The surface finish on your PCB protects exposed copper pads from oxidation and ensures reliable solder joints during assembly. Each finish type has different shelf life, solderability, flatness, and cost characteristics. In India, HASL (Hot Air Solder Levelling) is the default at most budget fabricators, but ENIG and OSP are increasingly available and sometimes necessary for fine-pitch components. This comparison guide helps you choose the right finish for your design requirements and budget.
Table of Contents
- HASL — Hot Air Solder Levelling
- ENIG — Electroless Nickel Immersion Gold
- OSP — Organic Solderability Preservative
- ENEPIG — Electroless Nickel Electroless Palladium Immersion Gold
- Other Finishes: Immersion Silver, Immersion Tin
- Side-by-Side Comparison
- How to Choose the Right Finish
- Frequently Asked Questions
HASL — Hot Air Solder Levelling
HASL is the most common and cheapest surface finish. The board is dipped in molten solder (typically 63/37 Sn/Pb for leaded HASL or SAC305 for lead-free HASL), and excess solder is blown off with hot air knives.
| Property | Value |
|---|---|
| Coating thickness | 1-40µm (uneven) |
| Shelf life | 12+ months |
| RoHS compliant | Lead-free HASL only |
| Solderability | Excellent — solder-to-solder bond |
| Pad flatness | Poor — dome-shaped pads |
| Fine-pitch capability | Not suitable below 0.5mm pitch |
| Cost | Lowest (base price at most fabricators) |
Best for: Through-hole assemblies, large SMD pads (0805 and above), prototypes, hobby projects. Avoid for: BGA, QFN, fine-pitch ICs (0.4-0.5mm pitch) due to uneven pad height.
ENIG — Electroless Nickel Immersion Gold
ENIG deposits a 3-6µm nickel layer followed by a thin 0.05-0.1µm gold layer over the exposed copper. The nickel acts as a diffusion barrier and the gold prevents nickel oxidation.
| Property | Value |
|---|---|
| Nickel thickness | 3-6µm |
| Gold thickness | 0.05-0.1µm (1-2 microinches) |
| Shelf life | 12+ months |
| RoHS compliant | Yes |
| Solderability | Very good |
| Pad flatness | Excellent — flat, coplanar pads |
| Fine-pitch capability | Excellent — suitable for 0.4mm pitch and BGA |
| Wire bonding | Not recommended (gold layer too thin) |
| Cost | ₹200-500 premium per panel over HASL |
Best for: Fine-pitch SMD, BGA, QFN, boards requiring long shelf life, and designs that need flat pads for reliable reflow. Known issue: Black pad — a nickel phosphorus defect that causes brittle solder joints. Choose a reputable fabricator with good ENIG process control.
OSP — Organic Solderability Preservative
OSP applies a thin organic compound (typically benzimidazole-based) over bare copper. It is invisible — the pads look like bare copper with a slight sheen.
| Property | Value |
|---|---|
| Coating thickness | 0.2-0.5µm |
| Shelf life | 6 months (sensitive to handling and humidity) |
| RoHS compliant | Yes |
| Solderability | Good (degrades with multiple reflow cycles) |
| Pad flatness | Excellent — copper surface is naturally flat |
| Fine-pitch capability | Excellent |
| Cost | Cheapest after HASL (sometimes equal) |
Best for: High-volume production assembled within 3-6 months of fabrication. Avoid for: Boards that will be stored for long periods, boards requiring multiple reflow passes (double-sided assembly), and hand soldering (flux is essential).
ENEPIG — Electroless Nickel Electroless Palladium Immersion Gold
ENEPIG adds a palladium layer between nickel and gold. This three-metal stack eliminates the black pad risk of ENIG and supports wire bonding.
| Property | Value |
|---|---|
| Nickel thickness | 3-5µm |
| Palladium thickness | 0.05-0.1µm |
| Gold thickness | 0.03-0.05µm |
| Shelf life | 12+ months |
| Wire bonding | Gold and aluminium wire compatible |
| Cost | Highest — ₹500-1,500 premium per panel |
Best for: Mixed assembly (SMD + wire bonding on same board), automotive electronics, medical devices, and mission-critical applications. Overkill for: Most hobby and prototype work.
Other Finishes: Immersion Silver, Immersion Tin
Immersion Silver (ImAg): Deposits 0.1-0.4µm silver on copper. Excellent solderability and flatness. Tarnishes over time (handle with gloves). Shelf life 6-12 months. Good for RF applications as silver has the lowest electrical resistance of any metal. Cost between HASL and ENIG.
Immersion Tin (ImSn): Deposits 0.8-1.2µm tin on copper. Good flatness and solderability. Forms tin whiskers over time, which can cause short circuits. Shelf life 6 months. Rarely used in India due to whisker concerns and limited fabricator support.
Side-by-Side Comparison
| Finish | Flatness | Shelf Life | Fine-Pitch | Cost | RoHS |
|---|---|---|---|---|---|
| Leaded HASL | Poor | 12+ months | No | ₹ (lowest) | No |
| Lead-free HASL | Poor | 12+ months | No | ₹₹ | Yes |
| OSP | Excellent | 6 months | Yes | ₹ | Yes |
| ENIG | Excellent | 12+ months | Yes | ₹₹₹ | Yes |
| Immersion Silver | Excellent | 6-12 months | Yes | ₹₹ | Yes |
| ENEPIG | Excellent | 12+ months | Yes | ₹₹₹₹ | Yes |
How to Choose the Right Finish
- Hobby/prototype with through-hole: Leaded HASL — cheapest, easiest to hand solder
- Prototype with fine-pitch SMD: ENIG — flat pads, long shelf life, available from JLCPCB/PCBWay at small premium
- High-volume production: OSP — cheapest flat finish, works if boards are assembled within 6 months
- RoHS export product: Lead-free HASL for through-hole dominant designs, ENIG for fine-pitch
- RF/microwave boards: Immersion Silver — lowest insertion loss
- Automotive/medical: ENEPIG — highest reliability, wire bonding compatible
Frequently Asked Questions
Which finish does JLCPCB use by default?
JLCPCB defaults to leaded HASL. You can select ENIG, lead-free HASL, or OSP during ordering. ENIG adds approximately $7-12 to a standard 5-piece prototype order. Lead-free HASL is a small upgrade over leaded HASL.
Can I hand-solder ENIG boards?
Yes, ENIG boards are easy to hand solder. The gold layer wets well with standard 60/40 or lead-free solder. Use flux for best results. The only finish that is difficult to hand solder is OSP after it has been stored for several months — the organic coating degrades and solderability suffers.
Is leaded HASL still legal in India?
Yes, India’s E-Waste Management Rules (2022) restrict lead in electronics sold commercially but exempt prototypes, R&D, and industrial equipment. For products sold to consumers, lead-free finishes are recommended. For export to the EU, RoHS compliance (lead-free) is mandatory.
What is black pad in ENIG?
Black pad is a defect where the nickel layer becomes excessively phosphorus-rich during deposition, creating a dark, brittle interface that does not form a reliable solder bond. It appears as a dark pad when the solder is removed. Choose manufacturers with tight ENIG process control (nickel phosphorus content 7-10%). ENEPIG eliminates this risk entirely.
How do I store PCBs to maximise shelf life?
Vacuum seal boards with desiccant packets immediately after receiving from the manufacturer. Store in a cool, dry place away from sunlight. For OSP boards, storage in a nitrogen environment extends shelf life. Always check solderability with a test board before assembling stored PCBs.
Browse soldering supplies, flux, and PCB materials for your assembly projects at Zbotic Soldering Tools — reliable delivery across India.
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