What is high density interconnection printed circuit board (HDI)?

The printed circuit board is a structural element formed by an insulating material supplemented by conductor wiring. In the final product, integrated circuits, transistors, diodes, passive components (such as resistors, capacitors, connectors, etc.) and various other electronic components are mounted on the PCB board. By connecting wires, electronic signal connections and its function can be formed.

Under the premise that electronic products tend to be more complex, the contact distance of integrated circuit components is reduced, and the speed of signal transmission is relatively increased, which is followed by an increase in the number of wires and the length of the wires between the points is locally shortened, these require high-density line configuration and micro-hole technology to achieve the goal. Wiring and bridging basically have difficulties for single and double-sided board, so the circuit board will be multi-layered, and as the signal lines continue to increase, more power layers and ground layer are necessary means of design. These have prompted the Multilayer Printed Circuit Board to become more common.

For the electrical requirements of high-speed signals, the board must provide impedance control with AC characteristics, high-frequency transmission capability, and reduce unnecessary Electromagnetic Interference (EMI). With the structure of Stripline and Microstrip, multi-layering becomes a necessary design. In order to reduce the quality of the signal transmission, an insulating material with a low dielectric constant and a low attenuation rate is used. In order to meet the miniaturization and array of the electronic component assembly, the circuit board also continuously increases the density to meet the demand. The emergence of assembly methods such as BGA (Ball Grid Array), CSP (Chip Scale Package), and DCA (Direct Chip Attachment) has pushed printed circuit boards to an unprecedented high-density state.

Holes less than 150um in diameter are known in the industry as Microvias. The circuit made by the micro-hole geometry technology can improve the efficiency of assembly, space utilization, etc., and also necessary for the miniaturization of electronic products.

For circuit board products of this type, there have been many different names in the industry to call such boards. For example, European and American operators used production process is sequential construction method, therefore, this type of product is called SBU. As for the Japanese manufacturer, the hole structure made by this kind of product is much smaller than the previous hole, therefore, the production technology of this kind of product is called MVP (Micro Via Process). Also have some people also call this type of product is BUM (Build Up Multilayer Board) because the traditional multi-layer board is called MLB (Multilayer Board).

The IPC Board Association of the United States has proposed to refer to this type of product as the general name of HDI (High Density Interconnection Technology).