Protruding Metal Layer for Thermal Stress Absorption in PCBs
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Solution Overview
Problem
Existing printed wiring boards face challenges in achieving secure and reliable connections between electronic components and wiring boards, particularly due to warping caused by thermal expansion and contraction, which can lead to connection failures and reduced reliability.
Innovation Solution
A printed wiring board structure featuring a resin insulation layer with a first conductive layer embedded within, a second conductive layer on the surface, a via conductor for electrical connection, and a solder-resist layer with a metal layer and barrier-metal layer on the first conductive layer, where the metal layer protrudes from the resin surface to absorb stress and enhance adhesion, and a manufacturing method involving a carrier with a metal film, forming conductive layers, and selective etching to create the desired pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional printed wiring board structure is used, then manufacturing is simple, but connection reliability deteriorates due to warping from thermal expansion and contraction
Solution Approach 1:
The conductive layer is segmented into multiple functional layers: an embedded first conductive layer for electrical connection and a protruding metal layer for stress absorption and soldering. This segmentation allows each layer to perform its specific function independently, improving connection reliability while managing thermal stress.
Solution Approach 2:
The patent uses a composite structure combining resin insulation material with multiple conductive layers (copper, nickel, etc.). The resin provides insulation and structural support, while the metal layers provide conductivity and stress absorption, creating a composite material system that addresses both electrical and mechanical requirements.
2Strength
If the conductive layer is embedded in the resin surface, then adhesion is improved, but stress absorption during thermal expansion deteriorates
Solution Approach 1:
The metal layer extends from the embedded conductive layer in the thickness dimension, protruding from the resin surface. This dimensional transition allows the metal layer to absorb thermal stress through elastic deformation while the embedded portion maintains strong adhesion to the resin, simultaneously achieving both adhesion and stress absorption.
3Stress or pressure
If the metal layer protrudes from the resin surface, then stress absorption improves, but manufacturing precision deteriorates due to etching control difficulty
Solution Approach 1:
A barrier metal layer (nickel) is introduced as an intermediary between the copper metal layer and the resin insulation layer. This barrier layer serves as an etching stopper that prevents etching solution from penetrating into the resin, allowing precise control of the metal layer pattern and protrusion height while maintaining manufacturing precision.
4Manufacturing precision
If a barrier metal layer is added, then etching control improves, but device complexity increases
Solution Approach 1:
The barrier metal layer performs multiple functions simultaneously: it acts as an etching stopper to control pattern precision, provides a diffusion barrier to prevent metal migration, enhances adhesion between the copper layer and resin, and contributes to the overall structural integrity. This multi-functionality justifies the additional layer by consolidating multiple protective and control functions into a single element.
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 enhances connection reliability by mitigating stress from thermal expansion and contraction, preventing cracking and connection failures, and allowing for adjustable solder bump sizes to ensure secure mounting of electronic components, thereby improving the overall reliability and durability of the printed wiring board.
Implementation Method 1
warping caused by thermal expansion and contraction
Implementation Method 2
the metal layer protrudes from the resin surface to absorb stress
Data Source
AI summary
A printed wiring board includes an insulation layer, a first conductive layer embedded into first surface of the insulation layer, a second conductive layer formed on second surface of the insulation layer, a via conductor penetrating through the insulation layer and electrically connecting the first and second layers, and a solder-resist layer covering the first layer and having an opening structure forming an exposed structure of the first layer. The exposed structure is formed to connect an electronic component to the first layer, and the first layer has a barrier-metal layer and a metal layer on the first layer such that the barrier-metal layer is on surface of the first layer and includes metal different from metal forming the metal layer and that the metal layer is on surface of the barrier-metal layer in the exposed structure and protruding from the first surface of the insulation layer.