Patterned Underfill Reservoir for Void-Free Semiconductor Packaging
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Solution Overview
Problem
Achieving a void-free underfill in semiconductor devices is challenging due to inhomogeneous propagation speeds of underfill material, leading to air trapping and contamination of wire bond pads, as the material flows slower through contact elements than along the semiconductor chip edges.
Innovation Solution
A patterned structure on the substrate extends from under the semiconductor chip through a keep-out zone, acting as a reservoir to control the underfill material flow, slowing its propagation along the chip edges and ensuring it flows faster through contact elements, thus preventing air bubbles and contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If underfill material is allowed to flow freely during underfilling, then the underfilling process is simple, but air bubbles are trapped and wire bond pads are contaminated
Solution Approach 1:
The substrate surface is segmented into different zones with varying wettabilities. A keep-out zone is created around the semiconductor chip perimeter using a less wettable material or coating, while the center region maintains high wettability. This segmentation guides the underfill material to flow only through the contact elements and not contaminate the wire bond pads in the keep-out zone, thereby achieving void-free underfilling without compromising process simplicity.
Solution Approach 2:
Different regions of the substrate are given different local properties regarding wettability. The area under the semiconductor chip is made highly wettable to ensure complete underfilling, while the perimeter keep-out zone is made less wettable to prevent underfill material from reaching the wire bond pads. This local differentiation of surface properties solves the contradiction by controlling material flow paths without adding complex process steps.
2Productivity
If underfill material propagation speed is increased along chip edges, then underfilling is faster, but air bubbles are trapped before material flows through contact elements
Solution Approach 1:
The substrate surface wettability is locally optimized to control underfill propagation speed in different regions. The center region under the chip has high wettability to maintain fast propagation speed and high productivity, while the perimeter keep-out zone has reduced wettability to slow down propagation near the edges. This local differentiation ensures uniform underfill propagation throughout the chip area, preventing air bubble trapping while maintaining overall underfilling speed.
Solution Approach 2:
The underfill propagation dynamics are made spatially variable through differential wettability. The system transitions from uniform propagation (which causes air trapping) to dynamically controlled propagation where speed varies by location. The keep-out zone acts as a speed-regulating region that slows down material flow near chip edges, ensuring synchronized arrival of underfill material at all contact elements and eliminating air bubble formation.
3Quantity of substance
If underfill material wets the wire bond pads, then complete coverage is achieved, but contamination occurs and device reliability decreases
Solution Approach 1:
The substrate surface is segmented into an active underfill zone and a keep-out zone. The keep-out zone is positioned between the chip edges and the wire bond pads, creating a physical barrier through differential wettability. This segmentation allows complete underfill coverage of the chip area while preventing material from reaching the wire bond pads, thus eliminating contamination while maintaining full coverage where needed.
Solution Approach 2:
The keep-out zone acts as an intermediary barrier between the underfill material and the wire bond pads. This intermediate region with reduced wettability properties prevents direct contact between the underfill material and the wire bond pads, serving as a protective buffer zone that allows complete underfilling of the chip area while blocking contamination of sensitive external structures.
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 patterned structure effectively prevents air bubble trapping and contamination by ensuring complete underfilling without voids, maintaining the integrity of wire bond pads and improving thermal expansion mismatch distribution.
Implementation Method 1
the propagation speed of the underfill material in these paths is strongly inhomogeneous. Air may be trapped when the propagation speed of the underfill material in these paths is strongly inhomogeneous.
Data Source
AI summary
A semiconductor device includes a substrate, a semiconductor chip, and an array of contact elements electrically coupling the substrate to the semiconductor chip. The semiconductor device includes an underfill material between the substrate and the semiconductor chip and between the contact elements. A patterned structure is arranged on the substrate and extends from under the semiconductor chip through a keep-out zone around an edge of the semiconductor chip. The patterned structure provides a reservoir for the underfill material.