Multi-Chip Package Heat Spreader Bonding for Lower Thermal Resistance
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Solution Overview
Problem
Multi-chip IC packages face challenges with structural/mechanical strength and thermal performance due to thin metallization layers and poor thermal conductivity between IC chips, leading to hot spots and difficulty in interconnection with host substrates.
Innovation Solution
A bonded integrated heat spreader is directly attached to each IC chip using a thin bond line, enhancing mechanical strength and thermal conductivity, and interconnected through redistribution layers on a sacrificial interposer, which is later removed to expose the RDL structure for further interconnect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple IC chips are assembled into a multi-chip unit with thin metallization layers for electrical interconnection, then integration density and electrical connectivity are improved, but structural/mechanical strength deteriorates due to thin film materials being prone to cracking
Solution Approach 1:
A sacrificial interposer is introduced as a temporary intermediary structure during the assembly process. The interposer provides mechanical support and enables precise alignment of multiple IC chips and redistribution layers. After assembly, the interposer is selectively removed to expose the RDL structure for further interconnect formation, having served its mediating function during the critical assembly phase.
Solution Approach 2:
The sacrificial interposer is prepared in advance with all necessary redistribution layers and interconnect structures before the IC chips are attached. This preliminary preparation ensures that the thin metallization layers are already in place and properly positioned, allowing the chips to be interconnected without requiring subsequent manipulation of the fragile thin films.
2Productivity
If multiple IC chips are assembled into a multi-chip unit, then functional integration is improved, but thermal performance deteriorates due to poor thermal conductivity in regions between individual IC chips
Solution Approach 1:
The sacrificial interposer serves as a thermal intermediary during assembly, providing a thermally conductive pathway between chips. After the interposer is removed, the exposed RDL structure and bonding interfaces create direct thermal paths between the IC chips, eliminating the thermal resistance that would exist with traditional mold materials filling the gaps between chips.
Solution Approach 2:
The interposer and RDL structure provide locally optimized thermal conduction pathways at the interfaces between IC chips. Rather than relying on bulk mold material with poor thermal conductivity, the design creates high-quality thermal contact regions where heat can efficiently transfer from one chip to another through the metallization layers and bonding interfaces.
3Adaptability or versatility
If IC chips of differing thicknesses are assembled into a multi-chip unit, then design flexibility is improved, but thermal conduction deteriorates due to increased material of poor thermal conductivity between chips and thermal solutions
Solution Approach 1:
The sacrificial interposer acts as a thickness-compensating intermediary during assembly. It provides a uniform reference plane that allows IC chips of varying thicknesses to be positioned and bonded accurately. The interposer's structure absorbs the thickness variations, enabling all chips to be aligned properly with the RDL and thermal solutions without requiring excessive amounts of low-conductivity mold material.
Solution Approach 2:
The interposer is prepared in advance with built-in compensation for expected thickness variations among different IC chips. This preliminary action ensures that when chips are attached, the thermal interface materials and heat spreaders can make optimal contact with all chips simultaneously, minimizing the total thickness of poor-conductivity materials in the thermal path.
4Temperature
If a bonded integrated heat spreader is directly attached to each IC chip using a thin bond line, then thermal conductivity is improved, but manufacturing complexity increases
Solution Approach 1:
The sacrificial interposer serves as a mediating structure that enables thin bond lines between the heat spreader and IC chips. During assembly, the interposer provides a stable platform for positioning and bonding. After removal, it leaves behind precisely positioned bonding interfaces that maintain the thin bond line geometry, achieving excellent thermal contact without requiring complex direct bonding equipment or processes.
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 improves both mechanical and thermal performance by providing a robust and efficient heat dissipation mechanism, reducing hot spots and enhancing the structural integrity of multi-chip units.
Implementation Method 1
thermal performance because, compared to a monolithic IC chip, the various small IC chips assembled together are less capable of spreading heat across the assembly due, at least in part, to relatively poor thermal conductivity in regions between the individual IC chips
Data Source
AI summary
A multi-chip unit suitable for chip-level packaging may include multiple IC chips that are interconnected through a metal redistribution structure, and that are directly bonded to an integrated heat spreader. Bonding of the integrated heat spreader to the multiple IC chips may be direct so that no thermal interface material (TIM) is needed, resulting in a reduced bond line thickness (BLT) and lower thermal resistance. The integrated heat spreader may further serve as a structural member of the multi-chip unit, allowing a second side of the redistribution structure to be further interconnected to a host by solder interconnects. The redistribution structure may be fabricated on a sacrificial interposer that may facilitate planarizing IC chips of differing thickness prior to bonding the heat spreader. The sacrificial interposer may be removed to expose the RDL for further interconnection to a substrate without the use of through-substrate vias.