Lead Frame Dummy Leads Mitigate Encapsulation Burrs

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Solution Overview

Problem

During the encapsulation process of semiconductor die packaging, misalignment of active leads with the mold chase can lead to deformation and the formation of burrs, which may cause electrical shorts, especially as lead pitch decreases, and the removal of tie bars from active leads introduces additional risk of deformation.

Innovation Solution

Incorporating dummy leads on either end of active lead rows, connected by tie bars, which remain outside the package body and are removed during the trim and form process, allowing active leads to maintain flexibility and avoid deformation during encapsulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If active leads are made rigid to maintain position during encapsulation, then alignment precision improves, but flexibility is lost causing deformation and burr formation

Engineering Contradiction:

Improvealignment precisionVSAvoidlead flexibility

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The lead frame is segmented into active leads and dummy leads with distinct functions. Active leads maintain flexibility for burr mitigation while dummy leads provide the rigid positioning structure needed for alignment precision during encapsulation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Dummy leads act as intermediary elements that absorb the alignment constraints and forces during encapsulation, protecting the active leads from deformation while maintaining their flexibility and electrical function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If tie bars are removed from active leads after encapsulation, then device complexity reduces, but additional cutting operations increase the risk of deformation

Engineering Contradiction:

Improvestructure simplicityVSAvoiddeformation risk

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Dummy leads are designed as temporary, disposable structures that serve their positioning function during encapsulation and are then removed during trim and form operations, enabling safe removal of tie bars without deformation risk.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

Dummy leads are pre-positioned and attached to active leads before encapsulation to provide protective positioning. This preliminary action ensures that when tie bars are later removed, the active leads are already in their final positions, eliminating deformation risk from additional cutting.

Inventive Principle:

Principle #10Preliminary action

3Area of stationary object

If lead pitch is decreased to increase component density, then area utilization improves, but misalignment sensitivity increases causing more burr formation

Engineering Contradiction:

Improvepackage area utilizationVSAvoidalignment sensitivity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The positioning and alignment function is extracted from the active leads and transferred to the dummy leads. This allows active leads to maintain flexibility for burr mitigation while dummy leads provide the precise positioning needed for decreased lead pitch applications.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS10037935B1Lead frame with dummy leads for burr mitigation during encapsulation

Publication Date: 2018.07.31 NXP USA INC

AI summary

Embodiments of a lead frame for a packaged semiconductor device are provided, one embodiment including: a die pad; a first row of active lead fingers that are laterally separated from one another along their entire length; a package body perimeter that indicates placement of a package body of the packaged semiconductor device, wherein the package body perimeter is located laterally around the die pad; a first dummy lead finger positioned in parallel next to an initial active lead finger of the first row of active lead fingers, wherein the first dummy lead finger and the initial active lead finger are laterally separated from one another along their entire length, and wherein the first dummy lead finger is separated from the package body perimeter by a gap distance; and a first tie bar connected to an outside edge of the first dummy lead finger.