A multilayer Printed Circuit Board (PCB) is primarily made by laminating multiple layers of materials together under intense heat and pressure. This process bonds the separate layers into a single, sturdy board with internal conductive patterns.
The Core Lamination Process
To produce a multi-layer PCB, alternating layers of epoxy-infused fiberglass sheet called prepreg and conductive core materials are laminated together under high temperature and pressure using a hydraulic press. This lamination step is crucial for creating a solid, multi-layered structure.
Here's a breakdown of the key elements in this process:
- Materials:
- Conductive Core Materials: These are typically fiberglass reinforced epoxy sheets with copper foil laminated onto one or both sides. They contain the etched copper traces for the inner layers.
- Prepreg: This is a reinforcing material, usually fiberglass, that has been pre-impregnated with a resin (like epoxy) that is partially cured. It acts as the adhesive that binds the layers together.
- Equipment:
- Hydraulic Press: A powerful press capable of applying significant downward force.
- Conditions:
- High Temperature: Heat is applied to the stack of materials.
- High Pressure: The hydraulic press applies high pressure to the stack.
How the Layers are Joined
During the lamination cycle, the high temperature and pressure applied by the hydraulic press have a specific effect:
- The heat causes the resin within the prepreg material to fully cure and flow.
- The pressure ensures that the flowing resin fills any voids and creates a strong bond between the conductive core layers.
- This action causes the prepreg to melt and join the layers together, creating a monolithic multilayer PCB structure.
In essence, the prepreg transforms from a sheet into an adhesive and insulating layer that permanently bonds the conductive cores carrying the circuitry patterns. This intricate process ensures that all layers are perfectly aligned and securely joined, forming the robust foundation of a multilayer PCB.
