Terminal Structure With Projected Metal Layer to Restrict Solder Overflow
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Solution Overview
Problem
Conventional wiring substrates experience solder layer sagging during the reflow process, leading to potential short circuits between adjacent solder layers.
Innovation Solution
A terminal structure is designed with a protective metal layer that includes a projection extending outward from the side surface of the wiring layer, an intermetallic compound layer formed at the interface between the protective metal layer and the solder layer, and a solder layer covering only the upper surface of the intermetallic compound layer, preventing solder overflow and short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder layer is formed on protective metal layer during reflow process, then bonding strength between solder and protective metal layer is improved, but solder layer sags and causes short circuiting between adjacent solder layers
Solution Approach 1:
The protective metal layer is designed with different local structures: a flat upper surface area where the solder layer is formed to ensure proper bonding, and side surface areas that remain exposed to prevent solder overflow. This local differentiation allows the solder to bond strongly where needed while preventing sagging-induced short circuits at the edges.
Solution Approach 2:
The protective metal layer is pre-formed with specific dimensional relationships (upper surface area smaller than side surface projection) before the solder layer is applied. This preliminary structural preparation ensures that when solder is applied and heated during reflow, it is geometrically constrained to remain within boundaries that prevent short circuiting.
2Strength
If solder layer covers side surface of protective metal layer, then bonding area is increased, but solder overflow occurs causing short circuits
Solution Approach 1:
The protective metal layer is designed with different local structures: a flat upper surface area where the solder layer is formed to ensure proper bonding, and side surface areas that remain exposed to prevent solder overflow. This local differentiation allows the solder to bond strongly where needed while preventing sagging-induced short circuits at the edges.
Solution Approach 2:
The protective metal layer's surface is segmented into distinct functional zones: an upper surface area for solder bonding and side surface areas for overflow prevention. This segmentation creates clear boundaries that guide solder placement and prevent harmful overflow while maintaining adequate bonding area.
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 effectively restricts solder overflow, enhances bonding strength, and maintains controlled solder dimensions, reducing the likelihood of short circuits and improving connection reliability.
Implementation Method 1
an intermetallic compound layer formed at an interface between the protective metal layer and the solder layer
Data Source
AI summary
A terminal structure includes a first wiring layer, an insulation layer covering the first wiring layer, an opening extending through the insulation layer, via wiring formed in the opening, a second wiring layer electrically connected to the via wiring on the insulation layer, a protective metal layer formed on the second wiring layer, a solder layer formed on the protective metal layer, and an intermetallic compound layer formed between the protective metal layer and the solder layer. The protective metal layer includes a projection projecting further outward from a side surface of the second wiring layer. The intermetallic compound layer covers only the upper surface of the protective metal layer. The solder layer covers only an upper surface of the intermetallic compound layer and exposes the side surfaces of the intermetallic compound layer, the protective metal layer, and the second wiring layer.