Wiring Board Wettability Zoning for Flip-Chip Solder Containment
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Solution Overview
Problem
In semiconductor devices with flip-chip bonding, solder can spread over electrodes beyond design assumptions, leading to undesirable results such as electrical connectivity issues and warping during the reflow process.
Innovation Solution
A wiring board design featuring a conductive layer with distinct wettability zones, including a first connection portion with high solder wettability and a lead-out portion with lower wettability, connected via a wiring portion, helps control solder spread and maintain electrical connections by using a combination of gold and copper as primary components in these zones, and an insulating layer to manage solder flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder is applied to connect semiconductor chips to substrate in flip-chip bonding, then electrical connections are established, but solder may spread over electrodes beyond design range causing undesirable results
Solution Approach 1:
The conductive layer is divided into distinct regions with different solder wettability characteristics: a first region with high wettability that promotes solder attachment, and a second region with low wettability that prevents solder spread. This local differentiation of surface properties enables precise solder containment within electrode boundaries while maintaining reliable electrical connections.
Solution Approach 2:
The patent modifies the wettability parameter of the conductive layer by applying different treatments or materials to different regions. The first region is treated to exhibit high solder wettability (enhancing solder adhesion), while the second region maintains low wettability (restricting solder flow). This parameter variation across the conductive layer surface controls solder behavior during the bonding process.
2Strength
If solder wettability is increased to ensure good solder attachment, then connection strength improves, but solder spread beyond electrodes increases
Solution Approach 1:
The conductive layer exhibits spatially varying wettability properties: the first region (under the electrode) has high wettability to ensure strong solder attachment and joint strength, while the second region (surrounding the electrode) has low wettability to prevent solder from spreading beyond the electrode boundaries. This local quality differentiation simultaneously achieves both strong joints and precise solder containment.
Solution Approach 2:
The conductive layer is segmented into functionally distinct zones: a central first region that promotes solder wetting for strong attachment, and a peripheral second region that repels solder to maintain precision. This segmentation allows the system to exhibit contrasting wettability behaviors in different spatial locations, resolving the contradiction between strength and precision.
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 reduces solder spread and maintains reliable electrical connections, enhancing the reliability of flip-chip bonding and reducing the likelihood of open states during the reflow process.
Implementation Method 1
The conductive layer includes a first connection portion exposed from the insulating layer and having a first wettability to solder, a lead-out portion connected to the first connection portion and exposed from the insulating layer and having a second wettability to solder
Data Source
AI summary
According to one embodiment, a wiring board, includes a conductive layer on a first surface and an insulating layer covering a portion of the conductive layer. The conductive layer includes a first connection portion exposed from the insulating layer and having a first wettability to solder, a lead-out portion connected to the first connection portion and exposed from the insulating layer and having a second wettability to solder, and a wiring portion connected to the first connection portion via the lead-out portion and covered with the insulating layer. In some examples, the first connection portion may be coated with a gold layer and the conductive layer may be copper or a copper alloy material.