HDI PCB manufacturer

HDI PCB Application Fields

Definition and Classification of HDI PCB

HDI PCB Grade Illustration (Taking 6-Layer HDI PCB as an Example)

• First-Order HDI PCB (1+n+1): The blind vias are distributed as 1-2, 2-5, and 5-6 layers. Laser drilling is required for the 1-2 and 5-6 layer pairs, which is the most basic type of HDI PCB with relatively simple process control.
• Second-Order HDI PCB (2+n+2): The blind vias cover 1-2, 2-3, 3-4, 4-5, and 5-6 layers, requiring two laser drilling and two lamination processes. The specific process flow is as follows: first drill the embedded vias for 3-4 layers, then perform lamination for 2-5 layers; conduct the first laser drilling for 2-3 and 4-5 layers, followed by the second lamination for 1-6 layers; perform the second laser drilling for 1-2 and 5-6 layers, and finally drill through vias. Second-order HDI PCB can be further divided into two types:
  • Staggered Second-Order HDI PCB: Blind vias (e.g., 1-2 and 2-3 layers) are arranged in a staggered manner without overlapping.
  • Stacked Second-Order HDI PCB: Blind vias (e.g., 1-2 and 2-3 layers) are stacked, such as the blind via distribution of 1-3, 3-4, and 4-6 layers.
• Higher-Order HDI PCB: Following the same principle, higher-order HDI PCBs (3+n+3, 4+n+4, 5+n+5, 6+n+6, etc.) are developed by increasing the number of laser drilling and lamination cycles, which are mainly used in ultra-high-density electronic products such as high-end servers and precision medical equipment.

• Manufacturing Process: HDI PCB is mainly manufactured by lamination technology, and the number of lamination cycles directly determines its technical grade. Ordinary HDI PCBs adopt one-time lamination, while high-order HDI PCBs require two or more lamination processes, combined with advanced technologies such as stacked vias, via filling electroplating, and laser direct drilling. For PCBs with more than 8 layers, the manufacturing cost of HDI technology is lower than that of traditional complex lamination processes.
• Electrical Performance: HDI PCB has higher electrical performance and signal integrity compared to standard PCB. It also provides better improvement in radio frequency interference (RFI), electromagnetic interference (EMI), electrostatic discharge (ESD), and heat conduction. The high-density integration (HDI) technology enables the miniaturization of terminal product design while meeting higher requirements for electronic performance and efficiency.
• Process Difficulties: First-order HDI PCB has a simple process and easy control. The main challenges of second-order HDI PCB lie in layer alignment, drilling accuracy, and via electroplating quality. Second-order HDI PCB has three common design schemes:
  • Staggered Design: Each order of blind vias is arranged in a staggered manner, and adjacent second layers are connected through middle-layer wires, equivalent to two first-order HDI structures.
  • Stacked Design: Two first-order vias are overlapped to achieve second-order interconnection; the processing process is similar to two first-order vias but requires strict control of key process points.
  • Direct Drilling Design: Directly drill vias from the outer layer to the third layer (or n-2 layer), which has higher drilling difficulty compared to the previous two schemes.
    
    

HDI PCB Stack-Up Design and Key Points

Key Advantages of Microvias in HDI PCB

• Optimizing HDI PCB wiring: Reasonable via layout improves signal integrity and increases internal routing space.
• Saving layout space: For finer-pitch BGA components (which pose increasing challenges to PCB design), HDI PCB design rules allow for staggered and blind vias. For example, overlaying microvias on through-holes or placing microvias on top of through-holes can significantly save PCB layout space.

HDI PCB Stack-Up Design Method

1. Determine Trace Size: First, adjust the trace width and thickness to ensure controlled impedance. A preliminary estimate of layer thickness is required based on prior experience. Alternatively, the BGA pitch can be used to set an upper limit on the trace width, and this value is used to determine the layer thickness required to achieve the desired line impedance.
2. Estimate Nets per Layer: Once the required trace width/layer thickness (and the spacing between differential trace pairs) is determined, the space occupied by the signal layer within the HDI PCB layout area can be roughly estimated. This requires specifying an estimate of the HDI PCB size; multiplying the approximate number of BGA breakout channels per unit area by the PCB area gives the number of nets per layer. This value is then used to estimate the total number of signal layers required in the HDI PCB stack-up.
3. Calculate Total Layer Count: Divide the total number of nets by the number of nets per layer to get an estimate of the signal layers (not the total number of layers). Finally, add power and ground layers to the HDI PCB stack-up to obtain the initial stack-up scheme.

Advantages of HDI PCB

1. Cost Optimization: For PCBs with a density of more than 8 layers, the manufacturing cost of HDI technology is lower than that of traditional complex lamination processes.
2. Increased Circuit Density: Enhances the interconnection between traditional circuit boards and components, enabling higher integration.
3. Support for Advanced Manufacturing Technologies: Facilitates the adoption of advanced construction processes such as stacked vias and laser drilling.
4. Superior Electrical Performance: Offers higher electrical performance and signal integrity compared to standard PCB.
5. High Reliability: Ensures stable operation in harsh working environments.
6. Improved Thermal Performance: Enhances heat conduction efficiency, reducing the risk of overheating in high-power devices.
7. EMC Optimization: Effectively improves resistance to radio frequency interference (RFI), electromagnetic interference (EMI), and electrostatic discharge (ESD).

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