Printed Wiring Board With Differential Copper Foil Thickness
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Solution Overview
Problem
High-frequency LSIs require printed wiring boards with low dielectric constants and thermal expansion coefficients to maintain signal transmission integrity and prevent via conductor separation due to stress concentration, which existing technologies fail to achieve without compromising impedance characteristics or production yield.
Innovation Solution
A printed wiring board design featuring a core insulation layer with a resin and via conductors, laminated with interlayer insulation layers and conductive layers, where the core insulation and interlayer insulation layers have a dielectric constant of 4.0 or lower and a thermal expansion coefficient of 85 ppm/°C or lower, and the copper foil thickness of the first conductive layers is greater than that of the second conductive layers to enhance rigidity and connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dielectric constant of insulation layers is reduced to maintain signal transmission integrity at high frequencies, then signal transmission quality is improved, but the thermal expansion coefficient increases causing stress concentration and via conductor separation
Solution Approach 1:
The patent applies parameter changes by carefully selecting and controlling the dielectric constant and thermal expansion coefficient parameters of the insulation layer materials. By optimizing these physical parameters within specific ranges, the patent achieves a balance between signal transmission integrity (requiring low dielectric constant) and thermal stress resistance (requiring controlled thermal expansion coefficient), thereby resolving the contradiction between these two opposing requirements.
Solution Approach 2:
The patent employs composite materials by combining resin materials with specific properties in the insulation layers. The use of composite material formulations allows simultaneous achievement of low dielectric constant for high-frequency signal transmission and controlled thermal expansion coefficient to prevent stress-induced via conductor separation, thus resolving the technical contradiction.
2Strength
If copper foil thickness of first conductive layers is increased to enhance rigidity and connection reliability, then via conductor separation is prevented, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies local quality by differentiating the copper foil thickness between first and second conductive layers based on their specific functional requirements. The first conductive layers, which require higher rigidity and connection reliability to prevent via conductor separation, are equipped with greater copper foil thickness. This localized differentiation optimizes structural strength where needed without unnecessarily increasing manufacturing complexity across the entire board.
Solution Approach 2:
The patent implements partial action by applying increased copper foil thickness only to the first conductive layers where it is most critical for preventing via conductor separation, rather than uniformly increasing thickness across all conductive layers. This selective approach achieves the necessary connection reliability while minimizing overall manufacturing complexity and material usage.
3Reliability
If skip layers are used to maintain impedance characteristics, then signal transmission quality is improved, but manufacturing yield decreases
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the dielectric constant and physical dimensions of the insulation layers to inherently maintain impedance characteristics without requiring skip layers. By carefully controlling material properties and layer geometry, the patent achieves both good signal transmission quality and high manufacturing yield through conventional lamination processes.
Solution Approach 2:
The patent applies the extraction principle by eliminating the need for skip layers from the manufacturing process. Through proper selection and design of insulation layer materials and structures, the patent extracts away the problematic skip layer step, thereby maintaining impedance characteristics while improving production yield by using standard continuous lamination processes.
Data Source
AI summary
A printed wiring board includes a core insulation layer including a resin and having a via conductor through the core insulation layer, a first conductive layer formed on the core layer and including a copper foil and a plated film, an interlayer insulation layer formed on the first layer and including a resin, the interlayer layer having a via conductor through the interlayer layer, and a second conductive layer formed on the interlayer layer and including a copper foil and a plated film. The first layer includes a conductive circuit, the core and interlayer layers have dielectric constants of 4.0 or lower for signal transmission at frequency of 1 GHz and thermal expansion coefficient of 85 ppm/° C. or lower at or below Tg, and the foil of the first layer has thickness greater than thickness of the foil of the second layer.