Semiconductor Die Pad Undercut for Better Package Heat Dissipation

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Solution Overview

Problem

The trend towards semiconductor die miniaturization poses a challenge for achieving improved thermal dissipation performance in packages for small dice, as existing solutions such as die pad enlargement and leadframe redesign are complex and costly.

Innovation Solution

A method is introduced to enlarge the back or bottom area of a die pad by forming a recess around its periphery and filling it with thermally conductive material, such as copper, using techniques like laser direct structuring (LDS) or laser-induced forward transfer (LIFT), without affecting the die size or die-to-lead bond length.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If die pad area is enlarged to improve thermal dissipation, then thermal dissipation performance is improved, but device size increases

Engineering Contradiction:

Improvethermal dissipation performanceVSAvoiddevice size

Core Design Contradiction:

TemperatureVSArea of stationary object

Solution Approach 1:

The patent extends the die pad area in the vertical dimension by creating an undercut structure where the die pad protrudes laterally beyond the encapsulation structure at its bottom surface. This allows increased thermal dissipation area without increasing the top footprint of the device, effectively solving the contradiction between thermal performance and device size.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Temperature

If leadframe dimensions are modified to accommodate die pad enlargement, then thermal dissipation is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvethermal dissipation performanceVSAvoidleadframe design complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

Instead of enlarging the die pad at the top surface within the encapsulation boundary, the patent inverts the approach by extending the die pad laterally at the bottom surface below the encapsulation. This inversion allows thermal dissipation enhancement without requiring complex leadframe redesign, as the leadframe can maintain its original top configuration.

Inventive Principle:

Principle #13The other way round (Inversion)

3Temperature

If wire bonding length is increased due to die pad enlargement, then thermal dissipation is improved, but electrical resistance increases

Engineering Contradiction:

Improvethermal dissipation performanceVSAvoidelectrical connection reliability

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

By extending the die pad laterally at the bottom surface rather than at the top, the patent maintains short wire bonding lengths from the die to the leadframe while still increasing the thermal dissipation area. This resolves the contradiction by providing extended thermal pathways in the vertical dimension without increasing electrical connection paths.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 approach enhances thermal dissipation performance by increasing the die pad area at the bottom side of the package, thereby improving heat dissipation without increasing the overall device size or the length of electrical connections.

Implementation Method 1

a laser beam can be used to form a recess around the periphery of the bottom surface of a die pad

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Implementation Method 2

Thermally conductive material (metal as copper, for instance) is filled (e.g., grown) in the recess

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Implementation Method 3

A seed layer or the full desired thickness of copper can be jet-printed, optionally followed by electroplating

Methodology Applied

Scientific EffectElectroplating: Electroplating

Implementation Method 4

Laser direct structuring (LDS) material can be used as a package molding material, and thermally conductive material (metal as copper, for instance) can be grown in the recess resorting to conventional in standard LDS processing (electroless plus electroplating)

Methodology Applied

Scientific EffectElectroless plating: Electrodeposition

Implementation Method 5

Thermally conductive material (metal as copper, for instance) can also be grown in the recess resorting to laser-induced forward transfer (LIFT) processing

Methodology Applied

Scientific EffectLaser-induced forward transfer: Laser Ablation

Data Source

PatentEP4273923B1Method of manufacturing semiconductor devices and corresponding semiconductor device

Publication Date: 2025.02.12 STMICROELECTRONICS SRL

Figure 1A~3B
Figure 4~5

AI summary

At least one semiconductor chip or die (14) is arranged on a first surface of a thermally conductive die pad (12A) in a substrate such as a leadframe. An encapsulation (20) of insulating material in molded onto the die pad (12A) having the semiconductor die (14) arranged on the first surface. At the second surface of the die pad (12A), opposite the first surface, the encapsulation (18) borders on the die pad (12A) at a borderline around the die pad (12A). A recessed portion (120A) of the encapsulation (18, 20) is provided, e.g., via laser ablation, at the borderline around the die pad (12A). Thermally and electrically conductive material such as metal material (122A) is filled in the recessed portion (120A) of the encapsulation (18, 20) around the die pad (12A). The thermally conductive die pad (12A) is augmented by the filling of thermally and electrically conductive material (122A) in the recessed portion (120A) of the encapsulation (18, 20) thus improving thermal performance of the device (10).