Immersion Tin
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0.8-1.2 um
Tin thickness per IPC-4556
6-12mo
Typical shelf life
≤0.2um
Surface flatness for fine pitch
100%
RoHS /lead-free process
What Is Immersion Tin?
mmersion tin — also called ISn, ImSn, chemical tin or white tin — is a lead-free surface finish applied to bare copper through a chemical displacement reaction.
Immersion tin is not electroplated tin. Instead of building up metal with current, a controlled chemical bath displaces a thin layer of pure tin onto the exposed copper surface. The result is a smooth, uniform coating that:
- • Prevents copper oxidation before and during assembly
- • Stays perfectly flat — unlike HASL it leaves no uneven solder bumps
- • Contains no nickel or gold layers (unlike ENIG), keeping cost low
How the finish is applied
Clean & micro-etch
Bare copper is cleaned and lightly micro-etched for a consistent active surface.
Pre-dip & activate
A pre-dip prepares and activates the copper for uniform deposition.
Immersion tin deposition
Tin is deposited by chemical displacement to a controlled 0.8–1.2 µm layer.
Rinse & post-treatment
Boards are rinsed and finished to stabilize the tin and control grain size.
Benefits & Limitations at a Glance
An honest look at what immersion tin does well — and the trade-offs you need to plan around.
Why designers choose it
The reasons immersion tin keeps winning fine-pitch and lead-free jobs.
Excellent solderability
Strong wetting with lead-free solder; reliable SMT joints and fewer assembly defects.
Ultra-flat surface
~0.2 µm planarity supports fine-pitch components down to 0.4 mm pitch and BGA.
Cost-effective
A lead-free finish at lower cost than ENIG — a strong mid-price choice.
RoHS & eco-friendly
Lead-free, cyanide-free chemistry for compliant, environmentally conscious production.
Limitations to plan around
Being upfront about the risks is part of engineering the right board.
Shorter shelf life
Typically 6–12 months; solderability degrades faster than ENIG after storage and heat.
Tin whisker risk
Pure tin can grow conductive whiskers over time — mitigated with controlled thickness and process.
Limited multi-reflow
Thinner deposit wears under repeated reflow cycles; not ideal for many rework passes.
Handling & storage sensitive
Needs controlled humidity, gloves, and timely assembly to keep solderability.
Immersion Tin vs. Other Surface Finishes
Surface finish drives solderability, yield, reliability, shelf life and cost. Here is how immersion tin stacks up.
Typical performance of common lead-free finishes (values are typical industry figures)
| Property | Immersion Tin | HASL | ENIG | OSP |
| Surface flatness | Excellent(~0.2 m) | Poor (2-5 m) | Excellent | Excellent |
| Solderability | Excellent(lead-free) | Good | Excellent | Good |
| Fine-pitch support | Yes (≤ 0.4mm) | Limited | Yes | Yes |
| Shelf life | 6-12 months | ~12 months | ~12 months | 3-6 months |
| Relative cost | Medium | Low | High | Low |
| Lead-free / RoHS | Yes | Yes | Yes | Yes |
How to choose
- Pick immersion tin when you need a flat, lead-free surface for fine-pitch / BGA boards and want to save cost vs. ENIG.
- Pick ENIG for the longest shelf life, maximum reflow robustness and extreme reliability requirements.
- Pick HASL only for coarse-pitch, cost-driven boards; avoid it for fine-pitch and high-density designs.
Reliability & Design for Manufacturability
Tin whiskers, coating thickness and layout rules are the three things engineers most want nailed down.
Tin whisker mitigation
Whiskers are thin conductive filaments that can grow from pure tin and cause shorts. Modern immersion tin with controlled process reduces this risk substantially:
Keep tin between 1.0–1.2 µm — thicker layers (≥ 2.5 µm) increase internal stress and whisker growth.
Use matte, fine-grain tin deposits (grain < 1 µm) with organic additives and grain refiners.
Apply thermal anneal (1–2 h at 150 °C) to relieve internal stress.
Avoid mechanical stress on the deposit in handling and press-fit designs.
Thickness & IPC-4556
Coating thickness directly controls reliability. Too thin dissolves into solder and exposes copper; too thick invites whiskers and bridging.
Optimal range for solder joints: 1.0–1.2 µm
IPC-4556 minimum: 0.8 µm; aerospace/harsh use: ≥ 1.3 µm
Every PCBWDX order ships with XRF thickness verification.
DFM design rules
Minimum pad size: ≥ 0.2 mm
Trace-to-pad spacing: ≥ 0.1 mm
Use liquid photoimageable solder mask (LPISM) for better tin adhesion.
Compatible with standard FR-4, high-Tg FR-4 and flex substrates.
Designed for lead-free solder alloys (Sn-Ag-Cu).
Built for reliability
Quality is verified, not assumed. Our immersion tin line is monitored and documented at every batch:
XRF thickness measurement on every panel.
Solderability and wetting verification per batch.
Micro-sectioning for cross-sectional integrity.
IPC-4556 compliance with test reports on request.
Where Immersion Tin Shines
Immersion tin is the go-to finish for boards that need flat, lead-free, fine-pitch surfaces at a mid-range cost.
Fine-pitch SMT & BGA
Flat, uniform surface for 0.4 mm pitch and below, reducing bridging and improving yield.
High-density boards
HDI and dense layouts benefit from the smooth finish and consistent joint formation.
LED & lighting modules
Reliable solder joints for high-volume, cost-sensitive LED and lighting PCBs.
Memory & storage
Flat pads and good lead-free wetting for memory modules and storage controllers.
Consumer electronics
A cost-effective RoHS finish for high-volume consumer and prototype runs.
Rapid prototyping
Fast, flat lead-free finish ideal for quick-turn prototypes and low-volume production.
Shelf Life & Storage
Immersion tin has a shorter usable window than ENIG, so storage discipline matters. Typical shelf life is 6–12 months, but time alone does not tell you when solderability drops — process, heat and storage all play a role.
For the best results, assemble boards promptly after delivery, and keep them in original vacuum packaging until use. If a board sits past the window, run a wetting / solderability check before assembly rather than guessing from age.
Recommended storage conditions
Keep in vacuum-sealed packaging until assembly.
Store at controlled room temperature and low humidity.
Handle with gloves; avoid touching exposed tin pads.
Use boards within 6–12 months of manufacturing.
Verify solderability before soldering older stock.
Immersion Tin Done Right
Two decades of PCB manufacturing, every surface finish verified, and a quote in hours — not days.
20+
Years of PCB manufacturing experience
UL / RoHS
Certified processes and compliant materials
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Quote with just your Gerber files
Frequently Asked Questions
Is immersion tin the same as HASL?
No. Immersion tin is a chemical displacement finish deposited on copper; HASL applies and levels molten solder. Immersion tin is much flatter and better for fine pitch.
How long does immersion tin last?
Typical shelf life is 6–12 months. Storage conditions and thermal history matter — run a solderability check before assembling older stock.
Does immersion tin cause tin whiskers?
Pure tin can grow whiskers, but modern immersion tin with controlled thickness (1.0–1.2 µm), fine-grain deposits and thermal anneal reduces the risk substantially.
When should I choose immersion tin over ENIG?
Choose immersion tin when you need a flat, lead-free surface for fine-pitch boards and want to save cost. Choose ENIG for the longest shelf life and maximum reflow reliability.
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