Stencil Printer Illumination for Coated Pad Inspection
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Solution Overview
Problem
Traditional stencil printers face challenges in accurately imaging and inspecting solder paste deposits on circuit boards, especially when pads are coated with non-reflective or less-reflective coatings, as these coatings reduce the effectiveness of traditional thresholding techniques used for differentiation.
Innovation Solution
The use of long-wavelength light, such as infrared light with a wavelength between 670 and 825 nanometers, in conjunction with white light, for illumination, combined with an off-axis illumination system, enhances the visibility of solder paste deposits by penetrating coatings and improving image clarity, allowing for more accurate contrast recognition and inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional on-axis white light illumination is used, then the imaging system can capture images of solder paste deposits on uncoated pads, but the ability to differentiate deposits on pads with non-reflective coatings deteriorates
Solution Approach 1:
The patent changes the wavelength parameter of the illumination light from traditional visible white light to long-wavelength infrared light. This parameter change allows the light to penetrate non-reflective coatings that block shorter wavelengths, enabling the imaging system to detect solder paste deposits on coated pads by capturing infrared radiation emitted or reflected from the deposits themselves.
Solution Approach 2:
The patent substitutes the traditional optical reflection-based imaging mechanism with a thermal radiation detection mechanism. Instead of relying on light reflection from metallic surfaces (which fails with non-reflective coatings), the system detects infrared radiation naturally emitted by the solder paste deposits, replacing the reflection-based optical path with a radiation-based detection approach.
2Device complexity
If on-axis illumination is used, then the setup is simple and direct, but the ability to illuminate irregularly shaped surfaces and capture consistent images deteriorates
Solution Approach 1:
The patent transitions from on-axis illumination (one-dimensional direct path) to off-axis illumination (introducing angular dimension). By positioning the light source at an angle to the optical axis, the system creates multiple illumination paths that can reach irregular surfaces from different angles, ensuring uniform illumination across varied topographies and improving image consistency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the accuracy of solder paste deposit inspection on coated pads, enabling better alignment and detection of defects, even with non-reflective coatings, by ensuring consistent illumination and enhanced image sharpness.
Implementation Method 1
a first illumination element comprising a long-wavelength light source configured to illuminate at least the portion of the surface of the electronic substrate by generating long-wavelength light
Implementation Method 2
an imaging system constructed and arranged to capture an image of the electronic substrate, the imaging system comprising a camera element configured to capture the image
Data Source
AI summary
A stencil printer apparatus for depositing a solder paste onto the surface of the electronic substrate, comprising a frame, a stencil coupled to the frame, the stencil having a plurality of apertures, a dispenser coupled to the frame, the stencil and the dispenser being configured to deposit the solder paste onto the electronic substrate, an imaging system constructed and arranged to capture an image of the electronic substrate, and a controller coupled to the imaging system and configured to control movement of the imaging system to capture the image. The imaging system comprises a camera element configured to capture the image of at least the portion of the surface of the electronic substrate, and a first illumination element comprising a long-wavelength light source configured to illuminate at least the portion of the surface of the electronic substrate by generating long-wavelength light. Other embodiments and methods are disclosed.