1、 Core process technology
Multi layer PCB manufacturing integrates precision materials science and microfabrication technology, with the core process as follows:
Inner layer graphic production
Pattern transfer: Apply a photosensitive dry film on a copper-clad substrate, form a circuit pattern through exposure and development, and then etch to remove excess copper foil .
Browning treatment: Micro etching the copper surface to generate an oxide layer, enhancing interlayer bonding and preventing high-temperature delamination (plate explosion).
Lamination process
Stack the inner layer board, semi cured sheet (prepreg), and copper foil according to the design, and vacuum hot press at 180-200 ℃ and 200-400psi pressure for 60-90 minutes to ensure uniform resin flow without bubbles.
Drilling and hole metallization
Drilling types: through holes (penetrating the entire board), blind holes (outer to inner layers), buried holes (connecting between inner layers), laser drilling can achieve 0.05mm micro holes of .
Copper electroplating: After chemical deposition of copper seed layer, the entire board is electroplated, and the copper thickness of the hole wall needs to be ≥ 25 μ m to ensure conductivity reliability.
Outer layer wiring and surface treatment
Repeat the graphic transfer process to create the outer circuit, and increase the copper thickness by 5 for graphic electroplating.
Surface treatment: ENIG is used for high-density BGA (gold thickness 0.025-0.127 μ m), while HASL has low cost but poor flatness.
Solder mask and testing
Apply solder mask ink to protect the non welding area, and print the component part number 8 with characters.
Electrical testing (such as flying pin testing) verifies connectivity, and AOI detects visual defects.
Technical difficulties and breakthroughs:
Inter layer alignment: For boards with more than 16 layers, an alignment accuracy of ± 25 μ m is required, relying on high-precision exposure equipment.
Impedance control: The high-speed board requires a tolerance of ± 5%, which can be achieved by adjusting the line width/dielectric thickness to .
High frequency materials: 5G communication adopts Rogers RT/duroid 5880 (Dk=2.2), reducing the loss in the 28GHz frequency band by 40%.
2、 Core advantages and limitations
Advantages:
High density integration
The vertical stacking design reduces wiring area, and the smartphone motherboard integrates processor/memory/sensor through 8-12 layer boards.
Signal integrity optimization
The dedicated layer and power layer suppress EMI, and differential signal wiring reduces crosstalk by 60%, supporting 10Gbps+high-speed transmission (such as PCIe 5.0).
Thermal management and power stability
The power plane reduces impedance and ripple noise can be controlled within 50mV; The heat conduction layer or metal substrate (such as aluminum substrate) improves the heat dissipation efficiency by .
Lightweight and Reliable
Replace multiple single panels, reduce equipment weight (such as aerospace equipment), and enhance vibration resistance with a laminated structure.
Limitations:
High cost: The cost of 8-layer board is 4 times that of double-sided board, due to the material (high-frequency substrate is 5-8 times more expensive) and complex process.
Design threshold: It is necessary to simulate signal integrity, and blind buried hole design increases the difficulty by .
Difficulty in maintenance: Inner layer faults require X-ray or layered testing, with a low success rate of 9% in repair.
3、 Application Fields
Multilayer PCBs are irreplaceable in the high-end electronics field:
Typical product technical requirement cases and performance in application fields
Communication equipment 5G base station antenna/Massive MIMO high-frequency low loss, impedance controlled hybrid board (FR-4+Rogers) achieves 18GHz insertion loss ≤ 0.5dB/inch1
Automotive electronic battery management system (BMS)/millimeter wave radar temperature resistance (-40-125 ℃), anti vibration 10 layer BMS board control ripple<50mV; 77GHz radar accuracy ± 0.1 °
Computing hardware AI server/GPU acceleration card high-density wiring, high-speed signal 12 layer board supporting 10Gbps GPU interconnect
Consumer electronics, smartphones/wearable devices, miniaturization, flexible rigid combination folding screen. The phone adopts an 8-layer rigid flexible combination board
Industrial and medical industrial controllers/endoscopes with high reliability and chemical corrosion resistance. Flexible multi-layer boards for medical probes compatible with curved pipelines
4、 Industry Trends
High density interconnect (HDI) technology
Laser blind hole+Build up process achieves line width/line spacing ≤ 50 μ m, meeting the requirements of chip packaging.
Materials Innovation
Nano filler resin (Dk<3.0) reduces high-speed signal loss, and ceramic substrate improves heat dissipation efficiency by .
Breakthrough in localization
Jieduobang and other manufacturers have mastered the alignment accuracy of 16 layer boards ± 25 μ m, and high-frequency mixed pressure plates replace imported ones.
green manufacturing
Lead free tin spraying, wastewater recycling technology to reduce pollution, and research and development of biodegradable substrates
