Aramid Paper for PCBs: Resin Penetration and CTE
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Solution Overview
Problem
Existing aramid papers used in electronic applications face challenges in achieving sufficient resin impregnation and homogeneity, particularly at lower thicknesses, which affects their dimensional stability and insulating properties due to high coefficients of thermal expansion and potential resin micro-cracks.
Innovation Solution
An aramid paper with a density of 0.20-0.65 g/cm3, comprising 10-40 wt.% para-aramid shortcut and 10-80 wt.% para-aramid fibrid, ensuring good resin adhesion and penetration, and a grammage of 30-280 g/m2, with at least 70 wt.% para-aramid components, is developed to address these issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If woven sheets of para-aramid yarn are used in printed circuit boards, then low CTE is achieved, but resin micro-cracks occur at yarn crossover points
Solution Approach 1:
The patent uses a composite structure combining para-aramid yarns (for low CTE) with para-aramid pulp and floc (to fill gaps and prevent micro-cracks). This composite approach allows the material to benefit from both the low thermal expansion of yarns and the crack-prevention properties of the pulp-floc matrix.
Solution Approach 2:
The patent introduces para-aramid pulp and floc specifically at the yarn crossover points where micro-cracks tend to form. This local reinforcement addresses the specific problem area without changing the overall yarn structure, preventing micro-cracks while maintaining low CTE.
2Stability of the object's composition
If high-density para-aramid papers are used, then low CTE and freedom from microcracks are achieved, but resin impregnation is insufficient
Solution Approach 1:
The patent optimizes the density parameter of the aramid paper to balance two competing requirements: high enough density to maintain low CTE and prevent micro-cracks, but low enough to allow sufficient resin impregnation. The patent specifies a density range of 0.20-0.65 g/cm³ to achieve this balance.
Solution Approach 2:
The patent uses a composite of para-aramid yarns, pulp, and floc where the pulp and floc components create a more open, absorbent structure that facilitates resin impregnation while the overall composite maintains low CTE through the para-aramid content.
3Length of moving object
If paper thickness is reduced, then thinner substrates are achieved, but homogeneity becomes difficult to obtain
Solution Approach 1:
The patent uses para-aramid pulp and floc as fillers that distribute uniformly throughout the paper matrix, ensuring homogeneous properties even in thin papers. The pulp and floc particles fill gaps between yarns uniformly, preventing variations in density and resin impregnation that would otherwise occur in thin sections.
Solution Approach 2:
The composite structure of yarns, pulp, and floc creates a statistically homogeneous material even at thin dimensions. The random distribution of pulp and floc particles compensates for variations in yarn placement, maintaining uniform properties throughout the thin paper.
Data Source
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AI summary
The invention pertains to an aramid paper suitable for use in electronic applications which has a density of 0.20-0.65 g/cm3 and a grammage of 30-280 g/m2, which paper comprises 10-40 wt.% of aramid shortcut with a linear density of 2.6 dtex or lower and a length of 0.5-25 mm and 10-90 wt.% of aramid fibrid, wherein the aramid shortcut comprises at least 70 wt.% para- aramid shortcut and the aramid fibrid comprises at least 70 wt.% para-aramid fibrid. It has been found that the use of a paper with the above properties in electronic applications ensures a low CTE in combination with good homogeneity and a good dimensional stability resulting from good resin adhesion and penetration. The invention also pertains to the use of the aramid paper in a composite sheet comprising at least one layer of aramid paper and a resin, or in a substrate board for electronic applications, e.g., in a printed circuit board, or in a backing for a solar cell.