How Micro Vias Are Used in Harsh Environments

Micro Vias Are Used in Harsh Environments

In printed circuit boards, micro vias save space by allowing traces to travel between layers. They are a key element in high-density interconnects, and they help designers pack in more functionality into tight spaces. However, microvias pose a few challenges and require specialized PCB fabrication processes to meet stringent quality and reliability requirements.

One of the primary concerns about using micro vias is their reliability in harsh environments. The environment may cause the copper plating on the surface of the via to fail due to thermal cycling. This stress puts pressure on the copper, causing it to crack or delaminate. This can lead to a loss of conductivity, a failure of the via, or a short between two stacked microvias or a microvia and its pad.

To mitigate these concerns, PCB fabricators must carefully select the materials used to construct microvias. This includes the laminate, copper filler material, and plating process. In addition, the manufacturing process must be able to handle the size and precision of the microvias. Advanced imaging and microscopy techniques are utilized to inspect the integrity of the vias after drilling and metallization, ensuring that they meet specified tolerances.

How Micro Vias Are Used in Harsh Environments

The voids in microvias must also be reliably plated and filled. This requires a precise and stable plating process, and the use of additives in the filler material to prevent void formation during plating. The microvias must be plated using pure copper or an epoxy + copper resin, and they typically start with a conformal coating. The manufacturer then uses pulse plating to fill the body of the microvia with solid copper and eliminate voids. Additives are necessary in the plating process, as voids tend to concentrate along walls and the top surface of the microvia if they are not present.

As a general rule, a microvia should not be larger than 1:1 in its aspect ratio. Larger ratios can cause problems during drilling, laser drilling, and plating. Moreover, mechanical drills cannot drill a hole with such a small diameter without causing defects in the copper plating.

When designing a PCB with microvias, designers must carefully choose the size and shape of each. The designer must work with the fabricator to ensure that the stackup is compatible with the fabrication process and that the fabrication process can drill the microvias properly. This can be done by building up the proposed stackup in a CAD program, and then sending it to the fabricator for review.

The best way to avoid these issues is to consult with the fabrication house in advance of starting on the design. This will help to minimize the number of changes required throughout the design phase, and it will reduce manual routing time. In addition, the fabricator can provide the designer with information about the fabrication process and any limitations on the use of microvias that may be applicable to their particular project. By following these tips, the designer can ensure that they are using the best possible microvia technology for their application.

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