RF Wafer Packaging Without Silicon Handle Substrate
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Solution Overview
Problem
Conventional silicon handle substrates for RF devices suffer from harmonic distortion and low resistivity, leading to inadequate thermal and electrical performance, particularly due to increased heat generation and densely integrated high-speed transistors.
Innovation Solution
A radio frequency (RF) device with enhanced thermal and electrical performance is achieved through a wafer-level packaging process using a Si—SiGe—Si structure, where a second mold compound without silicon material is applied over the active layer, and a first mold compound encapsulates bump structures, both with high thermal conductivity and low dielectric constant, to improve heat dissipation and reduce harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional silicon handle substrates are used for RF device fabrication, then manufacturing cost is reduced and production capacity is increased, but thermal performance deteriorates and harmonic distortion increases
Solution Approach 1:
The patent removes the silicon handle substrate from the RF device structure, retaining only the active device layer and back-end-of-line (BEOL) structures. This extraction eliminates the source of harmonic distortion while preserving the beneficial low-cost silicon fabrication process. The removed silicon substrate is replaced with a support structure that provides mechanical strength without the detrimental electrical properties.
Solution Approach 2:
The patent employs a composite structure combining the silicon active device layer with a non-silicon support structure and mold compound. This composite approach allows the device to benefit from silicon's excellent semiconductor properties while avoiding its harmful thermal and electrical characteristics. The mold compound with high thermal conductivity (greater than 1 W/m·K) compensates for the removed substrate's thermal management function.
2Ease of manufacture
If conventional silicon handle substrates are used for RF device fabrication, then manufacturing cost is reduced and production capacity is increased, but electrical performance deteriorates due to low resistivity
Solution Approach 1:
The silicon handle substrate is completely removed from the structure, eliminating the source of low resistivity and associated electrical performance degradation. The extraction leaves only the necessary active device regions while removing the problematic bulk silicon that causes harmonic distortion and resistivity issues.
Solution Approach 2:
A non-silicon support structure and mold compound serve as intermediaries to provide the mechanical support previously given by the silicon substrate. These materials have high resistivity and do not generate harmonic distortion, while still allowing the silicon active layer to function properly. The mold compound with dielectric constant less than 8 provides electrical isolation and support without interfering with device performance.
3Productivity
If densely integrated high-speed transistors are used to increase functionality, then device capability is improved, but heat generation increases significantly
Solution Approach 1:
The patent converts the harmful heat generation from densely integrated transistors into a manageable thermal conduction problem. By using a mold compound with high thermal conductivity (greater than 1 W/m·K), the heat generated by the transistors is efficiently conducted away from the active regions. The thermal pathways are designed to redirect heat flow from the heat-generating transistors through the mold compound to external heat sinks.
4Temperature
If silicon handle substrate is removed to improve thermal and electrical performance, then thermal conductivity and resistivity are improved, but structural support is reduced
Solution Approach 1:
The patent creates a composite structure where the non-silicon support structure and mold compound provide mechanical strength to replace the removed silicon substrate. The mold compound with high thermal conductivity serves dual functions: providing structural support and enabling efficient heat dissipation. This composite approach allows the device to achieve both improved thermal performance and adequate mechanical strength.
Solution Approach 2:
The patent changes the physical parameters of the support materials, specifically selecting a mold compound with high thermal conductivity (greater than 1 W/m·K) and low dielectric constant (less than 8). These parameter changes ensure that the replacement structure provides both mechanical support and superior thermal management compared to the original silicon substrate.
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 solution effectively enhances thermal and electrical performance of RF devices by improving heat dissipation and reducing harmonic distortion without increasing package size, addressing the limitations of conventional silicon handle substrates.
Implementation Method 1
both with high thermal conductivity and low dielectric constant, to improve heat dissipation
Data Source
AI summary
The present disclosure relates to a radio frequency device that includes a device region with a back-end-of-line (BEOL) portion and a front-end-of-line (FEOL) portion, first bump structures, a first mold compound, and a second mold compound. The FEOL portion includes an active layer, a contact layer, and isolation sections. Herein, the active layer and the isolation sections reside over the contact layer, and the active layer is surrounded by the isolation sections. The BEOL portion is formed underneath the FEOL portion, and the first bump structures and the first mold compound are formed underneath the BEOL portion. Each first bump structure is partially encapsulated by the first mold compound, and electrically coupled to the FEOL portion via connecting layers within the BEOL portion. The second mold compound resides over the active layer without a silicon material, which has a resistivity between 5 Ohm-cm and 30000 Ohm-cm, in between.