RFIC Plating Reducing RF Loss via On-Die Passive Placement
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Solution Overview
Problem
The increasing cost of gold in nickel/gold (Ni/Au) surface plating for RFICs leads to higher packaging costs, and the alternative nickel/palladium/gold (Ni/Pd/Au) plating results in increased radio frequency (RF) signal losses due to higher sheet resistance and ferromagnetic effects, impacting product performance and yield.
Innovation Solution
Implementing a thinner gold layer in the Ni/Pd/Au surface plating and reconfiguring the solder mask to exclude plating on trace edges and sidewalls, as well as strategically placing on-die passive devices in the RF upper path to reduce RF signal losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Ni/Pd/Au surface plating is used to reduce gold cost, then packaging cost is reduced, but RF signal loss increases due to higher sheet resistance
Solution Approach 1:
The patent applies different plating configurations to different areas of the substrate. Wire bond pads use Ni/Pd/Au plating to reduce cost, while RF traces and bonding pads use Ni/Au plating to maintain low RF loss. This local differentiation allows the system to achieve cost reduction in non-critical areas while preserving signal integrity in critical RF paths.
Solution Approach 2:
The patent segments the substrate into different functional zones with different plating requirements. The wire bond area is separated from the RF signal area, allowing independent optimization of each zone. The solder mask is configured to expose only wire bond pads for Ni/Pd/Au plating while keeping RF traces covered, creating distinct plating regions.
2Ease of manufacture
If Ni/Pd/Au plating is applied to trace edges and sidewalls, then wire bondability is improved, but RF current loss increases due to skin effect and eddy current effect
Solution Approach 1:
The solder mask is configured to create different plating conditions for different areas. Wire bond pads have exposed edges and sidewalls that receive Ni/Pd/Au plating for good wire bondability, while RF traces are covered by the solder mask preventing plating on their edges and sidewalls, thus maintaining low RF loss by allowing RF current to flow on the copper surface.
Solution Approach 2:
The solder mask acts as an intermediary that controls which areas receive plating. By strategically positioning the solder mask to cover RF trace edges and sidewalls while exposing wire bond pad edges and sidewalls, it mediates between the conflicting requirements of wire bondability and RF signal integrity.
3Adaptability or versatility
If on-die passive devices are connected through bonding pads, then circuit functionality is achieved, but RF signal loss increases due to high RF loss bonding pad
Solution Approach 1:
The patent applies different plating materials to different circuit elements based on their functional requirements. On-die passive devices (capacitors, inductors, resistors) are connected through bonding pads that use Ni/Au plating to minimize RF loss, while wire bond pads use Ni/Pd/Au plating for cost efficiency and wire bondability. This local material differentiation optimizes both functionality and performance.
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 solution reduces RF signal losses by minimizing the path for RF current through high-resistance areas, thereby improving product performance and yield while maintaining lower packaging costs.
Implementation Method 1
Due to the skin effect and eddy current effect on the RF current traveling through the plated wire-bonding areas
Implementation Method 2
Due to the skin effect and eddy current effect on the RF current traveling through the plated wire-bonding areas
Implementation Method 3
The copper trace edges and sidewalls free from the Ni/Pd/Au plating around the wire-bonding areas provide a low resistive path for the RF current
Implementation Method 4
Ni/Pd/Au has a much higher radio frequency sheet resistance than Ni/Au due to thin palladium and gold layers and the ferromagnetic nature of nickel
Data Source
AI summary
To reduce the radio frequency (RF) losses associated with high RF loss plating, such as, for example, Nickel/Palladium/Gold (Ni/Pd/Au) plating, an on-die passive device, such as a capacitor, resistor, or inductor, associated with a radio frequency integrated circuit (RFIC) is placed in an RF upper signal path with respect to the RF signal output of the RFIC. By placing the on-die passive device in the RF upper signal path, the RF current does not directly pass through the high RF loss plating material of the passive device bonding pad.