Via-in-Pad Technology
Via-in-Pad (VIP) is a common technology in printed circuit board (PCB) design, especially in high-density interconnect (HDI) boards and high-frequency applications. It is a design method that places the "through hole" (via) of the circuit board directly on the pad (pad). Usually, this design is mainly used in situations where the layout space of tiny pads or through holes is very limited. The following details the characteristics, advantages and challenges of Via-in-Pad technology.
1. Basic concept of Via-in-Pad
In traditional PCB design, pads are areas used to connect component pins to PCB circuits, while vias are used to achieve electrical connections between different layers. Usually, pads and vias are designed separately, but in Via-in-Pad design, vias are placed directly on the pad area, usually for connecting surface mount component (SMD) pins.
2. Application scenarios of Via-in-Pad
Via-in-Pad technology is mainly used in the following situations:
High-density interconnect (HDI) board: As the size of electronic devices becomes smaller and smaller, the space utilization requirements of PCBs are getting higher and higher. Via-in-Pad can help designers achieve electrical connections in extremely small spaces.
Tiny surface mount components (SMD): Especially microchips or very precise IC packages (such as BGA, CSP packages), which have high pin density, Via-in-Pad can help layout these components and ensure effective electrical connections.
High-frequency/high-speed circuit design: In high-frequency or high-speed circuit design, Via-in-Pad technology can reduce the complexity and parasitic capacitance of signal paths, thereby improving signal integrity.
3. Advantages of Via-in-Pad
Space saving: Embedding via directly into the pad can effectively save PCB space, which is suitable for high-density layout with very small component pin spacing.
Improve electrical performance: By shortening the signal path, reducing signal delay and loss, it is particularly suitable for high-frequency and high-speed design.
Improve welding quality: By embedding via into the pad, the welding surface becomes smoother, which helps to improve the reliability of welding, especially in the welding process of surface mount components.
4. Challenges of Via-in-Pad
Manufacturing cost: Since embedding via in pad requires special process treatment (such as using blind or buried via technology), this design increases the complexity and cost of PCB manufacturing. Especially in the design of multi-layer boards, VIP requires more sophisticated production technology.
Reliability issues: Via-in-Pad design may result in low mechanical strength of pads, and the connection between via and pad may be loose due to welding thermal stress or vibration during welding, which in turn affects the long-term reliability of the circuit.
Process limitations: During the production process, the steps of drilling holes in pads, filling vias and copper coating are very complicated, which may lead to a decrease in yield. In addition, when filling vias, special attention should be paid to the stability and surface flatness of the filling material to ensure the quality during welding.
Thermal management issues: Since VIP design affects the distribution of heat flow, it may have an adverse effect on the thermal management of high-power components. Vias are directly located on pads, which may affect the heat dissipation, especially in high-frequency, high-power applications.
5. Via-in-Pad Solution
To solve the challenges of Via-in-Pad design, there are usually the following solutions:
Via Filling: Filling via with metal or resin material to improve the stability of the pad and avoid soldering problems caused by excessive via aperture.
Blind and buried via technology: These technologies can make via only exist between specific layers without affecting the function and appearance of the pad.
Interlayer connection: Avoid directly inserting via into the pad by designing a reasonable interlayer interconnection path, thereby reducing thermal stress and electrical problems.
Design and manufacturing optimization: By optimizing PCB design and selecting materials and technologies suitable for VIP, the yield rate in the production process is ensured.
6. Common Via-in-Pad Application Examples
BGA package: BGA (Ball Grid Array) package usually requires dense electrical connections, so embedding via into the pad through Via-in-Pad technology can effectively provide electrical connections for BGA package.
CSP packaging: CSP (Chip Size Package) packaging also often uses Via-in-Pad technology, especially when the design requires small size and high pin density.
High-frequency/high-power applications: In some high-frequency or high-power applications, VIP can improve signal integrity and electrical performance and reduce unnecessary parasitic effects.
7. Summary
Via-in-Pad is an important technology used to solve space and electrical performance problems in high-density PCB design. Although it has advantages such as improving electrical performance and space utilization, it also faces challenges such as cost, manufacturing difficulty and reliability. With the advancement of PCB manufacturing technology, especially in the fields of HDI, micro packaging and high-frequency circuits, the application of Via-in-Pad technology is becoming more and more extensive.
When using Via-in-Pad in design, designers need to weigh various factors, reasonably select filling, welding and other processes, and fully verify reliability to ensure the long-term stability and performance of the circuit.
