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High-density Multilayer PCBs

What is HDI PCB?

High Density Interconnect, or HDI, circuit boards are printed circuit boards with a higher wiring density per unit area than traditional printed circuit boards (PCB). In general, HDI PCBs are defined as PCBs with one or all of the following: microtraces, VIP (Via In Pad), microvias, blind vias, buried vias or other microvia technique, built-up laminations and high signal performance considerations.

Benefits and Challenges of Using HDI

  • Placement Feasibility – SMT Parts will not fit with room for pin escapes to PTH vias, so use VIP via in pad.

  • High Speed or RF performance – unwanted parasitics or excess inductance from standard PTH vias

  • Requirement for thin PCBs in some market spaces.

  • Back to back large active BGA’s on both sides of PCB.

  • RF on Primary Side / Digital on Secondary side

HDI uTraces - Using mSAP and SAP

Upcoming manufacturing process development will allow circuits to be designed with  lines and spaces in the range of 1-2 mil (25-50uM) with strict impedance control

mSAP – Modified Semi-Additive Process

With mSAP, a much thinner copper layer is coated onto the laminate, and plated in the areas where the resist is not applied thus, the “additive” nature of the process. The thin copper remaining in the spaces between conductors is then etched away. Whereas trace geometries are chemically defined during subtractive processes, mSAP allows trace geometries to be defined via photolithography.

SAP – Semi-Additive Process

Although the semi-additive process (SAP) used in the IC substrate board can realize more precise circuit fabrication, but there is a problem that the manufacturing cost is high and the production scale is small, thus restricted to ICs as of today

Capabilities in Manufacturing High Density PCB

Monthy Capability3900 m²/month
Layer10 Layers
MaterialFR4, TG180
Finished board thickness2m
Min Trace Width/Space3.5mil
Min hole size0.2mm
Min copper in hole thickness1oz
Outer layer Finished copper thickness1.5oz
Inner layer base copper thickness1oz
Impedance Control Tolerance±10%


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