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EPD-Electronics Packaging Designer

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PCB Surface Processes

Purpose of PCB Surface Finish

*Provides a solderable surface for Component assembly.

*Protect Copper Surface from Oxidation.

*Provide a surface appropriate for wear related parts.

High Performance Surface Finish

*Mixed Technology Board Designs

*Solderable,SMT and Thru-hole

*Wire Bondable

*Contact Resistance

*Co-Planar Surfaces

*Compatability with variety of fluxes & paste

*Cost effective

*Environment

Available Surface Finishes

*Electroless Nickle-Immersion Gold

*Immersion Silver

*Hot Air Solder Level

*Organic Solderability Preservative

*Electrolyte Nickel – Hard Gold

*Electrolyte Nickel – Soft Gold

Surface Finish Details

*Electroless Nickel-Immersion Gold (ENIG)

A two layer, gold over nickel, metallic surface finish plated onto the copper base by means of a chemical decomposition process

Advantage:

  • Typical Thickness: 3-8 uin gold over 150-250
  • uin nickel
  • Excellent Corrosion resistance
  • Good for aluminium wire bonding
  • Excellent flatness for fine-pitch technology
  • Excellent Solderability
  • Excellent shelf life(12 mo)
  • Good surface contrast
  • Good contact resistance
  • High Aspect Ratio Capability

Disadvantage:

  • Narrow process window
  • Higher cost than HASL(1.5 to 2.0 times)
  • Back pads: brittle solder joints
  • Fatigue failures on large BGA packages
  • Skip plate
  • Extraneous nickel plating
  • Solder mask capability with the nickel bath
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