How to Evaluate Laser Drilling Capabilities

The via is the soul of FPC's conduction of different layers of circuitry. In traditional rigid PCBs, mechanical drilling is commonly used. However, on FPC, a material as thin as a cicada's wing, mechanical drilling is extremely prone to causing material tearing and rough hole walls. The precise control of laser drilling technology and subsequent chemical electroplating directly determines the end-life and long-term reliability of multilayer flexible boards.

I. UV Laser vs. CO2 Laser: Choosing the Best Option for Your Process

Laser processing isn't a one-size-fits-all approach. In the field of micro-apertures, choosing the right light source is like choosing the right cutting tool; precise switching is essential to meet process requirements:

Physical Characteristics of the Two Mainstream Laser Technologies

• CO2 Laser (Carbon Dioxide): High speed and processing efficiency, but due to its thermal processing and high energy, it easily leaves scorch marks on the edges of the PI substrate; it is best suited for drilling large through-holes or removing localized coverlays.
• UV Laser (Ultraviolet Light): Belongs to the "cold processing" of photochemistry, it can directly break the molecular bonds of materials, resulting in clean and smooth cuts. For micropores smaller than 0.1mm, precision UV laser is the only option to ensure clean, residue-free pore walls.

II. The Pitfalls of PTH: Desmear

After laser drilling, the process immediately enters the most easily overlooked, yet most fatal, hidden minefield: the pore wall metallization and desmearing process.

Chain Reaction of Bottom Separation

• Resin Residue: The instantaneous high-temperature burning of the laser leaves molten resin residue (smear) at the bottom of the micropore.
• Poor Copper Foil Bonding: If the desmear process is not thorough enough, the subsequent electroplated copper cannot perfectly bond with the blind hole copper foil at the bottom of the hole.
• Thermal Cycling Landmine: This is a serious hidden danger. Products test normal during factory inspection, but typically, after three months of use by the customer and several cycles of thermal expansion and contraction, a sudden short circuit occurs, leading to a persistently high rework rate.

III. Practical Perspective: How to Evaluate Drilling Capabilities?

When visiting the process site to verify suppliers, it is essential to move beyond simple hardware specifications and establish evaluation standards from a practical mass production perspective.

Risk Control Decision Considerations for Engineering and Procurement

• Engineering Inspection Points: Always request metallographic cross-sections from suppliers and carefully observe whether the blind hole walls are straight, whether the copper plating thickness is uniform, and whether there is excessive shrinkage at the hole opening.
• Procurement Risk Management: Drilling speed and descaling processes directly affect production capacity and pricing. If a supplier offers a unit price significantly lower than the market price, be sure to confirm whether they have privately simplified the necessary time for descaling or secondary chemical electroplating to expedite production.

IV. Key Indicator Differences in Laser Drilling Process

The following summarizes the differences in performance between the two mainstream laser technologies and the core technologies for subsequent inspection in the multilayer flexible circuit board manufacturing process: