Stackup The order in which the layers are to be bonded together. The outer layer copper foils, layers 1 and 4 are purchased in sheet form. For a 1 oz finished copper weight typically a ½ oz foil would be used during bonding process to form the outer layers. +44 (0)

Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) FOIL PRE-PREG INNER LAYER Layer stackup FOIL Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER +44 (0)

Layer stackup Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) FOIL PRE-PREG INNER LAYER FOIL Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER +44 (0)

Layer stackup FOIL PRE-PREG INNER LAYER FOIL Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER +44 (0)

Layer stackup FOIL PRE-PREG INNER LAYER FOIL Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER +44 (0)

Layer stackup FOIL PRE-PREG FOIL Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER +44 (0)

Layer stackup Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG FOIL PRE-PREG INNER LAYER +44 (0)

Layer stackup Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER FOIL PRE-PREG FOIL +44 (0)

Bonding – Heat Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) Layer 1 (Outer) Layer 4 (Outer) Layer 2 (Inner) Layer 3 (Inner) FOIL PRE-PREG INNER LAYER FOIL PRE-PREG FOIL Bonding Once the layers are built up heat is applied over a period of time, this is to allow the Pre-Preg material time to melt and flow evenly between the layers, this is in effect the material that sticks the layers together. +44 (0)

Bonding – Multilayer Press Layer 1 (Outer) Layer 2 (Inner) Layer 3 (Inner) Layer 4 (Outer) FOIL PRE-PREG FOIL Bonding Layers are pressed together over a set period of time typically a bonding cycle will last for approx. 4 hours. Bonding capacity would depend on the number of openings and size of press. +44 (0)

Drilling of a Panel Layer 1 Layer 4 CopperLaminate Drilled Hole Drilling The holes are drilled for both thru-hole components and via connections. Once plated this will form the connection from 1 side of the PCB to the other, at the same time connecting the inner layers where required. +44 (0)

Electroless Copper Process Addition of Copper to all Exposed Surfaces Layer 1 Layer 2 Layer 3 Layer 4 Copper Drilled Hole Plating Plating is the same process for 2 or 4 Layer. The aim is plate down the barrel of the hole to make the connection from 1 side of the PCB to the other. +44 (0)

Layer 1 Layer 2 Layer 3 Layer 4 Laminating and Imaging of External Layers UV sensitive film is laminated over top and bottom surfaces of PCB It is then exposed and developed, leaving an exposed image of the PCB pattern Copper The outer layer track patterns are photo-imaged onto the panels using UV sensitive film. Imaging +44 (0)

Layer 1 Layer 2 Layer 3 Layer 4 Electro-plating Process 1 Additional Copper to all Exposed Surfaces Laminated Film Plate Additional Copper Electro-plating increases the copper thickness on the outer layers and through the barrel of the hole. The copper foils for a 4 layer or the starting copper weight on 2 layer boards is most commonly ½ oz the plating then increases the finished copper weight to the desired 1oz each side. Plating +44 (0)

Layer 1 Layer 2 Layer 3 Layer 4 Electro-plating Process 2 Add Tin over Exposed Copper Areas Laminated Film Additional Copper Tin Plating A tin plate is added to all exposed copper areas, this act as a mask during the etching process. +44 (0)

Layer 1 Layer 4 Electro-plating Process 3 Remove Laminated Film Laminated Film Removed Tin Plating Layer 2 Layer 3 Film Strip The laminated film is removed to expose copper areas ready for the etching process. +44 (0)

Etch Process - Remove Exposed Copper Copper Removed Tin Plating The etching process removes unwanted areas of copper. The etch process produces an etch back or undercut of the tracks. This means that tracks will end up approximately 0,025 mm (0.001) thinner than the original design. Etching Process Layer 1 Layer 4 Layer 2 Layer (0)

Layer 1 Layer 2 Layer 3 Layer 4 Tin Strip - Remove Tin Plating Tin Plating Removed The Removal of Tin will very slightly reduce the copper thickness (T) on the outer layers Tin Strip +44 (0)

PCB is now complete except for surface finishes and panel routing/punching Layer 4 Layer 1 Via HoleSMD Pad Tracks +44 (0)

Solder Mask Application Image, Develop and Cure Layer 4 Layer 1 UV Image, Develop and Cure The image is semi cured and then UV image exposed. Any areas that are not exposed to the UV light are then dissolved in the developer, exposing the areas where the final surface finish is required. Solder Mask +44 (0)

Surface Finish Process Layer 4 Layer 1 Apply Solder to Exposed Copper Areas Surface Finish (Tin / Lead, Gold, Silver, OSP, Tin) is usually only added to pads. The solder mask prevents coating of any other areas. Surface Finish +44 (0)

Component Ident SCL Ident / Silk Screen An optional component Ident or Silk Screen is printed onto the PCB. +44 (0)

Routing or Punching The circuit profile is then punched or routed. +44 (0)

Testing and Inspection All PCBs are 100% Electrically tested All PCBs are 100% Visually Inspected +44 (0)