Sub-assembly
BLDC Driver Board (PCBA), 24 V sensorless FOC
The driver built into the motor's rear end cap: an MCU running sensorless field-oriented control, a three-phase gate driver and six power MOSFETs switch the motor phases from the 24 V supply. Heat from the MOSFETs, solder voiding under their pads, EMC and full functional testing decide its reliability.
✓ Expert reviewed All content on this page has been reviewed by a senior motor engineer.
Component BOM
Electronic and other components, grouped by function (not part numbers). ★ marks items critical to performance.
| Part | Material | Key specification | Qty | Representative suppliers |
|---|---|---|---|---|
| Bare PCB | Printed Circuit Board (bare board)Purchased component | FR-4, 2-layer, 2 oz copper for power paths, 1.6 mm, round board to fit the rear cap | 1 | SuntakShenzhen, KinwongShenzhen, FastprintGuangzhou+1 more → |
| ★Motor-control MCU | Motor-control Microcontroller (MCU)Purchased component | 32-bit Arm Cortex-M class with motor-control timers and fast ADCs | 1 | FortiorShenzhen, Nations TechShenzhen, CmsemiconShenzhen+1 more → |
| Gate driver | Three-phase Gate Driver ICPurchased component | Three-phase half-bridge driver with bootstrap supply and under-voltage lockout | 1 | Allegro MicroSystemsShenzhen, FortiorShenzhen, CmsemiconShenzhen+1 more → |
| ★Power MOSFETs | Power MOSFETPurchased component | N-channel 40–60 V, a few mΩ Rds(on), PDFN 5×6 or TO-252 | 6 | Blue RocketFoshan, RuichipsShenzhen, GofordShenzhen |
| ★DC-link capacitors | Aluminium Electrolytic CapacitorPurchased component | 35–50 V, low ESR, 105 °C, ripple-current rated for the PWM frequency | 2–4 | BerylZhaoqing, E-TAKDongguan, Su'sconDongguan |
| Shunts, passives and protection | Passive Components (chip resistors, MLCC)Purchased component | Current-sense shunts, decoupling, TVS and reverse-polarity protection | Per schematic | FenghuaZhaoqing, EYANGShenzhen, MilliohmShenzhen+1 more → |
| Power and control connector | Lead Wires & ConnectorsPurchased component | Power + PWM / 0–10 V input, direction, FG and alarm outputs | 1 set | MolexShenzhen, WoerShenzhen, XSD CableDongguan+2 more → |
| Conformal coating | Potting Compound / Conformal CoatingAuxiliary material | Acrylic or silicone, 25–75 µm, connectors masked | As required | MaxAdhesiveDongguan, YaonengShenzhen, BornsunShenzhen+4 more → |
| Solder paste | Solder Paste (lead-free)Auxiliary material | Lead-free SAC305, type 4, no-clean | As required | VitalShenzhen, Yik Shing TatShenzhen, Jufeng SolderShenzhen |
Process flow
7 main process steps, with the equipment and instruments used at each step, their main suppliers, and the technical control points.
- 1
Solder-paste printing & SPI
Paste is printed through a stencil; large MOSFET pads use a windowed aperture to limit voiding.
- International
- Koh YoungShenzhen, ASMPT, FUJI Corporation+1 more →
- Mainland China
- GKGDongguan, JT AutomationShenzhen
Technical control points:
- ▪Paste volume and offset — Volume 70–130% of nominal; offset ≤ 25% of padCheck: SPI; 100%
- 2
Placement & reflow
Components are placed and reflow-soldered; MOSFET exposed pads are checked for voids by X-ray.
