Flip-Chip Sensor Edge Mounting With Underfill Dam
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Solution Overview
Problem
Existing sensor assemblies face challenges in manufacturing efficiency and ensuring that the sensing area remains accessible and free from underfill or solder flux during flip-chip mounting, which can lead to alignment issues and coverage of the sensing area.
Innovation Solution
The sensor chip is designed with a sensing area in one section and contact pads in another, extending over the substrate edge, with a capillary barrier and dam to prevent underfill or solder flux from reaching the sensing area, allowing for larger positioning tolerances and reliable retention of the underfill or solder flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sensor chip is mounted with the sensing area accessible through a window, then the sensor can measure environmental parameters, but the underfill may cover the sensing area causing alignment issues
Solution Approach 1:
The sensor chip is divided into distinct functional sections: a sensing section with the sensing area and a contact section with contact pads. This segmentation allows the sensing area to be positioned in a specific region while contact pads are located in another region, enabling the window and dam structure to be designed independently to protect the sensing area during manufacturing while maintaining sensor functionality.
Solution Approach 2:
The dam structure serves as an intermediary element between the underfill and the sensing area. It is positioned between the window and the sensing area to prevent underfill from reaching the sensing area, thus protecting the sensor while allowing the window to maintain its protective function for the chip during mounting.
2Reliability
If a dam is added to prevent underfill from covering the sensing area, then the sensing area is protected, but the alignment between window, dam and sensing area becomes more complex
Solution Approach 1:
The dam structure is merged with the substrate edge configuration, where the substrate edge itself extends between the sensing section and contact section. This integration allows the dam to be formed as part of the substrate structure rather than as a separate component, simplifying the overall structure while maintaining the protective function against underfill.
Solution Approach 2:
The substrate edge configuration automatically provides the dam function without requiring additional alignment processes. The edge of the substrate naturally extends between the sensing and contact sections, creating a self-aligning structure that prevents underfill from reaching the sensing area without complex external alignment mechanisms.
3Ease of manufacture
If the sensor chip extends over the substrate edge, then positioning tolerances are relaxed, but the underfill or solder flux may seep into the sensing section
Solution Approach 1:
The dam structure acts as an intermediary barrier positioned between the underfill/solder flux and the sensing area. It intercepts the underfill or solder flux before it can reach the sensing section, thus protecting the sensor while allowing the chip to extend over the substrate edge for easier positioning.
Solution Approach 2:
The harmful underfill or solder flux is extracted and contained within the dam structure, separating it from the sensing area. The dam creates a contained space where the underfill or solder flux is trapped, preventing it from migrating to the sensing section and causing damage.
4Reliability
If a dam extends from the first edge to the second edge of the sensor chip, then underfill or solder flux access to the sensing section is blocked, but the manufacturing process becomes more complex
Solution Approach 1:
The dam structure is merged with the substrate edge configuration, where the substrate edge itself extends between the sensing section and contact section. This integration allows the dam to be formed as part of the substrate structure rather than as a separate component, simplifying the overall structure while maintaining the protective function against underfill.
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 enhances manufacturing ease and reliability by preventing underfill or solder flux from covering the sensing area, ensuring the sensor's accessibility and accuracy, particularly in applications like consumer electronics and hard disk drives.
Implementation Method 1
The edge of the substrate forms a capillary barrier for the underfill or solder flux when the same is filled into the gap between sensor chip and substrate
Implementation Method 2
a dam is advantageously arranged at the edge of the substrate. The dam extends between the sensor chip and the substrate, i.e. it blocks the gap between the sensor chip and the substrate for the underfill or solder flux
Data Source
Figure 1~2
Figure 3~5
Figure 6~8
AI summary
The sensor assembly comprises a substrate (1), such as a flexible printed circuit board, and a sensor chip (2) flip-chip mounted to the substrate (1), with a first side (3) of the sensor chip (2) facing the substrate (1). A sensing area (4) and contact pads (5) are integrated on the first side (3) of the sensor chip (2). Underfill (18) and/or solder flux is arranged between the sensor chip (2) and the substrate (1). The sensor chip (2) extends over an edge (12) of the substrate (1), with the edge (12) of the substrate (1) extending between the contact pads (5) and the sensing area (4) over the whole sensor chip (2). A dam (16) can be provided along the edge (12) of the substrate (1) for even better separation of the underfill (18) and the sensing area (4). This design allows for a simple alignment of the sensor chip on the substrate (1) and prevents underfill (18) from covering the sensing area (4).