The connection between stacked dies is migrating from solder to copper. Traditional stacks use microbumps - tiny solder balls - but solder limits how fine the pitch can go and how short the path can be. Direct copper-to-copper hybrid bonding removes the solder, and a 2023 Avago/Broadcom application brings that to memory stacks.
The application US20230343771A1 (published October 26, 2023; Avago Technologies International Sales Pte. Limited - a Broadcom entity; CPC H01L 25/18 multi-chip assembly, H01L 24/80 bonding processes, H01L 24/05/08 bond structures) describes copper-bonded memory stacks. As a published application, it signals where Broadcom's memory-integration thinking was heading.
Why copper bonding for memory specifically? Memory stacks want maximum interconnect density between layers, and copper hybrid bonding allows a pitch finer than solder can reach, with lower resistance and shorter paths. Denser, shorter connections mean more bandwidth and less energy per bit between the stacked dies - the core memory-stack metrics.
Broadcom is an AI-infrastructure heavyweight (custom silicon, networking), and its interest in copper-bonded memory fits a pattern: the companies assembling AI systems are reaching down into how the memory itself is integrated, because memory integration is where a lot of system bandwidth is won or lost.
This sits in the broad hybrid-bonding thicket alongside TSMC, Adeia, Intel, and others. Each is staking claims on bonding processes and structures; the Broadcom application's particular angle is applying copper bonding to the memory-stack interconnection specifically.
For the reader, remember it is an application, not a grant - a directional signal of intent and priority, not a fenced claim. The discipline is to treat published applications as roadmap evidence: this is where copper-bonded memory was being staked out in 2023, by a major AI-infrastructure player.