How to Source Magnetic Components from China: A Buyer's Checklist

Sourcing magnetic components from China is routine for most power-electronics OEMs — yet the difference between a smooth program and an eighteen-month quality firefight usually comes down to how well the specification and the supplier verification were handled before the first purchase order. This checklist is written from the buyer’s side of the table: what to put in the RFQ, what to demand from the supplier, and which signals tell you a factory can hold tolerance at volume.

It applies to ferrite cores, powder cores, nanocrystalline and amorphous cores, wound inductors, high-frequency transformers, common mode chokes and current transformers.

1. Specify the application envelope, not a competitor’s part number

Cost and quality problems usually start when a buyer sends another vendor’s part number and asks for “the same thing.” That number encodes one supplier’s internal choices — core shape, material grade, winding layout, potting compound — and copying it badly is more expensive than specifying the function.

Electrical: inductance and tolerance at a stated test frequency and bias, DCR or winding resistance, isolation voltage, leakage inductance limit, interwinding capacitance limit, saturation current at a defined inductance drop.
Thermal: ambient range, allowable temperature rise, insulation class (A/B/F/H), expected hot-spot temperature.
Mechanical: footprint, height limit, pinout, terminal plating, mounting method, weight ceiling.
Environmental: RoHS, REACH, halogen-free, UL 94 V-0, moisture sensitivity level, conformal coating or potting requirement.
Reliability: qualification standard (AEC-Q200 for automotive, IEC 60601-1 for medical, IEC 62368-1 for IT and AV), expected life, thermal cycling and vibration profile.
Commercial: annual volume, forecast shape, target cost, PPAP level, Incoterms, packaging and labeling rules.

2. Verify the factory, not the catalogue

A four-page catalogue proves a supplier can photograph parts. It says nothing about process capability. Ask for evidence that is expensive to fake:

Evidence	What it proves	What to check
ISO 9001 certificate + audit report	Documented quality system	Certificate scope covers the exact product family; expiry date is current
IATF 16949 (automotive)	Process control and traceability	Whether the specific plant is certified, not just the group
Material datasheets with lot numbers	Core material is not substituted	Grade, permeability tolerance, curie temperature, loss curve at your frequency
Process capability (Cpk) on key dimensions	Tolerance holds at volume	Cpk ≥ 1.33 on gap, height, pin position, inductance
Test data per lot	100% or AQL-based verification	Inductance, DCR, hipot, turns ratio — with the actual limits used
Change-notification procedure (PCN)	No silent material or process swaps	Written commitment to notify before any material, winding or supplier change

A factory that cannot produce a Cpk study, or that answers “we always do it this way,” is a sampling risk you will pay for later in field returns.

3. Build a complete RFQ package

The RFQ should be answerable without a phone call. Include the drawing with tolerances, the electrical specification table, the qualification standard, annual and monthly volumes, target price and target lead time, the sample quantity required, and the report format you expect back. Suppliers who return a fully-tabulated response are usually the ones who will also return a compliant FAI.

4. Sample and first-article: the cheapest gate you will ever buy

Never approve volume on a datasheet alone. Request 5–10 samples and a first-article inspection report (FAI) with measured values against every drawing dimension. Then verify independently:

Inductance at the specified frequency and DC bias — the bias point is where most “equivalent” parts diverge.
Saturation behaviour: sweep current and record the inductance drop; confirm the rated Isat corresponds to the stated roll-off.
Hipot and insulation resistance at the rated voltage, plus partial discharge for medium-voltage isolation parts.
Thermal soak at maximum ambient with rated load: measure hot-spot rise, not case temperature at the edge.
Destructive cross-section on one sample: winding order, creepage distance, insulation margin, solder fill.

5. Commercial terms that protect the program

Set Incoterms explicitly (FOB versus DDP changes landed cost by double digits), agree a packaging standard that survives air freight, and fix the MOQ against your real forecast rather than a promotional number. Ask for a documented sub-supplier list for the core material — the magnetic core is the single most common point of silent substitution, and it changes loss, saturation and EMI behaviour without changing the part number.

6. Red flags worth walking away from

Price quoted far below the material cost of the core alone.
No written change-notification clause, or refusal to name the core material grade.
Test reports that only show inductance, with no DCR, hipot or bias data.
Reluctance to allow a third-party or on-site audit.
Samples that pass but whose lot data differ from the sample values.

7. Working with a magnetic-core specialist

Shaanxi SiRui Technology manufactures the Magnetic Core series in-house — Mn-Zn and Ni-Zn ferrite, iron powder, sendust, high flux, MPP, nanocrystalline and amorphous cores — and winds them into inductors, transformers, common mode chokes and current transformers. Because core production and winding sit in the same plant, material grade, gap and AL value are controlled at the source rather than negotiated across a supply chain. Buyers receive lot-level test data, FAI reports and a written PCN commitment as standard.

For an RFQ package review, send your drawing and electrical specification to sales@sirui-tech.com. A typical response includes a proposed core grade, a costed BOM and a sample plan within two working days.

FAQ

What is a realistic MOQ for custom magnetics? For standard core shapes and existing winding fixtures, 500–1,000 pieces per run is common. A new core tooling or a bespoke bobbin usually starts at 3,000–5,000 pieces.

How long does a first sample take? A wound sample from an existing core family is typically 7–10 working days; a new core geometry plus qualification reports takes 4–6 weeks.

Do I need to specify the core material myself? No — specify the loss, saturation and size targets and let the supplier propose a grade, then require the grade to be locked in writing with a PCN clause.

How to Source Magnetic Components from China: A Buyer’s Checklist