Multilayer PCB Metallization Quality Control via Series Via Circuit
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Solution Overview
Problem
Existing methods for controlling the quality of metallization in printed circuits with multiple layers do not effectively measure the thickness of intermediate layers or ensure proper alignment of vias with respect to their metal borders and track portions, leading to potential defects in metallization and increased electrical resistance.
Innovation Solution
A method involving a control circuit with n vias connected in series between electrical terminals, passing current through track portions of each layer, measuring potential differences, and comparing them to threshold values to validate the metallization quality, including the thickness and alignment of metal borders and track portions across all layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical continuity tests are used to control metallization quality, then surface defects can be detected effectively, but information about the thickness of the deposited metallized layer is not provided
Solution Approach 1:
The patent introduces an intermediary measurement approach by using the electrical resistance of the metallized layer as a mediator to infer thickness information. Instead of directly measuring thickness, the method measures electrical resistance which correlates with thickness, thereby obtaining thickness information indirectly through an intermediary parameter that is easily measurable.
Solution Approach 2:
The patent replaces direct mechanical or physical thickness measurement systems with an electrical measurement system. By substituting a complex thickness measurement apparatus with a simple electrical resistance measurement, the system can obtain thickness information without requiring additional mechanical measurement equipment.
2Measurement precision
If a control circuit with n vias connected in series is used to measure potential difference, then comprehensive quality control of all layers is achieved, but the device complexity increases
Solution Approach 1:
The control circuit with series-connected vias serves multiple functions simultaneously: it measures the thickness of metallized layers, detects alignment quality between vias and metal borders, assesses metallization continuity, and evaluates overall connection quality. This multi-functional approach allows comprehensive quality control using a single integrated measurement system.
Solution Approach 2:
The measurement system is segmented into multiple discrete via elements connected in series, where each via contributes to the overall measurement. By dividing the measurement into segments (individual vias), the system can localize defects to specific layers or regions while maintaining a unified measurement approach across all layers.
3Ease of manufacture
If the control method measures only outer layers metallization, then the measurement process is simple, but the thickness of intermediate layers and alignment of vias cannot be controlled
Solution Approach 1:
The series connection of multiple vias spanning different layers ensures continuous measurement action through all intermediate layers. The electrical current flows continuously through each via and the metallized layers connecting them, enabling uninterrupted measurement of thickness and alignment quality across the entire multilayer structure without requiring separate measurement steps.
Solution Approach 2:
The patent extends the measurement from a two-dimensional surface measurement (outer layers only) to a three-dimensional volumetric measurement by incorporating vias that penetrate through intermediate layers. This adds the vertical dimension (through-thickness direction) to the measurement, enabling assessment of intermediate layer metallization and via alignment that were previously inaccessible.
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 method allows for a comprehensive, non-destructive quality control of metallization across all layers, detecting defects such as low metallization thickness and misalignment, thereby ensuring the production of compliant printed circuits with reduced electrical resistance.
Implementation Method 1
A current of defined intensity is then applied between the two electrical terminals of the control circuit and the corresponding potential difference between the electrical terminals is measured
Data Source
AI summary
A multilayer printed circuit having a control circuit including n vias that are connected in series between a first and a second electrical terminal so that an applied electric current passes at least partially through each one of the n vias. The control circuit includes track portions in each one of the layers, each one of the n vias connecting a track portion of one layer to a track portion of another layer. The control circuit includes a measurement device for measuring a potential difference across its terminals, storage for storing a threshold value and a comparator for comparing the potential difference with the threshold value so as to validate the printed circuit when the potential difference is lower than the threshold value.