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Driving Innovation: The Flash Cutting Process

During the creation of a multilayer board, the lamination process naturally results in excess resin (known as "flash)" being squeezed out and solidified along the sides of the PCB panel. While the consistency and size of this flash provide process engineers with valuable insight into lamination parameters, the flash itself must be completely removed before subsequent manufacturing steps.

The panel edge shape and quality are often overlooked, but can directly influence final product yield and operational safety:

• Equipment protection: A sharp, uneven, or burred panel edge can damage the lamination rollers of expensive equipment, such as dry film laminators, leading to significant maintenance costs and downtime.
• Plating contamination: Edges with burrs can lead to contamination during the plating process. These small, unsecured particles of copper or resin can disconnect and fall into the plating solution, potentially leading to improper plating parameters and bath contamination.
• Fiducial accuracy: If subsequent processes rely on the position of fiducials according to the panel edge, any residual flash or rough contour might affect the positioning during subsequent processes.
• Operator safety: Sharp edges pose a direct physical hazard, risking injury to operators during manual handling steps.

Therefore, the methodical elimination of flash and the precise forming of the panel edge after lamination are important steps for manufacturers focusing on quality and stable production.

Possible Ways to Eliminate Flash

Table 1 lists several methods to eliminate the flash and create the shape of the panel edge.

Looking at Solutions
When considering options for the flash removal process, focus on maximizing efficiency and integrating registration data:

• Routing: Routing machines can perform flash cutting.
• Stand-alone CCD-based flash cutting: Established solutions include CCD-based flash cutting machines. If positioned after the X-ray registration process, these machines accurately use the drilled holes for alignment, ensuring the subsequent flash-cutting is performed with high precision relative to the inner pattern.
• Inline integrated flash-cutting: Solutions that directly connect the flash-cutting machine and the X-ray drilling machine inline. This integrated system eliminates intermediate handling, optimizing the entire registration-to-flash-cutting workflow.
• Stand-alone flash-cutting machine equipped with a small X-ray source: A machine can integrate a small, dedicated X-ray source directly into the flash-cutting machine. It allows the machine to perform pattern registration without relying on pre-drilled holes, providing flexibility and speed by cutting the flash earlier in the process cycle.
• High-volume flash-cutting machine: The machine should be engineered for exceptional speed and integrated functionality. This system will use a guillotine mechanism combined with a precision router to deliver rapid and comprehensive panel finishing. The guillotine performs flash cutting, and the router performs edge beveling and corner rounding in 30 seconds. If your process involves pin-lamination, its advantage is that it can deburr the pin-lam holes in the same step. This functionality ensures optimal quality for subsequent processes with no need for extra manual steps.

A Method to Create the Shape of the Edge
For example, there is a machine with a configuration that includes an X-ray source. The sophistication of the flash-removal process in that machine is found in the unique design of the cutting tool and its synchronized machine functions.

The flash-cutting process, edge beveling, and corner rounding are all performed by one specialized tool in a single pass. The tool has a unique shape designed to aggressively destroy the flash, turning it into fine dust particles rather than large debris strips. This minimizes the risk of contamination in subsequent plating baths. Simultaneously, the tool creates a clean, beveled edge, and a final chamfering pass rounds the corners.

The entire machine operation is governed by a thickness measurement device that accurately measures the panel thickness at the point of cutting. This compensation ensures that the tool cuts consistently relative to the actual panel thickness, minimizing variations and maximizing the accuracy of the final edge shape, essential for uniform quality.

Summary
The success of high-end PCB fabrication often hinges on processes that seem small and "invisible." While small-volume manufacturers might find it difficult to justify a dedicated flash-cutting system, mid-sized and/or high-end production lines might find that investing in a precise flash-cutting system is an investment in yield and stability.

Ultimately, many factors influence the result in the PCB process: machines, processes, materials, operators, process engineers, supporting chemicals, tools, room conditions, and more. Improving each factor allows companies to gradually enhance overall quality, micron by micron, improve accuracy, and steadily improve stability and yield day by day.

This column originally appeared in the November 2025 issue of PCB007 Magazine.