QFN Sensor Package Thermal Deformation Prevention

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Solution Overview

Problem

Conventional electronic control apparatuses with sensor units in cavities face challenges in downsizing due to the thickness of semiconductor packages, which are affected by thermal expansion differences between the sensor body and the printed wiring board, leading to unstable sensor outputs and accuracy issues.

Innovation Solution

The electronic apparatus features a semiconductor package with a sensor unit mounted on a mounting member via a bonding material, where the region below the sensor unit has a through hole, and the package is configured as a QFN structure with leads inside a sealing resin, preventing contact with the mounting member during thermal deformation and eliminating the need for a cavity, thus allowing for downsizing while maintaining stable sensor outputs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a cavity is provided in the mounting member to prevent contact between the semiconductor package and the mounting member during thermal deformation, then the sensor output stability is improved, but the device size increases

Engineering Contradiction:

Improvesensor output stabilityVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The invention transitions from a through-hole structure (vertical dimension) to a convex portion structure (horizontal dimension protrusion). The convex portion extends in the thickness direction from the front surface of the substrate, creating a physical barrier that prevents contact between the semiconductor package and substrate during thermal deformation, while occupying minimal space.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The convex portion acts as an intermediary element between the substrate and the semiconductor package. It provides a physical barrier that mediates the interaction between these two components, preventing direct contact and the associated harmful effects during thermal expansion and contraction.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If the semiconductor package is mounted directly on the substrate, then the device complexity is reduced, but thermal deformation causes unintended contact leading to sensor output discontinuity

Engineering Contradiction:

Improvemounting structure complexityVSAvoidsensor output continuity

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The convex portion is pre-formed on the substrate before the semiconductor package is mounted. This preliminary structural preparation ensures that when the semiconductor package is subsequently mounted, the convex portion is already in position to prevent contact during thermal deformation, avoiding sensor output discontinuity without requiring complex additional mounting structures.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If a through hole is used below the sensor unit, then contact prevention is achieved, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvecontact preventionVSAvoidthrough hole alignment precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

Instead of creating a through-hole that passes completely through the substrate (requiring high precision alignment from both sides), the invention uses a convex portion that protrudes from the front surface. This inverts the approach from subtractive (hole) to additive (protrusion), significantly reducing manufacturing precision requirements while achieving the same contact prevention function.

Inventive Principle:

Principle #13The other way round (Inversion)

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

This configuration enables both downsizing of the electronic apparatus and stabilization of sensor outputs by preventing unintended contact between the semiconductor package and the mounting member, even with solder bonding, thereby improving accuracy and preventing discontinuities in sensor readings.

Implementation Method 1

the semiconductor package being mounted on the mounting member via a bonding material

Methodology Applied

Scientific EffectSolder bonding: Soldering

Implementation Method 2

a sealing resin that covers a part of the lead frame and the sensor unit

Methodology Applied

Scientific EffectPhysical containment: Physical Containment

Data Source

PatentUS11691869B2Electronic apparatus including semiconductor package

Publication Date: 2023.07.04 PANASONIC IND CO LTD

AI summary

An electronic apparatus includes a semiconductor package including a sensor unit that outputs a signal responding to an applied physical quantity, mounted on a mounting member. An island projected region is defined as a region in the mounting member obtained by projecting an outline of an island on which the sensor unit is mounted, and a part of or entire of the island projected region is configured as a through hole or a concave portion.