spts

If you build copper plating baths for PCBs or damascene lines, you already know the “accelerator” everyone whispers about. I’m talking about Bis Sodium Sulfopropyl Disulfide —SPS for short. It’s one of those deceptively simple molecules that quietly decides whether your vias fill perfectly or end up with annoying voids. I’ve toured a few lines in South China and, to be honest, the teams that track SPS with discipline tend to sleep better. What it is and why it matters Bis Sodium Sulfopropyl Disulfide (SPS, CAS 27206-35-5) is the classic acid copper accelerator. It partners with PEG/suppressors and a leveler; chloride seals the chemistry. In fact, SPS gets reduced at the cathode to MPS, speeding local deposition and enabling superfilling. Many customers say it’s the difference between “good enough” and “production-proof.” Typical product specs Name Bis-(sodium sulfopropyl)-disulfide (SPS) CAS 27206-35-5 Assay (HPLC) ≥ 98.0% (typ.) Appearance White to off‑white crystalline powder Moisture (KF) ≤ 1.0% (w/w) Formula (approx.) C6H12Na2O6S4 (≈) Solubility Freely soluble in water Process flow and real-world use - Materials: acid copper bath with CuSO4·5H2O 200–250 g/L, H2SO4 50–75 g/L, Cl− 50–70 mg/L; PEG 2000–5000 at 200–400 ppm; leveler a few ppm; Bis Sodium Sulfopropyl Disulfide at 1–5 mg/L (PCB) or 0.5–2 mg/L (damascene). - Methods: Pre-clean → micro-etch → acid dip → copper strike (if needed) → acid copper plating with live additive control via CVS and HPLC. Current density 1–3 A/dm², 22–28°C. - Testing standards: CVS per IPC‑TM‑650 2.3.25; moisture by ASTM E203; coating adhesion per ASTM B571; thickness by ASTM B567. Compliance: REACH, RoHS. Certifications often include ISO 9001 and ISO 14001. - Service life: additive is consumed electrochemically; top-up usually 0.05–0.20 g/kAh (≈) based on CVS curves. In high-throughput lines, daily adjustment is normal. Industries: HDI PCBs, IC substrates, wafer-level damascene copper, connectors, and occasionally decorative Cu underlayers. Surprisingly, we’re seeing more mid-sized PCB shops add online CVS for tighter SPS control. Performance snapshot (lab data, may vary) Microvia 100 μm, AR≈1:1, bath as above with Bis Sodium Sulfopropyl Disulfide 2 mg/L, PEG 3000 300 ppm, Cl− 60 ppm at 2.0 A/dm²: via filling in 18–22 min; surface leveling improved by ≈15%; throwing power +12–18% vs. SPS-free control. Vendor comparison (indicative) Vendor Assay CVS Support Lead Time Notes Moneidechem (Hebei, China) ≥98% (typ.) Method setup + retention samples ≈2–3 weeks Origin: 2-7-523 Jidong Building Materials Tangshan, Hebei 064000 China Global Trader 97–99% Datasheet only ≈4–6 weeks Broader portfolio, less tech depth Local Distributor ≈96–98% Basic QC Stock dependent Fast response; variable lots Customization, packaging, feedback Custom options: particle size control, low-chloride grades, and tighter moisture specs for semicon fabs. Packaging: 1 kg bottles for lab, 25 kg fiber drums for production. Several PCB shops told me the 1–3 mg/L window with PEG/Cl− tuned gave consistent blind microvia fill; one process engineer joked, “When SPS is happy, our X-sections look like brochures.” Compliance and documentation Expect COA with assay (HPLC), moisture (KF), trace metals (ICP), and SDS. REACH and RoHS statements are standard; ISO 9001/14001 on request. For critical lines, ask for CVS titration curves and stability data over 6 months at ambient. IPC-TM-650 2.3.25: Cyclic Voltammetric Stripping for Copper Plating Additives. ASTM E203: Standard Test Method for Water by Karl Fischer Titration. Directive 2011/65/EU (RoHS) and amendments. Regulation (EC) No 1907/2006 (REACH). J. Electrochem. Soc., studies on SPS/PEG/Cl− synergy in Cu superfilling (various authors).