Introduction to HDI PCBs: Packing More Power in a Smaller Package
- TapRen Team
- Mar 27
- 8 min read
Updated: Apr 2
Abstract
The relentless miniaturization trend in electronics demands ever-smaller yet more powerful components. This article examines the fascinating world of high-density interconnect (HDI) PCBs and their technological marvels. We'll explore their intricate construction, advantages over traditional PCBs, and the innovative applications where HDI PCBs push the boundaries of what's possible. By the end, you'll gain valuable insights into these miniature masterpieces and their transformative role in modern electronics.
Introduction
HDI PCBs are printed circuit boards with a higher wiring density per unit area compared to traditional PCBs. They achieve this through the use of microvias, fine lines, and thinner materials. Different types include 1-n-1, 2-n-2, and any layer HDI, each offering varying levels of complexity and performance. The relentless pursuit of smaller and more powerful electronic devices drives innovation across the industry. From smartphones that fit in your pocket to wearables seamlessly integrating with your body, miniaturization is a defining trend. However, this trend poses a significant challenge: packing more functionality into a smaller space without compromising performance.
High-Density Interconnect (HDI) PCBs are the answer to the miniaturization challenge. These PCBs take traditional printed circuit board (PCB) technology to the next level, utilizing advanced techniques to create intricate pathways for electrical signals on a significantly reduced footprint. This allows for the integration of more complex circuitry within smaller devices, paving the way for a new era of compact and powerful electronics.
Recommended reading: Materials used in PCB Manufacturing
Demystifying the HDI PCB
High-Density Interconnect (HDI) PCBs achieve remarkable miniaturization through several ingenious features that overcome the limitations of traditional PCBs. Here’s a closer look at these key elements:
Different Types of HDI PCB Stackup
According to the IPC-2315 standard from the IPC, there are 6 basic types of stack-ups. These stack-ups types include I, II, III, IV, V and VI. However, the last three types are more expensive and have minimum use. So we will only discuss the first three types of vias. Moreover, the standard differentiates HDI stack-ups on the basis of the vias type. Such as micro, buried, blind and plated through vias.
1. HDI Type I: These types have a structure of a laminated core having at least just a single layer of micro vias. These vias can exist on one or both sides of the circuit. Type I HDI use blind and PTH vias. However, it doesn’t use buried vias.
2. HDI Type II: This type includes different blind and buried vias on a laminated core. Fabricators can stagger different micro vias and stack them relative to buried vias.
3. HDI Type III: To construct this type, the manufacturer uses micro vias, buried and blind vias on a laminated core. Moreover, this type includes at least two layers of micro vias on one side of the board or both. You can stagger micro vias over other micro vias. Furthermore, you can stack them over other buried vias.
Ultra-Fine Lines and Spaces
Traditional PCBs contain large, well-spaced electrical traces that resemble vast city avenues. HDI PCBs, on the other hand, use significantly thinner lines and smaller spacing to accomplish miniaturization. Lines can be as thin as 50 microns (µm) or less, transforming multi-lane avenues into narrow pathways. Denser circuitry layouts are made possible by minimizing the spacing between lines as well. Fabricating these ultra-fine lines involves precise photolithography and etching, with advanced techniques to manage electrical signal integrity. For example, modern smartphones use HDI PCBs with lines and spacing as tight as 5 µm, enabling powerful features in compact devices.
Microvias
Traditional PCBs include large vias, which are holes connecting different layers of the PCB. These holes range from 100 to 150 µm in diameter, to link conductive layers, just like city tunnels. This restricts the number of connections in small areas. With HDI PCBs, complex signal routing is made possible by the use of microvias instead of large vias. Microvias are substantially smaller vias (30–75 µm). This increases via density, allowing for more complex designs on a smaller footprint. Although creating microvias calls for specific methods, the benefits include less signal loss, longer signal routes, and more layers. High-end graphics cards, for instance, employ HDI PCBs, which have more than 1,000 microvias per square centimeter, to ensure effective signal routing in a small package.
