Lead Frame Plating Segmentation for Wire Bonding
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Solution Overview
Problem
Conventional lead frame manufacturing processes face issues with connection failures and reduced bonding strength due to changes in the crystal structure of plating layers caused by coining processes, leading to defective wire bonding and potential short-circuiting of adjacent leads.
Innovation Solution
The lead frame design features a plating layer that covers only the upper and side surfaces of the distal portions of inner leads, with the basal portions and dam bars remaining outside the plating layer, and a manufacturing method that forms the inner leads with a constricted intermediate portion and basal portions after the plating layer is established, avoiding changes in the plating layer's crystal structure during coining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plating layer is formed on the inner lead before coining process, then the mounting characteristics and wire bonding connectivity are improved, but the crystal structure of the plating layer changes and bonding strength decreases
Solution Approach 1:
The patent divides the inner lead into three distinct portions: distal portion (with plating layer), intermediate portion (transition zone), and basal portion (without plating layer). This segmentation allows the plating layer to be applied only where needed for wire bonding, while avoiding the coining process on plated areas, thus preventing crystal structure changes and maintaining bonding strength.
Solution Approach 2:
The plating layer is applied locally only to the distal portion of the inner lead where wire bonding is required, rather than uniformly across the entire inner lead. This local application ensures that the plating layer provides its beneficial effects for connectivity without undergoing harmful crystal structure changes in the bonding-critical intermediate and basal portions.
2Manufacturing precision
If coining process is performed on the distal portion of inner lead, then the surface is flattened and mounting characteristics are improved, but the crystal structure changes and connection reliability decreases
Solution Approach 1:
The patent segments the inner lead such that the distal portion receives the plating layer and is excluded from the coining process, while only the unplated intermediate and basal portions undergo coining. This ensures surface flatness is achieved where needed without compromising the crystal structure and connection reliability of the plated distal portion.
3Reliability
If the plating layer covers the entire inner lead, then the mounting characteristics are improved, but the risk of short-circuiting between adjacent leads increases
Solution Approach 1:
The plating layer is applied locally only to the distal portion of each inner lead where wire bonding connectivity is required, rather than covering the entire inner lead. This localized approach maintains the beneficial mounting characteristics at the bonding interface while reducing the overall plated surface area, thereby minimizing the risk of short-circuiting between adjacent leads.
Solution Approach 2:
The patent extracts the plating layer from the intermediate and basal portions of the inner lead, retaining it only on the distal portion. This extraction eliminates unnecessary plating in areas where it could cause short-circuits while preserving the essential plating function for wire bonding connectivity.
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
This approach enhances wire-bonding characteristics, reduces connection failures, and prevents short-circuiting by limiting the plating layer's exposure to the encapsulation resin, thereby maintaining sufficient bonding strength and preventing electrical shorts.
Implementation Method 1
electrolytic plating is performed using the mask 110 as a plating mask and the metal plate 100 as a power supplying layer to form a plating layer 101 on the upper surface of the metal plate 100 located outside the mask 110
Data Source
AI summary
A lead frame includes a dam bar and leads connected by the dam bar. Each lead includes an inner lead, which is located at one side of the dam bar, and an outer lead, which is located at the other side of the dam bar and formed integrally with the inner lead. Each inner lead includes a basal portion located at a side closer to the dam bar, a distal portion located at the opposite side of the basal portion, and an intermediate portion connecting the distal and basal portions and having a width that differs from the distal portion. A plating layer covers an upper surface and a side surface of the distal portion and at least part of a side surface of the intermediate portion. Side surfaces of the basal portion and the dam bar are entirely located outside the plating layer.