Semiconductor Lead Layout with Successive Bends for Underfill Coverage
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Solution Overview
Problem
In semiconductor devices, the underfill process often leaves hollow regions around corner portions of the semiconductor element, exposing leads to moisture and increasing the risk of corrosion, especially when leads are laid out straight or with single bends, which can lead to bubble formation and further corrosion issues.
Innovation Solution
The leads connected to electrodes near the corner portions are designed with multiple successive bends or curved portions, directing them towards the short side of the semiconductor element, ensuring they are covered by the underfill and reducing the likelihood of bubble formation, while also potentially connecting leads of the same potential to prevent short-circuits and using dummy bumps on flexible substrates to prevent short-circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the lead is led out straight from the underfill region across the nearest long side of the semiconductor element, then the lead layout is simple, but hollow regions are generated around corner portions and the lead may suffer from corrosion by moisture
Solution Approach 1:
The lead is designed with a bent shape instead of a straight configuration. Specifically, the lead has a first bent portion bent in a first direction and a second bent portion bent in a second direction different from the first direction. This curved path allows the lead to be fully covered by the underfill material, eliminating hollow regions around corner portions and preventing moisture penetration that would cause corrosion.
2Reliability
If the lead is bent once at a right angle toward the short side, then the lead can avoid hollow regions, but the fluidity of the underfill is reduced and bubbles can be generated
Solution Approach 1:
Instead of using sharp right-angle bends, the lead employs multiple bent portions with gradual curvature changes. The first bent portion is bent in a first direction and the second bent portion is bent in a second direction different from the first direction. This multi-directional bending creates a smoother, more gradual curvature that maintains underfill fluidity during the filling process, preventing bubble generation while still ensuring the lead is fully covered.
3Reliability
If the lead is bent multiple times to improve underfill coverage, then corrosion resistance improves, but the lead layout becomes more complex
Solution Approach 1:
The lead layout applies bending only in specific local regions where needed to achieve full underfill coverage, rather than making the entire lead path complex. The first bent portion and second bent portion are strategically positioned to cover critical areas around corner portions, while other sections of the lead maintain simpler configurations. This localized application of complexity minimizes overall device complexity while ensuring corrosion resistance.
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 corrosion of leads by ensuring they are fully covered by the underfill, reduces bubble formation, and enhances the reliability of the semiconductor device by eliminating short-circuit tendencies and improving layout flexibility.
Implementation Method 1
The underfill is dripped, after the semiconductor element is placed on the substrate, along one of the long sides of the semiconductor element, is filled between the substrate and the semiconductor element, and extends such that all the regions between the semiconductor element and the substrate and regions on the substrate adjacent to all sides of the semiconductor element are covered
Implementation Method 2
The leads on the substrate are laid out in various patterns. Heretofore, the patterns described e.g. in JP-A-2004-193223 and JP-A-2005-93468 have been disclosed. The substrate has a region (overcoat region) covered by an overcoat such that the overcoat region is continuous to or overlaps with the underfill region. Portions of the leads that are outside the underfill region on the substrate are covered by the overcoat in order to protect them from corrosion caused by moisture, or the like
Data Source
AI summary
A semiconductor device includes a substrate having a plurality of electrodes and a plurality of leads that are connected to the electrodes and a semiconductor element that is mounted on the substrate. The semiconductor element has a rectangular shape including a long side, a short side, and a corner portion, and has bumps connected to the electrodes. An underfill is filled between the substrate and the semiconductor element and extends on the substrate around the semiconductor element. An overcoat covers the leads on the substrate. At least one of the plurality of leads that is connected to the electrode corresponding to the bump arranged nearest to the corner portion along the long side of the semiconductor element has at least two successive bent portions that are bent in the same direction and is laid out toward the short side of the semiconductor element in a plan view.