Outer-Layer Copper Smoothing for RF Packaging Substrates
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Solution Overview
Problem
In electronics packaging, copper surfaces on outer layers of substrates are often too rough, affecting mechanical adhesion but not adequately smoothed by existing treatments like CZ8401+OAP, which have poor adhesion to solder mask after thermal processing, leading to reduced peel strength and suboptimal electrical performance.
Innovation Solution
Applying a protective coating such as Organic Solderability Preservative (OSP) or Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) to radio-frequency circuits and components like wire bond pads and flip chip bump pads on the outer layers to reduce surface roughness and enhance adhesion without covering RF critical circuits with solder resist.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing treatments like CZ8401+OAP are applied to copper surfaces, then surface roughness is reduced, but adhesion to solder mask deteriorates after thermal processing
Solution Approach 1:
The patent changes the chemical composition parameters of the protective coating by replacing traditional CZ8401+OAP treatments with OSP or ENEPIG coatings. This parameter change maintains surface smoothness (Ra 0.3-0.4 μm) while improving thermal stability and adhesion properties after reflow processing.
Solution Approach 2:
The patent employs composite material structures: OSP provides a organic protective layer with good adhesion, while ENEPIG creates a multi-layer inorganic composite (Ni-P alloy + Pd + Au) that combines smooth surface properties with excellent solder mask adhesion and thermal stability.
2Strength
If copper surfaces are left rough, then mechanical adhesion is improved, but electrical performance deteriorates
Solution Approach 1:
The patent applies different surface treatments to different functional areas: OSP or ENEPIG coatings are applied to RF circuit areas requiring smooth surfaces for electrical performance, while maintaining adequate adhesion through the chemical composition of these coatings.
Solution Approach 2:
The patent optimizes the surface roughness parameter to a specific range (Ra 0.3-0.4 μm) that balances both mechanical adhesion and electrical performance requirements, rather than maximizing roughness for adhesion alone.
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 achieves a smoother copper surface with a roughness average of 0.3-0.4 μm, improving electrical signal transmission and mechanical adhesion while maintaining compact module thickness without adding extra layers, thus enhancing the performance of radio-frequency front-end module products.
Implementation Method 1
a protective coating configured to reduce surface roughness of the outer layer
Implementation Method 2
improving electrical signal transmission and mechanical adhesion
Data Source
AI summary
According to certain aspects, a packaging substrate can include a plurality of layers including an outer layer, and one or more components on a surface of the outer layer. The one or more components can include a radio-frequency circuit, where the radio-frequency circuit is covered by a protective coating configured to reduce surface roughness of the outer layer and not covered by solder resist.