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Process, Material Selection, And Application Areas of Multi-layer Printed Circuit Boards

Views: 0     Author: Site Editor     Publish Time: 2025-06-23      Origin: Site

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1、 Core process technology

1. Precision lamination and interconnection process

The core of multi-layer PCB lies in interlayer alignment and bonding, and key technologies include:

Laminated laminate

Material stacking: The inner core board (copper-clad substrate) and the semi cured sheet (PP sheet) are alternately stacked and pressed under high temperature (180 ℃± 5 ℃) and high pressure (300-400 psi) in a vacuum environment.

Positioning system: Front positioning (PIN-LAM, accuracy ≤ 75 μ m) is used for high-density boards; MASS-LAM has higher efficiency and lower cost.

Micro hole processing

Laser drilling: CO ₂/UV laser drilling blind buried holes (aperture 0.1-0.2mm), with a depth to diameter ratio of 8:1, supporting high-density interconnection of more than 20 layers.

Resin plug hole: The through-hole is filled with epoxy resin to prevent welding short circuits, which is a mandatory requirement in the automotive electronics field.

Surface Treatment

ENIG immersion gold: high solder joint strength (45MPa), corrosion-resistant, used for BGA packaging;

OSP lead-free processing: environmentally friendly and low-cost, suitable for consumer electronics.

2. Breakthrough in advanced technology

HDI (High Density Interconnect) technology

Using arbitrary layer micropores (pore size 50 μ m) and laser direct imaging (LDI), the line width/spacing reaches 40 μ m, reducing the volume by 50% compared to traditional PCBs.

Rigid flexible combination design

The flexible zone (PI substrate) and rigid zone (FR-4) are mixed and compressed to adapt to dynamic structures such as foldable screens and mobile phone shafts.

Thin core layer processing

0.15mm ultra-thin core board replaces POFV process to solve the problem of resin plug hole deformation in ultra-thin boards (0.3mm).

2、 Material selection and performance comparison

The performance of multi-layer PCBs is highly dependent on the substrate, and the mainstream materials and applicable scenarios are as follows:

Material type, characteristics, advantages, limitations, applicable scenarios

FR-4 epoxy resin has low cost (¥ 20-50/㎡), flame retardancy (UL94 V-0), high mechanical strength (bending resistance>400MPa), and high high-frequency loss (Df> 0.02@1GHz )Consumer electronics motherboards and industrial control devices 68

High Tg epoxy resin has excellent heat resistance (Tg ≥ 170 ℃) and is suitable for lead-free soldering (peak 250 ℃). The cost is 30% higher than standard FR-4 for automotive ECU and high-power power module 6

Polyimide (PI) is flexible and bendable, resistant to high temperatures (300 ℃), highly resistant to radiation and moisture absorption (>2%), and expensive (¥ 80-120/㎡) for aerospace sensors and foldable screen smartphones

PTFE (Teflon) has extremely low high-frequency loss (Df< 0.002@10GHz )Stable dielectric constant (Dk ≈ 2.1), difficult processing (requires plasma activation), extremely high cost (¥ 200-300/㎡), 5G base station antenna, millimeter wave radar 93

Ceramic substrate (LTCC) has high temperature resistance (>800 ℃), high thermal conductivity (24-170 W/mK), high brittleness, difficult to repair military communication, and high-power lasers

The golden rule for selecting materials:

First choice for cost-effectiveness: FR-4 (accounting for 70% of global usage);

High frequency and high speed: PTFE or modified FR-4 (mixed pressure design reduces costs by 30%);

Extreme environment: PI or ceramic substrate.

3、 Application Fields and Typical Cases

1. Communication and computing (accounting for 45%)

5G base station: mixed voltage PTFE+FR-4, 12 layer board supports 28GHz RF, impedance control ± 3%.

AI server: 20 layer HDI board, embedded resistance and capacitance technology integrated GPU/CPU, signal rate 112G PAM4.

2. Automotive electronics (accounting for 25%)

Autonomous driving domain controller: 8-layer aluminum substrate+2oz thick copper, thermal conductivity of 4.0W/mK, vibration resistance of 20G.

800V battery management system: 6-layer ceramic filled FR-4, withstand voltage of 3kV, insulation resistance>100G Ω.

3. Consumer electronics (accounting for 20%)

Smartphone: 10 layers of arbitrary HDI (thickness ≤ 1.0mm), supporting dynamic folding screen structure.

AR/VR equipment: 6-layer rigid flex bonding plate, bending radius 3mm, transmission 4K@120Hz Video.

4. Special fields

Medical imaging: Low loss modified FR-4 (Df<0.02) ensures MRI signal accuracy.

Aerospace: Polyimide multilayer board, resistant to cosmic rays>100krad, used for satellite communication.

 4、 Process Challenges and Response Strategies

Technological progress in challenge solutions

Ultra thin board warpage symmetrical laminated design+low CTE material (CTE<10ppm/℃) laser real-time compensation pressing parameters

High frequency material processing is difficult, PTFE surface plasma activation → improving copper foil adhesion. Domestic hydrocarbon resin (Dk=3.0) replaces imports

Uneven pulse reverse electroplating and oscillation filling technology for micro hole electroplating, with a depth to diameter ratio of 12:1, breakthrough in micro hole capability

5、 Future Trends and Selection Suggestions

Technological Evolution Direction

High frequency: 6G promotes the research and development of nano ceramic substrates with Dk<3.0;

Miniaturization: laser micro hole aperture reduced to 30 μ m, 42 layer board thickness ≤ 0.8mm;

Green manufacturing: Halogen free FR-4 penetration rate>80% (driven by EU RoHS)


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