Layer buildup

Multilayer circuit boards comprise outer and inner layers (copper layers) and help to achieve more complex, denser wiring structures.

Multilayer circuit boards are grouted using the following components:

  • Copper foil
  • Prepreg (pre-impregnated fibreglass/resin composites)
  • Core (prepreg grouted between 2 copper foils)

Prepregs and cores are also available in High-Tg and halogen-free types.

Available prepregs, cores, and foils

 

Rules for layer buildup

Please observe the following rules for the design of the layer buildup:

Wrong: Right:
  • Layer buildup foil techniques

1) Use foil techniques
inner layers composed of cores.
outer layers composed of copper foil and prepreg.
Advantages:

  • Improved dimensional stability
  • Reduced costs
 
Wrong: Right:
  • Layer buildup prepregs

2) Keep the number of prepregs low
Use at most 2 prepregs per layer (also recommended by IPC).

Exceptions with only 1 prepreg: Many layers in a multilayer with defined total thickness, use of microvias (aspect ratio).

Exceptions with 3 and more prepregs include (for example) large thickness of the copper foil on the cores.

Advantages:

  • Improved dimensional stability
  • Reduced costs
  • Reduces thickness tolerance
 
Wrong: Right:
  • Layer buildup copper thickness

3) Identical copper thickness on the cores
Always plan the cores with identical copper cladding.

Advantages:

  • Less bowing, twisting, or deformation
  • Symmetric design
  • Reduced under etchingg
 
Wrong: Right:
  • Printed Circuit symmetric layer buildup

4) Symmetric design
Ensure a uniform distribution of the 3 components: prepreg, core, and copper foil

Advantages:

  • Less bowing, twisting, or deformation
  • Reduced costs
  • Improved process reliability
 

SBU-Multilayer

Multi CB can also create sequential layer buildups (= SBU), in which multiple pressure sequences are used. This permits use of blind vias and buried vias, allowing even higher integration levels. 

For SBU multilayers, the circuitry is divided in a bi- or multilayer core and one or multiple external microvia layers (vias with diameter smaller than 150µm).

Lasered blind vias

Blind vias are lasered for diameters smaller than 150µm. The prepreg and copper foil are then replaced by RCC (Resin Coated Copper) foil, whose resin is similar to the epoxy in FR4.

Electric strength

To maintain the highest possible capacitance between two large-area potentials, the layer spacing should be as small as possible. The necessary voltage separation between the potential and bordering layers require a minimum thickness. The following value may be used to calculate the optimum spacing:

The electric strength of FR4 is approx. 30 kV/mm.

Additional information:

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Pricing Examples

Printed Circuit Boards always include:

- E-Test
- Solder-stop 2x
- Marking print 1x
- Gerber-Import
- Scoring (series)
- Design-Rule-Check

- Tooling costs
- Photoplot
- Conductors 150μm
- Drill holes 0,3mm
- Unlimited drilling
- HAL, FR4 1,6, 35μm Cu
Prototypes
2 layers - 6 WD
41,- €
1 Printed circuit board 100x100mm
4 layers - 6 WD
118,- €
1 Printed circuit board 160x100mm
6 layers - 8 WD
148,- €
1 Printed circuit board 160x100mm
Series
e.g. 100 pcs. Eurocard 100x160mm
2 layers - each
4,76 €
 
4 layers - each
7,41 €
 
6 layers - each
11,20 €
 
8 layers - each
16,05 €
 
SMD Stencils
max. 200x300mm - 3WD
47,50 €
1 Stencil, including 1000 pads
max. 600x600mm - 3WD
90,44 €
1 Stencil, including 2500 pads

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News

14.05.2013
Multi CB in outer space

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17.04.2013
Better prices, shorter production times

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01.12.2012
4 layer prototypes even faster!

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