Sensor magnetic assemblies fail procurement reviews for one reason: RFQs are often geometry-only, while production performance depends on geometry + magnetic circuit + test method + process control.
This checklist is designed for Hall and MR sensor programs where output stability matters as much as piece price.
1. Project context block (put this at the top of RFQ)
Start with one short context section:
- product function and failure consequence
- development stage (concept, prototype, pilot, volume transfer)
- launch timeline and critical milestones
Suppliers will quote differently for a proof-of-concept sample versus a launch-bound pilot lot. Context reduces assumption mismatch.
2. Performance specification at measurement point
Define magnetic output in measurable terms:
- target field/flux/force at a named measurement location
- tolerance window (minimum / nominal / maximum)
- measurement condition (gap, orientation, fixture, temperature)
- required repeatability level
Do not rely on magnet grade names alone. Two assemblies with the same grade can produce very different sensor output.
3. Full assembly context (not magnet only)
Magnetic behavior depends on surrounding structure.
Mandatory RFQ fields:
- housing/return-path material and key dimensions
- sensor-to-magnet alignment references
- nearby ferromagnetic components affecting field path
- packaging-space constraints that affect circuit design
When these fields are missing, suppliers either overdesign (higher cost) or underdesign (higher risk).
4. Tolerance priorities and datum strategy
Separate what is critical from what is flexible.
| Priority Level | Typical Features |
|---|---|
| Critical | Air-gap interfaces, alignment datums, concentricity affecting field vector |
| Important | Mating dimensions impacting assembly consistency |
| Flexible | Cosmetic edges and non-functional surfaces |
Buyer benefit: this reduces unnecessary machining cost while protecting sensor performance.
5. Environmental and lifecycle requirements
Include lifecycle stress profile explicitly:
- continuous and peak temperature with dwell time
- humidity/corrosion/media exposure
- vibration/shock conditions if relevant
- required service life and allowed drift
These lines directly influence material recommendation (SmCo vs NdFeB, coating, retention method) and validation plan.
6. Validation and evidence package
For prototype and pilot approval, request these deliverables:
- magnetic output test method and fixture definition
- first-article dimensional report on critical features
- pre/post stress performance comparison (if lifecycle-sensitive)
- lot traceability records for material and process
Require pass/fail rules in writing. "Meets expectation" is not an acceptance criterion.
7. Manufacturing control fields
Ask suppliers to provide process controls on failure-sensitive steps:
- polarity/orientation verification method
- adhesive or press-fit process window
- in-process sampling and reaction plan
- final release criteria and stop-ship trigger
This is where supplier quality discipline becomes visible before volume risk appears.
8. Commercial and change-control lines
Include commercial control terms in the same RFQ package:
- NRE scope and payment logic
- prototype quantity and lead-time commitment
- volume forecast bands
- Incoterm and destination
- post-approval change-control and requalification triggers
Combining technical and commercial assumptions in one document reduces re-quote loops.
9. Quote normalization sheet (how buyers compare offers)
When quotes return, compare on normalized columns:
- assumption completeness
- validation scope included/excluded
- process-control depth
- lead-time realism
- NRE transparency
- risk notes from supplier
Lowest unit price with hidden exclusions is usually the most expensive launch path.
10. RFQ checklist before release
Before sending RFQ, confirm:
- performance target includes test condition and tolerance band
- magnetic circuit context is provided
- critical datums and tolerance priorities are marked
- environment and lifecycle profile is complete
- validation deliverables and acceptance criteria are explicit
- prototype and production assumptions are separated
- NRE and change-control terms are written
Teams that apply this checklist generally cut clarification cycles and improve first-pass prototype quality.
11. Advanced Deep Dive: Temperature Coefficient of Remanence (α)
When dealing with Hall sensors, buyers often forget that magnetic flux drops linearly as temperature rises, dictated by the Temperature Coefficient of Remanence (α), which is roughly -0.11% / °C for NdFeB.
Case Study: Automotive Throttle Position Sensor
- The Oversight: An RFQ specified "minimum 500 Gauss at 3mm gap," which the supplier easily met at 20°C (room temperature). However, at the automotive operating requirement of 125°C, the flux dropped by 11.5% to 442 Gauss, falling below the Hall IC's activation threshold.
- The RFQ Correction: We restructured the buyer's RFQ template to demand: "Minimum 500 Gauss at 3mm gap at 125°C."
- The Engineering Result: To meet this, we shifted the baseline design to output 570 Gauss at 20°C, ensuring sufficient thermal margin. We also selected an SH-grade magnet to guarantee the operating point stayed safely above the "knee" of the demagnetization curve.
For a pre-RFQ sanity check, send your draft package to [email protected] or WhatsApp +8618857971991 (Open WhatsApp).
