Dual-Sided PCB Post-Bump Structure for Fine-Pitch Reliability
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Solution Overview
Problem
Existing package substrates face limitations in responding to fine pitches and are prone to issues like solder cracks, bridges, and collapse due to the use of solder balls, which also result in warpage and reduced reliability.
Innovation Solution
A printed circuit board with post bumps on both sides, where each device is mounted on both surfaces, and a molding layer is used to maintain balance, allowing for improved connection reliability and heat dissipation, and eliminating the need for separate seed layers for electroplating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder balls are used to connect substrates, then connection is achieved, but fine pitch response is limited and reliability deteriorates due to solder cracks, bridges, and collapse
Solution Approach 1:
The patent changes the connection structure from spherical solder balls to cylindrical post bumps with enlarged cross-sectional areas. This parameter change in shape and dimensions improves both fine pitch response and connection reliability by providing a larger bonding area and better mechanical strength without the defects associated with solder balls
Solution Approach 2:
The patent extracts and eliminates the solder ball component entirely, replacing it with a post bump structure that integrates the connection function directly into the substrate assembly. This removal of the separate solder ball element prevents solder-related defects while maintaining connection functionality
2Stability of the object's composition
If devices are mounted on both surfaces with molding layers, then warpage is minimized and balance is maintained, but device complexity increases
Solution Approach 1:
The patent employs asymmetric molding layer configuration where molding layers are selectively applied to specific surfaces based on device distribution. This asymmetric approach maintains structural balance and minimizes warpage by compensating for uneven device placement without requiring symmetric molding on both sides, thus avoiding unnecessary complexity
Solution Approach 2:
The molding layers serve multiple functions simultaneously: they provide structural support, maintain substrate balance, enable device mounting surfaces, and facilitate heat dissipation. This multi-functionality reduces the need for additional separate components, thereby managing complexity while achieving warpage control
3Reliability
If post bumps are used instead of solder balls, then fine pitch response improves and reliability enhances, but manufacturing process complexity increases
Solution Approach 1:
The patent merges the post bump formation process with the existing substrate manufacturing process. The post bumps are formed as integral parts of the substrate through the same molding and processing steps used for the substrate itself, eliminating the need for separate post bump fabrication and assembly operations. This integration maintains manufacturing simplicity while achieving improved connection reliability
Data Source
AI summary
A printed circuit board according to an embodiment includes an insulating layer; a first pad disposed on an upper surface of the insulating layer; a second pad disposed on a lower surface of the insulating layer; a first device mounted on the first pad; a second device mounted on the second pad; a first molding layer disposed on the insulating layer and molding the first device; and a second molding layer disposed on the lower surface of the insulating layer and molding the second device, wherein a lower surface of the second molding layer is positioned on the same plane as a lower surface of the second device.