Shiny side of 12 µm foil with LD treatment

• Laser drilling benefits:
  • Smaller hole size versus mechanical drills.
  • Reduces CO₂ ablation threshold energy by more than 3X over standard copper foils.
  • Improves microvia hole quality.
  • Ultrathin carrier foils are not required.
    
    
• Processing benefits:
  • Eliminates conformal mask for CO₂ laser drilling.
  • Eliminates chemical processing before laser drilling.
  • Reduces post drill cleaning.
  • Improves outerlayer to innerlayer registration.
  • Enables high throughput CO₂ laser drilling of copper clad laminates.
    
    
• Real estate and design benefits:
  • Increases active component density and reduces form factors.
  • Improves signal routing through reduction of SMT via and pad sizes.
  • Reduces capture pad size requirement.
  • Increases ability to laser drill sub 100 µm (0.004") diameter microvias.
  • Simplifies sequential build-up fabrication.

Overview
LD copper foil was developed to meet the challenges of high density circuitry with small microvia interconnects in advanced printed wiring boards. LD foil allows manufacturers using CO₂ laser drills to consistently lase less than 100 µm (0.004") diameter microvias without the issues of copper overhang and resin crack defects associated with conventional foils. As an additional benefit, cycle times for board build are dramatically shortened by eliminating conventional conformal mask process steps for CO₂ lasers.

LD copper foil is manufactured by applying a microthin, nickel-based surface treatment to copper foil in a proprietary process. The finished product, patent pending, is a foil with a low reflectivity, energy absorbing treatment that is available in a variety of formats that is ready to be laser drilled. During laser drilling, thermal energy rapidly transfers to the copper foil and the underlying dielectric resulting in efficient material removal and a uniform microvia.

Clean, quality microvia formation in sequential build-up and conventional glass-epoxy constructions is a necessity for high yields. CO₂ lasers have become the preferred microvia drilling technology because of their high productivity, modest investment costs and low operational costs versus other laser systems. LD foil enables direct laser drilling of copper clad laminates with standard foil thicknesses resulting in large and reliable throughput.

LD foil is offered in roll and sheeted form or, preferably, in a CAC^® format for enhanced use. By virtue of being provided in CAC format, damage to the proprietary treatment before laser drilling is eliminated during the steps prior to laser drilling.

Advantages

• Process Reliability – The energy absorbing qualities of the surface treatment provide for reduced copper overhang and resin crack defects. Improved registration results since the microvias are drilled after lamination with the innerlayers. LD treated 12 µm (0.375 oz) foil can typically be drilled with one pulse of 15 mJ energy from a CO₂ laser as compared to multiple shots of 35 mJ needed to drill standard 12 µm (0.375 oz) foil.
• More Efficient Energy Absorption – The proprietary nickel-based surface treatment is thin, uniform, microrough and dark in color. The low reflectivity color allows lower CO₂ laser energy required for ablation. LD foil has good absorption at 10 µm (0.0004") wavelength due to its color and optimized surface roughness. Less laser power is required to drill through a 12 µm (0.375 oz) thick LD foil when compared to a matte finish 3 µm copper foil from a carrier.
• Reduces Fabrication Steps – Laminates made with LD foil come ready for laser processing directly out of the box. Conventional conformal mask processing steps are completely eliminated. A soft etch is recommended to remove any debris from the lasing operation. A variety of standard etchants can remove the LD treatment efficiently and completely, with sulfuric peroxide or sodium persulfate the preferred etch processes.
• Excellent Resistance to Handling Defects – LD foil has been demonstrated to be resistant to surface scratches that are common with other types of finishes used for direct copper ablation. The customer can be confident that the uniform, scratch-free surface will consistently ablate yielding optimum microvia quality. Added insurance is provided when LD foil is supplied in a CAC format, combining the best features of both products.

Specifications
LD foil is provided in a variety of foil widths and thicknesses using JTCS Double Treat copper foil. Thicknesses of 9 µm (0.25 oz) and 12 µm (0.375 oz) are commonly available with other foil thicknesses available on request.

	As-drilled cross sections of 9 µm LD Foil
	100 µm diameter via - resin type Pulses: 15 mJ x 1 shot + 1.5 mJ x 1 shot
	120 µm diameter via - prepreg type Pulses: 22 mJ x 1 shot + 4 mJ x 3 shots