Leadframe Flank Plating and Trenching for Isolated Leadless Packages

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Solution Overview

Problem

Existing leadless semiconductor packages face challenges in achieving full thickness electroplating of leads while ensuring subsequent electrical isolation for reliable solder fillet formation and visual verification of connections.

Innovation Solution

The development of leadframe designs that allow for full thickness electroplating of leads by half-etching techniques, followed by selective trenching to ensure electrical isolation and expose flanks for reliable solder fillet formation, facilitating visual verification of connections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If full thickness electroplating is performed on leads, then solder fillet formation is improved, but electrical isolation becomes difficult to achieve

Engineering Contradiction:

Improvesolder fillet formationVSAvoidelectrical isolation

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The leadframe is divided into multiple segments: full-thickness lead portions that extend through the encapsulant for soldering, and isolated portions that are electrically separated. This segmentation allows different regions of the same leadframe to serve different functions - some for electrical connection and others for isolation, resolving the contradiction between achieving full thickness plating for reliable soldering while maintaining electrical isolation where needed.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the leadframe are given different properties: some areas have full-thickness leads with electroplating for solder fillet formation, while other areas have etched or isolated portions for electrical isolation. This local differentiation of properties allows the same component to simultaneously achieve both reliable soldering and electrical isolation in different locations.

Inventive Principle:

Principle #3Local quality

2Reliability

If leads are exposed for soldering, then connection reliability is improved, but visual verification becomes challenging

Engineering Contradiction:

Improveconnection reliabilityVSAvoidvisual verification

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent utilizes the visual characteristics of solder fillets formed on the exposed lead flanks to provide visual verification. The solder material creates distinct visual features (fillets) that can be easily detected and measured, transforming the invisible electrical connection into a visible indicator of proper soldering, thereby resolving the contradiction between connection reliability and visual verification.

Inventive Principle:

Principle #32Color changes

3Area of stationary object

If package footprint is reduced, then space efficiency is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvepackage footprintVSAvoidleadframe etching and trenching

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The leadframe is pre-configured with specific geometric features and etched patterns before encapsulation that facilitate subsequent manufacturing steps. The preliminary structuring of the leadframe with defined lead portions and isolation regions enables more precise and controllable trenching and plating operations, reducing the overall manufacturing precision burden while achieving compact packaging.

Inventive Principle:

Principle #10Preliminary action

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 enables reliable electrical interconnection and visual verification of solder fillets, enhancing manufacturing efficiency and reducing the likelihood of electrical shorts, while maintaining a reduced package footprint.

Implementation Method 1

half-etching techniques, followed by selective trenching to ensure electrical isolation and expose flanks

Methodology Applied

Scientific EffectEtching:

Implementation Method 2

full thickness electroplating of leads

Methodology Applied

Scientific EffectElectroplating: Electroplating

Implementation Method 3

Solder is reflowed between leadframe contacts and contact pads on PCB to form a metallurgical and electrical connection

Methodology Applied

Scientific EffectSoldering: Soldering

Data Source

PatentUS12424522B2Leadless semiconductor packages, leadframes therefor, and methods of making

Publication Date: 2025.09.23 SEMICON COMPONENTS IND LLC

AI summary

A leadframe includes a frame, a die pad, a contact including a flank adjacent to the frame, a first tie bar between the frame and die pad, and a second tie bar between the die pad and contact. The leadframe is disposed over a carrier. A semiconductor die is disposed over the die pad. An encapsulant is deposited over the leadframe and semiconductor die including between the carrier and half-etched portions of the leadframe. A first trench is formed in the encapsulant to remove a portion of the frame and expose the flank of the contact. A conductive layer is formed over the flank by electroplating. A second trench is formed in the encapsulant through the second tie bar after forming the conductive layer.