What are HDI PCBs? HDI PCBs, also known as double-sided or multilayer printed circuit boards, are designed to provide a high degree of interconnectivity in a compact form factor. They achieve this by incorporating microvias, which are tiny holes drilled through the board’s layers, allowing for the routing of conductors between layers. This technology enables the creation of dense and intricate circuits, making them ideal for high-density applications.

Advantages of HDI PCBs for High-Density Applications

a. Increased Density: HDI PCBs offer a higher density of interconnections, allowing for more components to be mounted on a smaller board surface area. This is particularly crucial for applications such as smartphones, wearables, and other portable devices, where space is at a premium.

b. Reduced Size and Weight: The compact nature of HDI PCBs enables the creation of smaller and lighter electronic devices. This is especially important in industries such as aerospace and defense, where weight reduction is a critical factor.

c. Improved Electrical Performance： The use of microvias in HDI PCBs allows for precise and controlled routing of conductors, resulting in improved electrical performance. This is essential for applications that require high-speed data transmission, such as computer boards and communication systems.

d. Enhanced Reliability: HDI PCBs are designed with precision and care, ensuring reliable connections and reducing the risk of failures. This is crucial for high-stakes applications like medical devices and industrial control systems.

HDI PCB Assembly Process

The assembly of HDI PCBs involves several steps, including design, fabrication, and manufacturing. The design phase focuses on creating a layout that optimizes the interconnections while considering the constraints of the application. The fabrication process involves the creation of microvias and the deposition of conductive layers, while the manufacturing process includes plating, drilling, and lamination.

Applications of HDI PCBs in High-Density Electronics

a.Smartphones and Tablets: HDI PCBs are extensively used in smartphones and tablets to accommodate the numerous components and high-speed data connections required for these devices.

b. Wearable Electronics: The compact size and lightweight nature of HDI PCBs make them ideal for wearable devices, such as smartwatches and fitness trackers, where space is limited.

c. Aerospace and Defense: HDI PCBs are used in aerospace and defense applications to reduce weight and increase the reliability of electronic systems, which are crucial in critical situations.

d. Medical Devices: The precise and controlled interconnections provided by HDI PCBs are essential for medical devices, where reliability and performance are paramount.

e. Computer Boards and Communication Systems: High-speed data transmission and increased density are key requirements for computer boards and communication systems, making HDI PCBs an excellent choice.

HDI PCBs have emerged as a game-changer in the electronics industry, enabling the creation of high-density applications that were once considered impossible. With their increased density, reduced size and weight, improved electrical performance, and enhanced reliability, HDI PCBs have become an indispensable part in various industries. As technology continues to advance, the capabilities of HDI PCBs are likely to expand further, enabling the development of even more sophisticated and compact electronic devices.

High density interconnect (HDI) designs stretch the limits of trace, via, and layer density to great extent. These boards have high layer counts with very complex traces and via. Moreover, HDI PCBs passes through different fabrication and assembly processes than conventional PCB.

There are 6 kinds of diversity in HDI boards, through via from surface to surface, with buried via and through via, two or more HDI layer with through via, passive substrate with no electrical connection, coreless construction using layer pairs and alternate constructions of coreless constructions using layer pairs.

Solder Joint Quality
It’s easier for professional to address solder joint issues with soldering iron when it comes to SMT connectors with a double row. However, it gets tricky for an SMT connector with multiple rows. Therefore, a proper processing method that is first-time-right is necessary.

Major issues that can cause a bad solder Joint are as follow:

Accuracy of solder paste deposit
The volume of solder paste deposit
Stencil opening and thickness
PCB flatness
Reflow temperature profile

Because of diversity of various assembly shop, it is not feasible to define a single set of rules to solve all the mentioned issues. Furthermore, the involvement of several variables complicates the solution, which are, Equipment underuse, Brand of solder paste and its chemical constituency, Board design and component density.

Which Integrated Circuit is Solutions for High-Density I/O Needs:
Most recent development in ICs is BGA (Ball Grid Array) packaging, which is proven vital for high-density applications. BGA applications use a spherical solder ball attached to the component lead to provide more solder without using a heavy paste.

For the best solder joints on a PCB, following the manufacturer’s guidelines from datasheet offers maximum success. Most manufacturers provide a PCB footprint for their components, along with the necessary tolerances, optimum layout and thickness for the stencil, guidelines for the printing process for solder masks, tolerances for component placement, suitable profiling for reflow ovens, and considerations for rework.

Stencil and Footprint: It is strongly recommended that PCB designers take reference for component footprint and stencil layout from the component manufacturer’s website. When designers use the provided footprint and stencil layouts, their chances of achieving proper solder joints increase manyfold.

Screen Printing Process: It is necessary for the solder to covers the entire pad to make ideal solder joint. To achieve this, an aperture in the stencil should be larger than the pad. High-accuracy registration ensures the solder paste location with respect to the solder balls or charges offers good contact between them.

Component Placement: As a more advanced trend near-to-perfection placement of SMT is achieved by pick-and-place equipment. As the solder melts in the reflow oven, the weight of the component aid in its orientation on the PCB.

Reflow Oven Profiling: According to the standard IPC/JEDEC J-STD-020, SMT components must withstand a peak temperature of 260 °C and a temperature of 255 °C for 30 seconds. To ensure the solder balls or chargers are reaching the proper temperature, thermocouples should be placed through the back of the PCB reaching the center of the component.

Conclusion
Although processes will always have flaws, with proper processing it is possible to reduce the need for reworking the assembly, scrapping it, and generating lower profits. Importance of proper processing methods will continue to gain importance as the electronics industry makes denser assemblies with smaller components.