Direct Chip Bonding Without Solder Balls for Thinner Stacks
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Solution Overview
Problem
Existing chip-to-wafer (C2W) and chip-to-chip (C2C) bonding processes using solder balls or copper pillars with solder caps result in increased chip thickness and inefficiencies due to the use of additional materials, which are large and cumbersome.
Innovation Solution
A direct bonding method and device that eliminates the need for solder balls or copper pillars by using a direct bond, such as metal-metal solid body bonds, diffusion bonds, or hybrid bonds, with a bond strength of more than 0.1 J/m2, occurring at temperatures below 400°C without a liquid phase, and involving a cleaning process to ensure contamination-free bond surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder balls or copper pillars with solder caps are used for chip bonding, then reliable electrical connection is achieved, but chip thickness increases and manufacturing complexity increases
Solution Approach 1:
The patent removes the intermediate solder balls or copper pillars from the bonding process, achieving direct metal-to-metal contact between chips. This extraction of the intermediate element eliminates the thickness increase while maintaining reliable electrical connection through direct diffusion bonding of aluminum or copper layers.
Solution Approach 2:
The patent employs asymmetric bonding approaches where one chip has a metal layer (aluminum or copper) that diffuses into the corresponding metal layer of the other chip. This asymmetric diffusion process enables direct bonding without requiring symmetric intermediate elements like solder balls, thereby reducing overall thickness while ensuring reliable connection.
2Reliability
If solder balls or copper pillars with solder caps are used for chip bonding, then electrical connection is established, but device complexity and material requirements increase
Solution Approach 1:
The patent eliminates the need for solder balls, copper pillars, and associated cap structures by implementing direct diffusion bonding. This removal of intermediate components and simplification of the bonding process reduces material requirements and manufacturing complexity while maintaining reliable electrical connection through direct metal diffusion.
Solution Approach 2:
The patent changes the bonding parameters from traditional soldering temperatures to controlled diffusion bonding temperatures (typically 200-400°C for aluminum, or similar ranges for copper). This parameter change enables direct metal-to-metal bonding without intermediate solder elements, simplifying the overall device structure and reducing material complexity.
3Productivity
If direct bond is used without intermediate materials, then chip thickness is reduced and throughput is increased, but bond surface cleanliness requirements increase
Solution Approach 1:
The patent implements preliminary cleaning and preparation of bond surfaces before the direct diffusion bonding process. This may include removing native oxides, controlling surface contamination, and ensuring proper surface finish. By performing these preparatory actions in advance, the patent enables direct bonding without intermediate materials, thereby reducing chip thickness and increasing throughput while maintaining adequate bond surface cleanliness through controlled preprocessing.
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 direct bond method reduces chip stack thickness, increases throughput, and enhances chip communication efficiency while maintaining strong bond strength, all without the production of a liquid phase.
Implementation Method 1
The bond surfaces are cleaned by means of plasma and/or wet-chemical methods
Implementation Method 2
A direct bond is in particular understood to be a metal-metal solid body bond, in particular diffusion bond
Data Source
AI summary
A method for bonding chips onto a substrate or onto further chips. The chips are bonded onto the substrate or the further chips by means of a direct bond.