Asymmetric Core Positioning for Printed Wiring Board Warpage Control
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Solution Overview
Problem
Multilayered printed wiring boards face warpage issues due to differences in the remaining copper rate between the upper and lower surfaces, which existing manufacturing methods fail to adequately address, especially in thin boards with lamination of insulating layers.
Innovation Solution
The solution involves shifting the core material in each insulating layer towards the first surface side in the thickness direction, resulting in a smaller total area for first-surface-side conductive layers compared to second-surface-side conductive layers, and using a glass cloth core material arranged closer to the upper surface to generate stress that alleviates warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the core material is positioned at the center of the insulating layer, then the structure is symmetric and easy to manufacture, but warpage occurs due to imbalance in remaining copper rate between upper and lower surfaces
Solution Approach 1:
The patent applies asymmetry by intentionally positioning the core material (glass cloth) off-center within the insulating layer, specifically closer to the first surface side. This asymmetric positioning compensates for the imbalance in remaining copper rate between the upper and lower surfaces, generating counteracting stress that reduces warpage. The core material is positioned such that the distance from the first surface to the center of the core material is smaller than the distance from the second surface to the center of the core material.
2Manufacturing precision
If the total area of first-surface-side conductive layers is made smaller than second-surface-side conductive layers, then stress is generated to alleviate warpage, but the design flexibility is reduced
Solution Approach 1:
The patent applies local quality by creating a specific area relationship between conductive layers on different surfaces. The total area of first-surface-side conductive layers is designed to be smaller than the total area of second-surface-side conductive layers, which generates internal stress that counteracts warpage. This is achieved by adjusting the area of conductive layers in specific regions rather than uniformly across the entire board, allowing localized optimization of the area ratio to control warpage while maintaining design flexibility.
3Stability of the object's composition
If more insulating layers are laminated to build up the board, then the board thickness increases providing better structural stability, but warpage becomes more difficult to control
Solution Approach 1:
The patent applies parameter changes by modifying the positioning parameter of the core material within the insulating layer. Specifically, the core material is positioned asymmetrically closer to the first surface side, which changes the stress distribution parameter in the laminated structure. This parameter change compensates for the warpage tendency that increases with more insulating layers, allowing better warpage control even as the board thickness and number of laminated layers increase.
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 effectively reduces warpage in thin printed wiring boards by balancing stress across layers, making handling and lamination easier and minimizing the likelihood of warpage despite differences in copper rates between surfaces.
Implementation Method 1
the core material of the insulating layer is shifted toward the first-surface side from the center of the insulating layer in the thickness direction of the insulating layer
Data Source
AI summary
A printed wiring board includes multiple insulating layers laminated on each other and each including resin and core, the insulating layers having first-surface sides and second-surface sides on the opposite side, respectively, and including multiple first insulating and second insulating layers, multiple first-surface-side conductive layers formed on the first-surface sides of the first insulating layers, respectively, multiple second-surface-side conductive layers formed on the second-surface sides of the second insulating layers, respectively. The insulating layers include one or more insulating layer having the core positioned such that the core is shifted toward the first-surface side from the center in the thickness direction, the insulating layers include a central insulating layer positioned in the center of the insulating layers, and the first-surface-side and second-surface-side conductive layers are formed such that the first-surface side conductive layers have the total area which is set smaller than the total area of the second-surface-side conductive layers.