Design and Manufacturing Notes for HDI PCB
HDI board (High-Density Interconnector) is a circuit board with a relatively high line distribution density that uses micro blind buried hole technology. HDI board has inner and outer layers of lines and then uses drilling, in-hole metallization, and other processes to connect the internal layers of each layer of lines. Unlike normal PCBs, HDI PCBs are smaller in size and have more circuits. There are micro holes on the board to realize communication between multiple layers using laser drilling. Besides, there are buried holes and blind holes, which can meet the requirement of higher circuit density. HDI PCB plays an important role in electronic manufacturing due to its advantages.
Advantages of HDI PCB
1. Reduce PCB cost: when the PCB density increases to more than eight layers, the cost of HDI manufacturing will be lower than the traditional complex lamination process.
2. Increase line density: interconnection between traditional circuit boards and parts
3. Facilitate the use of advanced PCB manufacturing technology
4. Better electrical performance and signal accuracy
5. Better reliability
6. Improve thermal performance
7. Improve radio frequency interference/electromagnetic interference/electrostatic discharge (RFI/EMI/ESD)
8. Improve design efficiency
Tips while Designing HDI PCB
HDI PCB has higher and more strict requirements for signal integrity, so while designing HDI boards, the designer needs to pay more attention to this point. At the same time, choosing the right material is also important for keeping signal integrity and impedance and heat dissipation features. Layer count and stack-up layer order are crucial in the design process.
The structure of an HDI PCB should be structural symmetry. If the stack-up structure is improper, it will cause bad performance, EMI problems, and crosstalk. To eliminate these questions, all the high-speed signals should be provided with ground planes above and below for the signal return route.
1. In the design process, the width and space of electronic components need to be considered, to make sure the signal integrity.
2. To form a high-density circuit in a limited space, the complexity of connections between high-density layers containing a large number of elements must be considered
3. Proper material should be chosen based on the design since the material will influence the quality of the final PCB and even the product.
4. Reasonable heat dissipation plan for the electronic components, the components need to be placed and arranged after analyzing the heat distribution.
5. Aspect Ratio: keep through drilling hole(1:10) and HDI (1:0.75) aspect ratio
6. Stack-up cycle: limit the stack-up cycle to 3 cycles
7. Board thickness: highly use micro holes, blind holes, and buried holes to reduce the board thickness
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8. Signal return route: place ground or power plane layers to provide a return path for the signal.
9. Minimum inductance path: the signal return route should be confirmed as per the minimum inductance path.
The below notes also need further attention:
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Main Manufacturing Procedure for HDI PCB
1. Design: according to the project requirement and design standards, do the design on the software. During design, the circuit layout, hole diameter, and layer counts should be considered to ensure the performance and reliability of the PCB.
2. Laser drilling: Laser drilling technology is a feature of the HDI board. Laser drilling technology can make micro holes with the advantages of high accuracy, speed, and less harm to the hole wall. In the process, need to control the position, diameter, and depth of the holes to meet the design requirement.
3. Electroplating: after laser drilling, the boards will do electroplating to form a conductive layer on hole walls. While electroplating, need to control the thickness and uniformity of the plating layer to ensure conductivity and reliability.
4. Surface finish: to improve the corrosion and wear resistance, surface treatment is a must process. Normal surface finishes are ENIG and immersion silver for HDI PCB. During the surface treatment, the plating thickness and quality should be strictly controlled to meet the design requirements.
5. Test and inspection: after fabrication, the boards need to be tested to ensure quality and performance.
Points When Manufacturing HDI PCB
The supplier or factory has to ensure that design requirements are followed and optimized and guarantee manufacturing efficiency and effectiveness. The following is an explanation of what is involved in the manufacturing process.
1. High-density HDI PCB requires more precise technology and equipment, the cost is much higher, and the designer and factory should work together for better cost planning.
2. During the design process, the manufacturing procedure and manufacturability should be considered to avoid the problem of difficult fabrication.
3. While fabrication, the process parameters and fabrication accuracy should be strictly controlled.
4. By integrating the design and manufacturing processes, manufacturers can create a robust and efficient framework to maintain quality and smooth operation during all phases of production. The manufacturing process for HDI PCBs is designed to produce superior, reliable, high-quality, and efficient electronic devices that meet consumer requirements and industry standards.
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