Advanced Materials
HDI PCBs rely on advanced materials to ensure flawless miniaturized functionality. Unlike traditional FR-4, they use low-dielectric constant (Dk) materials to minimize signal delays and ensure effective high-frequency transmission by reducing capacitance between conductive lines. Materials with high thermal conductivity are used to effectively dissipate heat, avoiding overheating and maintaining peak performance. Selecting the appropriate materials is essential, taking into account things like chemical compatibility, moisture absorption, and thermal expansion. In high-power computing processors, high-Tg resins, aramid reinforcements, and metal base materials are popular options that offer structural integrity and effective heat management.
Miniaturized Components
In HDI PCBs, the concept of miniaturization goes beyond the board. They are usually used in conjunction with surface-mount technology (SMT) components to achieve notable size reductions. There is no need for through-hole components with large leads because these tiny, light components are glued straight onto the PCB surface. As a result, electronic devices are much smaller and lighter. Using SMT components needs accurate soldering techniques and placement to achieve dependable connections. Applying solder paste, precisely positioning the components, and utilizing a reflow oven to solidify their placement are all steps in the process. This is demonstrated by the use of tiny SMT components on HDI PCBs, such as integrated circuits, resistors, and capacitors, in modern smartphones. This makes it possible to create small, feature-rich devices with potent processors and amazing capabilities.
HDI Vs Standard PCB
Some key differences between HDI board and conventional PCB are shown in the following table:
Feature | HDI PCB | Standard PCB |
Component Density | Higher | Less |
PCB Size | Smaller and lighter | Larger and Heavier |
Via Type | Blind, buried, and microvias | Through holes |
Number of Layers | Lower | Higher |
Compatibility | Compatible with high-pin count and low-pitch packages | May face compatibility issues with low-pitch packages |
Manufacturing Techniques
1. Super-Tiny Connections
Traditional PCBs use drilled holes (vias) to connect wiring layers. However, in HDI PCBs, space is limited. That's where microvias and blind/buried vias come in:
Microvias: Microvias are drilled between the PCB layers and are extremely small connecting holes—much smaller than a human hair. They make it possible to connect more wiring in a smaller space. This is essential for intricate HDI designs, particularly in contemporary smartphones where a variety of processors and functions must communicate with one another flawlessly. Microvias, for instance, are used in smartphones to effectively connect high-speed processors, memory, and sensors. The specifications for HDI microvias are outlined in the international standard to ensure performance and dependability. Manufacturers can create more functional, electrically efficient, and dense electronics in smaller, more potent forms using microvias.
Blind Vias: In HDI PCB, blind vias play an essential part in linking individual internal layers without obvious surface penetration. This method ensures controlled impedance with precise via placement, improves signal integrity by shortening signal routes, and maximizes space by freeing up the surface for more components. Blind vias can be formed with a laser or controlled depth drill, which improves manufacturability and permits variable design without compromising production. Blind vias are essential in miniaturized electronics like wearables, cellphones, and high-end computers because of these benefits.
Buried Vias: Buried vias in PCBs offer advanced interconnectivity by residing exclusively within internal layers, unseen from the board's surfaces. They improve the efficiency of signal routing by creating specific vertical connections between layers, which is important for complicated devices with elaborate operations, such as scientific calculators. Also, buried vias protect high-speed signals from outside interference, which is essential for preserving signal integrity in PCBs that are tightly packed. They offer variable design layouts and maximize surface area for important components by ensuring precise placement and constant electrical performance through the use of techniques like laser drilling. Buried vias are crucial components found in high-speed networking equipment, smartphones, and tablets because they allow for compact, high-performance circuits without compromising functionality or manufacturability.
