SWIR-LED-Based Internal-Defect Inspection for Resin, Plastic and Silicon Products in Manufacturing

Introduction

Internal cracks, voids, delaminations or foreign particles in resin encapsulants, injection-moulded plastics and silicon wafers often remain hidden to visible or X-ray systems. Short-Wave Infra-Red LED illumination (1 000–1 900 nm) penetrates these materials, is strongly absorbed by water or organic contaminants, and scatters less than shorter wavelengths, giving high-contrast, non-destructive images at production-line speed. The paper explains the physics, on-line integration and economic value of Zhuhai Tianhui SWIR-LED that are already raising yield and cutting recall risk in electronics, automotive, packaging and semiconductor fabs.

Physics & Key Advantages

• Penetration depth: 2–15 mm in epoxy mould-compounds, 5–20 mm in PE/PP, whole-thickness for 200 µm Si wafers

• Spectral fingerprints: –OH (1 450 nm, 1 940 nm), –CH₂ (1 210 nm, 1 730 nm), Si–Si phonon (1 100 nm) → automatic material/defect classification

• 10–30× lower Mie scattering than 850 nm → sharper images through filler particles or surface texture

• Solid-state, TEC-less, AEC-Q102 qualified emitters; lifetime >50 000 h, drift <0.1 nm °C⁻¹

• Die-level footprint 1.6 × 1.6 mm enables inline “micro-cells” inside moulding machines or wafer probers

Inspection Solutions by Material

3.1 Resin (epoxy, acrylic, silicone)

Principle: transmission or back-scatter at 1 310 nm / 1 550 nm reveals density variation; 1 450 nm maps moisture ingress.

Use-cases

Electronic packages: detect 5 µm void under die pad; false-reject <0.3 %, cycle time 0.8 s per package

Automotive ignition-coil potting: 100 % inline check for ≥20 µm bubbles; saved 1.2 M RMB yr⁻¹ scrap

3.2 Plastics (PE, PP, PA, PET, PC)

Principle: different –CH overtones give spectroscopic contrast between grades; foreign resin or oil shows negative peak at 1 710 nm.

Use-cases

Food tray thermoforming: 240 m min⁻¹ line, 2 kHz SWIR strobe, 100 % inspection for 50 µm gels; recall events zeroed since 2022

Recycling flake sort: 1 210 nm / 1 650 nm dual-LED + InGaAs array separates PE from PP at 3 t h⁻¹, purity >98 %

3.3 Silicon (wafers, ingots, PV cells)

Principle: SWIR >1 100 nm overcomes Si band-gap; cracks or stacking-faults scatter photons, appearing bright on dark background.

Use-cases

MEMS through-wafer crack: 200 µm thick, 2 µm crack width, detected at 5 wafers min⁻¹

Solar cell micro-crack & finger interruption: electroluminescence replaced by 1 310 nm SWIR-LED for 30 % CapEx reduction, same 0.2 % false accept

Economic Impact

Real-time feedback loop: SWIR signal fed to IMM or die-bonder → automatic pack-pressure or dispense-speed tweak → yield ↑2–4 %, rework ↓35 %, recall risk ↓90 %.

ROI example (automotive ECU resin moulding):

Line output 5 M units yr⁻¹

Module cost 180 k RMB, payback 7 months

Scrap saving 0.5 % = 2.1 M RMB yr⁻¹

Technology Road-Map & Challenges

2025 – 6-channel monolithic SWIR-LED (1 100/1 210/1 310/1 450/1 550/1 650 nm) + ASIC photon-counting ROIC, 5 Gbps MIPI interface for 3-D tomographic reconstruction

2026 – AI-driven “self-training” model: learns new resin grade in <30 min from 100 labelled images; target <0.1 % false reject

2027 – Hybrid SWIR + 60 GHz radar micro-module: radar locates delamination plane depth, SWIR confirms chemistry—single 12 × 12 mm sensor head

Challenges:

Very dark carbon-filled compounds (>5 %) need 2 W sr⁻¹ radiance—addressed by Tianhui 2 mm² chip-level stacked dies

Data privacy in fabs: edge inference, no image leaves plant, AES-256 encrypted logging

Zhuhai Tianhui Turn-Key Modules

TH-SWIR-1310-1550-IPC: two-LED 1 W, IP67, 45° optic, up to 5 kHz strobe for high-speed cameras

TH-SWIR-QUAD-1650: four wavelengths on 3.5 × 3.5 mm COB, reflow-compatible, MTBF 80 000 h

Evaluation kit: SWIR-EVB-Manu—includes LED controller, InGaAs camera, SDK (Python / C++), sample GAN-based defect classifier; start inspection within 4 h

Custom services: wavelength selection (1 000–1 900 nm), FWHM 20–100 nm, ceramic/TO-can/COB, drive electronics, calibration fixtures compliant with ISO 13485 & IATF 16949.