Thermal Interface Material Compressive Stress for Semiconductor Lid
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Solution Overview
Problem
Thermal interface materials (TIM) between semiconductor chips and lids suffer from moisture and temperature-induced thermal degradation, leading to unreliable low-temperature operation and performance degradation due to uneven stress distribution and tearing during the curing process.
Innovation Solution
A method involving attaching a semiconductor chip to a substrate, applying TIM, and positioning a lid with a force applied to its distal ends to bow the center portion away from the chip, allowing the TIM to cure under increased temperature, then removing the force to create a structure with more compressive stress at the center, thereby offsetting tensile strain and enhancing thermal reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thermal interface material is applied between the chip and lid without pre-compression, then the assembly process is simple, but the TIM suffers from moisture and temperature-induced thermal degradation and tearing
Solution Approach 1:
The lid is pre-compressed during assembly to create compressive stress in the TIM before the package is subjected to thermal and moisture environments. This preliminary compression prevents TIM degradation and tearing during subsequent thermal cycling and curing processes.
Solution Approach 2:
Compressive stress is applied to the TIM in advance to counteract the tensile strains that would otherwise occur during thermal expansion and die flattening. This preliminary anti-action prevents TIM failure before it can occur during normal operation.
2Device complexity
If the lid is rigid and flat, then the structure is simple, but the TIM experiences uneven stress distribution and tearing during curing
Solution Approach 1:
The lid is designed with a bowed or curved configuration rather than being perfectly flat. This curvature allows the lid to apply more uniform compressive stress across the TIM during assembly and curing, preventing stress concentration and tearing while maintaining structural integrity.
3Strength
If the TIM is compressed uniformly across the entire surface, then the thermal contact is improved, but the center portion experiences excessive compression and potential failure
Solution Approach 1:
The lid applies different levels of compression to different regions of the TIM. The bowed lid configuration provides greater compression at the edges and less compression at the center, creating a non-uniform stress distribution that prevents TIM failure while maintaining adequate thermal contact across the interface.
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 prevents thermal degradation by maintaining compressive stress in the TIM, ensuring reliable low-temperature operation and improved thermal performance across various stress conditions, including temperature fluctuations and humidity.
Implementation Method 1
the center portion of the thermal interface material comprises more compressive stress relative to compressive stress at the end portions of the thermal interface material
Implementation Method 2
the temperature of the assembly is increased in this position thus allowing the seal and thermal TIM to cure into a solid or gel-like material
Implementation Method 3
the method removes the force from the distal ends of the lid to cause the center portion of the lid to return to a position closer to the semiconductor chip
Data Source
AI summary
A method attaches a semiconductor chip to a substrate, applies a thermal interface material to a top of the semiconductor chip, and positions a lid over the semiconductor chip typically attached to the substrate with an adhesive. The method applies a force near the distal ends of the lid or substrate to cause a center portion of the lid or substrate to bow away from the semiconductor chip and increases the central thickness of the thermal interface material prior to curing. While the center portion of the lid or substrate is bowed away from the semiconductor chip, the thermal interface material method increases the temperature of the assembly, thus curing the thermal interface material and lid adhesive. After the thermal interface material has and adhesive have cured, the method removes the force from near the distal ends of the lid or substrate to cause the center portion of the lid to return to a position closer to the semiconductor chip, creating a residual compressive stress in the thermal interface material thus improving thermal performance and thermal reliability.