Backside RDL Warpage Control for TSV 3D IC Stacks
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Solution Overview
Problem
The mass reflow process for flip-chip attachment of large thin dies with through-silicon-vias (TSVs) in 3D IC stacks often results in warpage control issues, particularly on the backside of thinned TSV dies, which can prevent top die attachment due to non-flat surfaces required for micropillars interconnects, and this problem worsens with higher back-end-of-line (BEOL) layers.
Innovation Solution
A method and device that form a network of redistribution layer (RDL) lines on the backside of thinned TSV dies with under bump metal (UBM) structures to control warpage, using copper (Cu) RDL lines with high compressive stress and UBM capture pads, which are formed simultaneously to ensure a flat surface for top die attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mass reflow process is used for flip-chip attachment, then throughput is improved, but warpage control deteriorates
Solution Approach 1:
The patent applies preliminary action by forming RDL lines with high compressive stress on the backside of the TSV die before the flip-chip attachment process. This pre-applied compressive stress counteracts the tensile stress that develops during subsequent mass reflow processing, thereby maintaining warpage control while enabling high-volume throughput production
2Adaptability or versatility
If number of BEOL layers is increased, then functionality is improved, but warpage severity increases
Solution Approach 1:
The patent applies local quality by concentrating the stress compensation function specifically on the backside of the TSV die through localized RDL line formation. This localized compressive stress structure addresses the warpage issue caused by multiple BEOL layers without requiring changes to the front-side functionality or interconnect architecture
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
The RDL structure effectively controls warpage on the backside of TSV dies, ensuring a near-flat surface for top die attachment and reducing the need for additional process steps, enhancing the packaging of TSV dies in 3D IC stacks.
Implementation Method 1
forming the RDL lines with a high compressive stress
Data Source
AI summary
A method of forming a network of RDL lines on the backside of a thinned TSV die to control warpage and the resulting device are provided. Embodiments include providing a thinned TSV die of a 3D IC stack, the thinned TSV die having a front side and a back side; forming a plurality of RDL lines across the backside of the die; and forming a plurality of UBM structures across the backside of the die.