Sulfur-Free Paper vs Traditional Paper: What's the Difference?

In high-precision electronics manufacturing—PCB assembly, immersion silver plating, and electroplating—every material that touches a board matters. A seemingly small choice, like the interleaving or packing paper used between panels, can cause product discoloration, creeping corrosion, or functional failures. This post explains why Sulphur Free Paper / Sulfur-Free Paper is different from ordinary paper, how it protects sensitive components, and what to look for when specifying it for your production line.

What is Sulfur-Free Paper?

Sulfur-Free Paper (also written Sulphur Free Paper) is manufactured to contain ultra-low sulfur and sulphide levels and avoid sulfur-bearing additives used in conventional pulping or processing. That low sulfur content reduces the release of volatile sulfur compounds that can react with silver, copper and other finishes used on PCBs and electroplated parts. In short: it’s paper engineered to be chemically “quiet” around sensitive metal surfaces.

Why sulfur matters in electronics packaging

Sulfur and related gases (H₂S, SO₂) — or even sulfur released slowly from some packaging materials — can react with metal finishes. Silver tarnishes to silver sulfide; copper can form copper sulfide and, under humid conditions, lead to dendritic or “creep” corrosion that spreads across PCB surfaces and can cause electrical shorts or degraded conductivity. In severe cases, unprotected finishes can degrade rapidly (weeks to days under bad conditions). Protecting boards from sulfur exposure is therefore a reliability requirement, not just cosmetic.

Key differences: Sulfur-Free vs Traditional paper (side-by-side)

• Chemical composition

  • Traditional paper: May contain sulfur-based chemicals from pulping, fillers, or processing aids that slowly emit reactive sulfur species.

  • Sulfur-Free paper: Produced and finished to meet very low sulfur thresholds (many suppliers target ≤50 mg/kg or similar test limits) and is often accompanied by test/cert reports.

• Effect on metal finishes

  • Traditional paper: Can cause yellowing, tarnish or creeping corrosion on silver and copper finishes when in prolonged contact or stored in humid environments.

  • Sulfur-Free paper: Dramatically reduces the risk of tarnish and surface discoloration, preserving electrical performance and appearance.

• Physical properties

  • Traditional paper: May shed fibers or powders and sometimes disintegrates on a production line.

  • Sulfur-Free paper: Usually manufactured with uniform fibers and stronger, low-lint structure to avoid dust, lint or breakage on automated lines—important for high-volume PCB handling.

Real-world benefits for PCB and electroplating workflows

1. Prevents discoloration and tarnish — switching to sulfur-free interleaving has been shown by many PCB shops to eliminate routine surface yellowing or silver discoloration previously seen with regular packing paper. This reduces rework and customer complaints.

2. Improves yield and reliability — less corrosion risk means fewer electrical failures in downstream testing and in-field reliability problems. Research on creep corrosion underscores how environmental sulfur sources accelerate failure mechanisms.
3. Cleaner production lines — low-lint, tear-resistant sheets minimize line stoppages and contamination of soldering/reflow operations.
4. Customizable for efficiency — sulfur-free sheets can be supplied in custom sizes and thicknesses to match panel formats and reduce material waste on a high-volume line (improves packing density and lowers cost per board). (This is now common practice in modern PCB lines.)

How to spec Sulfur-Free Paper — practical checklist

• Ask for quantified sulfur limits (e.g., mg/kg) and supporting lab test reports (SGS or equivalent). Suppliers typically list sulfur content and can provide certificates. 

• Confirm lint/particle performance — request technical data or lab reports on linting and particle generation if you run in-line automated handling or cleanroom environments. 

• Verify moisture and pH properties — acid-free and neutral pH properties help prevent other long-term degradation mechanisms. 

• Order samples and run a short exposure test — place the candidate paper in contact with representative boards (with the same surface finish) in your environment for a few weeks and inspect for tarnish or discoloration. Real-world tests often reveal issues lab data may miss. 

Common applications

• Interleaving between PCB panels during storage and transport

• Padding for electroplated or silver-plated components

• Cleanroom-compatible packing for semiconductor wafers and solar cells

• Any product packaging where metal finishes must remain pristine during storage, assembly or shipping.

FAQ 

Q: Is sulfur-free paper needed for all boards?
A: Not always. It’s most important when you have sulfur-sensitive finishes (immersion silver, exposed copper, silver plating) or operate in humid/contaminated environments. For high-value, high-reliability assemblies, it’s cost-effective insurance. 

Q: How is “sulfur-free” verified?
A: Suppliers provide chemical analysis / test reports showing low total sulfur/sulfide content and may note compliance to customer-specified limits (e.g., ≤50 mg/kg). Ask for current test certificates.

Conclusion — the “invisible guardian” your line may need

A small sheet of the right paper can prevent expensive downstream failures. Sulphur Free Paper / Sulfur-Free Paper acts as an invisible guardian for sensitive electronic finishes—preventing tarnish, reducing corrosion risk, and keeping your production line cleaner and more efficient. If you’re experiencing yellowing, unexpected tarnish, or lint-related defects, trialing properly certified sulfur-free interleaving tailored to your PCB sizes is a low-cost step with measurable ROI.