Capillary Bridge Underfill for Multi-Die Semiconductor Packaging
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Solution Overview
Problem
Conventional underfill processes for flip chip packaging are inefficient, leading to increased costs and defects due to uncontrolled underfill flow and the need for sequential application to each integrated circuit die, resulting in voids and non-uniform underfill density which can induce stress from thermal expansion.
Innovation Solution
The method involves spacing semiconductor dice close enough to form a continuous capillary region, allowing underfill to flow between adjacent dice and the substrate, forming a capillary bridge that controls underfill distribution and eliminates the need for sequential underfill application by using the capillary action to distribute underfill across multiple dice as a single unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If underfill is applied sequentially to each die using a needle dispenser, then complete underfill coverage can be achieved, but manufacturing time increases and throughput decreases
Solution Approach 1:
Multiple separate underfill application operations are merged into a single simultaneous operation by applying underfill to a group of adjacent dies at once. The underfill flows through continuous capillary regions formed by closely spaced dies, allowing one dispensing action to fill multiple dies concurrently, thereby increasing throughput while maintaining complete coverage.
Solution Approach 2:
The dies are positioned in advance at predetermined close spacing to form continuous capillary regions before underfill application. This preliminary arrangement of dies creates the conditions for simultaneous underfilling, enabling the underfill to flow continuously across multiple dies from a single application point without requiring sequential operations.
2Ease of manufacture
If sufficient spacing is provided between adjacent dice to allow needle dispensing, then underfill can be applied to each die, but underfill flow becomes uncontrolled and defects form
Solution Approach 1:
The spacing parameter between adjacent dies is changed from conventional larger spacing to a specific close spacing that enables capillary bridge formation. This parameter change transforms the underfill flow behavior from uncontrolled spreading to controlled capillary-driven flow, allowing complete filling while preventing defects such as voids and non-uniform density.
Solution Approach 2:
The mechanical needle dispensing system is replaced with a capillary action-based flow system. Instead of using a needle to mechanically push underfill under each die, the invention relies on capillary forces generated by the close spacing between dies to draw underfill through continuous capillary regions, providing superior flow control and eliminating needle-related defects.
3Productivity
If dice are spaced closely to form capillary bridges, then simultaneous underfilling of multiple dice is enabled, but precise positioning and alignment become more critical
Solution Approach 1:
Dies are positioned in advance at predetermined close spacing to form continuous capillary regions before underfill application. This preliminary precise positioning creates the capillary bridge network that enables subsequent simultaneous underfilling, making the initial placement accuracy critical for achieving the productivity benefits of the invention.
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 approach reduces manufacturing time and costs by allowing simultaneous underfilling of multiple dice, ensuring a seamless and uniform underfill bond that mitigates thermal stress and extends the lifespan of the semiconductor device.
Implementation Method 1
The underfill has properties that induce capillary action causing the underfill to flow into the gap between the bottom surface of the integrated circuit die and the top surface of the substrate
Implementation Method 2
a first one of the neighboring dice will contact a meniscus of a flange of an underfill along the perimeter of a second one of the neighboring die during underfill to form a capillary bridge between the respective capillary regions
Data Source
AI summary
In one embodiment, a method of forming a multi-die semiconductor device is provided. A plurality of dice is mounted on a semiconductor substrate, and neighboring ones of the dice are separated by a distance at which a first one of the neighboring dice will contact a meniscus of a flange of the neighboring die during underfill to form a capillary bridge between the neighboring dice. Solder bumps are reflowed to electrically connect contact terminals of the plurality of dice to contact terminals on a top surface of the substrate. Underfill is deposited along one or more edges of one or more of the plurality of dice. As a result of the capillary bridge formed between neighboring dice, flow of underfill is induced between the bottom surfaces of the neighboring dice and the top surface of the substrate. The dispensed underfill is cured.