Multilayer PCB | Types of PCB
Multilayer PCB is Printed Circuit Board with more than 2 layer. Multilayer PCB must have 3 conductive layers Interconnected with copper plated holes.
Multilayer PCB is a Printed Circuit Board with more than 2 layers. A Double-Sided PCB has two conductive layers on top and bottom of the PCB substrate. A Multilayer PCB must have a minimum of 3 conductive layers of conductive material or copper layer. All the layers are interconnected with copper plated holes. The layers can be 4, 6, 8…upto 40 layers.
A multilayer PCB is complex by design. The top and bottom layers look same as a double sided PCB but has staked layers on both sides of the core. All the layers are compressed to form a single Multilayer PCB where all the layers are interconnected via copper plated holes.
All the active and passive electronic components are assembled on top and bottom layers. All the inner stacked layers are meant for routing. Both through-hole electronic components and Surface Mount Components (SMD) can be soldered on either side of this type of PCB. SMD components can be soldered with Surface Mount Technology and other PCBA Tools. A general Multilayer PCB has following layer stacking:
- Top Layer ( Electronic Components)
- Inner Layer-1 (Routing)
- Inner Layer-2 (Routing)
- Inner Layer-3 (Routing)
- Bottom Layer ( Electronic Components)
Multilayer PCB Manufacturing Process
Multilayer PCB manufacturing process needs special precaution as there are more chances of cross connections, overlaps, tracing in copper areas, etc. The whole process needs to be done in an ESD-Safe and Cleanroom environment. Special manufacturing setup and equipment are needed for 8+ layer PCB manufacturing process.
Following are the steps involved in Multilayer PCB Manufacturing Process:
- The process starts with designing Layout of the PCB using any PCB designing software / CAD Tool (Proteus, Eagle, OrCAD).
- Next step is to make the Inner Layer Core. Laminate of desired thickness is treated with Copper foil, dry film resist and UV light to make the inner layer core.
- Next step is lamination. This process include: Inner layer core, prepeg sheets and copper foil sheets. The sheets of material are staked on each other and holes are used to align them as they are stacked up.
For a 4 layer board, Staking of layers is as follows: Bottom Layer of Copper Foil – Prepeg Sheets – The Inner Layer Core – More Prepeg Sheets – Finally Copper Foil Sheet on Top.
- Next step is to apply pressure, heat and vacuum using a heated hydraulic press. Vacuum is important to make sure there is no air trapped between the layers. This process ends over 2 hours depending on number of layers.
- Once cured, resins from the prepegs join the sheets, core, and foil together forming a multilayer PCB.
Video: How to Make a Printed Circuit Board (PCB) – Step By Step Guide & Tutorial
Benefits of Multilayer PCB
- Reduced PCB Size / small size (Saves space).
- High quality and density
- Better durability and flexibility
- Powerful with Single Connection Point
Disadvantages of a Multilayer PCB
- Higher manufacturing and production cost
- Complicated design and production
- Limited manufacturers
- Highly skilled and trained designer are required
- Increased production time
Uses of Multilayer PCB
Multilayer Printed Circuit Boards offer more flexibility and increased circuit density with reduces size. This is why many electronic companies in the world use these boards in several electronic devices and gadgets:
- Computers and Laptops
- Telecommunications Equipment – Mobile Phone, Tablets and other Hand Help Devices
- File server and Data storage
- Signal transmission, mobile phone repeaters, GPS
- Medical Equipment: Testing, X-Ray, Heart Monitor, CAT Scan
- Industrial Equipment
- Atomic and Nuclear Systems
- Military and Defense Equipment
- Anywhere, where complex Circuitry is needed.
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