DFM 101: Final Finishes—Electrolytic Nickel/Gold

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Introduction
One of the biggest challenges facing PCB designers is not understanding the cost drivers in the PCB manufacturing process. This article is the latest in a series that will discuss these cost drivers (from the PCB manufacturer’s perspective) and the design decisions that will impact product reliability.

Final Finishes
Final finishes provide a surface for the component assembler to solder, wire bond, or conductively attach a component pad or lead to a pad, hole, or area of a PCB. The other use for a final finish is to provide a known contact resistance and life cycle for connectors, keys, or switches. The primary purpose of a final finish is to create electrical and thermal continuity with a surface of the PCB.

There are several final finishes in use in the industry today. These include:

• ENIG (electroless nickel, immersion gold)
• ENIPIG (electroless nickel, immersion palladium, immersion gold)
• ENEPIG (electroless nickel, electroless palladium, immersion gold)
• ImmAg (immersion silver)
• ImmSn (immersion tin)
• Sulfamate nickel/hard or soft gold (electrolytic nickel/gold)
• HASL (hot air solder leveling)
  • SnPb (63/37 tin/lead)
  • LF (lead-free)
  • OSP (organic solderability preservative)

Final finishes are primarily application driven, so there are several considerations that should be part of any decision to choose a final finish:

• Lead-tolerant or lead-free (LF) process
• Shelf life
• Flatness
• Lead or ball pitch
• Wire bondability
• Lead insertion
• Solder joint integrity
• Corrosion resistance
• Potential problems
• Cost 

To read this entire article, which appeared in the December 2022 issue of Design007 Magazine, click here.

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