Microvia Copper Fill Process

Microvia copper fill is a technique used in high-density interconnect (HDI) PCBs to create reliable electrical connections between different layers. Here's a breakdown of the process:

Why copper fill?

• Improved Conductivity: Solid copper offers superior conductivity compared to alternative via plugging materials like epoxy resins. This translates to better signal transmission.
• Higher Reliability: Copper filled vias are less prone to cracking or delamination during thermal stress, enhancing the overall reliability of the PCB.
• Manufacturing Efficiency: Copper plating is a well-established process in PCB fabrication, allowing for efficient integration into the existing workflow.

The Copper Filling Process:

1. Preparation: The drilled microvias are cleaned and prepared for electroplating to ensure proper adhesion of the copper.
2. Electroplating: The PCB panel is placed in a plating tank containing a copper sulfate solution. An electric current is applied, causing copper ions to be deposited on the via walls and gradually fill the microvia.
3. Additives and Techniques: Special additives might be used in the solution to achieve conformal plating, ensuring complete filling and minimizing voids within the via. Techniques like horizontal or vertical plating equipment may be used depending on the via aspect ratio.
4. Resin Filling (Optional): After copper plating, some manufacturers might fill any remaining voids with conductive or non-conductive epoxy resin for additional stability.
5. Planarization: The PCB surface is polished to ensure a smooth and even finish.

Advantages of Copper Filled Microvias:

• Increased packing density of electrical connections in the PCB.
• Improved signal integrity due to superior conductivity.
• Enhanced reliability through robust via connections.
• Compatibility with existing PCB fabrication techniques.

Things to Consider:

• Copper filling process adds complexity to PCB manufacturing, potentially affecting cost.
• Microvia dimensions play a crucial role in achieving complete and void-free copper filling.

If you're designing HDI PCBs and require high-density, reliable connections, copper filled microvias are a strong option. However, discussing the design and feasibility with your PCB manufacturer is recommended.

Vias are critical to PCB functionality as the conduit for transferring signals between layers. Vias can remain open, tented over with soldermask or filled solid with either non-conductive or conductive material.

Conductively filled vias add capacity to the design, and using copper to fill the vias adds some benefits that other conductive material does not, including thermal and electrical conductivity. The high thermal conductivity of copper-filled vias provides an advantage in high heat applications and the added electrical conductivity provides superior current-carrying capability in high voltage applications.

ASC’s John Bushie takes us through the complex manufacturing process in this month’s video.

Copper Plated Filled Vias - YouTube