Surface finish affects solderability, shelf life, flatness, and reliability. Each of the five main options involves real trade-offs — and choosing the wrong one creates assembly problems that are expensive to diagnose. This guide compares every major finish, gives you a decision flow, and shows exactly how to specify your choice on an RFQ.
This guide covers all five major PCB surface finishes with side-by-side comparison of cost, surface flatness, shelf life, and best-fit applications. A step-by-step decision flow then helps you select the right finish for your specific design requirements — followed by precise specification language to include in your RFQ or purchase order.
Each finish protects the exposed copper pads against oxidation and maintains solderability until the board reaches the assembly line. The right choice depends on your component pitch requirements, storage duration, application type, and cost constraints.
Work through these questions in sequence. Stop at the first one that applies to your design.
If yes, HASL is disqualified — its surface height variance causes placement and solderability problems on fine-pitch pads. The remaining options (ENIG, OSP) both provide the flatness needed.
If YES → Eliminate HASL, continue to Q2OSP and Immersion Silver degrade within approximately 6 months, especially under humidity. If your inventory turns are slow, or boards need to survive a long supply chain before reaching the assembly line, choose ENIG or HASL.
If YES → Eliminate OSP and Immersion Silver, choose ENIG or HASLFor card-edge connectors (PCIe, M.2, memory slots, etc.), specify Hard Gold selectively on those areas regardless of the finish used on the rest of the board. The wear resistance of hard gold over hundreds of insertion cycles is not achievable with any other finish.
If YES → Specify Hard Gold for contact areas (combine with ENIG elsewhere)For designs operating above a few GHz where insertion loss in transmission lines is a measurable design parameter, evaluate Immersion Silver. The absence of a nickel barrier layer eliminates the high-resistance path that ENIG creates at microwave frequencies.
If YES → Evaluate Immersion Silver (account for handling and shelf life requirements)If none of the above applies, the decision is purely about cost versus long-term reliability. HASL (lead-free) is the lowest cost and simplest option for commodity applications. ENIG provides better long-term reliability and compatibility with fine-pitch components even when not strictly required — making it the better default for industrial, medical, or automotive-adjacent designs.
Cost priority → Lead-Free HASL | Reliability priority → ENIGNaming the finish type alone (e.g., "ENIG") is not sufficient for a production order. Specify thickness, applicable standard, and scope. Ambiguous specifications create opportunities for cost-cutting that may compromise reliability.
| Finish | Required Specification Details |
|---|---|
| HASL (Lead-Free) | State "Lead-Free HASL" explicitly. Alloy type: SAC305 (Sn96.5/Ag3/Cu0.5) unless otherwise required. Confirm RoHS compliance. |
| ENIG | Nickel: 3–5μm minimum. Gold: 0.05–0.1μm (Class 2) or 0.1–0.15μm for wire bonding. Specify Class 2 or Class 3 per IPC-4552. |
| OSP | State "OSP — Organic Solderability Preservative." Specify shelf life requirement from date of manufacture. Note if double-sided reflow is required. |
| Hard Gold | Nickel underplate: 3–5μm. Gold: 0.5–1.27μm (or per application). Specify application area precisely (e.g., "edge connector fingers only — see drawing zone X"). |
| Immersion Silver | Thickness: 0.1–0.4μm. Require anti-tarnish packaging (vacuum-sealed with desiccant). State shelf life requirement from date of manufacture. |
PCB surface finish selection comes down to three axes: component pitch, storage duration, and application type. Lead-Free HASL is the lowest-cost default for non-fine-pitch boards. ENIG is the best overall choice for fine-pitch components and reliability-critical designs but requires supplier process verification to avoid black pad. OSP offers flatness at HASL cost, but only for short-shelf-life applications and ideally single-reflow assemblies. Hard Gold is reserved for mechanical contact surfaces. Immersion Silver is the specialist choice for high-frequency RF circuits. When specifying to your manufacturer, always include thickness targets, applicable IPC standard, and scope of application — ambiguity in the spec is a cost-cutting invitation.
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Denro Keikaku is a direct partner of Chengde Technology (成徳科技) and specializes in cross-border PCB procurement with full English and Japanese technical support. All standard surface finishes — HASL, ENIG, OSP, Hard Gold, Immersion Silver — are available. No fees until a transaction is confirmed.