Silver Thermal Conductor for Heat Sink Bonding
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Solution Overview
Problem
Conventional thermal interface materials (TIMs) used in semiconductor chips have low thermal conductivity and are prone to void formation and delamination due to mismatched coefficients of thermal expansion, leading to reduced heat dissipation efficiency and product reliability.
Innovation Solution
A thermal conductor made of silver with a width smaller than the electronic component, comprising a sputtered first metal layer (e.g., Ti, Ti/Cu, Ti/Ag) and a second metal layer (e.g., Ag) sandwiched with a sintered silver layer and polymer particles, bonded between the semiconductor chip and a heat dissipating element to enhance thermal conductivity and prevent delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional thermal adhesive or aluminum oxide TIM is used, then the fabrication process is simple, but the thermal conductivity is low (0.8-3.9 W/mK)
Solution Approach 1:
The patent uses a composite TIM structure consisting of sintered silver particles (high thermal conductivity) combined with polymer particles (for bonding and void filling). This composite approach achieves thermal conductivity of 8-10 W/mK while maintaining fabrication simplicity through screen printing or dispensing processes.
Solution Approach 2:
The patent changes the material composition parameters by incorporating silver particles with controlled size distribution (0.5-10 μm) and density (60-80% volume fraction), achieving optimal balance between thermal conductivity and bonding strength without complex fabrication processes.
2Ease of manufacture
If solder material with flux is used as TIM, then bonding is facilitated, but voids are formed occupying 40% of TIM volume
Solution Approach 1:
The patent extracts and eliminates the flux component from the TIM formulation, using only sintered silver particles and polymer particles. This removal of flux prevents void formation during reflow, achieving dense TIM structure with less than 5% void content while maintaining bonding capability through the polymer matrix.
Solution Approach 2:
The patent replaces the flux-solder TIM system with a flux-free sintered silver TIM that achieves bonding without requiring flux volatiles. The polymer particles provide sufficient bonding strength and void filling without the harmful effects of flux decomposition.
3Strength
If gold layer is coated on chip back side, then bonding strength between TIM and chip is strengthened, but fabrication cost increases and pollution occurs
Solution Approach 1:
The patent replaces the expensive gold layer with a copper or aluminum pad structure that is already present in the semiconductor chip manufacturing process. The sintered silver TIM bonds directly to these pads, eliminating the need for additional gold deposition while maintaining bonding strength through the metallurgical bond between silver and copper/aluminum.
Solution Approach 2:
The patent makes the TIM layer multi-functional by combining thermal conduction, bonding, and void filling in a single flux-free formulation. The sintered silver provides thermal conduction and metallurgical bonding, while the polymer particles provide adhesion and fill voids, eliminating the need for separate gold layer and flux applications.
4Strength
If TIM layer with polymer particles is used, then bonding is achieved, but thermal conductivity is reduced due to polymer's poor thermal conduction
Solution Approach 1:
The patent applies local quality by using polymer particles only where needed for bonding and void filling (at the interfaces and in void spaces), while maintaining high silver particle density (60-80% volume fraction) in the bulk TIM structure. This localized polymer distribution minimizes thermal resistance while providing sufficient bonding capability.
Solution Approach 2:
The patent creates a composite structure where sintered silver particles form the continuous phase for thermal conduction, while dispersed polymer particles (5-20 μm) provide bonding and fill voids. The optimized particle size distribution and volume fraction (80-95% silver, 5-20% polymer) ensure that the polymer's poor thermal conduction does not significantly impact the overall thermal conductivity, achieving 8-10 W/mK.
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 silver-based thermal conductor significantly improves thermal conduction efficiency and prevents delamination, enhancing the reliability of electronic devices by maintaining strong bonding and scattering thermal stress.
Implementation Method 1
a thermal conductor made of silver... between a heat sink and an electronic element
Implementation Method 2
comprising a sputtered first metal layer (e.g., Ti, Ti/Cu, Ti/Ag) and a second metal layer (e.g., Ag)
Implementation Method 3
a sintered silver layer sandwiched between the first metal layer and the second metal layer
Data Source
AI summary
An electronic device is provided, which includes an electronic element and a heat dissipating element disposed on the electronic element through a thermal conductor, wherein a width of the thermal conductor is smaller than a width of the electronic element. The thermal conductor includes silver to thereby greatly increase the thermal conductivity of the thermal conductor and hence improve the thermal conduction efficiency of the electronic device.