2. Laser Drilling
Laser drilling revolutionizes HDI PCB manufacturing by achieving unparalleled precision in creating microvias. Unlike traditional methods, lasers focus intense light to ablate material with pinpoint accuracy, ensuring uniform via diameters and minimal irregularities that could disrupt signal integrity. It produces very little heat during operation, protecting the PCB materials around it and retaining electrical performance. High aspect ratio vias, which are necessary to join several PCB layers, are expertly created by laser drilling. Its adaptability to a range of PCB materials allows for automatic precision and cleanliness in complex designs. Modern electronics like smartphones and high-speed devices depend on this technology since it not only increases accuracy but also expedites production and guarantees consistent, high-quality vias across all HDI PCBs.
3. Sequential Lamination
Sequential lamination in HDI PCB fabrication is akin to crafting a multi-layered mille-feuille pastry, each layer meticulously prepared and stacked to form a complex structure. Here's how this vital technique unfolds:
Preparation: PCB layers are etched with circuit patterns on copper foils and coated with insulating resin prepreg, before assembly.
Stacking and Alignment: Layers are stacked in sequence with precise alignment of circuit features and microvias.
Lamination: Heat and pressure fuse the layers into a unified structure, ensuring strength and integrity.
Drilling and Plating: Microvias are drilled through the stack, and plated with conductive material to establish electrical pathways.
Sequential lamination enables dense electrical connections critical for devices like high-resolution cameras, supporting complex functionalities such as image processing and autofocus. This process drives miniaturization and enhances electronic performance.
Advantages of HDI PCBs
The use of HDI PCBs offers several advantages over traditional PCBs:
Improved Performance: The advanced design of HDI PCBs enables faster signal transmission and reduced signal interference, leading to improved overall device performance.
Enhanced Reliability: The use of high-quality materials and advanced manufacturing techniques in HDI PCBs contributes to their increased reliability and longer lifespan.
Reduced Size and Weight: The primary benefit of HDI PCBs is their significantly smaller size and lighter weight. This allows for the development of compact and portable electronic devices.
Increased Functionality: By packing more circuitry into a smaller space, HDI PCBs allow for the integration of additional features and functionalities within electronic devices.
HDI PCBs Electronic Applications
HDI PCBs are transforming various electronic applications:
Mobile Devices: Smartphones, tablets, and wearables all benefit from the miniaturization and performance enhancements offered by HDI PCBs.
Medical Devices: The compact size and high functionality of HDI PCBs make them ideal for medical imaging equipment, diagnostic devices, hearing aids, and portable medical devices, where precision and reliability are critical.
Aerospace and Defense: The miniaturization and reliability of HDI PCBs make them suitable for avionics, radar systems, and other high-performance applications.
Automotive Electronics: The increasing complexity of automotive systems, including advanced driver-assistance features, and infotainment systems, relies on the high performance and reliability of HDI PCBs.
Consumer Electronics: From high-definition televisions to gaming consoles, HDI PCBs contribute to improved functionality and sleeker designs in various consumer electronics.
Key Takeaway
HDI PCBs are miniature marvels of engineering, utilizing advanced techniques to pack more functionality into a smaller footprint. They offer significant advantages over traditional PCBs, including reduced size, improved performance, and increased functionality. HDI PCBs are revolutionizing the electronics industry by enabling the development of compact, powerful, and feature-rich devices across various applications. Understanding their structure, advantages, and applications highlights how HDI technology is shaping the future of electronics.
Tapren leads the technological revolution by offering exceptional HDI PCB solutions that meet the evolving demands of the electronics industry. Our commitment to quality and innovation ensures that each HDI PCB is designed and manufactured for optimal performance and reliability. Using the latest manufacturing techniques and advanced technology, Tapren produces HDI PCBs that adhere to the highest industry standards. With years of experience, their expert team tailors each product to specific application requirements, guaranteeing superior quality, enhanced performance, reduced size, and increased functionality. Continuous investment in research and development keeps Tapren at the forefront of industry trends, providing innovative solutions that drive progress.
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