Stacked Die Structure With Copper-Topped Lower Die
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Solution Overview
Problem
Copper-topped dies cannot be used as underlying dies in stacked die structures due to shorting issues, and existing solutions with insulating sheets provide poor mechanical stability.
Innovation Solution
A stacked die structure that includes a copper-topped lower die with a planarized non-conductive layer, such as benzocyclobutene, between the copper traces and conductive covers, and an adhesive layer for attaching an upper die, providing greater mechanical stability and electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If copper-topped die is used as underlying die in stacked structure, then electrical resistance is reduced, but shorting occurs between copper traces and upper die
Solution Approach 1:
A planarized non-conductive layer (such as benzocyclobutene) is introduced as an intermediary between the copper traces and the upper die. This layer provides electrical isolation to prevent shorting while maintaining the low resistance benefits of copper interconnects. The non-conductive layer is deposited over the copper traces and then planarized to provide a flat surface for subsequent bonding operations.
2Reliability
If insulating sheet is used to prevent shorting, then electrical isolation is provided, but mechanical stability deteriorates
Solution Approach 1:
The patent changes the physical and chemical parameters of the non-conductive layer by selecting materials with appropriate mechanical properties (such as benzocyclobutene) and controlling deposition parameters. The layer is formed with sufficient thickness and adhesion to provide both electrical isolation and mechanical stability, replacing the problematic insulating sheet with a more robust integrated layer.
3Reliability
If non-conductive layer is added for electrical isolation, then shorting is prevented, but device complexity increases
Solution Approach 1:
The non-conductive layer is merged with existing planarization layers in the stacking process. The layer serves multiple functions: electrical isolation, mechanical support, and planarization surface. By combining these functions into a single integrated layer rather than separate components, the structural complexity is minimized while achieving the required electrical isolation.
4Ease of operation
If copper traces are exposed for wire bonding, then electrical connection is enabled, but environmental protection is compromised
Solution Approach 1:
The non-conductive layer is applied selectively to areas where electrical isolation is needed while leaving copper bonding pads exposed for wire bonding. This local differentiation allows the structure to simultaneously provide environmental protection for the copper traces and maintain wire bonding capability at specific locations. The layer is deposited conformally and then patterned or planarized to expose only the necessary bonding areas.
Data Source
AI summary
A copper-topped die, which has exposed copper lines and pads, is utilized as the lower die in a stacked die structure. A non-conductive material is formed over the lower copper-topped die, and then selectively removed so that the non-conductive material covers and lies between the copper lines while none of the non-conductive material lies over the copper pads. An upper die is then attached to the non-conductive material.