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Driving Innovation: Depth Routing Processes—Achieving Unparalleled Precision in Complex PCBs

Vacuum Table With the Adaptor
For the most demanding depth routing applications, particularly those involving extremely thin or small panels, or panels with multiple cavities, maintaining absolute panel flatness and stability during machining is critical. A vacuum table or a specialized vacuum adaptor is imperative. By firmly holding the panel in place, the vacuum eliminates vibrations, prevents panel movement, and ensures optimal flatness across the working area. This rigid, consistent hold allows the machine's tools to perform accurate and repeatable depth routing processes, leading to superior quality results with the most delicate and challenging PCB designs.

Touch Probe
Building on the stability provided by a vacuum table or adaptor, the depth routing with touch probe control offers the highest level of accuracy for cavity creation. A specialized touch probe is mounted on the Z-axis, providing an independent and highly precise means of verifying and controlling the actual depth during the routing process.

There are several ways to use the touch probe technology:

1. Single Measuring + Routing:
   • Measure the panel surface: The touch probe precisely measures a single point on the panel surface to establish a definitive reference
   • Rout to defined depth based on panel surface: The routing path executes to the programmed depth, referencing the measured surface point
2. Multi-Measuring + Routing:
   • Measure the panel surface with a touch probe: The touch probe scans multiple points across the panel's surface
   • Different measuring points on panel surface/mapping process: This creates a more detailed topographical map of the needed area
   • Rout to defined depth based on mean value of mapped data: The routing path is dynamically adjusted based on an average or interpolated value from the mapped data points, compensating for localized surface irregularities across larger areas
3. Measuring after Routing:
   • Measure the panel surface: Take an initial surface reference
   • Measure a lower, already processed level and check the depth: After an initial routing pass, the touch probe measures the depth of the routed feature to verify precision. This could be a critical quality control step.
4. Adaptive Cavity Routing: This represents the pinnacle of precision, employing a closed-loop feedback system:
   • Measure surface by touch probe: Establishes the starting reference
   • Routing: Performs an initial routing pass
   • Measure depth with a with a touch probe: The probe measures the depth achieved after the pass
   • Final routing if necessary: If the measured depth deviates from the target, the machine performs a final, adaptive routing pass to achieve the specified depth. This process ensures unparalleled accuracy.

Laser Cases: When Mechanical Routing Reaches Its Limits
While mechanical depth routing offers immense capabilities, there are instances where its limitations require laser technology for skiving processes. These cases often arise when dealing with materials that are difficult to machine mechanically, when the required feature size and precision exceed mechanical capabilities, or when thermal impact needs to be minimized. Lasers, particularly high-end ones such as PICO-green, are perfect for tasks like removing thin coatings from copper pads or accessing contact pads with minimal damage.

A PICO-green laser can ablate microns with minimal impact on the next layer. This non-contact, highly precise, and localized energy delivery ensures minimal thermal impact on the surrounding material, preserving the integrity of sensitive copper pads and fine-line structures. Laser skiving provides superior control and cleanliness compared to mechanical methods for specific applications.

Summary
The ability to perform highly accurate depth routing is fundamental for producing today's complex PCB designs, including rigid-flex boards, PCBs with embedded components, and those requiring integrated heat sinks. Several machine features play a crucial role in ensuring depth routing accuracy. These include the previously discussed functions and capabilities, as well as clamped spindles that enhance tool stability, linear drives that enable precise and rapid movement, and adjustable valves that allow for accurate pressure control of the pressure foot, among other factors.

The strategic combination and correct use of these machine functions (or mix of functions), together with proper routing tools, suitable backup materials, and the expert work of a skilled process engineer, make it possible to produce the most intricate and demanding PCB designs. These advanced capabilities are essential for meeting the complex requirements of modern electronics, ensuring superior performance, reliability, and miniaturization.

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

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