- International
- Koh YoungShenzhen, ASMPT, FUJI Corporation+1 more →
- Mainland China
- GKGDongguan, JT AutomationShenzhen
⚙ X-ray Inspection SystemTest instrumentAutomatedSemi-automaticTechnical control points:
- ▪Reflow profile — SAC305: peak 235–250 °C, 45–90 s above liquidusCheck: Profiler; each shift and changeover
- ▪Voiding under MOSFET pads — ≤ 25% of pad area (IPC-7093 guidance)Check: X-ray; first articles and sampling
- 3
AOI & through-hole soldering
Joints are inspected optically; electrolytic capacitors and connectors are soldered by selective or hand soldering.
- International
- Koh YoungShenzhen, ASMPT, FUJI Corporation+1 more →
- Mainland China
- GKGDongguan, JT AutomationShenzhen
⚙ Soldering Robot / Soldering StationAutomatedSemi-automaticManual- International
- To be added
- Mainland China
- JT AutomationShenzhen, ATTENShenzhen, QuangangDongguan
Technical control points:
- ▪Solder-joint quality — IPC-A-610 Class 2Check: AOI; 100%
- ▪Capacitor polarity — All electrolytic capacitors correctly orientedCheck: AOI / visual; 100%
- 4
ICT & programming
Each board is tested on a bed-of-nails fixture, then the firmware is programmed and current-sense offsets are calibrated.
⚙ ICT / FCT Test System (with programming)Test instrumentAutomatedSemi-automatic- International
- To be added
- Mainland China
- Kingcable ATEShenzhen, LvdaoShenzhen, ProsystemsShenzhen+1 more →
Technical control points:
- ▪Shorts, opens and component values — Pass all ICT steps; supply rails within toleranceCheck: ICT; 100%
- ▪Firmware version and checksum — Matches the released version; logged per serial numberCheck: Programmer read-back; 100%
- 5
Functional test (FCT)
The powered board drives a reference motor or load emulator through start-up, speed control and protection checks.
⚙ ICT / FCT Test System (with programming)Test instrumentAutomatedSemi-automatic- International
- To be added
- Mainland China
- Kingcable ATEShenzhen, LvdaoShenzhen, ProsystemsShenzhen+1 more →
Technical control points:
- ▪Start-up and speed control — Starts reliably; speed follows PWM / 0–10 V input within tolerance; FG output correctCheck: FCT; 100%
- ▪Protection functions — Over-current, under-voltage and locked-rotor protections trip at the set thresholdsCheck: FCT; 100%
- ▪Standby current — Below specificationCheck: FCT; 100%
- 6
Conformal coating
The board is selectively coated, keeping connectors and test points clear, then cured and inspected under UV.
⚙ Selective Conformal Coating MachineAutomatedSemi-automaticTechnical control points:
- ▪Coating coverage and thickness — 25–75 µm; no coating in connectors (IPC-CC-830 materials)Check: UV inspection 100%; thickness on samples
- 7
Burn-in
Boards run powered at elevated temperature to screen early failures — 100% for new products, then sampling once failure data justify it.
⚙ Burn-in / Ageing ChamberTest instrumentSemi-automaticAutomated- International
- To be added
- Mainland China
- Kingcable ATEShenzhen, CosaiShenzhen, KOMEGDongguan
Technical control points:
- ▪Burn-in profile — Per plan (e.g. 50–60 °C, 2–8 h, with on / off cycles)Check: Chamber log; each batch
- ▪Failure analysis — Every burn-in failure analysed and fed backCheck: Failure report; each case
Reliability tests
- Temperature cycling of solder jointsIPC-9701 (e.g. -40 / +125 °C)
- Power cycling of the MOSFET stageOn / off load cycles until junction-temperature swing limits are verified
- Damp heat with biasIEC 60068-2-78 (e.g. 85 °C / 85% RH)
- ESD, EFT and surge immunityIEC 61000-4-2 / -4 / -5
- Conducted and radiated emissions (pre-scan)CISPR 11 / CISPR 14-1 depending on end use
- Step-stress (HALT) for design validationTemperature and vibration step-stress to find the design margins
Assembly-level tests for product validation; incoming tests for each component are on its material page.