Protective Layer on Conductive Posts for Solder Overflow Prevention
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Solution Overview
Problem
In semiconductor packaging, the liquid flux permeates through the protective layer during high-temperature processes, causing solder material overflow and short circuits due to the absence of a protective layer on the lead frame and conductive posts, leading to channeling of tin.
Innovation Solution
A supporting structure with a metal member having conductive posts, a protective metal layer, and stop bodies or conductors formed on the end surfaces of the conductive posts, where the protective layer is made of materials like aluminum, stainless steel, or chromium, preventing solder material overflow during reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is formed on the lead frame before solder reflow, then the protective layer should prevent solder overflow, but the liquid flux permeates through the protective layer during high-temperature process and damages it
Solution Approach 1:
The patent applies different properties to different parts of the protective layer. The protective layer has openings at specific locations (under conductive posts, near bonding pads) to allow flux penetration where needed, while maintaining integrity in other areas to prevent solder overflow. This local differentiation resolves the contradiction by allowing the protective layer to be both protective and permeable where required.
Solution Approach 2:
The protective layer is segmented into multiple regions with different functions: covered regions that prevent solder overflow, and opened regions that allow flux penetration. The openings are strategically positioned to create a segmented structure that simultaneously achieves both protection and controlled permeation, resolving the contradiction between preventing solder overflow and allowing flux access.
2Ease of manufacture
If the protective layer is removed to allow flux access, then flux can reach the lead frame, but solder material overflows and causes short circuits
Solution Approach 1:
Instead of completely removing the protective layer, the patent creates local openings only where flux access is needed (under conductive posts and near bonding pads). The rest of the protective layer remains intact to prevent solder overflow, thus achieving both flux access and solder connection integrity simultaneously.
Solution Approach 2:
The protective layer with openings acts as an intermediary structure that mediates between the need for flux access and the need to prevent solder overflow. It allows controlled flux penetration while maintaining physical barriers in critical areas, resolving the contradiction between ease of manufacture and reliability.
3Ease of manufacture
If flux is applied in liquid state during high temperature process, then it can effectively bond components, but it permeates along sides of conductive posts and damages the protective layer
Solution Approach 1:
The protective layer is designed with localized openings that control where flux can permeate. The openings are positioned to allow flux to reach bonding areas while preventing flux from damaging the protective layer in critical regions. This resolves the contradiction by making the protective layer selectively permeable rather than uniformly vulnerable.
Solution Approach 2:
The protective layer with pre-defined openings is formed before flux application, establishing controlled pathways for flux penetration in advance. This preliminary structuring prevents uncontrolled flux permeation that would damage the protective layer, while still allowing effective flux access for bonding.
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 protective layer prevents solder material overflow and short circuits, enhancing the reliability of the electronic package by maintaining the integrity of the solder connection during reflow.
Implementation Method 1
a protective layer formed on the metal member and the stop bodies
Data Source
AI summary
A supporting structure is provided, which forms a protective layer on a metal member having a plurality of conductive posts, and the protective layer is exposed from end surfaces of the conductive posts, such that conductors are formed on the end surfaces of the conductive posts, thereby avoiding damage of the protective layer.