Lamination and Drilling

Lamination and Drilling

Overview

Once the inner cores are ready, they must be pressed together with copper foils into a complete multilayer board — that is lamination. Then drilling punches through-holes that connect the layers, preparing for hole metallization. This article covers all six steps of the B stage.

Process Chain Overview

Lamination & drilling process chain
Brown Oxide → Riveting → Lay-up → Pressing → Post-treatment → Drilling
     │           │          │         │             │            └─ drill layer-to-layer vias
     │           │          │         │             └─ edge grinding / target drilling / routing; tooling holes
     │           │          │         └─ hot pressing (kraft paper + steel plates)
     │           │          └─ foil + prepreg + core lay-up
     │           └─ rivets pin multiple inner layers together
     └─ roughen copper surface to bond with resin

01 Brown Oxide

Purpose (three aspects):

1. Roughen the copper surface to increase contact area with resin
2. Improve wettability of the copper surface to flowing resin
3. Passivate the copper surface to avoid undesirable reactions

Main material: brown oxide solution MS100.

Note: the brown oxide film is very thin and scratches extremely easily — handle with care. Brown oxide quality directly determines copper-to-resin bonding after lamination; a scratch becomes a future delamination risk.

02 Riveting

Purpose: rivet multiple inner layers together to prevent interlayer slippage during subsequent processing (4-layer boards do not need rivets; they are used when layer counts are higher).

Main materials: rivets, prepreg (P/P).

Prepreg is the “glue” of lamination, composed of resin and glass fiber cloth:

• By glass cloth type: 106, 1080, 3313, 2116, 7628, etc.
• By resin cross-linking state, three classes:
  • A-stage: fully uncured
  • B-stage: semi-cured (production uses B-stage prepreg)
  • C-stage: fully cured

The lamination principle is exactly this: B-stage resin flows, fills, and cures under heat and pressure — bonding all layers into one.

03 Lay-up

Purpose: stack the pre-assembled panels into the form ready for pressing.

Main materials: copper foil, prepreg, inner cores. Electro-deposited copper foil by thickness:

Code	Thickness	Common name
T	12 μm	1/3 oz
H	18 μm	1/2 oz
1	35 μm	1 oz
2	70 μm	2 oz

The stacking order (foil-prepreg-core-prepreg-foil…) determines the final layer sequence and must strictly follow the engineered stack-up.

04 Pressing

Purpose: press the stacked panels into a multilayer board by hot pressing.

Main auxiliaries: kraft paper, steel plates, carrier plates.

During pressing, the stack is sandwiched between steel plates, with kraft paper providing pressure-transmission cushioning, while hot plates apply temperature and pressure. Multiple stacks can be pressed simultaneously, multiplying throughput — which is exactly what the carrier plate enables.

05 Post-treatment

Purpose: edge grinding, target drilling, and routing of the pressed panel for preliminary profile processing — meeting quality-control requirements and providing the tooling holes for subsequent processes.

Main materials: drill bits, routers.

“Target drilling” drills the target holes — establishing the unified datum system for all later registration steps (drilling, exposure, profiling).

06 Drilling

Purpose: drill through-holes on the board that connect the layers electrically.

Main materials and their roles:

• Drill bit: made of tungsten carbide, cobalt, and organic binders — the cutting core
• Entry board (aluminum sheet):
  • drill registration
  • heat dissipation
  • reduce hole-entry burrs
  • protect the panel surface from the pressure foot
• Backup board (composite, on the exit side):
  • protect the drilling machine table
  • prevent exit-side burrs
  • lower drill bit temperature
  • clean resin smear from the drill flutes

Drilling quality (hole-wall finish, hole-position accuracy) directly affects hole metallization yield — a rough hole wall or residual smear leads to discontinuous plating.

Summary

• Lamination = copper foil + prepreg (B-stage resin) + inner cores, hot-pressed and cured; brown oxide and riveting are the two quality prerequisites
• The copper foil thickness codes (T/H/1/2) appear in daily design communication — worth remembering
• The “entry board + backup board” system solves three problems: registration, heat, and burrs
• Post-treatment target holes establish the process-wide datum, paving the way for hole metallization

Next up: hole metallization — making the insulating hole walls “grow” copper to achieve true layer-to-layer electrical connection.

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