Multi-layer blind via PCBs exhibit improved reliability and electrical performance of electronic products.
They eliminate a significant number of through-hole designs, increase wiring density, and effectively save horizontal space.
Role of high-frequency blind via boards:
The production of high-frequency blind via boards enables the three-dimensional integration of PCB manufacturing processes, effectively saving horizontal space. It adapts to the technological advancements of modern PCBs with high density and interconnectivity in electronic products, as well as the continuous improvement and transformation of electronic chip structures and installation methods. This development has transitioned from components with plug-in pins to highly integrated circuit modules using ball grid array (BGA) solder joints.
Challenges with conventional HDI laser blind via processes:
The blind vias of high-frequency boards contain voids that trap air, which affects reliability after thermal shocks. The conventional methods to address this issue include filling the voids with resin through pressing or plugging the blind vias with resin. However, these two methods often result in unreliable PCBs and low production efficiency. To enhance process capability and improve HDI (high-density interconnect) technology, the electroplating filling process is adopted. This method involves filling the blind vias with electroplated copper, greatly improving reliability. Additionally, the flat surface after electroplating allows for the stacking of circuit patterns with blind vias, significantly enhancing process capability to meet the increasingly complex and flexible design requirements of customers.
The ability to electroplate fill blind vias is influenced by PCB board materials and the shape of the blind vias. To achieve satisfactory blind via filling with the desired copper thickness on the surface, advanced equipment, special copper plating solutions, and additives are required. These factors represent the key points and challenges of this technology.
Background of Resin Plugging:
The application of resin plugging technology in PCB high-frequency boards is becoming increasingly widespread, especially in high-layer and high-precision PCB multi-layer high-frequency circuit boards. Resin plugging is used to address a range of issues that cannot be solved by solder mask plugging or resin pressing. However, this process presents various difficulties due to the characteristics of the resin used in PCB fabrication.
Definition:
Resin plugging technology refers to the use of resin to fill the buried vias in inner layers, followed by lamination. It is widely used in PCB high-frequency boards and HDI boards. It can be categorized into traditional silk screen resin plugging and vacuum resin plugging. The traditional silk screen resin plugging is the most commonly used method in the industry.
Challenges in Control:
Common quality issues related to resin plugging and their improvement methods:
Common issues:
A. Air bubbles at the via openings.
B. Insufficient resin filling in the vias.
C. Delamination between the resin and copper.
Consequences:
A.No copper in the vias.
B.Raised solder pads leading to component mounting issues or component detachment.
C.Inability to create solder pads above the via openings, and trapped air affecting chip placement.
Preventive and improvement measures:
A. Select suitable plugging ink and control its storage conditions and shelf life. B. Implement standardized inspection procedures to avoid voids at the via openings. Improve plugging yield through excellent plugging techniques and proper silk screen conditions. C. For delamination issues between resin and copper, significant improvement can be achieved when the copper thickness on the via surface exceeds 15 m. D. Choose appropriate resins, especially in terms of Tg (glass transition temperature) and coefficient of thermal expansion. Implement suitable production processes and debonding parameters to prevent detachment of solder pads from the resin after heating.
Inner-layer HDI buried vias and blind vias resin plugging:
Common issues:
A.PCB delamination.
B.Resin protrusion at blind vias.
C.Lack of copper in the vias.
Consequences:
All the mentioned issues directly lead to product scrap. Resin protrusions often result in uneven circuitry and cause shorts.
Preventive and improvement measures:
A. Controlling the completeness of resin filling in inner-layer HDI vias is necessary to prevent delamination. If plugging is performed after circuitry, the time between plugging and lamination and the cleanliness of the board surface must be well controlled.
B. To control resin protrusions, proper grinding and flattening of the resin are necessary. Both vertical and horizontal grinding should be carried out to ensure thorough resin removal from the board surface. Any incompletely ground areas can be manually repaired. The maximum depression after grinding should not exceed 0.075 mm. Electroplating requirements: Perform electroplating according to customer's copper thickness requirements. After plating, perform slicing to confirm the depression of resin plugs.
Conclusion:
The technology of blind vias + resin plugging + back drilling has undergone years of development and continuously plays an essential role in high-end products. It has been widely applied in blind buried vias, HDI, thick copper, and other products, which are involved in various industries such as communication, military, aviation, power supply, and networking. As manufacturers of PCB high-frequency boards, we understand the characteristics and application methods of resin plugging technology. We need to continuously improve the process capabilities of resin plugging products, enhance product quality, and address related process issues to manufacture high-frequency PCBs with higher technological difficulty.
