PCB Foreign Substance Detection Using Positional and Size Thresholds
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Solution Overview
Problem
Existing board testing methods inaccurately determine the defectiveness of printed circuit boards due to incomplete inspection areas, leading to either false positives or false negatives in detecting foreign substances that may or may not cause functional issues, resulting in reduced yield.
Innovation Solution
A board testing apparatus that includes an image obtaining unit, a foreign substance detection unit, and a defective/non-defective judgment unit, which assesses the positional relationship between detected foreign substances and component mounting areas to determine if they overlap or are adjacent, using area and length threshold values to classify foreign substances as defective or non-defective.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the entire area of the printed circuit board is inspected for foreign substances, then the detection coverage is improved, but the number of false positive defects increases, reducing manufacturing yield
Solution Approach 1:
The patent applies local quality by differentiating inspection strictness across different regions of the printed circuit board. The component mounting area receives strict inspection since foreign substances here cause functional failures, while the resist area receives relaxed inspection since foreign substances here do not affect functionality. This regional differentiation resolves the contradiction by avoiding false positives in the resist area while maintaining detection accuracy in the component mounting area.
2Productivity
If only the component mounting area is inspected for foreign substances, then the number of false positive defects is reduced, but foreign substances in the resist area that may cause functional problems are missed
Solution Approach 1:
The patent segments the inspection process into two distinct parts: inspection of the component mounting area and inspection of the resist area. Each area is inspected with different criteria based on its functional importance. This segmentation allows the system to maintain high yield by avoiding false positives while ensuring reliability by detecting foreign substances in both areas that could potentially cause functional problems.
3Device complexity
If foreign substances are detected based on their position alone without considering size, then the inspection simplicity is improved, but the ability to detect potentially harmful foreign substances is reduced
Solution Approach 1:
The patent applies dynamics by making the inspection criteria adaptive rather than fixed. The judgment unit dynamically adjusts the inspection standard based on the foreign substance's position and detected size. Small foreign substances in the resist area are ignored, while larger foreign substances or those in the component mounting area trigger defect judgments. This dynamic approach resolves the contradiction by maintaining simple position-based inspection while adding size-based precision when needed.
Data Source
AI summary
A board testing apparatus including: an image obtaining device that obtains an image of an inspection object area in a printed circuit board, the inspection object area including a component mounting area; and a control device that detects a foreign substance in the inspection object area based on the image, determines that the foreign substance is defective upon detecting that the foreign substance overlaps the component mounting area or is adjacent to the component mounting area when a lump part of the foreign substance has an area greater than an area threshold value or a length greater than a length threshold value, and determines that the foreign substance is non-defective upon detecting that the foreign substance neither overlaps the component mounting area nor is adjacent to the component mounting area even when the lump part has the area or the length.