Chip Package Bump Connecting Structure for Reliability
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Solution Overview
Problem
Conventional flip chip packages experience reliability issues due to cracks in solder bumps near chip and carrier pads, especially with lead-free solder, leading to decreased performance over time.
Innovation Solution
A bump connecting structure comprising a first metal bump on the chip pad, a second metal bump on the carrier pad, and a middle metal part with a lower melting point, where the sum of the distances and heights of the bumps is less than 60 micrometers, enhancing connecting strength and reducing thermal strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder bumps are used for connecting chip and carrier, then electrical connection is achieved, but cracks appear in the solder bumps leading to decreased reliability
Solution Approach 1:
The bump connecting structure is divided into three distinct segments: a first metal bump on the chip pad, a second metal bump on the carrier pad, and a middle metal part connecting them. This segmentation allows each part to be optimized independently, with the middle metal part having lower melting point for stress relief while the outer bumps provide structural support, preventing crack propagation that would occur in a monolithic solder bump.
Solution Approach 2:
The invention uses composite material structure with at least two different metal materials having different melting points. The middle metal part has a lower melting point than the first and second metal bumps, creating a composite structure where the softer middle section absorbs thermal strain and mechanical stress, while the harder outer bumps provide structural integrity, thus preventing cracks.
2Strength
If multiple reflow processes are used for different metal parts, then connection strength is improved, but manufacturing complexity increases
Solution Approach 1:
The invention changes the melting point parameter of the middle metal part to be lower than the outer bumps, allowing selective melting and connection in a single reflow process. The middle metal part melts first to form connections, while the outer bumps remain solid to provide structural support, achieving strong connections without requiring multiple reflow cycles at different temperatures.
3Reliability
If bump heights and distances are increased, then connection reliability is improved, but package thickness increases
Solution Approach 1:
The invention applies local quality by making the middle metal part have different properties (lower melting point) compared to the outer bumps. This allows the middle section to be optimized for stress relief and connection formation, while the outer bumps are optimized for structural support, achieving reliable connections with minimized overall thickness through localized material optimization rather than uniformly increasing all dimensions.
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 proposed structure improves reliability, increases layout density, reduces package thickness, and simplifies the connection process with a single reflow step for the middle metal part, addressing the reliability and efficiency challenges of conventional flip chip packages.
Implementation Method 1
the melting point of the middle metal part is lower than that of the first metal bump and the second metal bump
Data Source
AI summary
A chip package includes a chip, a carrier, and at least a bump connecting structure for connecting the chip to the carrier. The bump connecting structure includes a first metal bump disposed on a chip pad of the chip and has a first height relative to a passivation layer of the chip, a second metal bump disposed on a carrier pad of the carrier and has a second height relative to a solder mask layer of the carrier, and a middle metal part disposed between the first and the second metal bumps. The sum of the minimum distance between the first and the second metal bumps, the first height of the first metal bump, and the second height of the second metal bump is less than 60 micrometers. The melting point of the middle metal part is lower than that of the first and the second metal bumps.