Kangchuang sulfur-free paper is a precision-grade industrial packaging paper engineered to eliminate sulfur contamination from contact with silver-plated, gold-plated, and copper electronic components. With certified sulfur content below 5ppm, it prevents tarnishing, oxidation, and surface discoloration in PCB manufacturing, LED assembly, hardware electroplating, and photovoltaic production. As an ISO 9001 certified sulfur-free paper manufacturer based in Dongguan, China, Kangchuang has supplied factories across 40+ countries since 2003 — factory-direct, with free samples shipped via DHL Express.
What is Sulfur-Free Paper?
Sulfur-free paper is a specialized industrial-grade packaging material manufactured through a controlled pulp processing and paper-making process that eliminates sulfur-containing compounds — specifically sulfur dioxide (SO₂), hydrogen sulfide (H₂S), and sulfate residues — from the final product. Unlike standard kraft paper or newsprint, which can contain sulfur residues from the wood pulping process (kraft pulping uses sodium sulfide), sulfur-free paper undergoes additional purification and pH-controlled manufacturing to achieve sulfur content below 20ppm, 10ppm, or ultra-low grades below 5ppm.
The critical distinction between sulfur-free paper and ordinary paper is not just purity — it is chemical inertness. When conventional paper contacts silver-plated electronic components, electroplated metal parts, or copper-based circuit boards, trace sulfur compounds in the paper react with the metal surface to form silver sulfide (Ag₂S), copper sulfide (CuS), or other tarnish compounds. This chemical reaction causes visible discoloration (blackening or yellowing of silver-plated surfaces), increased electrical resistance at contact points, adhesion failure in electroplated coatings, and long-term structural degradation of precision metal components.
Sulfur-free paper eliminates this reaction entirely by removing the reactive sulfur compounds before they can reach the metal surface. It functions as a chemically inert separator, interleaving layer, or wrapping material that physically isolates sensitive components while providing no chemical reactivity toward metal surfaces, adhesives, coatings, or electronic substrates.
Why PCB and Electronics Manufacturers Require Sulfur-Free Paper
In the PCB manufacturing industry, the silver immersion (ImAg) surface finish process deposits a thin layer of silver (typically 0.1–0.3 microns) onto copper pads to create solderable, electrically conductive surfaces. Silver is chosen for its excellent electrical conductivity and solderability — but silver has a significant vulnerability: it tarnishes rapidly when exposed to atmospheric sulfur compounds.
Even at concentrations as low as 10 parts per billion (ppb) of atmospheric hydrogen sulfide — concentrations common in urban industrial environments, near rubber or adhesive materials, and in cardboard packaging — silver surfaces will begin to tarnish within hours. When sulfur-free paper is used as the interleaving and wrapping material during PCB storage and transport, it removes the primary contact-transfer pathway for sulfur contamination, extending the storage life of ImAg-finished PCBs from days to months without tarnish formation.
In LED manufacturing, sulfur contamination is equally critical. LED packages contain silver-plated lead frames and silver-based die attach materials. Sulfur vapor that reaches the silver components causes LED chip lumen depreciation, color shift (shifting from white to yellow or green), and premature failure. Sulfur-free packaging paper, used in SMD component trays, LED reel packaging, and LED module interleaving, provides a sulfur-free microenvironment around the component during storage and shipment.
| SPECIFICATION | DETAILS / OPTIONS |
| Sulfur Content | Standard: ≤20ppm | Premium: ≤10ppm | Ultra-Low: ≤5ppm (custom available ≤2ppm) |
| GSM / Basis Weight | 40gsm | 50gsm | 60gsm | 70gsm | 80gsm | 100gsm | 120gsm (custom weights available) |
| Roll Width | 100mm to 1,600mm — custom slit widths for automated production lines |
| Sheet Sizes | 787×1092mm (standard) | 898×1194mm (large) | Custom cut sheets available |
| pH Value | 6.5 – 8.5 (acid-free, pH neutral) |
| Surface Resistance | Standard: Non-ESD | Anti-static grade: 10⁶–10⁹ Ω/sq (ESD-safe variant available) |
| Sulfate Content | ≤0.02% (200ppm) — well below industry tarnish risk threshold |
| Chloride Content | ≤30ppm — RoHS compliant halogen control |
| Surface Finish | Smooth, lint-free, dust-free — no fiber shedding |
| Whiteness | Natural white / off-white (bleached and unbleached options) |
| Packaging Form | Rolls (standard) | Sheets | Pre-cut interleaving sheets | Custom formats |
| Shelf Life | 12 months from manufacture — when stored at 18°C–25°C, away from direct sunlight and moisture |
| Storage Conditions | Cool, dry, ventilated warehouse. Sealed original packaging. Away from acids, solvents, and high humidity. |
| Compliance | RoHS 3 (EU 2011/65/EU + 2015/863/EU) | REACH | ISO 9001:2015 | SGS Test Certified |
| MOQ | 50kg for sample orders | 500kg for standard orders | Container load available |
| Lead Time | Sample: 3–5 business days | Standard order: 10–15 business days | Large orders: 20–25 days |
| Shipping | DHL Express (samples) | Sea freight FOB Dongguan (bulk) | Express air freight available |
Sulfur-free paper is an industrial-grade packaging paper manufactured to contain less than 20ppm of sulfur compounds — compared to standard kraft paper which can contain 50–500ppm of residual sulfur from the wood pulping process. The critical difference is chemical inertness: when regular paper contacts silver, copper, or gold-plated surfaces, its residual sulfur reacts with the metal to form tarnish (silver sulfide, copper sulfide). Sulfur-free paper eliminates this reaction entirely, making it the required packaging material in PCB, LED, electroplating, and optical glass manufacturing.
