BAW Microresonator Package Cavity Layout for Frequency Stability
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Solution Overview
Problem
In existing semiconductor packages with Bulk Acoustic Wave (BAW) resonators, the glob top material often delaminates from the molding material during curing, leading to undesired stress and frequency shifts in BAW devices due to the encapsulating mold compound's influence on mechanical stress.
Innovation Solution
A semiconductor package design that includes a cavity created via laser ablation in the mold compound, allowing a stress-absorbing glob top material to be applied directly over the BAW device, isolating it from external stresses and vibrations, while the mold compound covers only parts of the package, avoiding direct contact with the glob top.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glob top material is applied over the BAW device in a molded package, then the BAW device is protected against contamination and mechanical stress, but the glob top material delaminates from the molding material during curing causing frequency shifts
Solution Approach 1:
The package structure is segmented into distinct regions: a molded compound covering the substrate and bond wires, and a separate glob top material covering only the BAW device. This segmentation is achieved by removing mold compound from a cavity region before applying the glob top material, creating a clear boundary between the two encapsulating materials that prevents delamination while maintaining protection.
Solution Approach 2:
The mold compound is extracted or removed from the cavity region where the BAW device will be positioned. This creates a void space that allows the glob top material to be applied directly over the BAW device without being in contact with the mold compound, eliminating the delamination problem while preserving the protective function.
2Reliability
If mold compound covers the entire package including over the BAW device, then complete encapsulation is achieved, but mechanical stress from the mold compound affects the BAW device frequency
Solution Approach 1:
The harmful mold compound is extracted or removed from the cavity region directly over the BAW device. This creates a stress-free zone where the glob top material provides encapsulation without the mechanical stress and vibrations that would be transmitted by the mold compound, thereby protecting the BAW device frequency stability.
Solution Approach 2:
Different regions of the package receive different encapsulating materials with different properties. The mold compound provides general protection for the substrate and bond wires, while the glob top material provides localized stress-free protection for the BAW device. This local differentiation of material properties addresses the specific needs of different components.
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 configuration improves frequency stability by isolating the BAW device from mechanical stress and vibrations, reducing frequency shifts and enhancing the overall performance of BAW resonators by using a low elastic modulus glob top material that is distinct from the mold compound.
Implementation Method 1
mold compound is removed to create a cavity via laser ablation prior the attachment and integration of a BAW die into the package
Implementation Method 2
BAW devices use a piezoelectric effect to convert electrical energy into mechanical energy resulting from an applied radio frequency (RF) voltage
Data Source
AI summary
A semiconductor package comprises a leadframe having a die attach pad and one or more leads and a semiconductor die electrically connected to the die attach pad. A BAW device is attached to the semiconductor die. A mold compound surrounds the first semiconductor die and covers portions of the leadframe and a first portion of a top surface of the semiconductor die. The mold compound has a cavity area. The mold compound does not cover the BAW device or a second portion of the top surface of the semiconductor die in the cavity area. A glob top material is disposed within the cavity area. The glob top material covers the BAW device and the second portion of the top of the semiconductor die.