Patterned Die Attach Layer with Voids for Thermal Stress Relief
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Solution Overview
Problem
The mismatch in thermal coefficients of expansion (TCE) between semiconductor dies, die attach layers, and package substrates leads to mechanical stresses, cracks, and delamination in high-power semiconductor components, and existing customized alloys fail to effectively address these issues due to temperature-dependent changes and interfacial diffusion.
Innovation Solution
A patterned die attach layer with voids is used, allowing thermal expansion without accumulating mechanical stress, and a conductive coating is applied to reinforce the bond between the die and substrate, using materials like gold or gold-tin alloys in various geometric patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If customized alloys are used as die attach layer to match TCE, then thermal expansion mismatch is reduced, but the solution becomes complex and interfacial diffusion still occurs
Solution Approach 1:
The die attach layer is segmented into a patterned structure with voids distributed throughout, dividing the continuous material into regions that can independently accommodate thermal expansion. This segmentation allows the attach layer to maintain TCE matching while providing expansion space, reducing mechanical stress without requiring complex alloy formulations.
Solution Approach 2:
The die attach layer incorporates voids creating a porous structure that provides expansion space for thermal growth. This porous design allows the material to expand into the voids rather than generating stress, maintaining bond reliability while using simpler alloy compositions without requiring complex interdiffusion-resistant formulations.
2Reliability
If high working temperature alloys are used, then thermal expansion matching is improved, but die damage occurs due to excessive heat
Solution Approach 1:
The invention changes the physical structure parameter of the die attach layer by introducing voids, rather than changing the chemical composition to use high-temperature alloys. This structural modification allows the attach layer to accommodate thermal expansion at lower, safer temperatures, maintaining TCE matching effectiveness while avoiding die damage from excessive heat.
3Strength
If continuous alloy layer is used for die attach, then bonding strength is maintained, but mechanical stress accumulates during thermal expansion
Solution Approach 1:
The continuous alloy layer is segmented into a patterned structure with voids, creating discrete regions that can expand independently. This segmentation maintains bonding strength at the die-attach and attach-substrate interfaces while allowing the intermediate regions to expand into voids, preventing stress accumulation.
Solution Approach 2:
Material is extracted from the continuous die attach layer to create voids, removing the portions that would generate stress during expansion. The remaining conductive material maintains bonding function while the extracted void spaces accommodate thermal expansion, reducing mechanical stress on the bonds.
4Reliability
If specialized metal alloys are used, then TCE matching is improved, but interfacial diffusion still occurs changing material properties
Solution Approach 1:
The porous structure with voids reduces the amount of conductive material in contact with interfacial metallization layers, decreasing the opportunity for interfacial diffusion. The voids act as physical barriers that limit diffusion pathways, maintaining alloy composition stability while preserving TCE matching properties.
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 reduces or eliminates mechanical stress and enhances bond reliability by accommodating thermal expansion and preventing interfacial diffusion, thereby improving the performance and longevity of semiconductor devices.
Implementation Method 1
the layer includes a plurality of voids providing space into which portions of the conductive material may thermally expand
Implementation Method 2
High operating temperatures may cause the die attach layer to interdiffuse with these surface metallization layers
Data Source
AI summary
A semiconductor die is attached to a packaging substrate by a patterned layer of conductive metal that includes voids. The voids provide a space into which the metal may expand when heated in order to avoid placing mechanical stress on the bonds caused by mismatches in the thermal coefficients of thermal expansion of the die, the conductive metal bond layer and the substrate. An additional coating of conductive metal may be flowed over the bond lines to reinforce the bonds.