TL;DR: For conductive ink and functional paste sourced from China, the COA silver content value is almost never independently verifiable without XRF spot-testing — yet it’s the parameter that most directly determines resistivity performance in production.
TL;DR: In our document review program, roughly 60% of first-submission COAs from Chinese conductive ink suppliers are missing at least one mandatory field required for EU RoHS or REACH declaration, requiring at least one correction cycle before qualification can proceed.
What Each Core Document Should Actually Contain #
A Certificate of Analysis for conductive ink is not a formality. It’s the primary technical commitment the supplier makes about the material you will build into your product. When we review COAs in our incoming qualification process (logged as IQ-14 in our document control system), we check against a defined minimum field list — and what’s missing tells you as much as what’s present.
A complete COA for silver-based conductive paste should specify: silver content by weight percentage (typically 65–85 wt% for screen-printable grades), viscosity at defined shear rate and temperature (usually reported at 10 rpm and 25°C in Pascal-seconds), sheet resistance or bulk resistivity after curing at the specified profile, particle size D50 and D90, and cure schedule confirmation. Adhesion, flexibility (where relevant), and solvent system identity should also appear. If any of these fields contain a dash or are simply absent, that is not a minor documentation gap — a blank field means the supplier has not tested that parameter for this lot.
The Technical Data Sheet is a different document with a different function. A TDS describes what the material is designed to do under specified conditions. It should contain the full cure profile (temperature, time, atmosphere), recommended substrate and surface preparation, storage and shelf-life conditions, and minimum/maximum application viscosity range for the intended process. What it should not be is a repackaged marketing brochure with a single resistivity value and no process window.
The Safety Data Sheet (SDS, formerly MSDS) follows OSHA HazCom 2012 / GHS formatting requirements for US supply chains and EU CLP Regulation requirements for European destinations. For silver-based pastes, Section 3 (composition) and Section 8 (exposure controls) are the sections to read carefully. The silver compound speciation matters: elemental silver, silver oxide, and silver flake have different toxicological profiles, and an SDS that lists only “silver” without specifying form is incomplete under GHS.
| Document | Primary Function | Key Fields to Verify | Common Gap |
|---|---|---|---|
| COA (Certificate of Analysis) | Lot-specific measured values | Ag wt%, viscosity, resistivity, particle size D50/D90 | Missing resistivity or blank particle size |
| TDS (Technical Data Sheet) | Design specifications and process window | Cure profile, viscosity range, shelf life, substrate compatibility | No process window — only single-point values |
| SDS / MSDS | Hazard and handling information | GHS classification, Ag compound speciation, Section 8 controls | Ag form unspecified; outdated non-GHS format |
| Third-party test report | Independent performance verification | Test method cited, sample ID traceability, accreditation number | No accreditation number; no sample chain-of-custody |
| RoHS/REACH declaration | Regulatory compliance statement | Substance list, concentration thresholds, issuing date | Generic letter without CAS numbers or thresholds |
The interpretation point: a supplier who provides all five documents in correct format on first request is worth noting. In our qualification database, that happens with fewer than one in four new Chinese suppliers evaluated for high-specification conductive paste. The document set is the first filter — not because documents guarantee performance, but because poor documentation almost always predicts poor lot-to-lot consistency.
Where Documentation Failures Actually Originate #
The failure mode we see most often is not fabrication — it’s inheritance. A Chinese supplier qualifies a product using raw material from Compounder A, generates a COA and third-party test report from that qualification run, and then continues issuing the same document template against subsequent lots sourced from Compounder B. The resistivity values on the COA are real — for the original lot. What arrives at your facility may have the same product code, the same document header, and a meaningfully different silver particle morphology.
The mechanism behind this is straightforward: conductive ink performance is highly sensitive to silver flake aspect ratio and surface treatment chemistry, both of which vary between silver powder suppliers. A formulator switching silver source for cost reasons may not requalify resistivity if the change is within their internal viscosity tolerance window. Viscosity is easier to control and faster to check than fired resistivity, so it becomes the de facto release criterion — even when resistivity is the parameter your application depends on.
The consequence we’ve documented across multiple qualification programs: incoming batches that pass viscosity incoming inspection (±15% of nominal at 10 rpm/25°C) but fail fired sheet resistance by more than 20% relative to the approved-sample baseline. By the time the production line identifies the issue, the batch is either partially consumed or mixed into an assembly already downstream.
What to check: request three consecutive lot COAs before qualifying any new Chinese conductive paste supplier. If the resistivity values across those lots vary by more than ±10% relative, ask for the silver powder specification used in each lot and whether the silver source changed. A supplier who cannot answer that question has not characterized their own formulation stability.
A second failure pattern is the translation gap. Many Chinese suppliers generate their primary documentation in Chinese for domestic GB/T compliance and then produce English SDS and COA templates as a secondary exercise — sometimes using translation software, sometimes pulling English field labels onto Chinese-format data. The result is an English document where unit conventions, field labels, and test conditions are misaligned with what a Western buyer expects. We have reviewed COAs where “sheet resistance” was reported in Ω/□ without specifying film thickness, rendering the value uninterpretable for comparison against a spec sheet written in mΩ/□ at 25 μm. That is not a data problem. It is a documentation architecture problem, and correcting it requires more than asking the supplier to “resend the COA.”
