PCB Surface finishes

A printed circuit board surface finish can be either organic or metallic in nature. Comparing both types and all available options can quickly demonstrate the relative benefits or drawbacks. Typically, the decisive factors when it comes to selecting the most suitable finish is the end application, the assembly process and the design of the circuit board itself. Below you can find a brief summary of the most common finishes, however for further or more detailed information about any specific PCB surface finish, please contact NCAB Group and we will be more than happy to answer any of your questions.

Hard Gold / Edge Contacts

Minimum Gold thickness for Class 1 & 2 boards is 0.8 µm, and for Class 3 boards 1.25 µm. Minimum Nickel thickness for Class 1 boards is 2 µm, and for Class 2 & 3 boards 2.5 µm. Shelf life: 12 months

  1. Durable surface resistant to mechanical friction. This is where it performs best.
  2. Long service life
  3. RoHS compliant
  1. Expensive
  2. Poor solderability, therefore selective plating only is recommended.

HASL – Tin/Lead hot air solder level

Typical thickness 1 – 40um. Shelf life:12 months

  1. Excellent solderability
  2. Inexpensive / Low cost
  3. Allows large processing window
  4. Long industry experience / well known finish
  5. Multiple thermal excursions
  1. Difference in thickness / topography between large and small pads
  2. Not suited for < 0,5µm pitch SMD & BGA
  3. Bridging on fine pitch
  4. Not ideal for HDI products

LF HASL – Lead Free hot air solder level

Typical thickness 1 – 40um. Shelf life: 12 months

  1. Excellent solderability
  2. Relatively inexpensive
  3. Allows large processing window
  4. Multiple thermal excursions
  1. Difference in thickness / topography between large and small pads – but to a lesser degree than SnPb
  2. High processing temperature – 260-270 degrees C
  3. Not suited for < 0,5µm pitch SMD & BGA
  4. Bridging on fine pitch
  5. Not ideal for HDI products

ENIG – Immersion gold / Electroless Nickel Immersion Gold

Typical thickness 3 – 6um Nickel / 0.05 – 0.125um Gold. Shelf life: 12 months

  1. Immersion finish = excellent flatness
  2. Good for fine pitch / BGA / smaller components
  3. Tried and tested process
  4. Wire bondable
  1. Expensive finish
  2. Black pad concerns on BGA
  3. Can be aggressive to soldermask – larger soldermask dam preferred
  4. Avoid soldermask defined BGA’s
  5. Should not plug holes on one side only

ENEPIG – Electroless Nickel Electroless Palladium Immersion Gold

Typical thickness = Nickel 3 – 6 µm / Palladium is 0.05 – 0.3 µm / Gold 0.05 – 0.125 µm Shelf life = 12 months

  1. Excellent for wire bonding
  2. Free from black pad concerns
  3. Immersion finish = excellent flatness
  4. Palladium reduces impact of nickel on high speed designs
  1. Expensive finish
  2. Not widely available
  3. Solderability influenced by palladium deposit

Immersion Sn – Immersion Tin

Typical thickness ≥ 1.0µm. Shelf life: 6 months

  1. Immersion finish = excellent flatness
  2. Good for fine pitch / BGA / smaller components
  3. Mid range cost for lead free finish
  4. Press fit suitable finish
  5. Good solderability
  1. Very sensitive to handling – gloves must be used
  2. Tin whisker concerns
  3. Aggressive to soldermask – soldermask dam shall be ≥ 127µm
  4. Baking prior to use can have a negative effect
  5. Not recommended to use peelable masks
  6. Should not plug holes on one side only

Immersion Ag – Immersion Silver

Typical thickness 0.12 – 0.40um. Shelf life: 6 months

  1. Immersion finish = excellent flatness
  2. Good for fine pitch / BGA / smaller components
  3. Mid range cost for lead free finish
  1. Very sensitive to handling / tarnishing / cosmetic concerns – gloves must be used
  2. Special packaging required – if packaged opened and not all boards used, it must be resealed quickly.
  3. Short operating window between assembly stages
  4. Not recommended to use peelable masks
  5. Should not plug holes from one side only
  6. Reduced supply chain options to support this finish

OSP (Organic Solderability Preservative)

Typical thickness 0.20-0.65µm. Shelf life: 6 months

  1. Excellent flatness
  2. Good for fine pitch / BGA / smaller components
  3. Inexpensive / Low cost
  4. Can be reworked
  5. Clean, environmentally friendly process
  1. Very sensitive to handling – gloves must be used and scratches avoided
  2. Short operating window between assembly stages
  3. Limited thermal cycles so not preferred for multiple soldering processes (>2/3)
  4. Limited shelf life – not ideal for specific freight modes and long stock holding
  5. Very difficult to inspect
  6. Cleaning misprinted solderpaste can have a negative effect on the OSP coating
  7. Baking prior to use can have a negative effect

ENEPIG

Electroless Nickel Electroless Palladium Immersion Gold. Typical thickness = Nickel 3 – 6um / Palladium is 0.05 – 0.3um / Gold 0.05 – 0.125um. Shelf life = 12 months

  1. Excellent for wire bonding
  2. Free from black pad concerns
  3. Immersion finish = excellent flatness
  4. Palladium reduces impact of nickel on high speed designs
  1. Expensive finish
  2. Not widely available
  3. Solderability influenced by palladium deposit

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