900–1700 nm Imaging for Silicon, Dark Plastics and Moisture Discrimination
- Discrete SWIR LED wavelengths at 1050, 1200, 1300, 1450 and 1550 nm match specific material absorption bands.
- Silicon transparency above 1100 nm enables wafer and packaged-semiconductor internal inspection.
- Water absorption at 1450 nm enables moisture measurement in food, pharma and agricultural products.
- Dark plastic and opaque packaging transmission exposes hidden defects invisible under visible or NIR.
- InGaAs sensors required — typically one order of magnitude more expensive than silicon sensors.
- SWIR-corrected lenses (900–1700 nm) required for high-performance imaging; standard glass exhibits chromatic aberration.
Short-wave infrared (SWIR) illumination extends machine vision into the spectral range between roughly 900 nm and 1700 nm, opening up inspection capabilities that are impossible at visible and near-infrared wavelengths. SWIR penetrates silicon, dark plastics and some packaging materials, enabling inspection of internal features that would otherwise require destructive testing or X-ray imaging. The combination of SWIR illumination with InGaAs sensors has transformed quality control in semiconductor manufacturing, electronics assembly, agriculture, food sorting and pharmaceutical inspection.
Working Principle of SWIR Illumination
SWIR illumination is produced by specialised LEDs or by halogen lamps with selective filtering. LED-based SWIR sources are available at discrete wavelengths in the 1050, 1200, 1300, 1450 and 1550 nm bands, each chosen for specific material interactions. Halogen-based SWIR illumination provides broadband emission across the full SWIR range but is less efficient and less suitable for pulsed operation.
The principal characteristic of SWIR illumination is its ability to transmit through materials that are opaque at visible and near-infrared wavelengths. Silicon, for example, becomes transparent above its bandgap absorption edge at approximately 1100 nm, allowing SWIR inspection of internal features in silicon wafers and packaged semiconductor devices. Many dark plastics that strongly absorb visible light transmit substantial fractions of SWIR illumination, enabling inspection of hidden components and verification of assembly integrity through black housings.
Material Interactions in the SWIR Range
Water absorbs strongly at 1450 nm, which makes this wavelength useful for moisture content measurement in food, pharmaceuticals and agricultural products. Many hydrocarbons absorb at 1200 to 1300 nm, which provides selective contrast on plastics, oils and organic contaminants. Inorganic materials such as glass and ceramics are generally transparent across the SWIR range, while metals reflect with high efficiency similar to their behavior in the visible.
Typical Industrial Applications
SWIR illumination is essential for inspection of silicon wafers, photovoltaic cells and semiconductor devices, where internal defects, contamination and structural anomalies must be detected through the silicon substrate; quality control of black or dark plastic products where visible imaging is impossible; moisture content measurement in food, pharmaceutical and agricultural products; sorting of recycled plastics by polymer type; inspection of packaged products through opaque packaging; quality control of multi-layer assemblies where internal layers must be verified without disassembly; and any application requiring transparency through visible-opaque materials. SWIR-specific geometries are engineered within the Custom LED Illuminators portfolio.
Selection Criteria and Design Considerations
The wavelength selection depends on the material to be inspected. Silicon transmission requires wavelengths above 1100 nm, with 1300 nm being the standard choice for good transmission and adequate sensor sensitivity. Moisture measurement requires the 1450 nm water absorption band. Plastic discrimination uses multiple wavelengths across the 1200 to 1700 nm range. Spectrophotometric characterisation of the target material is essential before selecting the inspection wavelength.
The sensor must be matched to the SWIR illumination. Standard silicon sensors lose all sensitivity above 1100 nm. SWIR imaging requires InGaAs sensors, which are sensitive from approximately 900 to 1700 nm but cost an order of magnitude more than equivalent silicon sensors. The sensor cost is often the dominant component of a SWIR inspection system and must be considered at the project planning stage.
Optical Components for SWIR
Standard glass lenses absorb significantly above approximately 1700 nm and may exhibit chromatic aberration in the SWIR range. SWIR-corrected lenses, designed for the 900 to 1700 nm band, are required for high-performance imaging. Beamsplitters, polarisers, filters and other optical components must also be specified as SWIR-compatible to avoid unexpected absorption or aberration.
Integration and Limitations
SWIR inspection systems are more expensive and more complex than visible or NIR systems, primarily due to the cost of InGaAs sensors and SWIR-specific optics. The choice of SWIR is justified only when the inspection task requires penetration through visible-opaque materials, sensitivity to water absorption, or chemical-physical discrimination that cannot be performed at shorter wavelengths.
The other limitation is the limited resolution of typical InGaAs sensors compared to silicon sensors of equivalent cost. SWIR cameras are available with VGA and SXGA resolutions, which are adequate for many industrial applications but may be insufficient for very small features or large fields of view. For applications where SWIR penetration is desired but ultra-high resolution is also required, hybrid systems combining SWIR imaging with high-resolution visible imaging provide a practical compromise.
RODER Vision SWIR LED Illuminators
RODER Vision engineers application-specific SWIR LED illuminators in the 900–1700 nm range for industrial vision inspection requiring transmission through silicon, dark plastics and opaque packaging, or selective absorption-based material discrimination.
- Linear SWIR configurations for inline web and wafer inspection — LED Bar Illuminators
- Application-specific SWIR wavelengths, geometries and assemblies — Custom LED Illuminators
For high-power pulsed SWIR operation synchronised with InGaAs camera triggering, the RODER catalogue includes dedicated LED drivers and electronic controllers compatible with industrial machine vision controllers and PLCs.