PCB Pad Stack Structure for Etch Control and Rework Yield
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Solution Overview
Problem
The rapid reaction of copper at pad positions on PCBs with solder during welding leads to large intermetallic compound thickness, resulting in low re-welding yield and issues like undercut and tip structures due to uneven etching rates, affecting the effective coverage of conductive layers.
Innovation Solution
A circuit board design with a first stacked structure that includes an etch stop layer, a first metal layer, and a first oxidation barrier layer, along with a second stacked structure having a bonding layer, a second metal layer, and a second oxidation barrier layer, to prevent undercut and tip structures during etching, ensuring effective coverage and improved re-welding yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper conductive material is used at pad positions for welding, then electrical conductivity is improved, but intermetallic compound thickness increases and re-welding yield decreases
Solution Approach 1:
The conductive layer is divided into multiple segments: a first conductive layer (Cu) for electrical conductivity and a second conductive layer (Ni-based alloy) for welding. This segmentation allows each layer to perform its specialized function, preventing excessive intermetallic compound formation while maintaining conductivity.
Solution Approach 2:
The Ni-based alloy layer acts as an intermediary between the Cu conductive layer and the solder. It mediates the welding process by forming a controlled, thin intermetallic compound layer, preventing the direct and excessive reaction between Cu and solder that would otherwise occur.
2Manufacturing precision
If etching process is applied to conductive layer, then pattern formation is achieved, but undercut and tip structures occur due to uneven etching rate
Solution Approach 1:
The Ni-based alloy layer has different etching resistance properties compared to the Cu layer. During etching, the Ni-based alloy etches at a different rate, creating a protective effect that prevents undercut and tip structures, ensuring uniform conductive layer coverage.
Solution Approach 2:
The Ni-based alloy layer is applied beforehand as a cushioning layer that protects against uneven etching. It compensates for potential etching rate variations, ensuring that the final conductive layer maintains proper coverage and shape without defects.
3Reliability
If oxidation barrier layer is added to protect copper, then oxidation resistance is improved, but device structure complexity increases
Solution Approach 1:
The oxidation barrier function is merged with the welding layer function by using a Ni-based alloy that provides both oxidation resistance and suitable welding properties. This consolidation eliminates the need for separate oxidation barrier and welding layers, reducing overall structure complexity.
Solution Approach 2:
The Ni-based alloy layer serves multiple functions simultaneously: it acts as an oxidation barrier, a welding layer, and an etching control layer. This multi-functionality reduces the total number of layers needed while maintaining all required protective and functional properties.
Data Source
AI summary
A circuit board and a method for manufacturing the circuit board, a functional backplate, a backlight module, a display apparatus, and a display panel are provided. The circuit board includes: a base substrate; a wire arranged on the base substrate, where the wire includes a first conductive layer; and at least one insulating layer arranged on a side of the first conductive layer away from the base substrate, where the at least one insulating layer covers the first conductive layer. The first conductive layer includes a first stacked structure on a side away from the base substrate and a second stacked structure proximate to the base substrate, and the first stacked structure includes at least an etch stop layer covering the second stacked structure.