Magnetic Component Supplier Audit Checklist: Six Stations and Ten Questions

Audit Before You Scale

Most sourcing problems with magnetic components appear after the second or third order, not on the first shipment: a material substitution that was never declared, a test station that drifts, a winding line that changes operators, a potting batch that cures differently in summer. A supplier audit done before volume ramp is the cheapest way to find these, because the fixes are still cheap at that point.

This checklist is written for a one-day audit of a magnetic component factory, organized so a buyer without deep winding experience can still ask the questions that expose risk.

Six Stations to Inspect, In Order

Audit stations and the specific evidence to request at each
Station	What to look at	Evidence to request
Incoming material	Core, wire, bobbin, tape, varnish stores; segregation and labels	Incoming inspection records, supplier certificates, FIFO evidence
Winding	Tension control, turns counting, layer insulation placement	Winding program sheets, machine calibration records
Assembly and soldering	Solder pot temperature logs, flux control, lead wire pull test	Daily temperature verification, pull strength data
Impregnation or potting	Varnish batch records, cure oven charts, potting ratio mixing	Cure profiles per batch, mix ratio records, hardness checks
Test	Hipot station, inductance meter, resistance measurement, test limits	Calibration certificates with traceability, MSA on the test stations, limit sheets
Packing and traceability	Label accuracy, lot coding, pallet configuration	Packing standard, traceability map from lot to material batches

Ten Questions That Reveal the Real System

Who approves a material substitution, and does the customer hear about it before or after the shipment?
What happens to a lot that fails hipot — is it reworked, and is rework recorded?
How is the solder pot temperature verified each shift, and what happens when it drifts?
Are the hipot and inductance test stations under calibration with a defined interval, and is there MSA data?
What is the actual AQL being applied, and does it match the drawing?
How is the core material identified in production — by label, by measurement, or by assumption?
Is there a documented first-article process, or is the first piece simply the first piece?
What is the scrap rate on the winding line, and what are the top three defect modes?
How long is material and finished-goods traceability retained?
Which sub-suppliers are single-sourced, and what is the plan if one fails?

Signals That Predict Trouble

Three patterns are worth weighting more than any certificate: floors that are clean but records that are handwritten and undated; a test station that cannot show a calibration sticker; and a sales engineer who cannot describe the winding structure of the part being quoted. Certificates (ISO 9001, IATF 16949) confirm a system exists on paper; the audit confirms it operates.

Also ask for the failure history of a comparable part over the last 12 months, and whether the top defect was caught in-house or by the customer. A supplier who answers that honestly is usually the safer partner than one with a perfect-looking record and no data.

What Good Audit Output Looks Like

A useful audit report lists findings by risk class, names the owner at the supplier for each, and sets a verification method and date. Findings should be tied to the PPAP or first-article file so they close before volume release rather than drifting into a quarterly review nobody reads. Three to five open findings after a first audit is normal; zero findings usually means the audit was too shallow.