What is HDI PCB?
High Density Interconnect (HDI) circuit board per unit area compared to more conventional boards. HDI boards are usually referred to as multilayer boards using one or a combination of the following technologies: joints/mesh smaller than 100 µm, blind and buried holes, sequential lamination, microvias (through-holes less than 0.2 mm in diameter), BGA (Ball Grid Array), Via-in-Pad and tapped holes.
HDI boards are primarily used for miniaturization, for very high density interconnects in separated function blocks and also when you need to interconnect multiple layers differently.
HDI boards can be flexible or as a rigid-flex combination.
Advantages of HDI boards?
The primary use of HDI PCBs stems from the push for miniaturization. Electronic devices were initially limited by the size of PCBs, which had to be adapted to existing components. This is most clearly seen in the first mobile phones, suitcase-sized devices, or at best the size and weight of a brick with significantly limited functionality compared to current smartphones.
With the development of SMT technology, the gradual shrinking of component housings, and the requirement to make more intensive use of board surface area for component embedding, HDI PCBs have been able to make much more use of limited surface area.
HDI PCBs offer advantages such as:
- Size - Portable devices as we know them today would not be possible without HDI PCBs. The small size of HDI PCBs makes them suitable for technology that we can carry and put in our pockets.
- Lower material costs - Due to their significantly reduced scale, HDI PCBs use far fewer materials with better performance than other types of PCBs.
- Faster prototyping - The time required to create an HDI PCB is shorter than designing several separately functioning simpler boards, resulting in less time spent designing and testing prototypes.
- Faster signal transmission - Because HDI PCBs take up less space than their predecessors, electrical signals must travel less distance. As a result, these boards have less signal loss and transition delay (impedance).
- Higher heat resistance - HDI PCBs are sometimes used in high-temperature applications that require them to operate in extreme conditions. Materials suitable for HDI boards have a higher comparable thermal resistance by default.
Requirements for HDI production
Special manufacturing techniques are required to produce HDI PCBs. It is essential to find a manufacturer that meets HDI manufacturing standards and also has the ability to produce the PCB as quickly as possible.
Efficient manufacturing should include:
- Digital process of motif illumination (LDI, MDI, etc.)
- Ability to drill micro-holes (mechanical or laser)
- Blind & hidden holes
- Stacked and staggered joints
- Sequential lamination
- Fill holes with epoxy paste
A significant increase in the number of interconnection holes is achieved on the same board area by using holes that are not drilled through the entire board, but only between the necessary layers within the board. This creates "buried" via holes which are then laminated into the board. In this way, the necessary via hole can be placed e.g. also under the SMT solder pad or under another "burried" via hole.
Simply using "burried" via holes would not yet produce the desired result unless combined with a reduction in the dimensions of all interconnection holes. The "microvia" interconnecting holes used are 200 microns or less in diameter.
In order to use "burried" via holes, a method of sequential lamination, known as SBU (Sequential Build-Up), must be used in the manufacture of the board.
The combination of conventional, "blind" and "burried" via holes of "microvia" dimensions using sequential lamination is the basis of HDI technology in PCB manufacturing.
HDI PCBs use the latest technology available to enhance functionality. This advancement in PCB technology supports advanced functionality in revolutionary new products including 5G communications, networking equipment, the Internet of Things, medical wearables for patient monitoring, and equipment for the military.
In short, HDI PCBs perform better, are ultimately more efficient. With a smaller footprint, these PCBs enable a wider range of applications, from aerospace to consumer products and wearable electronics.
Connect with our specialists