Leadframe Half-Etching for Side-Solderable Package Contacts
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Solution Overview
Problem
The existing manufacturing process for leadless semiconductor packages requires step cutting and plating, which increases manufacturing work and cost, as it necessitates exposing side surfaces for electroplating, complicating the packaging process.
Innovation Solution
A leadframe design where the side surfaces of contacts are exposed through a half-etching process, allowing for electroplating without the need for step cutting, with dambars and support structures ensuring the encapsulant does not cover these surfaces, enabling side solderability without additional processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If step cutting is performed to expose side surfaces for electroplating, then side solderability is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The leadframe is designed with pre-formed protruding portions that expose side surfaces of contacts before the encapsulation process. This preliminary exposure eliminates the need for subsequent step cutting operations, allowing electroplating to be performed directly on the exposed side surfaces while reducing manufacturing complexity
Solution Approach 2:
The leadframe is divided into multiple protruding portions, each exposing side surfaces of specific contacts. This segmentation allows selective exposure of different contact side surfaces, enabling targeted electroplating on individual contacts without requiring complex step cutting of the entire leadframe
2Reliability
If step cutting is performed to expose side surfaces, then electroplating can be applied, but manufacturing time and cost increase
Solution Approach 1:
The protruding portions are formed during the leadframe manufacturing process itself, exposing side surfaces before encapsulation. This preliminary exposure integrates the exposure function into the existing manufacturing flow, eliminating separate step cutting and plating operations that would reduce productivity
3Reliability
If dambars and support structures are added to protect exposed surfaces, then encapsulant coverage is prevented, but leadframe complexity increases
Solution Approach 1:
The protruding portions serve multiple functions simultaneously: they expose side surfaces for electroplating, maintain exposure during encapsulation, and provide structural support. This multi-functionality reduces the need for separate protective structures like dambars, simplifying the overall leadframe design
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 method reduces manufacturing complexity and cost by allowing electroplating of side surfaces without sawing, ensuring reliable solder fillets and improved visual inspection capabilities, while maintaining structural integrity and electrical connectivity.
Implementation Method 1
A leadframe design where the side surfaces of contacts are exposed through a half-etching process
Implementation Method 2
Electroplating is the more desirable plating method because a thicker and faster metal deposition occurs
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
A leadframe is formed by chemically half-etching a sheet of conductive material. The half-etching exposes a first side surface of a first contact of the leadframe. A solder wettable layer is plated over the first side surface of the first contact. An encapsulant is deposited over the leadframe after plating the solder wettable layer.