Sn-839 is a methanesulfonic acid bright tin plating process built for continuous lines. Tin methanesulfonate supplies the metal, methanesulfonic acid carries the bath, and two liquid additives — a carrier and a brightener — are dosed separately so the deposit can be corrected one property at a time. It is meant for the parts that leave a reel line and go straight into stamping, forming, reflow or soldering: strip, wire, connectors and lead frames.
Copper alloy strip is the most common base, and tin plating on copper is where the process earns its keep. The layer has to stay solderable through storage and through the heat of assembly, not just look bright on the day it is plated. Steel and alloy strip used for terminals and lead frames run through the same bath. Tin metal sits at 50–80 g/L and the plating solution works at 18–25 °C, close to ambient, so there is no long heat-up before the line can produce.
In the sequence the tank sits between pretreatment and the rinse-and-dry stages. Cathode current density runs 5–40 A/dm² with 1–3 V across the tank, and at 20 A/dm² the bath deposits at least 10 µm per minute — a rate that suits a cell whose dwell time is measured in seconds rather than minutes.
| Parameter | Range | Typical setting |
|---|---|---|
| Tin metal (Sn²⁺) | 50–80 g/L | 50 g/L |
| Methanesulfonic acid | 150–220 g/L | 200 g/L |
| Carrier (Sn-839A) | 15–25 ml/L | 20 ml/L |
| Brightener (Sn-839B) | 3–10 ml/L | 5 ml/L |
| Bath temperature | 18–25 °C | 18–25 °C |
| Cathode current density | 5–40 A/dm² | 20 A/dm² |
| Anode to cathode area ratio | 2 : 1 | 2 : 1 |
| Tank voltage | 1–3 V | 1–3 V |
| Deposition rate | At least 10 µm/min at 20 A/dm² | — |
The process of electroplating puts the tin down; what happens after the part leaves the tank decides whether the layer was any good. Two things matter most. The first is brightness across the whole current density band, so a part with a high-current edge and a shielded area does not come out two-tone after reflow. The second is defects: pinholes and fogging are the two that most often send a plated reel to scrap, and the bath is formulated to keep both rare rather than to sort them out afterwards.
Organic content in the layer is kept very low, and that shows up later in the run. Low organics mean minimal discolouration after steam and heat treatment, so a part that has been through reflow or a steam ageing check on an electronic plating line still matches the sample that was signed off. Solderability follows the same property: the surface wets cleanly and keeps wetting, including on parts that sit in stores before assembly.
Ductility and weldability are retained after storage as well, which is the practical question for anyone holding plated reels ahead of a build. If your specification quotes a corrosion, appearance or solderability test to a named standard, send it over — we will tell you which results this bath can support directly and which are better settled with a trial on your own line, because heat profiles differ from plant to plant.
Both additives are liquids supplied in drums, and the tin concentrate and the acid are the two components that need the most care in handling. Keep containers closed, store them out of direct sun in a dry, ventilated area, and keep acid and additives apart on the shelf. Methanesulfonic acid calls for the usual acid protection — face shield, gloves, apron — and a plumbed eyewash within reach of the make-up area. If you work in a hot climate, ask us for the storage guidance that applies to the batch you receive rather than assuming a warehouse temperature is fine.
The bath itself is an acidic tin solution. Rinse water and spent bath belong in the works' effluent treatment and should be neutralised and treated for tin before discharge, in line with your local rules; they should never go to a general drain. That is standard practice for a metal plating process, and it is worth writing into the operating instruction before the first drum arrives.
Ask for the safety data sheet for the additives and the tin concentrate before the first delivery, and check that the version you hold matches the batch you receive.
| Payment terms | 100% T/T in advance |
| Minimum order quantity | Varies by chemical; confirmed with our sales team for each order |
| Samples | Availability and trial quantity confirmed with your sales contact |
| Production lead time | 2 weeks |
| Box packing | 10 kg/box |
| Bag packing | 25 kg or 50 kg/bag |
| Drum packing | 20 kg, 25 kg, 30 kg or 200 kg per drum |
| IBC packing | 1,000 kg/IBC drum |
| Shipping | Per the terms agreed in the current contract |
| Batch record and warranty | Inspection certificate issued after delivery, stating the batch number and warranty period |
| Check | How it is done | When to run |
| Tin metal (Sn²⁺) | Titration, read against the 50–80 g/L band | Start of each shift and after any large replenishment |
| Methanesulfonic acid | Titration on the same sample, read against 150–220 g/L | Together with the tin determination |
| Carrier and brightener | Calculated from the working volume against the analysis result, never judged by eye or by colour depth | Every replenishment |
| Coating thickness | XRF on a plated coupon — on tin plating on copper strip the tin layer reads directly against the copper substrate — with coulometric stripping as an independent cross-check, and a cross-section if a customer queries the figure | At qualification, at the start of each run, and after any change to current density or line speed |
| Thickness against line speed | At 20 A/dm² the bath lays down at least 10 µm per minute, so a 1 µm layer needs roughly six seconds in the cell at that rate; a faster line calls for a higher current density inside the 5–40 A/dm² band, not a thinner deposit | Whenever line speed or the drawing thickness changes |
| Appearance | Coupon compared with a signed-off standard under fixed lighting, with the high-current edge and a shielded area both in view | Each reel or batch |
| Solderability | Steam ageing or the customer's own heat profile, then a wetting test on the aged surface | Per batch, or as the drawing requires |
| Corrosion and porosity | Only to the method named in the customer's specification — tell us the method and the acceptance figure before it goes on a drawing, because results move with layer thickness and substrate | On qualification and at the audit frequency your customer sets |
Pinholes and Fogging
Pinholes usually come from the tank rather than from the additive: filtration that has been let go, a carrier sitting at the bottom of its 15–25 ml/L range, or gas clinging to a part that moves too slowly through the cell. Fogging is a haze that survives rinsing. Before adding anything, confirm the plating solution is still inside 18–25 °C and that the brightener has not been pushed up in an attempt to lift gloss.
