Printed Wiring Board Stiffener Positioning for Warping Prevention
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Solution Overview
Problem
Thinner printed wiring boards face mechanical strength issues and warping during soldering reflow, making it difficult to mount IC chips due to significant thickness differences between metal plates and pads.
Innovation Solution
A multilayer printed wiring board design featuring a stiffener with openings and pads on the outermost resin insulation layer, where the stiffener and pads are formed at the same level, and the stiffener can be used as a power or ground layer, enhancing mechanical strength and productivity for solder bump formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the printed wiring board is made thinner to reduce weight and size, then the weight and dimensions are improved, but the mechanical strength decreases
Solution Approach 1:
The patent combines resin insulation layers with metal stiffener plates to create a composite structure. The resin layers provide electrical insulation and circuit functionality, while the metal stiffener plates provide mechanical strength and rigidity. This composite approach allows the board to be thin and lightweight while maintaining sufficient structural integrity.
Solution Approach 2:
The patent divides the printed wiring board into distinct functional regions: circuit areas with resin insulation layers and reinforcement areas with metal stiffener plates. This segmentation allows different materials to be optimally placed where needed - resin for electrical functionality and metal for mechanical support - resolving the contradiction between thinness and strength.
2Strength
If a metal plate (stiffener) is mounted on the printed wiring board to increase mechanical strength, then the strength is improved, but warping occurs during soldering reflow due to thickness differences between the metal plate and pads
Solution Approach 1:
The patent applies different properties to different parts of the board. The metal stiffener plates are positioned specifically in regions where mechanical strength is needed, while the pad areas maintain their original thickness for proper soldering. This localized differentiation resolves the warping issue by ensuring that only the necessary areas are reinforced without creating height differences that cause instability during soldering.
3Strength
If the metal plate is left on the printed wiring board in a framed configuration to provide reinforcement, then the mechanical strength is improved, but the amount of metal in the IC chip mounting area becomes substantially different from the reinforcement area, causing warping
Solution Approach 1:
The patent creates local quality differences by placing metal stiffener plates in specific regions while maintaining pad areas with appropriate metal thickness for soldering. This ensures that each area has the metal content appropriate for its function, preventing warping and maintaining positioning accuracy.
Solution Approach 2:
The patent aims to create equipotential conditions by balancing the metal distribution across different areas of the board. By carefully designing the stiffener plate configuration and positioning, the patent ensures that thermal and mechanical stresses are distributed evenly during soldering, preventing warping and maintaining conductor positioning accuracy.
Data Source
AI summary
To provide a novel multilayer printed wiring board in which a conductor on the outermost resin layer is positioned properly. Furthermore, to provide a novel multilayer printed wiring board in which productivity is enhanced when forming solder bumps on the pads for mounting a semiconductor element. In multilayer printed wiring board, multiple pads for connection with a semiconductor chip are formed on one surface, and on its opposite surface, external connection terminals for connection with another substrate are formed. The pads for connection with a semiconductor chip are formed in the central region of one surface, stiffener is formed in the peripheral region surrounding the pads for connection with a semiconductor chip, pads for connection with a semiconductor chip and stiffener are formed with the same material and are set to be the same height, and the actual area of the stiffener is determined according to the total area of the multiple pads for connection with a semiconductor chip.