Polyimide PCB Light Shielding for Inspection Accuracy
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Solution Overview
Problem
Existing printed circuit boards with transparent synthetic resin base films suffer from high light transmittance, leading to inspection errors during circuit defect determination, especially as the base film thickness decreases, resulting in increased error rates.
Innovation Solution
A printed circuit board with a polyimide-based base film and a conductive copper particle bond layer, where the external transmittance in non-formed regions is set to 70% or less of the internal transmittance, reducing light transmission from defect inspection systems while maintaining material properties and preventing degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent synthetic resin base film is used, then light transmittance is high, but inspection error rate increases due to light transmission to back surface
Solution Approach 1:
The base film is designed with different optical properties in different regions: the light-shielding layer is selectively formed in non-formed regions (areas without conductive patterns) to block light transmission, while the formed regions (conductive pattern areas) maintain their original transparency for proper electrical and optical functionality. This local differentiation resolves the contradiction by shielding light only where necessary for inspection accuracy.
Solution Approach 2:
A light-shielding layer is introduced as an intermediary element between the light source and the back surface of the base film. This intermediate layer selectively blocks light transmission in non-formed regions, preventing light from reaching the back surface and causing inspection errors, while not interfering with the functionality of conductive patterns.
2Productivity
If base film thickness is reduced, then productivity and miniaturization are improved, but inspection error rate increases due to higher light transmittance
Solution Approach 1:
The light-shielding layer is selectively applied only to non-formed regions where light transmission causes inspection errors, rather than uniformly across the entire base film. This allows the base film to be made thinner for productivity benefits while maintaining inspection accuracy in critical areas through localized optical control.
3Measurement precision
If a light-shielding layer is added to reduce transmittance, then inspection accuracy is improved, but device complexity increases
Solution Approach 1:
The light-shielding layer is formed only in non-formed regions (areas without conductive patterns) where light transmission would cause inspection errors. This selective formation minimizes the added structural complexity while achieving the necessary light transmission control for accurate inspection.
Solution Approach 2:
The light-shielding layer pattern is derived from the conductive pattern layout, creating a complementary structure that mirrors the non-formed regions. This copying approach simplifies the design process and reduces overall device complexity by reusing the existing pattern information.
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 solution effectively reduces inspection error rates by suppressing light transmission to the back surface, maintaining the polyimide's material properties and enhancing defect detection accuracy.
Implementation Method 1
An external transmittance for a wavelength of 500 nm in a conductive pattern non-formed region of the base film is 70% or less of an internal transmittance for a wavelength of 500 nm in a middle layer portion of the base film
Data Source
AI summary
A printed circuit board according to an embodiment of the present invention includes a base film containing, as a main component, a polyimide and a conductive pattern disposed on at least one surface of the base film. The conductive pattern includes a copper particle bond layer which is fixed to the base film. An external transmittance for a wavelength of 500 nm in a conductive pattern non-formed region of the base film is 70% or less of an internal transmittance for a wavelength of 500 nm in a middle layer portion of the base film.