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Most new components require high-density PCBs to enhance electrical performance. Used to regulate these and develop HDI printed circuit boards.
HDI board is one of the fastest developing technologies in PCB. These include blind holes and buried holes, and typically contain micropores with a diameter less than 0.1 millimeters.
A laser drilling machine must be used to drill holes with a diameter of less than 0.1mm. And the wiring and space are very compatible, so LDI machines must be used for production.
HDI printed circuit boards have higher circuit density than traditional PCBs. Here are the capabilities of iPCB HDI PCB Technics. Please take a look.
IPCB HDI PCB process capability
The Development Path of HDI Technology
For HDI technology, it is developed according to the Roadmap technology path of laminated board ->multi-layer board ->added layer multi-layer board ->high-density circuit board.
PCB boards, which originated around the 1960s, are typically electroplated through-hole boards produced from resin substrates. Due to its fast production replication, small size, and low unit price, it replaced early wire assembly products.
Gradually, with the miniaturization and multifunctionality of electronic products, the requirements for IC component contact distance and signal transmission speed are also increasing. Dual panel can no longer cope with complex signal and stability requirements, so circuit boards are gradually developing towards multi-layer circuit board. A circuit board that meets performance requirements by stacking multiple layers of circuit boards is called a multilayer board.
With the advent of the 4G and 5G era, current electronic devices must have high-frequency requirements, and corresponding circuit boards need to have characteristics such as impedance control, high-frequency transmission, and low radiation interference. This requires the use of insulation materials with low dielectric constant and low attenuation rate.
In addition, with the miniaturization of electronic devices, components have also become compact and miniaturized, leading to the development of BGA, CSP, DCA and other components, which has pushed circuit boards towards unprecedented high-density conditions. In order to meet high-density requirements, a microporous structure (pores with a diameter less than 150um or less are called micropores) is used to improve assembly and space utilization. For this type of circuit board, it is called an added layer multilayer board.
When the communication frequency is increased again, the layered multi-layer board cannot meet the demand. In order to improve the connection density of components, it is necessary to compress the space between circuits and connection points geometrically, or stack multiple components in the same position to increase the construction density. This technology is HDI technology, which stands for high-density circuit board technology.
Application scenarios of HDI technology
At present, the main application scenarios of HDI technology include carrier and intermediate boards, modules, portable products, and high-performance demand products.
1. Carrier board and intermediate board technology are used in applications such as recrystallization or wire bonding. Micro porous design allows for the construction of array configurations of contacts and windings in very high-density recrystallization areas.
2. Module: HDI technology can be used to construct modules that allow ICs to perform wire bonding, crystal bonding, or TAB connections on small substrates, or can also be used to manufacture intricate CSPs.
3. Portable products using HDI technology and miniaturized consumer products have a smaller appearance and more detailed feature dimensions.
4. High performance demand product: HDI PCB board and micro porous structure are used in combination for manufacturing high-level components, high I/O, small spacing components, especially high-density components.
The advantages of HDI technology
Introducing HDI technology brings many benefits in circuit configuration, component arrangement, data selection, product design, and manufacturing processes, all of which are areas for evaluating whether a product is intended. The specific benefits are reflected in:
1. The typical performance improvements include:
a、 Presenting relatively low parasitic power noise in via holes;
b、 Minimize the connection holes and branch structures of the circuit;
c、 There is a stable voltage channel;
d、 It can remove unnecessary decoupling capacitors;
e、 Low conversational style and general noise;
f. RFI/EMI interference has decreased significantly;
g、 A relatively close grounding plane and a relatively close distribution of electrical capacity;
h、 The surface grounding plane is matched with holes in the pad structure, which can block radiation effects;
2. Import advanced components
After using 0.8mm spacer elements in the IC assembly, HDI has more obvious advantages than laminated boards. For example, for FPGA high pin products, through-hole technology may require a 20 layer structure, while using HDI technology only requires about 60% of the layers. In addition, HDI technology blind holes also save space between the inner layer and the hole pad, and can also be designed with holes inside the pad.
3. The time for products to enter the market is accelerating
HDI technology adopts blind holes and hole in pad structures, which facilitate the configuration of electronic components and shorten the time for products to enter the market. At the same time, this design takes up less space, increases the efficiency of product design space, improves the application performance of BGA components, increases the flexibility of winding, and makes the circuit design simpler.
In addition, adopting blind and buried hole design to improve electrical performance can significantly shorten the system design adjustment time, reduce the work of signal synthesis and noise reduction, and minimize the opportunity for redesign.
4. HDI technology improves reliability
Compared with traditional through holes, the aspect ratio of blind holes is mostly less than 1:1, while traditional through holes are in the range of 4:1 to 20:1. This makes blind/microporous structures highly reliable for serial number transmission.
