Chip-on-Chip Assembly Using Thin Solder Layer and Intermetallic Compound
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Solution Overview
Problem
Existing chip-on-chip assembly methods face challenges with reliability, fine pitch limitations, and non-planarity issues due to the use of large gold bumps, which lead to spreading and inadequate filling of small holes, resulting in unreliable interconnections.
Innovation Solution
A method involving a thin solder layer with a contact angle of less than 90°, forming an intermetallic compound between the underbump metallization and the second chip's metallization, and using a flattened surface on the second chip to reduce voids and non-planarity, with a solder composition applied via immersion soldering and thermode bonding, allowing for a fine pitch and reduced risk of bump spreading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If large gold bumps are used for chip assembly, then the interconnection strength is improved, but the bumps spread out and flow together causing reliability issues
Solution Approach 1:
The patent changes the material parameter from gold to solder composition and controls the volume parameter of the interconnection material. By using a solder composition with controlled volume and forming an intermetallic compound, the method achieves reliable interconnections without the spreading and flowing problems associated with large gold bumps.
2Manufacturing precision
If a thick metallisation layer is used for underbump metallisation, then the filling of small holes is improved, but the pitch between bond pads cannot be made fine
Solution Approach 1:
The patent changes the thickness parameter of the metallisation layer from thick to thin. By using a thin metallisation layer combined with a solder composition that has good flow characteristics and forms intermetallic compounds, the method enables fine pitch assemblies while still achieving adequate hole filling and reliable connections.
3Stability of the object's composition
If a large solder volume is used, then the interconnection stability is improved, but the risk of neighbouring bumps flowing together increases
Solution Approach 1:
The patent optimizes the volume parameter of the solder composition to a small, controlled amount. By using a small solder volume that forms an intermetallic compound at the interface, the method achieves stable interconnections while preventing neighbouring bumps from spreading and flowing together.
4Strength
If the contact angle of the solder layer is large (greater than 90°), then the solder adhesion is improved, but the formation of intermetallic compounds is insufficient
Solution Approach 1:
The patent optimizes the contact angle parameter of the solder layer to be less than 90°. By controlling the contact angle to be acute, the method promotes both adequate solder adhesion and the formation of reliable intermetallic compounds at the interface between the solder composition and the metallisation.
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 enhances reliability and allows for a fine pitch assembly with reduced risk of voids and failures, achieving stable interconnections and tolerance to non-planarity, while minimizing the use of noble materials and enabling low-cost production.
Implementation Method 1
forming an intermetallic compound between the underbump metallization and the second chip's metallization
Implementation Method 2
heating to form the interconnection
Implementation Method 3
which layer makes a contact angle of less than 90° with the underbump metallization
Data Source
AI summary
An assembly (100) is provided comprising a first chip (20) and a second chip (30) which are interconnected through solder connections. These comprise, at the first chip, an underbump metallization and a solder bump, and, at the second chip, a metallization. In this case the solder bump is provided as a fluid layer with a contact angle of less than 90° C., and an intermetallic compound is formed on the basis of the metallization at the second chip, and at least one element of the composition is applied as the solder bump.