Semiconductor Device Stress-Absorbing Coupling Lead

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Solution Overview

Problem

The existing semiconductor device structures are prone to deformation due to thermal expansion differences between the base plate and sealing resin, leading to stress on the coupling lead and solder, which can result in crack formation and reduced reliability and lifespan.

Innovation Solution

A semiconductor device design where a second base plate with higher rigidity intersects the boundary line of deformation, reducing stress on joining materials and allowing leads to be positioned away from the deformation zone, thereby alleviating stress on solder joints and preventing crack formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the coupling lead portion is provided to intersect the gap portion between MOS-FETs to connect upper and lower arms, then electrical connection between arms is achieved, but the coupling lead portion is subjected to external force during thermal expansion, causing deformation and solder cracks

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidcoupling lead strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

A stress-absorbing portion is introduced as an intermediary element in the coupling lead structure. This portion acts as a mediator that absorbs thermal expansion stress through elastic deformation, protecting the solder joints from crack propagation while maintaining electrical connectivity between upper and lower arms

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The coupling lead's physical parameters are changed by introducing a stress-absorbing portion with specific geometric features (bent shape or reduced thickness). This modification changes the lead's mechanical properties, enabling it to flexibly absorb stress during thermal cycles without compromising electrical connection reliability

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the plate thickness of the coupling lead is increased to reduce deformation, then deformation is reduced and solder cracks are inhibited, but the cost and weight of the coupling lead increase

Engineering Contradiction:

Improvesolder joint reliabilityVSAvoidcoupling lead weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

Instead of uniformly increasing the entire coupling lead's thickness, the stress-absorbing portion is localized at specific positions where thermal stress is most concentrated. This local modification provides the necessary stress absorption capability while minimizing the overall weight and cost increase

Inventive Principle:

Principle #3Local quality

3Reliability

If the plate thickness of the coupling lead is increased to reduce deformation, then solder cracks are inhibited, but the amount of sealing resin increases and the device size increases

Engineering Contradiction:

Improvesolder joint reliabilityVSAvoidsemiconductor device volume

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The stress-absorbing portion is localized at specific positions rather than increasing the overall device dimensions. This localized approach provides the necessary stress absorption capability while minimizing the amount of additional sealing resin required and keeping the device compact

Inventive Principle:

Principle #3Local quality

4Reliability

If a bent portion is provided in the coupling lead to absorb stress, then stress on solder is reduced, but processing costs increase

Engineering Contradiction:

Improvesolder joint reliabilityVSAvoidprocessing ease

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The coupling lead is segmented into distinct functional portions: a rigid section for electrical connection and a flexible stress-absorbing section with bent geometry. This segmentation allows the stress-absorbing function to be integrated into the lead fabrication process itself, avoiding additional processing steps and reducing overall manufacturing complexity

Inventive Principle:

Principle #1Segmentation

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 design inhibits crack formation in the solder, improves the reliability and lifespan of the semiconductor device, and allows for downsizing and cost reduction by reducing the size and weight of the device.

Implementation Method 1

due to difference in thermal expansion coefficient between a base plate formed of, for example, copper, on which each MOS-FET is mounted and, for example, an epoxy resin which is used as the sealing resin

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentEP2701192B1Semiconductor device, inverter device provided with semiconductor device, and in-vehicle rotating electrical machine provided with semiconductor device and inverter device

Publication Date: 2017.11.01 MITSUBISHI ELECTRIC CORP

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AI summary

Provided is a semiconductor device including: a first MOS-FET (21) joined to a first base plate (11) via solder; a second MOS-FET (22) joined to a second base plate (12) via solder; a first lead (31) joining the first base plate (11) and the second MOS-FET (22); and a second lead (32) joining the second MOS-FET (22) and a current path member (13) that gives and receives current flowing through the MOS-FETs (21, 22) to and from the outside. The second base plate (12) is more rigid than both the leads (31, 32), a boundary line (D-D) intersects the second base plate (12) without intersecting both the leads (31, 32), the boundary line including a gap portion (52) along which both the MOS-FETs (21, 22) are opposed to each other, extending in the direction in which both the MOS-FETs (21, 22) are not opposed to each other.