Selective Leadframe Plating for PCB Solderability at Lower Cost
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Solution Overview
Problem
Leadframe packages face challenges in solderability due to non-wettable base metals like copper and copper alloys, requiring additional plating processes that increase manufacturing costs and complexity, especially for post-plating operations after encapsulation.
Innovation Solution
A leadframe package with selectively plated leads, where outer segments are pre-plated with a noble metal or alloy for improved solderability, and inner segments retain the base metal surface, eliminating the need for post-plating processes and simplifying the chip assembly process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire leadframe surface is pre-plated with noble metal, then solderability is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies plating only to specific regions of the leadframe where solderability is needed (exposed leads and pins), rather than the entire surface. This selective local plating reduces material costs while maintaining the required solderability for assembly operations.
Solution Approach 2:
The leadframe surface is divided into different functional zones: regions requiring solderability (exposed leads) are plated, while regions not requiring solderability (enclosed portions) remain as base metal. This segmentation allows differential treatment of different areas based on their functional requirements.
2Reliability
If post-plating is performed after encapsulation, then solderability of exposed leads is improved, but device complexity and manufacturing time increase
Solution Approach 1:
The patent performs plating on the leadframe before the encapsulation process, so that the solderability treatment is already in place before the leads are exposed. This eliminates the need for a separate post-plating step after encapsulation, reducing manufacturing complexity and cycle time.
Solution Approach 2:
By anticipating which leads will be exposed after encapsulation, the plating process is performed in advance on those specific regions. This preliminary action ensures that when the leads are exposed, they already have the required solderable surface finish.
3Reliability
If noble metal plating is applied to enclosed portions of leads, then corrosion resistance is improved, but material cost increases
Solution Approach 1:
The patent applies corrosion protection selectively: exposed portions receive noble metal plating for both corrosion resistance and solderability, while enclosed portions rely on the inherent corrosion resistance of the base metal or receive minimal protection. This local quality approach reduces noble metal consumption while maintaining adequate corrosion resistance where needed.
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 selective plating reduces manufacturing costs and simplifies the assembly process by enhancing solderability and corrosion resistance, while maintaining the integrity of the base metal within the encapsulation, thus improving the reliability and efficiency of the chip packaging process.
Implementation Method 1
The exposed portions or outer segments, of the leads include a plating or coating layer of a material that enhances the solder wettability of the leads to the PCB through solder bonding.
Implementation Method 2
The outer segments of the leads are pre-plated, namely the plating layer or film is formed before the leadframe is used in an assembly process.
Data Source
AI summary
The present disclosure is directed to a leadframe package with a surface mounted semiconductor die coupled to leads of the leadframe package through wire bonding. The leads are partially exposed outside the package and configured to couple to another structure, like a printed circuit board (PCB). The exposed portions, namely outer segments, of the leads include a plating or coating layer of a material that enhances the solder wettability of the leads to the PCB through solder bonding. The enclosed portions, namely inner segments, of the leads do not include the plating layer of the outer segment and, thus, include a different surface material or surface finish.