NCAB GROUP

PCB Surface Finishes

A 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 PCB itself. Below you can find a brief summary of the most common finishes, however for further or more detailed information, please contact NCAB Group and we will be more than happy to answer any of your questions.

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 < 20mil 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 < 20mil 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
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 ≥ 5 mil
  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
  4. Can be reworked
  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