It is easy to get lost in the world of PCB materials. There are so many acronyms, terms, and abbreviations that a PCB engineer can come across as foreign from another. Among the many acronyms in the PCB industry is HDI. Many people in the PCB industry know what HDI is, but they are not familiar with the meaning of this acronym. HDI stands for High-Density Interconnect, representing a board construction where the traces of a layer are close together, forming a grid matrix on a substrate. It has been widely used for higher-level interconnection layers like signal/power layer planes.
The selection of high-density interconnect (HDI) printed circuit board (PCB) materials is critical to consider during the design and prototype stages. Often, many of these options are confusing and, at times, misleading. Thankfully, we have done some of the hard work for you by researching through manufacturer-specific data sheets, blog posts, and articles that cover the topic of PCB design in depth.
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Important Considerations for Selection of HDI PCB Materials
Many factors need to be considered to ensure that HDI PCBs meet your specific requirements. Here, we take a look at some of the most important factors to consider when choosing material for HDI PCBs so you can make an informed decision.
1. Material Thickness
The thickness of the material is an important factor when choosing fabric for HDI PCB. It should be thick enough to withstand the required mechanical loads and provide flexibility while remaining as thin as possible to reduce costs. In general, the minimum thickness of copper foil used in HDI PCBs ranges from 0.05mm to 0.2mm, depending on the requirements of the product application and board thickness.
2. Dielectric Constant
The dielectric constant is the most important property to consider when choosing a material for an HDI circuit board. The dielectric constant determines how well an insulator (FR-4) can withstand high voltages without arcing or shorting. High dielectric constants mean higher breakdown voltages and lower leakage currents. High-frequency applications require high dielectric constants because they must withstand high voltages without arcing or shorting. Low leakage current allows for greater efficiency in high-frequency circuits because it reduces the amount of power wasted due to resistance in the circuit lines.
3. Number of Layers
The number of layers used for each side of an HDI PCB. This varies depending on how many layers are needed for your specific design, but will typically range from two to six layers per side depending upon your product’s requirements.
Choosing the Right Material for HDI PCB Manufacturing
There are many different materials used to manufacture HDI PCBs, each with its unique characteristics and benefits. Most PCBs are made from one or more types of FR-4 epoxy laminate, which is a high-density fiberglass circuit board with copper foil applied on both sides. The copper serves as an electrical conductor, provides mechanical strength, and prevents corrosion.
Each of these materials has different advantages and disadvantages depending on your specific application requirements and budget constraints. Here are the three most commonly used materials used for HDI PCBs:
FR-4 is the most commonly used material for HDI PCB. It is a glass-reinforced epoxy laminate with high dielectric strength and low thermal coefficient of expansion. FR-4 has a high level of dimensional stability, and its electrical properties are stable at high temperatures. It can withstand a wide range of environmental conditions without degrading.
FR-4 is commonly used as the base material for HDI (high density interconnect) printed circuit boards due to its excellent electrical properties and ease of tooling. HDI PCBs are produced by stacking copper layers on top of a fiberglass core, then laminating them together using an epoxy resin. The result is an extremely strong board with superior mechanical properties, excellent thermal conduction, and a low dielectric constant.
Polyimide material is a high-temperature insulating material with a glass transition temperature (Tg) of 400°C. Polyimide materials can be used for HDI PCBs because they have excellent thermal stability and good chemical resistance to most common solvents and acids. They also offer a low coefficient of thermal expansion, which is important for high-frequency applications where the electrical properties of the circuit board change as it gets hot or cold. It can be applied to both sides of the copper foil in HDI PCBs and provide electrical insulation between the copper foil layers. In addition, polyimide provides excellent mechanical protection for copper foil layers against mechanical damage.
3. Rogers 4350B
Rogers 4350B material is a single-sided, surface mountable, thermally conductive material that can be used for HDI PCBs. It has a thermal conductivity of 0.69 W/mK and a surface resistivity of 5.7 X 10 mega-ohms per square. Rogers 4350B is available in both foil and sheet form. Rogers 4350B is commonly used as an HDI material, but it can also be used in other applications such as CIGS solar panels, where high thermal conductivity is required to efficiently transfer heat away from the solar cells.
The Bottom Line
The global PCB industry is evolving at an increasingly faster pace. New materials are being introduced to meet new challenges in the electronics industry, and HDI boards are also one of these hot topics. However, not all manufacturers will choose the same materials to make HDI boards; they will use different materials based on additional requirements. There are various important factors in selecting the best element for a particular application. The Rogers RO4350B is our top choice for HDI PCBs at Hemeixinpcb because it works well with many applications.
With the increased demand for HDI PCB materials, we will see more focus on quality and new applications to come. Consumers have been demanding higher quality from the PCB industry, which means that manufacturers will need to find ways to deliver better materials to make tighter component spacing possible. The growth rate is expected to increase gradually.