Conductive Buffer Layers for Reliable Direct Die Bonding
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Solution Overview
Problem
Semiconductor packages with stacked dies face challenges in reducing height and minimizing signal propagation delays due to bond wires, which also introduce variations in recess depths of conductive pads, affecting bonding integrity and reliability.
Innovation Solution
The introduction of a conductive buffer layer between conductive pads, which is porous and deformable, allows for wider tolerable limits in recess depth variations, providing a compressible cushion during thermal expansion and facilitating robust interconnects by forming electrically conductive structures during the annealing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bond wires are used to connect semiconductor dies, then electrical connectivity is achieved, but package height increases and signal propagation delays are introduced
Solution Approach 1:
The patent removes bond wires from the interconnect structure entirely, replacing them with direct die-to-die bonding. This extraction of the problematic element (bond wires) eliminates the height increase and signal delays they cause, while maintaining electrical connectivity through alternative means (conductive pads and bumps).
Solution Approach 2:
The patent introduces conductive bumps as intermediary elements between the conductive pads of adjacent dies. These bumps serve as the mediating structure that enables electrical connection without requiring bond wires, thus achieving connectivity while minimizing package height and signal propagation paths.
2Reliability
If conductive pads are recessed to enable direct bonding, then bonding integrity improves, but manufacturing precision requirements increase due to strict coplanarity control
Solution Approach 1:
The patent changes the physical state and mechanical properties of the conductive pad material by selecting materials with specific ductility and formability characteristics. This parameter change allows the pads to deform plastically during bonding, accommodating variations in recess depth and eliminating the need for strict coplanarity control while maintaining bonding integrity.
Solution Approach 2:
The patent designs the conductive pads with inherent mechanical compliance and deformability, which acts as a cushion against coplanarity variations. This beforehand cushioning through material selection and structural design absorbs the shocks of manufacturing variations, allowing broader tolerances on recess depth control.
3Ease of manufacture
If aggressive recess depths are used to facilitate bonding, then bonding process ease improves, but electrical conductivity may be compromised
Solution Approach 1:
The patent performs preliminary actions during pad fabrication by optimizing pad geometry, material composition, and mechanical properties before the bonding process. The pads are pre-engineered with sufficient material volume, ductility, and formability to accommodate aggressive recess depths while ensuring that adequate conductive material remains to maintain electrical conductivity after bonding.
Solution Approach 2:
The patent employs composite material structures for the conductive pads, combining materials with complementary properties such as high electrical conductivity, ductility, and formability. This composite approach allows the pads to be aggressively recessed during bonding while the remaining structure maintains both mechanical integrity and electrical conductivity.
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 solution relaxes the strict requirements on recess depth control, enhances bonding reliability, and maintains electrical conductivity, even with aggressive recess depths, thereby improving the yield and reducing costs associated with precise coplanarity control.
Implementation Method 1
The conductive buffer layer is malleable to deform in response to pressure applied to the conductive buffer layer
Implementation Method 2
both the first and second top surfaces of the first and second bond pads expand toward the bonding interface in response to heating the first and second semiconductor dies
Implementation Method 3
heating the first and second semiconductor dies attached to each other
Data Source
AI summary
Conductive buffer layers for semiconductor die assemblies, and associated systems and methods are disclosed. In an embodiment, a semiconductor die assembly includes first and second semiconductor dies directly bonded to each other. The first semiconductor die includes a first copper pad and the second semiconductor die includes a second copper pad. The first and second copper pads form an interconnect between the first and second semiconductor dies, and the interconnect includes a conductive buffer material between the first and second copper pads, where the conductive buffer material includes aggregates of conductive particles. In some embodiments, the first and second copper pads are not conjoined but electrically connected to each other through the conductive buffer material. In some embodiments, the conductive buffer material is porous such that the aggregates of conductive particles can be compressed together in response to the pressure applied to the conductive buffer layer.