Cu-to-Cu Bonding for Bridge Chip Interconnects
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Solution Overview
Problem
The incompatibility between copper (Cu)-to-Cu bonding temperatures and existing solder connections on packaging substrates leads to solder reflow and electrical failures in high bandwidth interconnects for bridge chips attached to logic and/or memory chips.
Innovation Solution
The method involves performing Cu-to-Cu bonding first, without solder, and then using solder bonding to attach the multi-chip structure to the packaging substrate, allowing for higher processing temperatures and accommodating chips of varying heights, while solder provides 'give' for warpage and non-planarity issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cu-to-Cu bonding is performed at high temperatures (≥300°C), then bonding strength and interconnect reliability are improved, but existing solder connections melt and cause solder reflow leading to electrical failures
Solution Approach 1:
The bonding process is segmented into two distinct stages: first performing Cu-to-Cu bonding between chips without solder present, then subsequently attaching the assembled chip structure to the packaging substrate using solder. This temporal separation allows each bonding type to occur under its optimal conditions without interfering with the other.
Solution Approach 2:
Cu-to-Cu bonding is performed as a preliminary action before solder attachment. By completing the high-temperature copper bonding first while chips are still separately attachable, the structure is prepared in advance to withstand subsequent soldering processes without compromising the already-formed copper bonds.
2Ease of manufacture
If solder bonding is used to attach chips to packaging substrate, then ease of manufacture and accommodation of warpage are improved, but processing temperature must be limited below solder melting point preventing Cu-to-Cu bonding
Solution Approach 1:
The manufacturing process is divided into two sequential steps: first Cu-to-Cu bonding at high temperature to join chips together, then solder bonding at lower temperature to attach the assembled structure to the substrate. This segmentation allows each step to occur under appropriate temperature conditions.
Solution Approach 2:
The Cu-to-Cu bonding between chips is performed as a preliminary action before the solder attachment to the substrate. This ensures that high-temperature bonding requirements are met before the temperature-constrained soldering step, enabling both processes to succeed.
3Ease of manufacture
If conventional solder joint is used for bridge chip connection, then manufacturing simplicity is improved, but inter-chip communication bandwidth and speed are reduced
Solution Approach 1:
The material parameter is changed from solder to copper for the bridge chip interconnect interface. Copper provides superior electrical conductivity and signal integrity for high-speed communications compared to solder, enabling increased bandwidth while maintaining manufacturing feasibility through the two-step bonding process.
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 enables the formation of high bandwidth interconnects with finer interconnect sizes and pitches, avoiding solder reflow and ensuring reliable connections between bridge chips and packaging substrates.
Implementation Method 1
Cu-to-Cu bonding is often carried out at temperatures greater than or equal to about 300° C.
Implementation Method 2
bonding the multi-chip structure to a packaging substrate via solder bonding
Implementation Method 3
This solder typically has a low melting point, e.g., of from about 221° C. to about 230° C.
Implementation Method 4
solder provides 'give' for warpage and non-planarity issues
Data Source
AI summary
Copper (Cu)-to-Cu bonding techniques for high bandwidth interconnects on a bridge chip attached to chips which are further attached to a packaging substrate are provided. In one aspect, a method of forming an interconnect structure is provided. The method includes: bonding individual chips to at least one bridge chip via Cu-to-Cu bonding to form a multi-chip structure; and bonding the multi-chip structure to a packaging substrate via solder bonding, after the Cu-to-Cu bonding has been performed, to form the interconnect structure including the individual chips bonded to the at least one bridge chip and to the packaging substrate. A structure formed by the method is also provided.