PCB Surface Finishing 101: Processes, Pros & Cons

8. Electroplated Nickel/Gold (Electroplated Ni/Au)

Electroplated nickel/gold sequentially deposits a nickel layer and then a gold layer on copper by electrochemical methods, used to suppress Cu–Au diffusion and to provide conductivity/wear resistance. According to the nature of the gold layer, it is divided into:

• Soft Gold (99.9%): used for wire bonding / high solderability;
• Hard Gold (99.6%): a gold alloy (containing cobalt/nickel/iron complexes), used for high-wear scenarios such as plug-in/contacts/gold fingers.

Typically, a 3–5 μm nickel layer is plated first, followed by 0.5–1.5 μm gold (depending on the application).

Process Essentials

• Adjust thickness and hardness via current density / time / solution composition;
• Soft gold has excellent solderability and bonding strength; hard gold is wear-resistant but not suitable for wire bonding;
• The real soldering IMC is still formed by the nickel layer, and the gold layer dissolves rapidly at the initial stage of soldering.
• Expensive; requires bus bars/segmentation, additional masking and etch-resist/tape steps; imposes higher requirements on layout/process.

8.1 Hard Gold

Hard electrolytic gold over low-stress nickel provides excellent wear resistance, making it suitable for edge-connector fingers, interconnect substrates, keyboard contacts, and other high-wear areas.

Process Essentials

• Military: gold 50–100 μin (>100 μin Ni base);
• Consumer: gold 25–50 μin;
• IPC solderable thickness recommendation: ≤17.8 μin (thicker reduces solderability).
• ~17 μin is generally not solderable; not suitable for wire bonding.

Pros and Cons (table)

8.2 Soft Gold

Soft gold has high purity (99.9%); its soldering/bonding performance is better than hard gold. It is suitable for wire bonding and for applications with higher requirements on solder-joint strength.

Pros and Cons (table)

Applicable / Limitations

• Applicable: gold fingers / plug-in contacts (hard gold), wire bonding / solderability-first (soft gold), highly reliable electrical contacts (e.g., CPU sockets, memory modules).
• Limitations: strict cost constraints; non-contact areas that require full sidewall encapsulation.

IV. Organic-Type Surface Finishing — OSP (Organic Solderability Preservatives)

OSP (also known as copper protector, Preflux) is a water-based organic molecule that selectively bonds with copper to form an organometallic layer (thickness about 0.10–0.60 μm), providing anti-oxidation/anti-sulfidation at room temperature; during reflow it is quickly removed by flux, and the bare copper immediately combines with solder to form a strong solder joint. Its function is limited to short-term solderability protection, but it is environmentally friendly, low-cost, and flat, making it very suitable for fine-pitch SMT.

Process Essentials

• Typical process: degreasing → micro-etching → acid wash → pure-water rinse → organic coating → rinse;
• Thickness cannot be measured (difficult to confirm online); an excessively thick coating may affect soldering;
• Not suitable for PTH; ICT may be affected; there is a risk of copper surface exposure before final assembly;
• Limited number of reworks (≤2 times); sensitive to handling;
• Not suitable for wave soldering/selective wave soldering (the surface is easily oxidized, causing soldering defects).

Pros and Cons (table)

Applicable/Limitations

• Applicable: cost-sensitive products, fine-pitch SMT, products with high flatness requirements but fast assembly cadence.
• Limitations: long-term storage, wave soldering/selective wave soldering, scenarios requiring PTH/ICT friendliness.

V. PCB Hybrid Surface Finishing Technology

A single surface finish is hard to cover all functional/cost/environmental needs, so hybrid surface finishing—using two or more processes in different areas on the same PCB—has become increasingly common, enabling a balance of high reliability in critical zones and cost reduction in non-critical zones.

Common Combinations

• ENIG + OSP
• Electroplated Ni/Au + ENIG
• Electroplated Ni/Au + HASL
• ENIG + HASL
• Lead-free HASL + gold fingers (electroplated hard gold)

Process Essentials

• Use immersion gold/electroplated gold in key connection/contact areas to ensure contact reliability, and use HASL/OSP in other areas to control costs;
• The sequence/masking/chemical compatibility of hybrid processes must be carefully designed;
• OSP uses water-based organic compounds that selectively bond with copper, which is more environmentally friendly than some metal finishes (the latter may have higher toxicity or energy consumption).

Applicable/Limitations (key-points)

VI. How to choose PCB Surface Finish?

PCB finish selection is the most important step in PCB manufacturing because it directly affects process yields, amount of rework, field failure rates, testability, scrap rates, and cost. To ensure high quality and performance of the final product, all important considerations for assembly must be taken into account in the surface finish selection.

