Leadless Flip-Chip Leadframe With Non-Conductive Ink Recesses

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Solution Overview

Problem

Conventional leadless flip-chip packages face limitations in achieving redistribution designs due to the inability of inner leads to accommodate varying chip bump positions and specifications, leading to restricted design flexibility and increased manufacturing complexities, such as short-circuit risks during etching and contamination issues with solder mask layers.

Innovation Solution

A leadframe design incorporating inner leads with bump-connecting terminals, outer terminals, and redistributed lead portions, where a non-conductive ink layer fills recessions on the lower surfaces of redistributed lead portions to fix and protect them, allowing for easy formation of a solder mask layer that exposes bump-connecting terminals while preventing contamination of outer terminals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If inner leads are used in leadless flip-chip packages, then packaging cost is reduced, but design flexibility is limited due to inability to accommodate varying chip bump positions

Engineering Contradiction:

Improvepackaging cost reductionVSAvoiddesign flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The inner lead is divided into three functional segments: bump-connecting terminal, redistributed lead portion, and outer terminal. This segmentation allows each part to be optimized independently, enabling the leadframe to accommodate various chip bump positions and configurations while maintaining cost-effectiveness

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a vertical dimension by forming recessions on the lower surface of redistributed lead portions and filling them with non-conductive ink. This three-dimensional structure provides additional design space and flexibility for accommodating different chip bump arrangements without increasing planar complexity

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Manufacturing precision

If recessions are formed on inner leads to define bump bonding region, then bump bonding control is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvebump bonding controlVSAvoidmanufacturing complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Non-conductive ink is introduced as an intermediary material to fill the recessions on the lower surface of redistributed lead portions. This ink layer serves multiple functions: defining the bump bonding region, providing electrical insulation, and protecting the leadframe structure, thereby achieving precise bump bonding control without complex manufacturing processes

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The leadframe structure combines metal inner leads with non-conductive ink filling in the recessions. This composite structure integrates electrical conductivity, mechanical support, and precise geometric definition into a single component, reducing overall manufacturing complexity while maintaining high precision

Inventive Principle:

Principle #40Composite materials

3Manufacturing precision

If solder mask layer is printed on inner leads, then bump bonding region definition is improved, but contamination of outer terminals occurs

Engineering Contradiction:

Improvebump bonding region definitionVSAvoidouter terminal contamination

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

Recessions are formed and filled with non-conductive ink on the lower surface of redistributed lead portions before applying the solder mask layer. This preliminary action creates a protective barrier that prevents solder mask contamination of the outer terminals while still allowing precise definition of the bump bonding region

Inventive Principle:

Principle #10Preliminary action

4Device complexity

If inner leads are etched to form leadless leadframe, then packaging structure is simplified, but short-circuit risk increases due to over-etching

Engineering Contradiction:

Improvepackaging structure simplificationVSAvoidshort-circuit risk

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Non-conductive ink is applied to fill the recessions on the lower surface of redistributed lead portions before the etching process. This ink layer acts as a cushioning protective layer that prevents over-etching and potential short-circuits between inner leads, while allowing the packaging structure to remain simplified

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS7312105B2Leadframe of a leadless flip-chip package and method for manufacturing the same

Publication Date: 2007.12.25 ADVANCED SEMICON ENG INC

AI summary

A leadframe of a leadless flip-chip package includes a plurality of inner leads, a non-conductive ink layer and a solder mask layer. The inner leads have a plurality of bump-connecting terminals, a plurality of outer terminals and a plurality of redistribution lead portions. A half-etched recession is formed on lower surfaces of the redistribution lead portions, and is filled with the non-conductive ink layer. The non-conductive ink layer fixes the redistribution lead portions onto the bump-connecting terminals. The solder mask layer is easily formed on the non-conductive ink layer and covers the inner leads.