Wiring Board Protrusion Electrodes for COF Stress Management
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Solution Overview
Problem
Conductive wirings in chip-on-film (COF) packaging are prone to breaks due to stress from protrusion electrodes, especially when the pitch of electrode pads is narrow, leading to instability and potential misalignment during semiconductor element mounting.
Innovation Solution
A wiring board design featuring conductive wirings with varying widths and protrusion electrodes of uniform height, where wider conductive wirings are positioned at stress-susceptible areas, and the protrusion electrodes have a curved outer surface and rectangular cross-section, formed through metal plating to enhance stability and connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pitch of electrode pads is narrowed to increase output, then the number of outputs increases, but the strength of conductive wirings degrades and breaks occur due to stress concentration
Solution Approach 1:
The patent applies local quality by varying the width of conductive wirings based on their position and stress susceptibility. Specifically, wirings that are more prone to stress concentration (such as those at the ends or isolated wirings) are made wider to enhance strength, while other wirings maintain narrower widths to achieve narrower pitch and higher output density. This selective width adjustment resolves the contradiction between increasing output and maintaining wiring strength.
2Length of moving object
If the width of conductive wiring is narrowed to reduce pitch, then the pitch decreases, but the strength of conductive wiring degrades and breaks occur
Solution Approach 1:
The patent implements local quality by differentiating wiring widths based on stress susceptibility. Certain wirings are intentionally made wider at specific locations where stress concentration is expected, while maintaining narrower widths in other areas to achieve overall pitch reduction. This localized width variation allows the structure to maintain both narrow pitch and sufficient strength where needed.
3Reliability
If protrusion electrodes are formed to ensure connection stability, then connection reliability improves, but stress concentration increases causing breaks in conductive wirings
Solution Approach 1:
The patent applies local quality by adjusting the width of conductive wirings based on their proximity to protrusion electrodes and stress susceptibility. Wirings that are more likely to experience stress concentration near protrusion electrodes are made wider to distribute stress, while other wirings maintain narrower widths. This selective approach allows connection stability to be maintained while reducing harmful stress concentration effects.
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 design effectively prevents breaks in conductive wirings near protrusion electrodes, ensures stable connections, and accommodates narrower pitches by distributing stress evenly, while maintaining consistent protrusion electrode heights for reliable bonding.
Implementation Method 1
protrusion electrodes formed of a plated metal in the vicinity of end portions of the conductive wirings, respectively
Data Source
AI summary
A wiring board includes a film base, a plurality of conductive wirings aligned on the film base, and protrusion electrodes formed of a plated metal in the vicinity of end portions of the conductive wirings, respectively. An outer surface at both side portions of the protrusion electrodes in cross section in a width direction of the conductive wirings defines a curve, and the protrusion electrodes in cross section in a longitudinal direction of the conductive wirings define a rectangular shape. The conductive wirings include a first conductive wiring having a wiring width of W1 and a second conductive wiring having a wiring width of W2 larger than W1, and the protrusion electrode on the first conductive wiring and the protrusion electrode on the second conductive wiring have a substantially same height. The wiring board is capable of supporting conductive wirings with a practically enough strength to withstand a stress applied during the connection between the protrusion electrodes of the film base and electrode pads of a semiconductor element, providing sufficient connection stability and coping with a narrow pitch of the semiconductor element.