Bis-(Sodium Sulfopropyl)-Disulfide, sold as SPS, is a water-soluble organic sulfur compound supplied as a white to yellowish powder. Copper platers add it to acid copper sulfate baths at 10–50 mg/L, where it does the brightening and grain-refining job in the additive package — the part that decides how fine the copper crystal structure grows and how evenly the finished deposit reflects light. Decorative finishers use it to build a level, bright copper layer under nickel and chrome. PCB shops use the same chemistry to grow fine-grained, low-stress copper in panels, patterns and HDI builds. It is one component of the chemical coating system rather than a complete process: it is dosed alongside a suppressor and a leveller, and the balance between the three sets the character of the deposit. Two assays are available, ≥90% and ≥95.0%, both as a free-flowing powder that is weighed straight into a stock solution.
| Chemical name | Bis-(Sodium Sulfopropyl)-Disulfide |
| Trade names | SPS, SPS-95 |
| CAS No. | 27206-35-5 |
| Molecular formula | C6H12Na2O6S4 |
| Molecular weight | 354.4 |
| Physical form | White to yellowish powder |
| Concentration (%) | ≥90% or ≥95.0 |
| pH | 2.0–6.0 |
| Solubility (20 °C) | 38% water solution, transparent and clear |
| Function in the bath | Brightener and grain refiner for the acid copper plating process |
| Typical dosage | 10–50 mg/L in acid copper sulfate baths |
| Additive compatibility | Non-ionic surfactants, polymeric amines, dyes and other sulfur-containing compounds |
| Packing | 25 kg per drum |
| Storage | Cool, dry place, container kept closed |
The molecule is a symmetric disulfide: two propane-sulfonate arms joined through an S–S bond and neutralised as the disodium salt. That structure explains the two things buyers care about. The sulfonate groups make the powder dissolve freely in water, and the disulfide linkage is the part that interacts with the copper surface during deposition. We supply two assays, ≥90% and ≥95.0%, both to the same specification; what changes is the active content, which is why the choice matters most in a tightly controlled metal plating process. The SPS-95 grade is the one to specify when your bath runs at the low end of the dosing range and you want the smallest possible swing in active content between lots. Colour runs from white to yellowish across both grades, and that range is normal for this chemistry — shade is not a purity marker, assay is. The material is acidic in solution, so choose mixing and dosing equipment that tolerates a mildly acidic stream.
Copper deposited from a plain sulfate bath grows coarse and dull. SPS changes that at a very small addition. Across the 10–50 mg/L range it adsorbs unevenly over the cathode, holds back deposition where it sits and forces the crystal structure to re-nucleate into finer grains. The visible result is a bright, level deposit; the invisible one is a denser, more uniform layer with lower internal stress. Because the effect is dose-dependent, the working range is a window rather than a minimum: too little and the deposit stays matt, too much and the layer can turn brittle or hazy. In a full package this product supplies the brightening and grain-refining role while a polyether suppressor controls thickness distribution and an amine leveller shapes the surface. The right balance is set on the line, as part of the plating process, not on paper — which is why the same product is tuned differently in every shop.
Brightness is the first thing anyone notices and the easiest thing to lose. Copper plated from an unbalanced bath scatters light off a rough surface and reads dull or milky; with the grain refined, the same thickness of copper reflects evenly and looks like a proper bright finish. The finer structure also cuts visible roughness, so parts come off the rack needing less polishing, and defects that would otherwise show through a thin nickel or chrome topcoat are less likely to form. On large work — long extrusions, big panels, racks of small parts — the improvement shows up first at the edges and in the low-current-density areas where coarse growth usually starts. A smoother copper surface also gives the next stage something to grip: nickel plating, paint, powder coat and other chemical coating steps all bond better to a fine-grained deposit than to a coarse one, and that carries straight through to how the finished part performs in service.
Two things decide whether a brightener is easy to live with: whether each drum behaves like the one before, and whether it is still the same powder after a season in the store. Every lot is checked against the same specification for assay, appearance and solubility, and the two grades let a plant standardise on one assay instead of re-tuning between deliveries. Moisture is the main enemy in storage — powder that has taken up water cakes, weighs badly and dissolves slowly — so keep the container closed and the store cool and dry. Handled that way, the material has a long shelf life and can be held as inventory rather than bought drum by drum. Before a new lot goes into a production tank, run the check you would run on any new chemical: dissolve a sample, confirm the solution is clear, and plate a Hull cell panel against your reference. Ten minutes at the bench is what protects a full tank from a surprise.
