Wiring Substrate Protruding Electrode Bridging Prevention
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Solution Overview
Problem
Existing wiring substrates with fine-pitch protruding electrodes face issues of bridging and short-circuiting due to the surface metal layer melting and flowing onto the insulating layer during the reflow process, particularly in the case of fine-pitch designs.
Innovation Solution
A wiring substrate design featuring a protruding metal layer with a bent peripheral surface that forms a space between the peripheral surface and the insulating layer, preventing the surface metal layer from contacting the insulating layer and thus avoiding bridging between adjacent electrodes, where the surface metal layer is made of a metal with a lower melting point than the protruding metal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface metal layer is formed to cover the entire surface of the conductive pillar including the insulating layer surface, then complete coverage and protection is achieved, but bridging and short-circuiting occurs during reflow process
Solution Approach 1:
The surface metal layer is segmented into two distinct regions: a first surface metal layer covering the conductive pillar, and a second surface metal layer covering the insulating layer surface but separated from the first layer. This segmentation prevents the metal layer from forming a continuous bridge between adjacent electrodes while maintaining protective coverage.
Solution Approach 2:
The insulating layer surface acts as an intermediary barrier between the surface metal layer and adjacent electrodes. By forming the second surface metal layer on the insulating layer surface that is separated from the first surface metal layer, the insulating layer prevents direct metal-to-metal contact that would cause bridging.
2Productivity
If fine-pitch electrodes are used to increase connection density, then productivity and integration are improved, but the risk of bridging during reflow increases
Solution Approach 1:
The segmented surface metal layer structure creates physical separation between adjacent fine-pitch electrodes, preventing the metal from bridging during reflow. This allows higher connection density to be achieved without compromising reliability.
Solution Approach 2:
The invention changes the geometric parameters of the surface metal layer by creating a stepped configuration with different heights over the conductive pillar and insulating layer. This parameter change ensures that even at fine-pitch dimensions, the metal layers remain separated by the insulating layer, preventing short-circuits.
3Area of stationary object
If the surface metal layer contacts the insulating layer surface, then complete coverage is achieved, but the metal flows onto adjacent electrodes during reflow
Solution Approach 1:
The surface metal layer is divided into separate first and second layers that do not form a continuous path. The second layer covers the insulating layer surface but is separated from the first layer, preventing metal flow onto adjacent electrodes while maintaining broad coverage.
Solution Approach 2:
The surface metal layer is designed as a thin film structure that conforms to the insulating layer surface topology. The second surface metal layer forms a thin film on the insulating layer that is separated from the first layer, providing coverage without creating bridging pathways.
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 prevents bridging and short-circuiting between adjacent protruding electrodes during the reflow process, maintaining the structural integrity and connectivity of fine-pitch electrodes on the wiring substrate.
Implementation Method 1
melting the surface metal layer by a reflow process
Implementation Method 2
forming a surface metal layer of a solder material on a conductive pillar protruding from an upper surface of an insulating layer by electroplating
Data Source
AI summary
A wiring substrate includes a wiring layer, an insulating layer covering the wiring layer, and a protruding electrode including a protruding metal layer and a surface metal layer. The protruding metal layer is connected to the wiring layer in an opening of the insulating layer, extends from within the opening to be stepped at the edge of the opening to extend outward onto the insulating layer, and includes a first surface contacting a surface of the insulating layer around the opening, a second surface, and a peripheral surface extending between the first and second surfaces, and bent inward to form a space between the peripheral surface and the surface of the insulating layer. The surface metal layer covers the protruding metal layer without contacting the surface of the insulating layer, and is formed of a metal having a lower melting point than the protruding metal layer.