What does OSP stand for on a PCB?

OSP stands for Organic Solderability Preservative. It is a thin organic film, typically 0.2 to 0.5 micrometres, applied to exposed copper pads on a PCB to prevent oxidation and keep the copper solderable until assembly.

Is OSP PCB finish RoHS and lead-free compliant?

Yes. OSP contains no lead and no heavy metals, so it is RoHS compliant and fully compatible with lead-free reflow assembly.

How long does OSP last (shelf life)?

Typically 6 to 12 months depending on packaging and storage. Vacuum-sealed bags with desiccant extend life; open shop-floor exposure, humidity and handling shorten it considerably.

Can OSP survive multiple reflow cycles?

OSP is best suited to one or two reflow cycles. Each thermal excursion consumes some of the film, so for triple-sided or rework-heavy boards a more robust finish such as ENIG is often preferred.

Should I choose OSP or ENIG?

Choose OSP for low cost, a perfectly flat surface and single or double reflow with quick assembly. Choose ENIG when you need long shelf life, multiple thermal cycles, gold wire bonding, contact or press-fit surfaces, or in-circuit test reliability.

FIN SURFACE FINISH · Cu–OSP

OSP PCB

Organic Solderability Preservative

A thin organic film — typically 0.2–0.5 µm — that bonds to exposed copper pads to stop them oxidising and keep them solderable until assembly. During reflow the flux dissolves the film and solder wets the bare copper underneath.

Read the full OSP PCB guide → Open the tools ↓

Film thickness

0.2–0.5 µm

Compliance

Lead-free · RoHS

Relative cost

Lowest

Best for

1–2 reflows

OSP PCB — a green circuit board with OSP-finished copper pads and a central BGA pad array

REF PCB-01 · OSP on bare Cu · BGA + SMD pads

U1 Definition

What is an OSP PCB finish?

An OSP PCB is a board whose exposed copper is coated with an Organic Solderability Preservative — sometimes called Entek or anti-tarnish. It is a water-based azole compound (a substituted benzimidazole or imidazole) that selectively bonds to copper through copper–nitrogen complexes.

The film is self-limiting: it grows only on copper and only to a controlled thickness, leaving the solder mask untouched. It is essentially colourless, so an OSP board looks like bare copper under the green mask. Its only job is to keep that copper clean and wettable from the fab line until the parts are soldered. For the full OSP PCB specification and ordering options, see the OSP PCB reference.

Because there is no metal plating, OSP adds no nickel, gold or tin to the stack-up — the pad you solder to is the original copper. That keeps the surface dead flat and the cost low, which is exactly why high-volume consumer boards lean on it.

SEC Cross-section

Stored / shelf life. The OSP film fully covers the copper, blocking oxygen and moisture so the pad stays solderable in the warehouse and on the line.

Solder mask Copper OSP film Solder

U2 Trade-offs

Advantages & limitations of OSP

OSP is the right call surprisingly often — but only when you respect what the thin organic film can and can’t do. Here is the honest balance sheet.

+ Advantages

Lowest-cost finishAmong the cheapest options available — minimal chemistry, no precious metals.
Perfectly flat & coplanarNo bumps or domes, so it’s ideal for fine-pitch QFN, BGA and dense SMD layouts.
Simple, fast, greener processFew steps and a water-based bath; lower energy and chemical load than plated finishes.
Lead-free & RoHS compliantNo lead, no heavy metals; drops straight into lead-free reflow.
No nickel layerAvoids nickel intermetallic and “black-pad” failure modes seen with ENIG.
Easy to strip & re-finishBoards can be re-coated within reason if the window is missed.

! Limitations

Limited shelf lifeTypically 6–12 months; humidity, heat and open handling shorten it fast.
Fragile to handlingFingerprints, gloves residue and abrasion damage the film — touch pads as little as possible.
Degrades with each reflowBest for 1–2 cycles; triple-reflow or rework-heavy boards risk poor wetting.
Hard to inspectThe film is transparent, so coverage and thickness can’t be judged by eye.
Weak contact / wear surfaceNot for edge-card fingers, press-fit, keypads or switch contacts.
ICT probing can be unreliableThe film is insulating; bed-of-nails test points may need extra probe force or paste.

U4 Selection

OSP vs other PCB surface finishes

How OSP stacks up against the finishes you’ll actually be choosing between. The OSP column is highlighted — toggle the buttons to explore.

$ = relative cost · pills = suitability

Property	OSP	Lead-free HASL	ENIG	Immersion Ag	Immersion Sn
Relative cost	$	$	$$$	$$	$$
Surface flatness	Excellent	Poor	Excellent	Excellent	Excellent
Shelf life	6–12 mo	12+ mo	12+ mo	~12 mo	~6 mo
Multiple reflows	1–2	2–3	3+	2–3	2
Fine-pitch / BGA	Yes	Limited	Yes	Yes	Yes
Gold wire bonding	No	No	Yes	No	No
Edge connectors	No	No	OK	No	No
Press-fit	No	No	OK	OK	Best
ICT probing	Fair	Good	Good	Good	Good
RoHS / lead-free	Yes	Yes	Yes	Yes	Yes

Bottom line: pick OSP for cost, flatness and quick single/double-reflow builds; step up to ENIG when you need shelf life, many reflows, wire bonding or contact surfaces.

U5 Engineering tools

Decide if OSP is right for your board

Two quick calculators built for the bench. Answers are typical-case guidance — always confirm against your fabricator’s datasheet and IPC requirements.

OSP Suitability Checker

Five questions about your build. We score OSP against the common alternatives and give you a verdict with reasoning.

OSP Shelf-Life Estimator

Enter when the boards were finished and how they’ve been stored to estimate the remaining solderability window.

PCB finishing / fabrication date

Storage condition

U6 Where it’s used

Typical OSP PCB applications

Where the flat-and-cheap profile of OSP wins in production.

📱

Consumer & mobile

High-volume, cost-sensitive boards assembled and shipped quickly — phones, tablets, accessories.

🔲

Fine-pitch & HDI

Dense BGA / QFN layouts where dead-flat pads are essential for reliable paste deposition.

⚡

Single-reflow assemblies

One-pass SMT boards where the film only has to survive a single thermal cycle.

🛠️

Prototypes & quick-turn

Fast iterations and short runs that will be populated soon after fabrication.

📟

IoT & wearables

Compact, price-driven modules without edge connectors or wire-bond dies.

💡

LED & lighting boards

Large flat copper areas where coplanarity and low cost matter more than longevity.