Copper Pillar Bump Pad Structure for Compact, Reliable BAW Packaging
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Solution Overview
Problem
Conventional bulk acoustic wave (BAW) resonators in RF circuitry are large due to wirebond packages, consuming significant area and limiting the size reduction of RF circuitry in wireless communications devices.
Innovation Solution
A BAW device with wafer level packaging, featuring a substrate, reflector, piezoelectric layer, electrode layer, passivation layer, under-bump metallization layer, and copper pillar structure, where the passivation layer covers the electrode layer, the under-bump metallization layer extends over openings, and the copper pillar structure covers the entire under-bump metallization layer, enhancing the reliability of electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wirebond packages are used for BAW resonators, then the device can be manufactured with conventional processes, but the cross-sectional area becomes large
Solution Approach 1:
The patent transitions from wirebond packaging to wafer-level packaging with copper pillar structures, changing the dimensional approach from external wire connections to integrated vertical pillars. This allows the device to maintain manufacturability while significantly reducing the cross-sectional area by eliminating the need for external wirebond space.
2Area of stationary object
If the size of BAW resonators is reduced, then the overall size of RF circuitry is reduced, but the reliability of electrical connections deteriorates
Solution Approach 1:
The patent uses vertical copper pillar structures that extend upward from the wafer surface, transitioning from planar connection approaches to three-dimensional vertical connections. This allows reduced resonator size while maintaining connection reliability through the vertical dimension, with pillars providing robust mechanical and electrical pathways.
Solution Approach 2:
The patent employs composite material structures including copper pillars with underlying metallization layers and dielectric materials, combining materials with complementary properties. The copper provides excellent electrical conductivity and mechanical strength, while the composite structure ensures reliable electrical connections even in miniaturized devices.
3Reliability
If copper pillar structure is used to cover the entire under-bump metallization layer, then the reliability and lifespan of the device is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent incorporates the under-bump metallization layer and copper pillar structure as integral parts of the wafer fabrication process, performing connection structure formation in advance during wafer-level packaging. This preliminary action during manufacturing reduces assembly complexity and improves reliability by ensuring proper metallization coverage before device assembly.
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 design significantly improves the reliability and lifespan of BAW devices by creating robust and reliable electrical connections, reducing the overall size of RF circuitry and increasing its reliability compared to conventional designs.
Implementation Method 1
a piezoelectric layer on the reflector and including a first opening through which a portion of the reflector is exposed
Data Source
AI summary
A bulk acoustic wave (BAW) device includes a substrate, a reflector on the substrate, a piezoelectric layer on the reflector and including a first opening through which a portion of the reflector is exposed, an electrode layer on the portion of the reflector exposed through the first opening, a passivation layer on the piezoelectric layer and a portion of the electrode layer and including a second opening through which a portion of the electrode layer is exposed, an under-bump metallization layer on the portion of the electrode layer exposed through the second opening and extending over the second opening and the first opening on the passivation layer, and a copper pillar structure on the under-bump metallization layer such that the entirety of the under-bump metallization layer is covered by the copper pillar structure.