HDI PCB Design Guidelines

Materials and Processes

• Use new, thinner dielectrics (this may require different impedance calculations and layer stackup configurations).
• Keep in mind that solder paste masks will have tighter clearances and need more rigid control.
• Know when and how to use new technologies, such as via-in-pad, and coordinate with your manufacturer.
• Include considerations for signal integrity, such as controlled impedance layers and appropriate reference planes. 
• Ensure the stackup design aligns with thermal management strategies to prevent hotspots and ensure uniform heat distribution.

Components

• Incorporate smaller component package sizes with high pin counts and pin pitches of 0.5mm.
• Use different routing strategies, which might impact via escape patterns.

Routing

• Calculate impedance, control trace, and space constraints for multiple connection types, including transmission lines, analog, power, etc.
• Manage sensitive routing with zones or rooms across the board for adherence to different routing constraints.
• Use multiple via types, including thru-hole, blind & buried, and microvias. Use your CAD’s constraint system to manage these vias and their applications.
• Use thinner traces to achieve smaller, more efficient layouts. Be careful when handling current capacity and signal integrity.

Simulation

• Analyze your HDI designs and run simulations in conjunction with the manufacturer’s requirements.

Vias 

• Use microvias, blind & buried, and staggered vias for layer transitions to save space and improve density. 
• Consider smaller diameters for finer pitch components, limiting their useful depth. 
• Manage via inductance and resistance, which can be critical in high-speed circuitry.
• Minimize the use of unnecessary vias to maximize space for routing and minimize signal integrity issues. 
• Consider via filling if thermal or mechanical stability is a concern.

Via Types

Micro Vias (Laser)

Small vias between layers (e.g., 1:2, 2:3). Can be stacked or spaced based on rules.

Core Drilled Vias

Larger mechanical vias (e.g., 1:8) are used for long spans through core layers.

Blind/Buried Vias

Used for intermediate connections (e.g., blind 1:2, buried 6:7).

Via Stacking Rules

Stacked All

Vias (e.g., micro to micro) are stacked directly on top of each other.

Coincident Only

Vias/pads must align exactly with no offset.

Edge-to-Edge

Vias placed with specific spacing, not stacked.

Mixed Stacking

Some layers allow stacked vias, while others use spacing.

Constraint Manager Setup

Via Stacking Rules

Define stacking rules (e.g., micro to micro, micro to core) per physical rule set.

Same-Net Spacing

Controls via spacing on the same net (can allow pad overlap or require separation).

Hole-to-Hole Constraints

Used when pad overlap is allowed (takes precedence over pad-to-pad DRCs).

Physical Rule Sets

Assign lists of usable vias for routing (e.g., 1:2, 2:3, 6:7, 7:8, 1:8).

Routing Modes

Working Layer Mode

Asks the user what destination layer is during routing and automatically selects the correct vias to get there.

Non-Working Layer Mode

Less granular control; may auto-insert a long via (e.g., 1:8) without stacking logic.

Via Control

Add Connect Mode

Start routing, and system prompts for next layer transitions.

Double-Click Layer Transition

System queues the appropriate via stack based on rules and the selected destination layer.

Stack Manipulation

Slide Stack

Move the entire via stack along the trace path.

Split Stack

Right-click command that allows peeling off selected vias from a stack for independent manipulation.

Excel-like Via Selection

Select via layers in a cross-section using click-and-drag (like selecting cells in Excel).

Blind, Buried, and Micro Vias

Allows the integration of compact vias that do not traverse the entire board.

Reduces the need for through-hole vias, enabling more compact, dense layouts.

Constraint Manager

Enables setting and managing specific design rules tailored to HDI requirements, such as via stacking and spacing.

Ensures compliance with manufacturing capabilities and adherence to precise HDI guidelines.

Automated Via Selection

Automates the process of selecting the appropriate via based on routing context and predefined rules.

Reduces manual errors and speeds up the design process while ensuring adherence to the guidelines.

Stacked Vias Capability

Provides the ability to create and modify stacked via structures easily.

Supports intricate layer transitions and optimizes vertical space within multilayer PCBs, crucial for high-density interconnects.

Slide Command for Via Adjustments

Allows for the splitting or adjusting of via stacks post-placement.

Facilitates iterative design adjustments crucial for meeting final design requirements and resolving manufacturing challenges.

Interactive Routing Modes

Enables manual routing guidance while automatically adhering to set constraints for spacing and via usage.

Allows for fine-tuning of the PCB layout to ensure optimal manufacturability.

Design for Manufacturability (DFM) Checks

Integrates DFM checks into the design process to identify potential production issues early.

Helps ensure that the HDI PCB can be manufactured without defects, adhering to design and industry standards.