About ENIG
Electroless Nickel and Immersion Gold has a flat solderable surface and allows tighter placement of surface mount pads. The finish is solderable and bondable with aluminum wire.
The process line is fully automated with vibration in all process stations to ensure bubbles are removed from the holes.
Electroless Nickel (EN Plating) is applied after copper trace/feature definition (after Cu plate, image, and etch operations). It can be applied before or after the solder mask application providing a conformal coating on all exposed copper surfaces including sidewalls.
The deposit is a nominal 120 – 240 micro-inches of approximately 93% purity nickel over exposed copper traces and features. Intrinsic to the electroless process is a significant amount of phosphorus co-deposited with the nickel. We also have two electroless nickel choices one 6-8% phosphorous and another with 8-10% phosphorous.
The electroless nickel acts as a barrier layer between the copper and the gold, preventing unwanted (non-solderable) intermetallic formation. The electroless nickel layer also adds strength to plated through holes and vias.
Immersion Gold is applied after the electroless nickel process during ENIG plating and provides a gold coating on all exposed nickel surfaces including sidewalls.
Gold is applied by a molecular replacement process in which previously deposited nickel molecules are replaced by gold molecules in a processing tank. The gold deposited is 99.99% pure, and its thickness can build up to 2 to 5 micro-inches. By design, the immersion deposition process is self-limiting. When the underlying nickel is completely covered the reaction will stop and no more gold will deposit. Immersion gold provides excellent solderability properties, and it retards the passivation (oxidation) of the nickel layer.
The combined nickel/gold, ENIG plating, and metallization provide excellent corrosion resistance, solderability, pad coplanarity, and shelf life. Electroless Nickel and Immersion Gold is a good choice for fine-pitch SMT and BGA technologies.
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General Information
Size limits – The size most often received is 24″ x18″ but panels can be any size up to 26″ x 30″.
Alternate Finishing (AFI) can plate the whole panel after you etch it. No tin or tin lead may be exposed anywhere on the panel including edges and inside holes.
We recommend that you run the panels through the solder strip with some extra time to ensure all the intermetallic layer is removed and that you bake the panels at 250 degrees F for one hour.
AFI can apply ENIG plating to the pads only. This is done after you apply the solder mask on the bare copper. If holes are plugged they need to be completely plugged flush. Holes that are partially filled with solder mask or plugged from one side cause incomplete catalyzation and some pads may not plate correctly.
We plate panels that have many different brands of solder masks and do not recommend any particular brand or model.
However, please follow closely any recommendations that your mask supplier has regarding preparing panels for electroless nickel and immersion gold plating.
The tin or tin-lead used for etch resist must be completely removed prior to solder mask application.
Avoid tight registration of the solder mask. If possible open a window around rows of fine-pitched features.
Solder masks must be fully cured during ENIG plating, however, take care not to over-cure them.
Boards must stabilize after processing. Panels that fail solder mask adhesion tests after processing will likely pass in as little as a few hours or the next day. For this reason we only tape test on waste areas of the panel for plating adhesion tests.
Pros and Cons of ENIG Plating
Electroless Nickel Immersion Gold, or ENIG, is a widely used surface finish for printed circuit boards because it combines durability with great conductivity. These factors greatly contribute to its acceptance as an industry standard used in applications ranging from consumer electronics to high-reliability sectors like aerospace and medical devices.
The ENIG plating process has many technical benefits that make it a favorable option for creating solderable surfaces on PCBs and other electronic components but it also has disadvantages that make other plating options more favorable. Here is a comparison of both.
| Advantages | Disadvantages |
|---|---|
| Flat Surface: ENIG plating results in a highly flat surface, ideal for fine-pitch components and complex PCB designs. | Higher Cost: ENIG is more expensive compared to other PCB finishes like HASL (Hot Air Solder Leveling). |
| Excellent Solderability: The gold layer offers excellent solderability, preventing oxidation and ensuring a longer shelf life. | Black Pad Defect: Improper process control can lead to “black pad,” a defect where the nickel corrodes, weakening solder joints. |
| Durability: The nickel layer is robust, providing wear resistance and protection from environmental factors. | Complex Process: The multi-step chemical process is more complex and requires careful monitoring, increasing production time and costs. |
| RoHS Compliance: Electroless Nickel Immersion Gold is a lead-free surface finish, meeting environmental regulations like RoHS (Restriction of Hazardous Substances). | Nickel Corrosion: The nickel layer, if not properly handled, can corrode, affecting the performance of the board. |
| Long Shelf Life: Due to the gold finish, ENIG can maintain solderability over a longer period compared to other finishes. | Longer Production Time: Due to the multiple layers and stringent quality control required for ENIG plating, it typically takes longer to manufacture compared to simpler finishes like OSP (Organic Solderability Preservatives). |
Work With Us
At Alternate Finishing, Inc., we can help you meet your ENIG finishing needs. We have quick turnarounds and deliver highly reliable finishes. Request a quote.