Rectangular Conductor Pad Layout for Stress-Resistant Wiring Substrates
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Solution Overview
Problem
Multilayer wiring substrates face issues with stress concentration and potential cracking or interfacial peeling due to differences in thermal expansion coefficients between conductor pads and insulating layers, particularly at the peripheral edges and corners of conductor pads.
Innovation Solution
A wiring substrate design featuring a conductor pad with a substantially rectangular shape, where the solder resist layer covers the short sides and corner portions, exposing 50% or more of the main surface and side surfaces at the long sides, thereby dispersing stress and preventing defects like cracking or peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conductor pad is formed with a conventional shape and the solder resist layer covers the entire pad, then the insulating layer is protected, but stress concentration occurs at the peripheral edges and corners causing cracking or interfacial peeling
Solution Approach 1:
The solder resist layer is selectively formed to cover only specific regions of the conductor pad (central region and portions of short sides) while leaving other regions (long sides and corner portions) exposed. This local differentiation allows the covered central region to provide mechanical protection and stress distribution, while the exposed peripheral regions accommodate thermal expansion differences and reduce stress concentration at critical corners and edges.
Solution Approach 2:
The conductor pad surface is segmented into multiple functional zones: a central covered region, exposed long side regions, exposed corner portions, and partially covered short side regions. This segmentation allows each zone to serve different functions - the covered central area provides structural support while the exposed peripheral areas accommodate stress from thermal expansion, preventing cracking and peeling.
2Reliability
If the solder resist layer covers the entire conductor pad surface, then protection is provided, but the pad area for bonding is reduced
Solution Approach 1:
The solder resist layer is applied non-uniformly, covering the central region and portions of short sides while deliberately leaving the long sides and corner portions exposed. This local quality approach ensures that the bonding area is maximized by keeping critical bonding regions exposed, while still providing protective coverage in the central area where mechanical support is most needed.
3Area of stationary object
If the conductor pad has a rectangular shape with all sides exposed, then bonding area is maximized, but stress concentration at corners causes cracking
Solution Approach 1:
The solder resist layer is strategically positioned to cover corner portions and the central region while leaving long sides exposed. This creates a protective framework at the corners where stress concentration occurs, preventing cracking, while maintaining adequate bonding area through the exposed long side regions and partially covered short sides.
Solution Approach 2:
The pad structure is segmented into protected corner regions and exposed bonding regions. The covered corner portions act as stress-absorbing elements that prevent crack initiation, while the exposed regions maintain bonding functionality. This segmentation resolves the contradiction between protection and bonding area by assigning different functions to different spatial zones.
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 design effectively suppresses defects such as cracking and interfacial peeling, ensuring a reliable connection while maintaining a high-density formation capability and signal transmission quality.
Implementation Method 1
the solder resist layer is formed such that the opening is exposing side surfaces at the long sides and 50% or more of the main surface and that the solder resist layer is covering side surfaces at the short sides
Data Source
AI summary
A wiring substrate includes an insulating layer, a conductor layer formed on a surface of the insulating layer such that the conductor layer includes a conductor pad, and a solder resist layer formed on the surface of the insulating layer such that the solder resist layer is covering the conductor layer and having an opening exposing the conductor pad. The conductor pad of the conductor layer has a substantially rectangular planar shape such that the conductor pads has a main surface, a pair of long sides, a pair of short sides and four corner portions, and the solder resist layer is formed such that the opening is exposing side surfaces at the long sides and 50% or more of the main surface and that the solder resist layer is covering side surfaces at the short sides.