In addition, the HDI PCB board adopts a thin structure and low Z-axis expansion coefficient data, which makes the HDI PCB board have low potential inductance and good thermal conductivity.
5. Lower cost
The use of HDI technology can reduce the number of circuit board design layers, increase component density, while improving system speed and adjusting impedance performance. Therefore, when combined, HDI multilayer structures have lower costs than traditional through-hole structures.
Difficulties in HDI technology
HDI technology has brought many benefits, but there are also many problems in specific implementation.
1. Predictability
Due to the limited use of HDI technology, there is not enough experience accumulated in current PCB design to estimate the stacking condition, drilling quantity, and price of HDI at the initial stage of project design. This contradicts the current quotation process and requires the accumulation of subsequent experience.
2. Design Model
For simple HDI structures, the community domain layout is simple and the design difficulty is low; For products with complex structures, it is necessary to use effective tools to import and model winding models, component data, geometric relationships, and circuit board dimensions, and simulate the performance of the final product accordingly. Currently, only a few manufacturers possess this capability.
3. Signal synthesis
The premise of using HDI structure is to understand the electrical improvement effect it can bring, but this poses certain conversion difficulties for traditional circuit board designs that currently prefer through-hole design.
4. Application of new materials
For HDI PCB boards, many new materials are currently being introduced, such as resin coated copper sheets, vacuum pressed dielectric layers, etc. The various parameters of these new materials have a significant impact on the characteristics of circuit boards and require continuous practice and exploration. Among various parameters, low loss substrate, low dielectric parameters, and high heat resistance are key.
5. Assembly issues
The fill in the blank structure can add inductance to the circuit, but it will increase the manufacturing cost of the circuit board by more than 10%. Therefore, how to choose these structures reasonably is related to the balance between performance and cost.
6. Testing
At the initial stage of HDI PCB board design, it is necessary to consider the combination of testing design, which requires joint planning by testing engineers and circuit board designers. This is beneficial for predicting possible fault conditions, planning testing strategies, and understanding the scope of faults in the later stage. This is quite important for mass production, involving product testing costs.
Reasonable testing design can reasonably anticipate the possible types of faults in each node, component, and board signal and provide a reasonable testing plan.
7. Cost estimation
How to create a Design Sheet in design? How to choose the best design parameters? The minimum aperture, hole circle, and line width have a significant impact on the yield performance, while data thickness, stacking structure, number of line holes, hole density, and other factors have a significant impact on the cost end.
In addition, final metal surface treatment, fill in the blank, allowable tolerances, and so on all have an impact on the cost end. Many parameters have a significant impact on both cost and performance. How to establish a model that balances experience and cost-effectiveness.
8. Design Tools
For HDI PCB boards, traditional through-hole automation design tools are no longer applicable. The current design tools are relatively expensive, but they have complete functions in blind micro hole design, stacking structure, winding, and other aspects.
9. Power performance and signal comprehensiveness
The electrical impact of holes in high-speed networks cannot be ignored. Through holes have high parasitic noise such as capacitance and inductance, while the surrounding structure of through holes brings more than ten times the amount of parasitic noise, which will become significant interference to signal performance. However, there are many through holes and blind holes in HDI, so how to combine structural design and signal influence for design is one of the important design considerations.
The design process of HDI technology is divided into six parts
1. System segmentation
At the beginning of new product design, the entire product will be decomposed into component levels for design and manufacturing. Reasonable system segmentation is beneficial for distinguishing system performance, accelerating design progress, and balancing structural configuration, components, risk control, and manufacturability in the early stages of design to ensure product success.
2. Product Design
Product design includes logic design, circuit simulation, component simulation, conventional IC, mechanical design, and so on. HDI PCB board have significant advantages in power and thermal management, which can improve the electrical and thermal characteristics of products.
3. Circuit board design and layout
Unlike traditional board structures, the design layout of HDI PCB boards affects their performance and manufacturing due to blind holes and buried holes. Therefore, it is necessary to fully carry out pre research work and fully understand the impact of various designs on performance and manufacturing.
4. Circuit board manufacturing
The contribution of circuit board manufacturing to the finished product is significant. The processes that have a significant impact include alignment, fine line imaging technology, metallization treatment, electroplating, and so on.
How to do these processes well and test them on HDI PCB board is the biggest requirement for each manufacturer.
5. Assembling different HDI PCB components on circuit boards requires different reflow operation curves and repair techniques. Due to the high density of components, HDI PCB board are relatively thin, which can easily cause different faults and risks during the reflow process.
For more assembly issues, thorough evaluation and testing are required during the specific manufacturing process.
6. Assembly testing
The final result step of HDI technology is assembly testing.
Reasonably arranging test pads can reduce the HDI PCB complexity and HDI PCB cost of testing, as well as unnecessary parasitic noise. Therefore, assembly testing should be considered from the beginning of the design.