Co-axial BGA Interconnect for Crosstalk Reduction
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Solution Overview
Problem
Conventional semiconductor packages with small solder ball-grid-array (BGA) pitch dimensions suffer from increased crosstalk coupling for high-speed I/O signals, leading to package footprint expansion and inhibited miniaturization, especially for signals above 20 Gbps.
Innovation Solution
The implementation of a semiconductor package with a co-axial BGA interconnect design, where a solder ball is surrounded by a conductive wall and metal shield, reducing the need for stacked or staggered micro-vias and minimizing crosstalk by directly connecting to inner PCB layers, and repurposing Vss BGAs as signal BGAs to reduce footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the solder ball-grid-array (BGA) pitch dimension is reduced to achieve package footprint reduction, then the package area is reduced, but the crosstalk coupling increases significantly for high-speed I/O signals
Solution Approach 1:
A co-axial conductive structure comprising a conductive wall and a metal shield is introduced as an intermediary between adjacent solder balls. The conductive wall is positioned between neighboring solder balls and the metal shield surrounds the solder ball, creating a shielding barrier that reduces electromagnetic coupling between adjacent high-speed signal paths while maintaining the reduced pitch dimension
Solution Approach 2:
The shielding structure is applied locally around each high-speed I/O solder ball rather than uniformly across the entire package. The co-axial configuration with conductive wall and metal shield creates localized electromagnetic isolation zones around critical signal paths, reducing crosstalk without requiring blanket shielding that would increase overall package size
2Object-affected harmful factors
If more Vss BGAs are introduced to serve as shielding and current return path for high-speed I/O signals, then the crosstalk coupling is reduced, but the package footprint and platform form-factor expand
Solution Approach 1:
The co-axial conductive structure serves multiple functions simultaneously: the conductive wall and metal shield provide electromagnetic shielding to reduce crosstalk, while also serving as current return paths for the high-speed signals. This multi-functionality eliminates the need for separate dedicated ground BGAs, reducing their number by up to 30% while maintaining shielding effectiveness
Solution Approach 2:
The shielding function and current return path function are merged into the same co-axial conductive structure. The conductive wall and metal shield that provide electromagnetic isolation also conduct the return current, combining what were previously separate functions performed by distinct ground BGAs into an integrated structure around each signal ball
Data Source
AI summary
According to various examples, a device is described. The device may include a printed circuit board. The device may also include a first recess in the printed circuit board, wherein the first recess comprises a circular side surface and a bottom surface. The device may also include a first solder ball disposed in the first recess. The device may also include a first conductive wall positioned behind the circular side surface of the first recess, wherein the first conductive wall surrounds a side surface of the first solder ball.