1. HDI is smaller and lighter

HDI board is made of traditional double-sided board as the core board through continuous lamination. This kind of circuit board is also called Build-up Multilayer (BUM). Compared with traditional circuit boards, HDI circuit boards have the advantages of 'light, thin, short and small'.

The electrical interconnection between HDI boards is realized through the connection of conductive through holes, buried holes and blind holes. Its structure is different from that of ordinary multilayer circuit boards. A large number of HDI boards use micro-buried blind holes. HDI uses laser direct drilling, while standard PCB usually uses mechanical drilling, so the number of layers and aspect ratio are often reduced.

2. Production process flow of HDI main board

The high-density of HDI board is mainly reflected in the hole, line, pad density and interlayer thickness.

● Micro-guide hole: The HDI board contains micro-guide hole design such as blind hole, which is mainly reflected in the high requirements of micro-pore forming technology with pore diameter less than 150um and cost, production efficiency and hole position accuracy control. In traditional multilayer circuit boards, there are only through holes and no tiny buried blind holes

● Refinement of line width and line spacing: it is mainly manifested in the increasingly strict requirements for wire defects and wire surface roughness. General line width and line spacing shall not exceed 76.2um

● High pad density: welding joint density is more than 50 per square centimeter

● Thinning of dielectric thickness: it is mainly manifested in the trend of interlayer dielectric thickness to 80um and below, and the requirements for thickness uniformity are increasingly strict, especially for high-density boards and packaging substrates with characteristic impedance control

3. HDI board has better electrical performance

HDI can not only make the design of terminal products smaller, but also meet higher standards of electronic performance and efficiency.

The increased interconnection density of HDI allows for enhanced signal strength and reliability. In addition, HDI board has better improvement for radio frequency interference, electromagnetic wave interference, electrostatic discharge, heat conduction, etc. HDI also adopts full digital signal process control (DSP) technology and a number of patented technologies, which have the ability to adapt to load in a full range and strong short-term overload capacity.

4. HDI board has very high requirements for buried hole plug hole

It can be seen from the above that HDI is superior to ordinary PCB in terms of size and electrical performance. Every coin has two sides. The other side of HDI is made as a high-end PCB. Its manufacturing threshold and process difficulty are much higher than that of ordinary PCB. There are also many problems to pay attention to during production, especially the hole plug.

At present, the core pain point and difficulty in HDI production and manufacturing is buried hole plug. If the HDI buried hole plug hole is not completed, major quality problems will occur, including uneven concavity and convexity of the plate edge, uneven medium thickness, and potholes on the pad.

● The uneven surface of the board and the uneven line will cause the beach phenomenon in the depression, which will cause the line gap, broken line and other defects

● Characteristic impedance will also fluctuate due to uneven dielectric thickness, resulting in unstable signal

● The unevenness of the bonding pad makes the subsequent poor packaging quality cause joint losses of components

Therefore, not all board factories have the ability and strength to do well in HDI, and Huaqiu has worked hard for this purpose for 8 years. Now, Huaqiu HDI has its own complete system. The whole process is not outsourced. It spends a lot of money to purchase advanced equipment. All quality acceptance standards have always adopted IPC2 standards, such as hole copper thickness ≥ 20 μ m. Ensure high reliability.