The third pattern is accreditation theatre. Third-party test reports from Chinese labs are not uniformly credible. A report from a CNAS-accredited laboratory (China National Accreditation Service, which holds mutual recognition under ILAC MRA) carries materially different weight than a report from an in-house lab with a formatted template designed to look like third-party testing. The tell: legitimate third-party reports include an accreditation number, a scope reference, and a unique sample chain-of-custody identifier. If the report lists the supplier’s own address as the testing location and lacks a CNAS or equivalent accreditation number, it is effectively a self-declaration.
Does a Chinese Supplier Need RoHS Certification to Ship to Europe? #
No — and this distinction matters for procurement. EU RoHS Directive 2011/65/EU imposes obligations on the manufacturer placing the product on the EU market, not on the upstream material supplier. Your Chinese conductive ink supplier is not legally required to hold RoHS certification. What they are required to provide — if you need to demonstrate compliance for your finished product — is a substance declaration listing that their material does not contain restricted substances above threshold concentrations (0.1 wt% for most restricted substances; 0.01 wt% for cadmium).
That declaration needs to be product-specific, lot-traceable, and signed by a named technical responsible. A one-page letter that says “our products comply with RoHS” with no substance list, no CAS numbers, and no concentration thresholds is not actionable documentation. We use a standard declaration template aligned with IEC 63000 for technical documentation for the assessment of electrical and electronic equipment with respect to RoHS — this format is widely recognized and gives you something to file against your own compliance obligation.
REACH operates differently. If your conductive paste contains a Substance of Very High Concern (SVHC) above 0.1 wt% in a supplied article, your supplier has a duty to communicate that information down the supply chain. For conductive pastes, watch the SVHC candidate list for specific silver compounds, certain solvents used as carriers, and any lead-containing formulations in older product lines. Requesting an explicit SVHC declaration (not just a general REACH compliance letter) is the correct document to ask for.
For Japan’s RoHS equivalent (J-Moss, IEC 62321), the threshold and substance list differ slightly from EU RoHS — specifically, the reporting format for homogeneous material versus article-level assessment. If you are supplying Japanese electronics OEMs, confirm which declaration format they require before accepting a European-format document from your supplier as sufficient.
Practical Guidance for Buyers #
When requesting documentation from a Chinese conductive ink supplier for the first time, do not start with the SDS. Start with the COA for the specific lot you are evaluating and the TDS for the product grade. The SDS is mandatory and you will need it, but it is the least variable document — a well-structured SDS tells you about hazard categories that rarely change between lots. The COA is where lot-specific deviation appears, and the TDS is where you will find whether the supplier has actually characterized the process window or simply published a single-point specification.
The specific risk to prepare for: suppliers who list resistivity on the COA without specifying the cure conditions used to generate that value. Fired resistivity for a silver paste is not an intrinsic material constant — it is a function of cure temperature, time, and substrate. A value reported without those conditions is unverifiable against your own process, and we have seen qualification failures where a 20-minute cure at 130°C (supplier’s lab condition) differs by more than 30% in sheet resistance from a 10-minute cure at 150°C (buyer’s production line condition).
Before volume commitment, insist on a process-matched test report: submit a set of your own substrates to a CNAS-accredited lab and have the supplier’s material cured under your specified profile, not theirs. This step adds 2–3 weeks to qualification but eliminates the most common post-qualification resistivity complaint. For high-volume programs, this is what we flag as mandatory in our AVL gate review before any supplier transitions from approved sample to production-quantity release.
For additional context on sealing and encapsulant documentation requirements that often accompany functional paste qualification packages, the specialty coatings category covers comparable documentation frameworks for adjacent materials.
Frequently Asked Questions #
What is the minimum acceptable silver content declaration on a COA for screen-printable conductive paste?
The COA should state silver content as a measured weight percentage for the specific lot, not a nominal range from the TDS. For standard screen-printable grades, silver content typically runs 65–80 wt%; what matters is that the COA value is a measured result with a stated test method (typically ASTM E1756 gravimetric or XRF), not a copied TDS specification.
Can we accept a supplier’s in-house test report instead of a third-party report for RoHS compliance?
It depends on your customer’s requirements and your own compliance risk posture. For CE marking purposes, a supplier’s self-declaration against IEC 63000 is technically permissible — but if you are supplying Tier 1 automotive or major consumer electronics OEMs, they will typically require third-party testing from a CNAS-accredited or ISO/IEC 17025-accredited lab. Check your customer’s supplier qualification manual before accepting self-declarations.
What should we do when a COA arrives with blank fields?
Return it immediately with a written request citing each missing field by name and the test method expected. Document the correction cycle date. Suppliers who require more than one correction cycle on a COA have a documentation process problem that will recur at production volume. In our qualification program, two failed correction cycles trigger a supplier risk escalation under our QC-07 material risk procedure.
Is a single REACH compliance letter sufficient for ongoing supply?
No. REACH declarations should be updated whenever the SVHC candidate list is revised (typically twice per year by ECHA), and whenever a supplier changes their formulation or raw material source. A declaration dated more than 18 months ago is a documentation gap that needs to be closed before regulatory audit, regardless of whether the material has changed.
Do Japanese buyers require different documentation than EU buyers for conductive paste?
For substance compliance, yes. J-Moss (IEC 62321) uses a different declaration format and Japanese OEMs commonly require JIG (Joint Industry Guide) format declarations in addition to RoHS substance data. A standard EU RoHS letter will not satisfy a Japanese OEM’s incoming documentation requirement without reformatting. Confirm the required template before your supplier prepares the declaration.
For buyers working across functional ink categories including specialty conductive materials used in printed electronics and EMI shielding, the conductive-functional-materials category contains parallel documentation guidance for adjacent material types.
Published by sinoraw.com Technical Team | Request a sourcing consultation
