High precision machining requirements
Interlayer alignment accuracy: ≤0.002 inches (about 50 μm), laser positioning and optical alignment technology are required.
High thickness-to-diameter ratio drilling: Drilling with a thickness-diameter ratio of > 10:1 requires a pulse plating process to avoid uneven copper thickness on the hole wall.
Resin Plugging: Prevents copper plating from penetrating into the inner layer, ensuring signal integrity.
Signal integrity optimization
Impedance control: By adjusting parameters such as dielectric thickness and copper foil roughness, the single-ended impedance is 50Ω and the differential impedance is 100Ω.
Backdrill process: Removes residual stubs to reduce signal reflections, typical stub length ≤ 8mil.
Embedded Capacitance (ENCAP): Integrates capacitance on the inner layer of the PCB to reduce power supply noise.
Flatness and reliability control
DUT Pad Flatness: Uses vacuum pressing and low-temperature curing process to reduce warping caused by plate stress.
Pad surface treatment: electrothin gold (2-5μin) + selective electrothick gold (20-50μin), taking into account solderability and wear resistance.
Non-Destructive Testing: Inner layer connections are inspected using X-Ray, and AOI (Automatic Optical Inspection) ensures that pads are defect-free.
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