Interlayer Insulating Film Bilayer Structure for PCB Adhesion
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Solution Overview
Problem
The challenge is to develop an interlayer insulating film for multi-layered printed wiring boards that maintains excellent handling properties while minimizing voids and surface irregularities, particularly when high amounts of silica filler are used, which can compromise adhesion between the insulating layer and electroless plated copper.
Innovation Solution
A bilayered interlayer insulating film structure is implemented, comprising a wiring embedding layer and an adhesion assisting layer, with a residual solvent content of 1-10% by mass, including an organic solvent with a boiling point of 150° C. to 230° C., and specific thermosetting resin compositions to enhance adhesion and reduce surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If high filling of silica filler is used in build-up material, then coefficient of thermal expansion is reduced and elastic modulus is increased, but adhesive force between interlayer insulating layer and electroless plated copper deteriorates
Solution Approach 1:
The invention applies local quality by creating a bilayered structure where the lower layer contains high silica filler content (40% or more) for thermal stability, while the upper layer has reduced silica filler content to maintain adhesion properties. This allows different regions of the interlayer insulating film to have optimized properties for their specific functions.
Solution Approach 2:
The interlayer insulating film is segmented into two distinct layers: a lower layer for thermal stability and an upper layer for adhesion. This segmentation resolves the contradiction by separating the conflicting requirements into different spatial zones within the same component.
2Stability of the object's composition
If high filling of silica filler is used in build-up material, then processing size stability is enhanced, but surface irregularities increase making fine wiring formation difficult
Solution Approach 1:
The upper layer of the bilayered structure has reduced silica filler content compared to the lower layer, creating a smoother surface while the lower layer maintains thermal stability. This local differentiation allows the surface to be suitable for fine wiring formation while the bulk maintains processing size stability.
3Strength
If surface roughness is increased to ensure anchoring effect, then adhesive force with electroless plated copper is improved, but conductor loss increases due to skin effect
Solution Approach 1:
The invention applies partial action by providing just enough surface roughness in the upper layer to ensure adequate anchoring effect for adhesion, rather than excessive roughness. This optimized level of roughness is sufficient for bonding while minimizing the negative impact on high-frequency signal transmission.
4Strength
If bilayered structure is used to separate functions, then adhesion is improved, but handling properties of film deteriorate when silica filler amount is increased
Solution Approach 1:
The bilayered structure applies local quality by concentrating the high silica filler content in the lower layer where it provides thermal stability without adversely affecting handling. The upper layer has reduced filler content, maintaining better handling properties while still providing the necessary adhesion function.
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 effectively improves handling properties, suppresses void formation, and reduces surface irregularities, ensuring strong adhesion between the insulating layer and conductor layers, while maintaining thermal stability and high-frequency performance.
Implementation Method 1
the residual solvent contains an organic solvent having a boiling point of 150° C. to 230° C. in an amount of 10% by mass or more in a total amount of the residual solvent
Implementation Method 2
an uncured build-up material (interlayer insulating film) is laminated on an inner layer circuit board, and then cured by heating to form an interlayer insulating layer
Implementation Method 3
The adhesive force between the surface of the interlayer insulating layer and the electroless plated copper is ensured by an anchoring effect of the irregularities on the surface of the interlayer insulating layer
Implementation Method 4
the electrical signals (current) flow only in the vicinity of the surface of a conductor by a phenomenon referred to as a so-called 'skin effect'
Data Source
AI summary
Provided is an interlayer insulating film for a multi-layered printed wiring board, including a wiring embedding layer (A) obtained by forming a thermosetting resin composition (I) into a layer, and an adhesion assisting layer (B) obtained by forming a thermosetting resin composition (II) into a layer, in which the interlayer insulating film contains a residual solvent in an amount of 1% to 10% by mass in a total amount of the wiring embedding layer (A) and the adhesion assisting layer (B), and the residual solvent contains an organic solvent having a boiling point of 150° C. to 230° C. in an amount of 10% by mass or more in a total amount of the residual solvent.