PCB Inner Layer Process: Panel Layout Explained
By PCBA PrototypePublished On: 2025-05-16Categories: Uncategorized0 Comments on PCB Inner Layer Process: Panel Layout Explained
By PCBA PrototypePublished On: 2025-05-16Categories: Uncategorized0 Comments on PCB Inner Layer Process: Panel Layout Explained
Definition of Panel Layout:
Before laminating multi-layer boards or base materials, it is necessary to align and stack inner layers, prepregs, copper foils, and other loose materials with steel plates, kraft paper padding, etc., to ensure accurate alignment (registration). This preparatory work before sending the materials to the laminating machine for hot pressing is called panel layout.
Base Materials Used in Panel Layout:
Base materials, also known as copper-clad laminates (CCL), are raw materials for printed circuit boards (PCBs) with different specified thicknesses. They are made by bonding copper foils together with prepregs under high temperature and pressure.
Copper Foils Used in Panel Layout:
There are two main types of copper foils used in the PCB industry: electroplated copper foils and rolled copper foils.
Electroplated copper foils are commonly used. One side is smooth (drum side), and the other side is a rough crystalline surface (matte side).
Prepregs Used in Panel Layout:
Prepreg (short for “pre-impregnated”) is a sheet-like bonding material composed of resin and a carrier.
- Resin: A thermosetting material and polymer. Epoxy resin is currently widely used.
- Glass Fabric: An inorganic material formed by high-temperature melting and cooling into a non-crystalline rigid structure, then woven into a reinforcing material by warp and weft yarns.
Types of Panel Layout Lamination:
- Mass Lamination
This method involves first positioning and riveting inner layers and sandwiching prepregs with hot-melt rivets, then adding copper foils before high-temperature lamination. This simplified, fast, and large-area lamination method can increase the number of “openings” (Openings) according to the base material approach, reducing labor and increasing production. - Pin Lamination
This is a small-area lamination method where inner layers, prepregs, and copper foils are first positioned with pins, pre-stacked, and then subjected to high-temperature lamination.
Panel Layout Process (Mass Lam)
- Automatic Copper Foil Cutting: Using an automatic reflow system, copper foils are cut to a fixed size of 1118×1280 mm.
- Prepreg Cutting: Cutting prepregs into required sizes.
- Prepreg Positioning Hole Drilling: Punching holes according to the spacing, quantity, position, and size of positioning holes used in pre-stacking.
- Hot-Melt Riveting: Fixing layers at the positioning hole positions used in pre-stacking.
- Steel Plate Cleaning: Removing adhesive residues and minor scratches from the surface of steel plates using mechanical grinding before pre-stacking.
- Kraft Paper: A material for heat insulation and pressure buffering.
- Pre-Stacking: Manually stacking inner layers and prepregs together.
- Panel Layout: Placing copper foils, steel plates, and kraft paper in sequence on the pre-stacked boards via an automatic reflow line.
Definition of Lamination Process:
The process of bonding inner layers, prepregs, and copper foils together under high temperature, high pressure, and vacuum conditions to form multi-layer PCBs is called thermal lamination.
Process Conditions:
- Providing the temperature required for prepregs to change from solid to liquid and undergo polymerization.
- Providing the pressure required for liquid resin to flow and fill the circuit space.
- Providing the vacuum degree required for volatile components to escape from the board.
Lamination Process:
- Pressing: Laminating the stacked PCBs under set temperature and pressure.
- Debonding: Separating the cooled laminated boards from the steel plates using an automatic reflow debonding system.
- Panel Separation: Separating boards according to the PNL (Panel) size.
- X-Ray Drilling: Using X-ray perspective and target positioning to drill positioning holes for the next drilling process.
- Edge Milling: Trimming uneven glue flow edges with a milling machine to achieve uniform dimensions as per engineering specifications.
X-Ray Drilling:
Through X-ray transmission, the surface copper foil is projected onto the inner layer targets, and drill bits are used to drill positioning holes at the corresponding positions of these targets.
Functions of Positioning Holes:
- Aligning inner layers in multi-layer boards.
- Serving as positioning holes for outer layer manufacturing to ensure alignment between inner and outer layers.
- The third hole is an anti-reverse hole to determine the board’s orientation.
X-Ray Drilling Schematic:
(Note: The diagram is omitted here and should be referenced in the original document.)
Edge Trimming:
Trimming the edges of semi-finished boards after lamination to the required dimensions as per MI (Manufacturing Instruction) requirements.
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