ENEPIG or Electroless Nickel Electroless Palladium Immersion Gold is a surface finish for Printed Circuit Boards. It has been around for a decade but only recently it has come back into vogue.
ENEPIG is suitable for soldering, gold wire bonding, aluminum wire bonding, and contact resistance. It is formed by the sequential deposition of electroless Ni (120 to 240 micro inches) followed by 2 to 10 micro inches of electroless Palladium with an immersion gold flash of 2 to 6 micro inches on the top. This surface finish has a higher pull strength compared to ENIG (Electroless Nickel Immersion Gold).
Earlier, the high price of palladium had kept it out of reach for most businesses. Now, with the price of palladium less than the price of gold, this surface finish becomes the best choice for wire bonding, ROHS assembly, and just all boards overall. ENEPIG works well with lead-free and conventional eutectic solder alloys (Eutectic means its 63% tin and 37% lead). ENEPIG is called the “Universal” surface finish as it can be used for all assembly processes.
So why is ENEPIG the “universal” finish?
Excellent ROHS lead-free and leaded solderability
- Because palladium completely dissolves into the solder leaving an oxide-free nickel surface which allows a reliable tin nickel intermetallic.
High wire bond pull strengths (aluminum wire: up to 10 gram-force; gold wire: up to 8 gram-force)
- After numerous tests, it holds high pull weights.
- Good for aluminum wedge and gold ball bonding.
Low contact resistance
- Due to the controlled deposition of precious metals, the electrical resistance is more uniform so it’s easier to predict amperage.
Suitable for conductive adhesives
- You can connect components without the use of solder.
Finish is corrosion resistant and pore-free
- Multiple layers of metal provide a higher corrosion-resistant coating.
Unlimited shelf life
- Doesn’t tarnish
Nickel acts as a barrier layer to further reduce copper dissolution during wave solder, thus ensuring good solderability.
- Nickel prevents the mixing of copper and solder.
ENEPIG delivers great solder joint strength with various alloys during multiple reflow soldering, especially SAC305. The middle palladium layer helps to stabilize and control the inner metallic layer. Because of the mixture, ENEPIG after testing showed amazing wire bonding, both with aluminum and gold. Sierra Circuits offers the option for ENEPIG finish on all of its products.
Sierra Standard Table
|Nickel (µ”)||Palladium (µ”)|| Plate Gold (µ”)|
|ENEPIG||125-250||4 – 8||1|
If the values aren’t specified then Sierra Standard Table will be considered.
Nickel and Gold Specifications & Standards
(Immersion Gold and ENEPIG)
|IPC-6012 Rev C||Sierra’s Standard *|
|Immersion Gold – minimum||Coverage and Solderable||1.00 µin min|
|Electroless Nickel – minimum||118 µin||125-250 µin|
|Electroless Palladium – minimum||2 µin||4.00 – 8.00 µin|
* If a range is not given the number in the Sierra Standards Column is the minimum.