Semiconductor Lead Frame with Thinned Portions for Thermal Stress Relief

Solution Overview

Problem

Packaged semiconductor devices face reliability issues due to stress on bonds between leads and substrates caused by temperature variations, leading to potential breakage of connections.

Innovation Solution

The implementation of lead frames with thinned or reduced cross-sectional areas at specific regions, allowing for increased flexibility and reduced stiffness, which mitigates stress during thermal cycling by enabling the leads to bend without breaking the bond with the substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the lead frame leads are made with uniform cross-sectional area, then the structural strength is maintained, but the stress on bonds between leads and substrate increases during temperature variations

Engineering Contradiction:

Improvestructural strength of leadsVSAvoidreliability of bonds between leads and substrate

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The lead frame leads are designed with varying cross-sectional areas along their length, creating regions of different stiffness. Specifically, the leads have a first cross-sectional area in the region adjacent to the substrate and a second cross-sectional area in the region extending outward, where the second area is smaller than the first. This local variation in geometry allows the leads to have different mechanical properties at different locations, enabling them to flex and accommodate thermal expansion differences while maintaining adequate structural strength where needed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the physical parameter of cross-sectional area along the length of the leads. By gradually reducing the cross-sectional area from the substrate-adjacent region to the outer region, the leads exhibit a gradient in stiffness that allows them to bend more easily at the outer portions while maintaining strength near the substrate connection. This parameter change enables the leads to absorb thermal stress through controlled deformation.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the leads are made thicker to reduce stress, then the bond reliability improves, but the flexibility to accommodate thermal expansion decreases

Engineering Contradiction:

Improvebond reliabilityVSAvoidflexibility to accommodate thermal expansion

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The lead frame leads are designed with varying cross-sectional areas along their length, creating regions of different stiffness. Specifically, the leads have a first cross-sectional area in the region adjacent to the substrate and a second cross-sectional area in the region extending outward, where the second area is smaller than the first. This local variation in geometry allows the leads to have different mechanical properties at different locations, enabling them to flex and accommodate thermal expansion differences while maintaining adequate structural strength where needed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The leads are designed to be dynamically adaptable through their varying cross-sectional geometry. The gradient in cross-sectional area allows the leads to change their effective stiffness in response to applied forces, being stiffer near the substrate for reliable bonding and more flexible at the outer regions for accommodating thermal expansion. This dynamic characteristic enables the leads to optimize their mechanical response based on the location and magnitude of applied stresses.

Inventive Principle:

Principle #15Dynamics

3Reliability

If the leads are made more flexible to accommodate thermal expansion, then the stress on bonds reduces, but the structural strength decreases

Engineering Contradiction:

Improvestress reduction on bondsVSAvoidstructural strength of leads

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The lead frame leads are designed with varying cross-sectional areas along their length, creating regions of different stiffness. Specifically, the leads have a first cross-sectional area in the region adjacent to the substrate and a second cross-sectional area in the region extending outward, where the second area is smaller than the first. This local variation in geometry allows the leads to have different mechanical properties at different locations, enabling them to flex and accommodate thermal expansion differences while maintaining adequate structural strength where needed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The leads are effectively segmented into different regions with different cross-sectional areas. The region adjacent to the substrate has a larger cross-sectional area for strength, while the region extending outward has a smaller cross-sectional area for flexibility. This segmentation allows each portion of the lead to be optimized for its specific function, creating a composite structure that achieves both strength and flexibility.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS9287200B2Packaged semiconductor device

Publication Date: 2016.03.15 NXP USA INC

AI summary

A packaged semiconductor device includes a lead frame having a plurality of leads; a semiconductor die mounted onto the lead frame; and an encapsulant surrounding the semiconductor die. At least a portion of each of the leads is surrounded by the encapsulant, wherein, each lead includes a thin portion external to the encapsulant and a thick portion that is surrounded by the encapsulant, wherein the thin portion is thinner than the thick portion.