PPM stands for ‘parts per million’ — the concentration of sulfur compounds in the paper by weight. The lower the ppm number, the purer the paper and the less risk of tarnishing. As a general selection guide: for standard hardware interleaving use ≤20ppm grade; for silver plating and PCB packaging use ≤10ppm; for ImAg-finish PCBs, high-frequency RF components, and precision contacts use ≤5ppm. If you are unsure which grade your application requires, request a free sample of multiple grades and conduct a tarnish test with your actual components before committing to a production order.
Kangchuang sulfur-free paper has a shelf life of 12 months from the manufacturing date when stored correctly. Correct storage conditions are: temperature 18°C–25°C (64°F–77°F), relative humidity below 65%, away from direct sunlight, sealed in original moisture-proof packaging, and isolated from solvents, acids, and materials that off-gas sulfur compounds (including rubber, certain adhesives, and uncured epoxies). Paper stored outside these conditions may show elevated sulfur content due to atmospheric absorption, reducing its protective effectiveness.
Yes. All Kangchuang sulfur-free paper grades are manufactured in compliance with EU RoHS 3 Directive (2011/65/EU as amended by 2015/863/EU) and REACH Regulation (EC 1907/2006). The paper is free from the 10 restricted substances under RoHS 3, including lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (CrVI), polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), DEHP, DBP, BBP, and DIBP. SGS-certified test reports are available upon request.
Yes, Kangchuang’s dust-free sulfur-free paper grade is suitable for ISO Class 6 (Class 1000) cleanroom environments and above. The paper is manufactured with a controlled surface cleanliness standard — no fiber shedding, no particle generation above 0.5 microns per specified test — making it compatible with LED chip assembly, MEMS device packaging, and precision optical manufacturing cleanroom environments. For Class 100 (ISO Class 5) environments, please contact us to discuss our ultra-clean production lot options.
These terms are sometimes used interchangeably but have a technical distinction. Sulfur-free paper is defined by what it does NOT contain — sulfur compounds that would react with metals. Anti-tarnish paper is defined by what it DOES contain — it typically refers to paper treated with a volatile corrosion inhibitor (VCI) or tarnish-inhibiting coating that actively neutralizes sulfur compounds in the surrounding atmosphere. Sulfur-free paper provides passive protection (removes the source of sulfur from the paper itself); VCI-treated anti-tarnish paper provides active protection (emits compounds that neutralize atmospheric sulfur). Kangchuang offers both pure sulfur-free paper and VCI-enhanced variants.
Standard sulfur-free paper provides physical separation from moisture but is not a moisture barrier on its own — it will absorb water if exposed to high humidity. For applications requiring both sulfur protection and moisture barrier properties, Kangchuang recommends combining sulfur-free paper with desiccant paper interleaving or using our PE-laminated sulfur-free paper variant, which adds a polyethylene moisture barrier coating to the sulfur-free base paper. This combination is used in export packaging of PCBs destined for sea freight shipment, where humidity in shipping containers can be significant.
For sample evaluation orders: minimum 1 roll or 50kg, shipped via DHL Express — available for free to qualified buyers in the USA, EU, and other regions. For standard production orders: minimum order quantity is 500kg (approximately 1–2 pallets depending on GSM and roll width). For container-load orders: full 20-foot container (FCL) shipments are available at our best FOB Dongguan pricing. We do not have a maximum order limit — we have supplied single purchase orders of 100+ metric tons to large electronics manufacturers.
Yes to both. For custom sulfur content: we can produce paper to specifications below the standard 5ppm grade, including 2ppm grades for the most sensitive applications, subject to additional testing and production lead time. For custom widths: our slitting equipment handles master roll widths up to 1,600mm and can precision-slit to any width down to 100mm with ±0.5mm edge tolerance. Custom GSM weights outside our standard range (40–120gsm) are also available with minimum order quantities — contact our engineering team with your application requirements for a custom quote.
The standard industry method for testing sulfur-free paper is the ASTM D644 or TAPPI T557 sulfate content test, combined with combustion analysis (Schöniger flask or bomb calorimetry) for total sulfur content. A practical field test used by PCB manufacturers is the ‘silver coupon tarnish test’: place a clean, freshly polished silver or ImAg-surface coupon in direct contact with the paper sample in a sealed container at 40°C and 75% relative humidity for 72 hours, then inspect for discoloration. Our production test reports using these methods are available for all production batches upon request.
Sulfur-free and acid-free refer to different chemical properties and are not the same thing — though high-quality sulfur-free paper is typically also acid-free. Acid-free paper has a pH of 6.5 or above (no acidic compounds that would degrade paper fibers or metal surfaces over time). Sulfur-free paper has sulfur content below a specified threshold (20ppm, 10ppm, or 5ppm). Kangchuang sulfur-free paper is manufactured to be both acid-free (pH 6.5–8.5) AND sulfur-free — this dual specification is important for long-term archival storage applications such as silver coin storage, precious metal jewelry packaging, and long-shelf-life electronic component storage.
Yes. Kangchuang regularly supplies sulfur-free paper to buyers in the United States, including PCB manufacturers, LED assembly facilities, hardware electroplating companies, and industrial packaging distributors. Sample shipments are sent via DHL Express (3–5 business days to most US locations, free of charge for qualified buyers). Production orders are shipped FOB Dongguan via sea freight (15–25 days transit to US West Coast ports, 20–30 days to East Coast). We prepare all export documentation including commercial invoice, packing list, certificate of origin, and material safety data sheet. Contact us for a freight quote alongside your production order quotation.
Kangchuang Paper specializes in high-quality industrial papers — sulfur-free, coated, release, and anti-rust. Tell us your requirements and we’ll recommend the right grade with fast turnaround.
