The classification of HDI products is determined by the recent development of HDI and the strong demand for its products. Mobile communication companies and their suppliers have played a pioneering role in this area and have identified many standards. Correspondingly, the demand for products has also led to changes in the technical limitations of mass production, and the price has become more affordable. Japan's consumer industry has taken the lead in HDI products. The computer and network community have not yet felt the pressure of the approach of HDI technology, but due to the increase in component density, they will soon face such pressure and enable HDI technology. The advantages of using HDI substrates on flip-chip packages are significant in view of shrinking spacing and increasing I/O counts.
HDI technology can be divided into several technology types. The main driving force for HDI products comes from mobile communication products, high-end computer products and packaging substrates. The technical requirements of these types of products are completely different. Therefore, HDI technology is not one kind, but there are several kinds, and the specific classification is as follows:
Miniaturized HDI products
HDI products for high-density substrates and subdivision functions
High-level HDI products
1.. Miniaturized HDI products
The miniaturization of HDI products initially referred to the reduction in size and weight of the finished product, which was achieved by its own wiring density design and the use of new high-density devices such as uBGAs. In most cases, its functionality continues to increase even as product prices remain stable or declining. The internal interconnection uses a buried hole process structure mainly for 6 or 8 layers. Other features include the following: 10mil pads, 3-5mil vias, most 4mil line width/spacer, board thickness up to 40mil, FR4 or high TG (160 °C) ) FR4 substrate. Figure 1 depicts the basic structure and main design rules of HDI.
Figure 1 Miniaturization of consumer products
This technology is relatively mature in HDI technology, and it is widely used in China. This design approach provides a good application for smaller sizes and higher densities, where the application includes pins for uBGA or flip chip.
2. HDI products for high-density substrates and subdivision functions
HDI boards of high-density substrates are mainly concentrated in 4 or 6-layer boards, and interconnections are realized by buried holes between layers, at least two of which have micro holes. The goal is to meet the increased demand for high-density I/O for flip-chips. The technology will soon be fused with HDI to achieve product miniaturization. Figure 2 depicts a typical substrate structure.
Figure 2 High-density IC substrate
3 High-level HDI products
The high-rise HDI panels are typically conventional multi-layer boards with laser drilling from the first to the second or the first to third layers. Microvias processing on glass reinforcement is another feature using the necessary sequential lamination process. The goal of this technology is to reserve enough component space to ensure the required impedance level. Figure 3 depicts a typical multi-layer board structure of this type.
Figure 3 High-level board for high-performance products
This technology is suitable for high-level HDI boards with high I/O counts or fine-pitch components. The buried-hole process is not a necessary process in such products. The purpose of the micro-hole process is to form high-density devices (such as high I/O). The dielectric material of the HDI product may be a backing copper foil ( RCF) or a prepreg.
In summary, there are five main drivers for the development of high-performance HDI products that must be considered. These factors alternate. These factors are: circuit (signal integrity) ; components; substrate; lamination and design rules; assembly process considerations, designing such a printed circuit board with microvia is a very complex task, although the circuit is considered Signal integrity is extremely important, but the cost factor cannot be ignored. Based on this, the compromise must be considered in the actual operation.