Heated Bond Head Direct Die Attach for LED Thermal Management

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Solution Overview

Problem

Existing die bonding methods for High Brightness LEDs face issues such as low thermal conductivity, flux residue leading to reliability problems, and slow solidification rates causing voids and chip degradation due to prolonged annealing times during the bonding process.

Innovation Solution

A direct die attach method involving a bond head heated above the melting point of the solder layer, which is then pressed onto a substrate preheated below the melting point, allowing for quick solidification and avoiding excessive heat exposure to the chip.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If direct eutectic die attach with preheated substrate is used, then bonding reliability is improved, but solidification time is prolonged causing voids

Engineering Contradiction:

Improvebonding reliabilityVSAvoidsolidification time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The substrate is preheated to a temperature close to but below the melting point of the eutectic material before bonding. This preliminary heating action reduces the temperature difference between substrate and eutectic layer during bonding, accelerating solidification after bonding while maintaining bonding reliability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The substrate temperature is changed from conventional lower temperatures to a specific range (200-260°C for gold-tin eutectic) just below the melting point. This parameter change accelerates heat transfer from the eutectic layer to the substrate, reducing solidification time and preventing void formation.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If substrate is preheated to high temperature for direct eutectic attach, then bonding speed is improved, but chip degradation increases due to prolonged annealing

Engineering Contradiction:

Improvebonding speedVSAvoidchip degradation

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The substrate temperature is optimized to a specific range (200-260°C) that is high enough to accelerate bonding and solidification but below the melting point of the eutectic material. This prevents prolonged annealing of already bonded chips while maintaining fast bonding speed.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The bonding process is made dynamic by rapidly bonding each chip and immediately removing it from the heated substrate. This dynamic approach minimizes the time each chip is exposed to high temperature, preventing degradation while maintaining productivity.

Inventive Principle:

Principle #15Dynamics

3Ease of operation

If flux eutectic die attach is used, then no external force is needed, but flux residue causes reliability issues

Engineering Contradiction:

Improveoperation simplicityVSAvoidpackage reliability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The flux material is completely removed from the bonding process. The invention uses direct eutectic bonding without flux, eliminating the source of reliability problems while maintaining operational simplicity through the self-fluxing property of the eutectic alloy.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of using flux that leaves harmful residues, the invention uses a disposable small amount of eutectic material that is consumed during bonding. The eutectic alloy serves as both the bonding material and flux substitute, eliminating residue issues.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 method enhances bonding reliability by preventing voids, reducing chip degradation, and improving thermal and electrical conductivity while maintaining productivity.

Implementation Method 1

heating a bond head to a bond head setting temperature T1, which is higher than Tm

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 2

heating the die towards temperature T1 so as to melt the solder layer

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 3

the solder layer is cooled towards T2 and solidifies

Methodology Applied

Scientific EffectCooling: Cooling

Implementation Method 4

the solder layer is cooled towards T2 and solidifies

Methodology Applied

Scientific EffectSolidification: Freezing

Implementation Method 5

heating the die towards temperature T1

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS7854365B2Direct die attach utilizing heated bond head

Publication Date: 2010.12.21 ASMPT SINGAPORE PTE LTD

AI summary

A method is provided for bonding a die comprising a solder layer which has a melting point Tm. A bond head is heated to a bond head setting temperature T1, which is higher than Tm, and a substrate is heated to a substrate setting temperature T2, which is lower than Tm. The bond head then picks up the die and heats the die towards temperature T1 so as to melt the solder layer. The solder layer of the die is pressed onto the substrate so as to bond the die to the substrate, and thereafter the bond head is separated from the die so that the solder layer is cooled towards T2 and solidifies.