Ground Ring Shielding for Crosstalk-Free WLCSP
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Solution Overview
Problem
High-frequency semiconductor devices face crosstalk issues due to unwanted noise propagation between transmission lines, which increases with signal frequency, affecting the electromagnetic compatibility of chip scale packages (CSPs).
Innovation Solution
A crosstalk-free CSP structure is achieved by forming signal pins on a semiconductor substrate with circuitry, encircling them with a ground ring, and coupling the ground ring to a grounded solder ball, effectively shielding the signal pins from interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the package size is decreased to achieve chip scale packaging, then the area occupied by the package is reduced, but the crosstalk between pins increases due to closer spacing
Solution Approach 1:
A ground ring is introduced as an intermediary structure between adjacent signal pins. This ground ring acts as a shielding barrier that intercepts and redirects electromagnetic fields, preventing direct coupling between neighboring pins. The ground ring is connected to ground through via holes, creating an equipotential barrier that reduces capacitive and inductive coupling effects between adjacent signal traces.
Solution Approach 2:
The ground ring is positioned specifically around each signal pin location, creating localized electromagnetic shielding zones. This local grounding approach provides targeted crosstalk reduction at critical pin locations without requiring a complete ground plane, thereby maintaining compact package size while addressing the harmful electromagnetic interference locally where it occurs.
2Speed
If signal frequency is increased to achieve higher processing speeds, then the operating speed of the device is improved, but the crosstalk between pins increases proportionally
Solution Approach 1:
The ground ring serves as a frequency-independent shielding structure that effectively reduces crosstalk across a broad frequency range. By providing a low-impedance path to ground at the signal frequency and its harmonics, the ground ring structure maintains its effectiveness even as operating frequencies increase to gigahertz ranges, enabling high-speed operation without proportional increase in crosstalk.
3Device complexity
If traditional pin arrangements are used without ground rings, then the device complexity is reduced, but electromagnetic compatibility deteriorates due to crosstalk
Solution Approach 1:
The ground ring structure is integrated into the existing pin array configuration without requiring fundamental changes to the pin arrangement pattern. The ground rings are formed in the same metal layers as the signal traces, using standard photolithography and electroplating processes, thus adding minimal manufacturing complexity while dramatically improving electromagnetic compatibility and reducing crosstalk between adjacent pins.
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 significantly reduces crosstalk, as demonstrated by a decrease in the s-parameter S21 from -34 dB to -57 dB at 5 GHz, ensuring system stability even at high frequencies.
Implementation Method 1
encircling the signal pin with a ground ring
Data Source
AI summary
A structure, a system, and a method for manufacture of crosstalk-free wafer level chip scale packaging (WLCSP) structure for high frequency applications is provided. An illustrative embodiment comprises a substrate on which various layers and structures form circuitry, a signal pin formed on the substrate and coupled with the circuitry, a ground ring encircling the signal pin, and a grounded solder bump coupled to the ground ring.