Thin Glass Cloth for Uniform Laser Drillability
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Solution Overview
Problem
The challenge lies in producing a thin glass cloth with uniform laser drillability and preventing pinholes, particularly for printed circuit boards with thicknesses of 16 μm or less, where existing methods struggle to maintain insulation reliability and machinability.
Innovation Solution
A glass cloth is developed with specific parameters: glass yarns of 3.0 to 4.5 μm filament diameter, weaving densities of 70 to 130 yarns/25 mm, a weft yarn coverage ratio between 0.50 and 0.83, and controlled tension and pressure during production to achieve uniformity and prevent pinholes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the glass cloth thickness is reduced to 16 μm or less by reducing filament diameter, number of filaments, or weaving density, then the thickness requirement is met, but uniform gapless arrangement of glass yarns becomes very difficult to achieve
Solution Approach 1:
The patent applies parameter changes by precisely controlling multiple parameters of the glass cloth: filament diameter (3.0-4.5 μm), number of filaments per yarn (20-55), weaving density (70-130 yarns/25 mm), and weft yarn coverage ratio (0.50≤R≤0.83). By optimizing these parameters within specific ranges, the patent achieves both thin thickness (16 μm or less) and uniform gapless yarn arrangement, resolving the contradiction between thickness reduction and manufacturing precision.
2Manufacturing precision
If ultrasonic irradiation is applied in liquid while applying tension to achieve uniform opening, then opening uniformity is improved, but pinholes occur due to narrowing of weft yarn width
Solution Approach 1:
The patent resolves this contradiction by changing the physical parameters of the glass cloth structure itself rather than relying on post-processing opening treatments. By controlling the weft yarn coverage ratio to 0.50≤R≤0.83 and maintaining specific weaving densities, the patent achieves both uniform opening and prevents pinhole formation inherent in the structure, eliminating the need for aggressive opening treatments that cause pinholes.
Solution Approach 2:
The patent applies beforehand cushioning by designing the glass cloth with inherent structural characteristics that prevent pinhole formation before the opening process. The controlled weft yarn coverage ratio and uniform yarn arrangement create a buffer that prevents resin dropout during subsequent opening and resin application, cushioning against the harmful effect of pinholes without compromising opening uniformity.
3Reliability
If glass yarns are arranged substantially without gaps to achieve uniform laser machinability, then laser drillability is improved, but it becomes difficult to produce thin glass cloth with thickness of 16 μm or less
Solution Approach 1:
The patent resolves this contradiction through comprehensive parameter optimization: using finer filaments (3.0-4.5 μm diameter) with more numerous but thinner yarns (20-55 filaments per yarn), combined with high weaving density (70-130 yarns/25 mm) and controlled coverage ratio (0.50≤R≤0.83). This parameter set achieves gapless uniform arrangement for laser machinability while maintaining thin overall thickness of 16 μm or less.
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
The solution results in a prepreg and printed circuit board with inhibited pinhole occurrence and uniform laser-machined hole diameters, enhancing the reliability and performance of thin printed circuit boards.
Implementation Method 1
Laser beam hole machining is used to form narrow-pitch vias in such printed circuit boards. In general, the insulating base material of a printed circuit board is a composite material composed of a matrix resin, which is an organic material, and a glass cloth, which is an inorganic material, wherein the organic material and the inorganic material are unevenly distributed. Thus, in laser hole machining, variations in hole diameter occur due to differences between the processing states of these materials
Data Source
AI summary
Provided is a glass cloth obtained by weaving a glass thread, which is made from a plurality of glass filaments, as a warp and weft. The average filament diameter of the glass filaments is 3.0-4.5 μm. The respective weaving densities of the warp and the weft constituting the glass cloth are, independently, 70-130 threads/25 mm. The standard deviation of weft width of the glass cloth is not more than 30 μm. The weft covering ratio R, which is represented by the expression R=Y/(25400/D) (where R is the weft covering ratio, Y is the average weft width, and D is the weft weaving density) satisfies the relational expression 0.50≤R≤0.83.