HDI PCBs enable you to pack more technology into tinier packages for use in medical, automotive and aerospace devices. These boards are constructed of multiple layers with buried and blind vias that must be properly designed to ensure impedance matching and minimize signal interference.
Always ask your board house about their fabrication methods. This will determine the necessary via size for your project, which impacts design for manufacturability.
Layout
Unlike traditional PCBs, HDI boards have compact layouts with tightly spaced high-density interconnects. As such, these circuit boards require more meticulous attention to detail for optimal signal integrity and impedance control. This includes optimized routing to minimize SI effect and careful component placements to ensure that signals don’t interfere with each other.
The layout for an HDI board can be complex due to higher connection densities and smaller pitch components. Consequently, it’s crucial that designers use high-performance PCB design tools that are rules-driven to make the task easy. These tools help to optimize layer stackups, visualize complex interconnects, and perform EMI analysis.
In addition to these features, HDI layouts also need to consider the metallization process, component arrangement, and escape routing for BGA components. Additionally, trace width, spacing, and annular ring size should be carefully chosen to avoid manufacturing issues such as plating problems and drilling problems.
Design for Manufacturability (DFM)
The DFM process ensures that a design is optimized for manufacturing. It reduces development time, improves product quality and lowers production costs. In addition, it helps companies meet sustainability goals.
DFM involves many different teams and tasks. Product managers, quality assurance and quality control (QA/QC) teams, procurement and supply chain management teams are hdi manufacturing process all involved in the DFM process. They set the quality standards and ensure that the manufactured products comply with these standards.
The DFM process requires careful planning and a deep understanding of the manufacturing process. It involves assessing the physical, mechanical and electrical properties of substrate materials to select those that align with HDI specifications. It also requires designing components that have fewer contact points. This reduces assembly time and makes it easier to test and verify the performance of the finished product. In addition, it saves valuable resources by reducing the amount of scrap material.
Material Selection
HDI PCB manufacturing is a more specialized process than standard PCBs, and requires more attention to detail. Choosing the right materials and design considerations will ensure a successful outcome.
To make an HDI circuit board, manufacturers must first create a detailed schematic layout. Using Computer-Aided Design (CAD) software can help with this. Next, they must determine the stack-up, which outlines the arrangement of conductive and insulating layers.
Fabricators then use laser drilling to create microvias in the inner layers of the board. They then fill these holes with conductive epoxy, silver-filled pastes or electrochemical plating. They also create a flat solderable surface on the top and bottom layers of the stack with ENIG, HASL or immersion tin.
The choice of material is crucial for HDI boards, as it influences the electrical performance of traces and the overall quality of the board. It is important to consider temperature, hdi pcb manufacturing CTE, dielectric loss and other factors during the selection process.
Stack-Ups
Stack-ups are the layer arrangement for a PCB and impact design flexibility, signal performance, EMI control, power delivery, and thermal management. PCB manufacturers offer a variety of different hdi stack up configurations to meet performance requirements, including multiple-layer build-ups and sequential laminations.
Typical PCBs are fabricated from a core, dielectric, and copper foil materials that are heat-pressed and glued together to form the board’s layers. The insulated core acts as an electrical insulator, while the copper foils serve as signal, ground, and power planes.
High-density interconnect (HDI) PCBs are a type of printed circuit board that features microvias, which are much smaller than traditional vias. This enables higher component densities and more complex and compact electronic devices. Choosing the right stack-up is crucial for successful HDI designs, and SierraConnect recommends consulting with your PCB manufacturer early on to determine which configuration is best suited for your application.
Via Selection
There are two basic HDI standard structures: sequential laminations/build-up and every layer interconnect (ELIC). Regardless of which structure is chosen, it’s important to plan efficient PCB stack-ups. Additionally, it’s necessary to select the appropriate microvias. Microvias are smaller than through holes and provide better reliability and signal conductivity.
Stacked vias require laser drilling to form and they are often used to route signals across multiple layers. However, it’s best to avoid using stacked vias unless they are absolutely needed. In addition, staggered vias are not ideal for HDI because they may interfere with the pad pitch and signal width.
In general, HDI PCBs utilize blind and buried vias to create layer interconnections. These vias should have low aspect ratios, ideally less than 1. Conventional buried vias in the center of the PCB stackup offer a connection through the thicker core layer and can have larger aspect ratios as they will be mechanically drilled.
PCB Assembly
The assembly process of HDI PCBs is complex, but the best practices can streamline workflow and minimize rework and errors. For instance, manufacturers can optimize their supply chain logistics by streamlining inventory control and ensuring that critical materials arrive on time and in the correct quantity. This ensures that production processes can continue without interruption and allows manufacturers to meet stringent quality standards.
Manufacturers can also maximize their efficiency by utilizing equipment specifically designed for high-density circuit board manufacturing. For example, laser drilling technology can reduce drill bit sizes and enhance precision during the formation of microvias, reducing assembly times while improving signal integrity and circuit performance.
With the right design tools, working with high-density PCB routing is a breeze. By using routing tools built on a rules-driven design engine, designers can quickly construct robust HDI layouts and satisfy fabricator DFM requirements. This includes determining trace width, via size, and placement/escape routing for BGA components.
