PCB Carbon Paste Resistor Laser Trimming Method
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Solution Overview
Problem
Existing methods for producing printed circuit boards with carbon paste resistance elements face issues such as printing blurs, film thickness dispersion, resistance variation due to heat and pressure during laminating, and inability to adjust resistance accurately using laser trimming, leading to inaccuracies in resistance values.
Innovation Solution
The method involves forming through or bottomed holes in a copper clad laminate, applying noble metal plating, filling with carbon paste, and forming a conductive layer, followed by trimming through an opening to adjust the resistance using laser processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If carbon paste is used to form resistance elements instead of chip resistors, then the printed circuit board area and thickness are reduced, but printing blur, film thickness dispersion, and resistance variation occur
Solution Approach 1:
The invention changes the physical state of the carbon paste from a printed film to a filled material in through-holes. By filling the through-holes with carbon paste and then plating the surface, the resistance element is formed in a three-dimensional cavity rather than as a two-dimensional printed layer. This parameter change from surface printing to volumetric filling eliminates printing blur and film thickness dispersion, achieving resistance accuracy within 1% without increasing the board area.
2Manufacturing precision
If through holes are filled with carbon paste to reduce printing dispersion, then printing problems are improved, but resistance cannot be adjusted using laser trimming
Solution Approach 1:
The invention segments the resistance element structure into multiple parts: the carbon paste filling provides the base resistance with good uniformity, while the plated surface layer is segmented to include a removable portion. This segmentation allows the plated surface to be partially removed by laser trimming to expose the carbon paste, enabling resistance adjustment while maintaining the benefits of filled through-holes for reduced printing dispersion.
3Reliability
If copper electrodes are used with carbon paste, then conductivity is achieved, but contact resistance increases due to moisture and oxygen exposure
Solution Approach 1:
The invention introduces a plated metal layer (such as nickel or gold plating) as an intermediary between the copper electrode and the carbon paste. This intermediate plating layer acts as a barrier that prevents moisture and oxygen from reaching the copper-carbon paste interface, thereby preventing contact resistance increase while maintaining good electrical conductivity. The plating layer serves as a protective mediator that isolates the carbon paste from harmful environmental factors.
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 allows for precise adjustment of resistance values to an accuracy of 1% or less, addressing the limitations of previous methods by stabilizing resistance and preventing moisture and oxygen interference, making it suitable for termination resistors and filters in transmission lines.
Implementation Method 1
applying noble metal plating into the through hole
Implementation Method 2
filling the through hole with carbon paste
Implementation Method 3
subjecting the carbon paste with which the thorough hole is filled to noble metal plating, conducting treatment and plating to form a conductive layer
Implementation Method 4
performing trimming through the opening to adjust the resistance of the resistor formed by the carbon paste
Data Source
AI summary
There is provided a method of producing a printed circuit board incorporating a resistance element capable of adjusting resistance after the resistance element has been formed and assuring a high accurate resistance. A method of producing a printed circuit board incorporating a resistance element using carbon paste includes the steps of: forming through holes 5, 6, 25 and 26 or a bottomed hole in a double-sided copper clad laminate; applying noble metal plating into the through hole or the bottomed hole; filling the through hole or the bottomed hole with carbon paste; subjecting the carbon paste with which the thorough hole or the bottomed hole is filled to noble metal plating, conducting treatment and plating to form a conductive layer; forming an opening 18 in the conductive layer on the end of the through hole filled with the carbon paste; and performing trimming through the opening to adjust the resistance of the resistor formed by the carbon paste.