Brightness That Drifts Mid-Shift
If the first reel is bright and later reels are semi-bright, the brightener is the first suspect. If the parts are bright but coverage is thin or missing in recesses, look at the carrier instead. Correcting one against a fresh analysis of tin and acid is faster than adding both and hoping the balance comes back.
Bright Edges, Dull Recesses
That is a current distribution question. Check the anode-to-cathode area at 2 : 1, check that contacts and jigging are clean, and check tin metal — at the low end of 50–80 g/L the shielded areas lose brightness first. Raising the tank current to compensate for a poor contact usually over-brightens the edge and makes the next problem.
Colour Shift After Reflow or Steam
Ask whether the bath changed or the oven did. Compare a coupon from the affected batch with the standard signed off at qualification, then check the brightener level and the heat profile against the one used at start-up. A gradual shift over weeks supports the bath; a step change on one day usually supports the oven or the ageing check.
Voltage Creeping Above 1–3 V
Rising voltage at a fixed current density normally means the anodes are partially filmed or the anode area has fallen away. Check the anode area, clean or replace as needed, and analyse tin before touching the additives.
When to Escalate
If two shifts of correction have not cleared the fault, stop adjusting and send three things: the last bath analysis with the tin and acid figures, a coupon from the affected reel photographed beside a good one, and the line settings — current density, line speed, temperature and anode area. From those we can usually name the cause in one exchange. Where the answer depends on seeing the tank, we say so and follow the case through with the supplying plant until the line is back in band, rather than leaving you to work out a process of electroplating fault alone.
Choosing the right match is where most sourcing decisions stall. As a trading supplier, we keep one point of contact from first enquiry to after-sales: tell us what you are making and the conditions you work under, and we shortlist the closest matches from our supplier network, compare specifications and arrange samples before you commit to a bulk order. If something does not behave as expected, we work with the supplying partner on the cause and a practical fix, and stay with the case until it is settled. Email, WeChat or WhatsApp enquiries get a reply within 24 hours.
The bath runs at 5–40 A/dm² and deposits at least 10 µm per minute at 20 A/dm², so a short cell can keep pace with a fast strip or wire line. Brightness holds across that current density band rather than only at one set point, which is what lets the line change jobs without re-tuning the bath for every part family.
Yes, within the working ranges. Tin metal can sit anywhere from 50 to 80 g/L, methanesulfonic acid from 150 to 220 g/L, and current density from 5 to 40 A/dm²; the carrier and brightener are dosed separately, so appearance and coverage can be moved independently. Temperature is the fixed point at 18–25 °C. For a new substrate or a very different part geometry, send us the details and we will suggest a starting point for the plating solution.
The tin additives are formulated without lead and cadmium, and the process is stated as aligned with RoHS and ELV requirements. The manufacturing site runs under clean production verification. For your compliance file, ask for the current declaration covering lead, cadmium and RoHS/ELV status when you place the order, so the paperwork travels with the goods rather than being reconstructed later.
Our technical team works through make-up, the analysis routine and troubleshooting with your line staff. If you are moving this product over from another tin system, send your current parameters and we will review them against this bath before the first charge. Where a problem needs eyes on the tank rather than an email, on-site consultation can be arranged. Start with a bath analysis and a test coupon result and we can usually narrow it down from there.
Strip, wire, connectors and lead frames. Copper alloy strip is the everyday case — tin plating on copper contacts and terminals — and the same bath covers the steel and alloy strip used for terminals and lead frames on electronic plating lines. If your part is a heavy one-off section rather than continuous strip, tell us the geometry before you commit: the current density band is wide, but the reel or rack arrangement still has to suit it.
By analysis rather than by habit. Tin metal and methanesulfonic acid are titrated on a fixed schedule, and the carrier and brightener are replenished separately against those numbers, so one additive never corrects a drift caused by the other — which is the most common way a process of electroplating goes quietly out of balance. Temperature stays in the 18–25 °C band and the anode-to-cathode area stays at 2 : 1.
That is what the low organic content is for. Discolouration after steam and heat treatment is minimal, so parts that go through reflow, baking or a steam check keep their appearance, and solderability is retained after storage. If your acceptance criterion is a specific colour or a specific test method, put a sample through your own heat profile before the first production batch — profiles differ from line to line, and a sample settles it faster than any discussion.