On a printed circuit board the copper has to do two jobs at once: carry current reliably and sit flat enough for the next layer to be built on top. SPS contributes the grain refinement that makes both possible. Panel plating and pattern plating put different demands on the same plating process — the first wants a uniform, fine-grained layer across the whole panel, the second wants a low profile so fine lines stay fine and the resist image is not distorted by rough copper underneath. Refined grain also means lower internal stress, which matters on multilayer boards and HDI builds where several copper and dielectric cycles are stacked and reflowed, and on foil where the same chemistry supports a low-profile surface. In a typical acid copper package this product sits in the brightener role, with a polyether suppressor controlling thickness distribution and an amine leveller shaping the surface; the three are tuned together and each dose is usually tracked analytically rather than by counting additions.
Wuhan Fengfan International Trade Co., Ltd is the trading arm of Wuhan Fengfan Electrochemical Technology Co., Ltd, a specialist chemical business with decades of work in surface finishing behind it. The catalogue covers plating intermediates, sultone and electrolyte additives, anodising chemicals, surfactants and a short line of bath-control equipment; this product belongs to the copper group, alongside DPS, MPS and ZPS. Our customers are formulators, job shops, PCB manufacturers and distributors — the kind of plants doing industrial metal plating where a bath has to run the same way every shift. Bath problems are worked on in a plating laboratory rather than answered from a specification sheet, and that is the standard we hold ourselves to when a tank starts drifting.
Because every space and daily routine is a little different, this product is offered so it can be matched to the way you actually intend to use it. Tell us where it will live — indoors or outside, the surface it will rest on, how often it will be moved, and who will be handling it — and we will confirm the specification that suits that setting. If your plans cover more than one kind of use, share both situations before ordering so the finish, size and any accessories can be checked against each one. Where a particular environment has its own requirements, such as weather exposure, heavy daily handling or a specific floor type, mention it when you enquire and we will confirm whether this item is the right fit or point you to a better option.
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.
Both grades are the same chemistry supplied to the same specification; the difference is active content. Take the ≥95.0% grade when your bath is dosed at the low end of the 10–50 mg/L range and you want the least variation between drums. For general decorative work where the bath is dosed in the middle of the range, ≥90% is normally sufficient. If you are unsure, tell us your current dose and tank volume and we will tell you which one keeps your addition closest to what you already run.
It is a white to yellowish powder with a fine, free-flowing granulation. A slightly deeper yellow shade is normal for this chemistry and does not indicate a purity problem — the assay figure is the number to check. The powder dissolves readily in water at ambient temperature.
10–50 mg/L is the working range for brightening and grain refinement. Where you sit inside that window depends on the suppressor and leveller already in your package, so treat 10–50 mg/L as a starting envelope and confirm the final figure on a Hull cell panel before you commit a production tank.
Three identifiers should match on every document that travels with the material: molecular formula C6H12Na2O6S4, molecular weight 354.4 and CAS number 27206-35-5. The full chemical name is Bis-(Sodium Sulfopropyl)-Disulfide. Read the formula as the disodium salt of a sulfur-linked organic sulfonate: the two sodium atoms shown as Na2 are what carry the powder into water, and the four sulfur atoms shown as S4 sit across the sulfonate groups and the disulfide link at the centre of the molecule. The molecular weight of 354.4 g/mol is the figure that corresponds to the formula as written, so use it whenever you convert a weighed amount into a molar concentration for bath make-up or for comparing one lot against another. In practice the CAS number is the handle buyers work with: quote it on enquiries so a supplier cannot answer with a look-alike grade under a different trade name, and check that the safety data sheet for the drum you receive carries the same number together with the assay you ordered. If your line needs the higher grade, write both the CAS number and the grade into the purchase description.
Weigh the powder, then dissolve it in demineralised water at ambient temperature, working comfortably below the 38% solubility ceiling. A 38% solution should come out transparent and clear; if it stays hazy, the powder has not fully dissolved or has picked up moisture. Dose from the stock under agitation rather than adding powder directly to the tank.
It is compatible with non-ionic surfactants, polymeric amines, dyes and other sulfur compounds such as DPS or EXP2887. The practical rule is to change one component at a time and plate a Hull cell panel after each change, because the ratio between brightener, suppressor and leveller is what actually sets the deposit.
Yes — the chemistry does not change. What changes is the control level: a decorative line judges the deposit against a visual limit sample, while a PCB line is holding fine-line definition, low profile and internal stress, so it usually runs a tighter dose and tracks it analytically. Whether your plant is doing decorative finishing or industrial metal plating, the same product and grade are used.
Three things: the appearance of the powder, the clarity of a freshly prepared solution, and a Hull cell panel plated against your reference. If the panel matches the reference across the current density range, the lot is behaving as expected. If it does not, stop and talk to us before the drum goes into the tank — in most cases the cause is visible on the panel.