1. PCB Surface Finish - Pad Flatness

As mentioned earlier, certain surface finishes can result in uneven surfaces, which can affect performance, solderability and other factors. If flatness is an important factor, consider surface finishes with thin, uniform layers. In this case, suitable options include ENIG, ENEPIG, and OSP.

2. Solderability and Wettability

Solderability is always a key factor when working with PCBs, and specific finishes such as OSP and ENEPIG have been shown to hinder solderability, while other finishes such as HASL are well suited.

3. Gold or Aluminum Wire Bonding

If your PCB requires gold or aluminum wire bonding, it may be limited to ENIG and ENEPIG.

4. Storage Conditions

As mentioned earlier, some finishes (such as OSP) can make PCBs brittle when handled, while other finishes increase durability. Prior consideration should be given when considering storage and handling requirements, and surface treatments that make PCBs brittle should be used only when risk-free storage and handling requirements can be met.

5. Soldering cycle time

How many times does a PCB have to be soldered and reworked? Many finishes are ideal for rework. However, other methods such as immersion tin are not suitable for rework.

6. PCB Surface Finish - RoHS Compliance

RoHS compliance is critical when determining the surface finish to be used. Generally, all finishes that use lead are not RoHS compliant and should be avoided.

Based on the description of each surface finish above, a number of attributes are the most important elements to use as selection criteria. The table below shows the attributes that each surface finish does and does not have.

Depending on the specific requirements and characteristics of the PCB product, you can follow this table to select the perfect surface finish option.

Conclusion 

When choosing PCB surface finishing, the process's fitness for purpose is always more important than fame: your component pitch, assembly process (reflow/wave/selective soldering), long-term storage needs, contact wear resistance, RF loss tolerance, and cost targets will all directly affect the final decision. To this end, NextPCB provides comprehensive finish selection and manufacturing collaboration, allowing design–manufacturing–assembly to start within the same process window from the very beginning.

NextPCB's comprehensive capabilities in surface finishing and manufacturing

Full spectrum of surface finishes: HASL (leaded/lead-free), ImSn (immersion tin), ImAg (immersion silver), ENIG (electroless nickel/immersion gold), ENEPIG (electroless nickel electroless palladium immersion gold), electroplated Ni/Au (hard gold/soft gold), OSP, and selective/partitioned hybrid finishes (such as “gold finger electroplating + other areas ENIG/HASL/OSP”).

• Manufacturing and assembly collaboration: supports multilayer/HDI, impedance control, high TG, thick copper, blind/buried vias/microvias, gold-finger chamfering, countersunk holes, V-Cut, selective electroplating, etc.; also provides one-stop SMT/PCBA (including BOM compatible alternatives, process fixtures, functional testing/aging, traceable barcodes).
• Quality control and data-based verification: XRF coating-thickness measurement, microsection (cross-section) analysis, ion contamination (ROSE) and solderability testing, 100% electrical test and AOI; materials and test reports (such as RoHS/physical properties/thickness data) can be provided as needed to support audits and compliant delivery.
• Engineering support (DFM/DFX): for fine-pitch/BGA/RF/high-speed/automotive/medical scenarios, provide surface-finish selection recommendations, reflow curves and assembly-window collaboration, impedance/material stack-up recommendations, reducing rework and failure rates in the early design stage.
• Delivery and service: smooth capacity expansion from prototyping to small batch to mass production; expedited options and global logistics support; one-to-one process-engineer communication to shorten the time to close issues.

How to get started quickly with NextPCB

• Still hesitating about which surface finish to choose? Send us your minimum component pitch, whether there are gold fingers/plug-in contacts, the assembly process (reflow/wave/selective soldering), whether long-term storage is required, and whether there are RF/high-speed lines. We will provide two to three feasible process routes (including pros/cons and notes) based on cost and reliability.
• Already have files ready to place an order? Directly upload Gerber/ODB++, BOM, and coordinates (Pick & Place), and note “surface-finish priority and alternatives.” If hybrid finishes or selective electroplating are required, mark the areas and boundaries. Engineers will conduct DFM review and confirm thickness/flatness/solderability windows.
• Want price comparison or risk assessment? Provide the current plan and pain points (such as black-pad risk, tin-whisker concerns, ICT yield, contact wear, RF insertion loss, storage-period requirements). We can issue targeted improvement suggestions and process comparison lists.

Act now: send us your project key points or documents, and let NextPCB's engineering team use the right surface finish + the right manufacturing window to help you get yield, reliability, and cost all right at the same time.