Lead Frame Paddle Locking Features for Delamination Prevention

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Solution Overview

Problem

Chip packages experience delamination and cracking due to shear and flexing stresses caused by thermal and electrical loads, which existing technologies fail to adequately address, particularly in products using high Young modulus die attach adhesive materials.

Innovation Solution

The introduction of novel mechanical paddle surface breaking locking features that interlock the molding compound to the paddle, including overhanging-top, step-out bottom, and extended edge step-out bottom locking features, formed through etching or stamping, to reduce shear stress and prevent delamination and cracking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If existing anchoring technologies are used to secure the lead frame to the molding compound, then the basic structural support is provided, but shear and flexing stresses build up causing delamination and cracking under thermal and electrical loads

Engineering Contradiction:

Improveresistance to delamination and crackingVSAvoidinterfacial bond strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The locking feature is divided into multiple functional segments: a locking portion that engages with the molding compound, an overhanging portion that extends beyond the paddle edge, and a stepped portion that creates mechanical interlocking. This segmentation allows each portion to address specific stress mechanisms independently, preventing delamination and cracking under thermal and electrical loads.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The locking feature concentrates mechanical interlocking capability at the critical paddle-molding compound interface, specifically at the edge regions where delamination and cracking typically initiate. The localized locking portions and overhanging features provide enhanced anchoring precisely where thermal and flexing stresses are most severe, rather than distributing weak anchoring across the entire interface.

Inventive Principle:

Principle #3Local quality

2Reliability

If high Young modulus die attach adhesive materials are used to improve electrical and thermal performance, then electrical and thermal performance is enhanced, but thermal stresses cause increased delamination and cracking

Engineering Contradiction:

Improveelectrical and thermal performanceVSAvoidthermal stress-induced delamination

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The locking feature with its overhanging and stepped portions is installed beforehand to create a mechanical cushioning effect at the paddle-molding compound interface. This pre-established mechanical interlocking absorbs and redistributes thermal stresses before they can cause delamination or cracking, protecting the high Young modulus adhesive material from stress-induced failure during thermal cycling.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Ease of manufacture

If the lead frame is simply anchored to the molding compound without additional locking features, then the manufacturing process is simple, but shear stresses cause package cracks under shock loads and thermal cycling

Engineering Contradiction:

Improveanchoring process simplicityVSAvoidresistance to shear stress and package cracking

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The locking feature merges multiple functions into a single integrated structure: the locking portion provides mechanical interlocking, the overhanging portion extends protection beyond the paddle edge, and the stepped portion creates geometric anchoring. This merged design prevents package cracking under shock loads and thermal cycling while being formable in a single stamping or etching operation, maintaining manufacturing simplicity.

Inventive Principle:

Principle #5Merging (Combining)

4Device complexity

If conventional anchoring methods are used, then the device complexity is low, but the mechanical interlocking between molding compound and lead frame is insufficient to prevent delamination

Engineering Contradiction:

Improveanchoring structure complexityVSAvoidmechanical interlocking strength

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The locking feature extends the anchoring interaction into additional spatial dimensions: the overhanging portion extends laterally beyond the paddle edge in the horizontal dimension, while the stepped portions create vertical dimension interlocking through height variations. This multi-dimensional engagement significantly enhances mechanical interlocking strength and delamination resistance compared to conventional planar anchoring methods.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS10290564B2Systems and methods for lead frame locking design features

Publication Date: 2019.05.14 INTERSIL AMERICAS INC

AI summary

Systems and methods for lead frame locking design features are provided. In one embodiment, a method comprises: fabricating a lead frame for a chip package, the lead frame having a paddle comprising a step-out bottom locking feature profile across at least a first segment of an edge of the paddle that provides an interface with a mold compound; etching the paddle to have at least a second segment of the edge having either an extended-step-out bottom locking feature profile or an overhanging top locking feature profile; and alternating first and second segments along the edge of the paddle.