Elastic Layer Decouples Stress in Cavity Package Molding
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Solution Overview
Problem
Conventional RF filter devices face hermetic seal breaches and solder joint failures due to stress exerted by molding compounds caused by thermal expansion differences and mechanical shocks, which compromise the integrity of cavity packages.
Innovation Solution
Incorporating an elastic layer between the cavity package and the molding compound to decouple stress, reducing the forces applied to the cavity package and maintaining the hermetic seal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cavity package is hermetically sealed and overmolded with epoxy molding compound, then the device provides protection and handling surface, but environmental factors cause stress that pulls the cavity package apart at its seal-ring
Solution Approach 1:
A compliant layer is introduced between the molding compound and the cavity package as an intermediary element. This layer absorbs and distributes the stress generated by thermal expansion differences and mechanical shocks, preventing direct transmission of forces to the seal-ring and solder joints, thereby maintaining hermetic seal integrity while accommodating environmental stressors.
Solution Approach 2:
The invention changes the mechanical parameter of the packaging structure by introducing a layer with different compliance characteristics. The compliant layer has higher elasticity and lower modulus compared to both the molding compound and the cavity package, allowing it to deform and absorb stress, thus resolving the contradiction between maintaining seal integrity and withstanding external forces.
2Adaptability or versatility
If different materials are used for cavity package and molding compound, then manufacturing flexibility is improved, but different CTE causes thermal expansion differences that exert stress on the cavity package
Solution Approach 1:
The compliant layer serves as a stress-absorbing intermediary between materials with different CTE values. It decouples the thermal expansion stresses generated by the mismatch between the cavity package and molding compound, allowing each material to expand and contract at its own rate without transmitting excessive stress to the cavity package structure.
3Ease of manufacture
If the cavity package is flip-chipped onto PCB and overmolded, then device integration is improved, but solder joints joining cavity package to PCB may break under stress
Solution Approach 1:
The compliant layer is applied beforehand to the cavity package before mounting and overmolding. This pre-applied cushioning layer is designed to absorb and distribute mechanical stresses and thermal expansion forces, protecting the solder joints from excessive forces that could cause failure during subsequent handling, thermal cycling, or mechanical shocks.
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 elastic layer effectively reduces stress on the cavity package, preventing seal-ring separation and solder joint failures, thereby enhancing the reliability and hermeticity of the packaged devices.
Implementation Method 1
an elastic layer formed over a top surface of the cavity package... The elastic layer is applied to the top surface of the cavity package, which reduces forces exerted on the cavity package by the molding compound under stress
Implementation Method 2
the different materials used for the cavity package and the molding compound typically have different coefficients of thermal expansion (CTE), resulting in different rates of expansion and contraction in response to temperature changes
Data Source
AI summary
A device includes a substrate; a cavity package having a first surface attached to the substrate, the cavity package enclosing an electronic circuit; an elastic layer formed on a second surface of the cavity package, opposite the first surface; and a molding compound formed on the substrate, encasing the cavity package and the elastic layer. The elastic layer decouples stress between the cavity package and the molding compound encasing the cavity package, for maintaining structural integrity of the cavity package and for preventing separation of the cavity package from the substrate.