Basic Die Bonding Process & Quality

Basic Die Bonding Process & QualityBasic Die Bonding Process & Quality

Typical Die Bonding SequenceTypical Die Bonding Sequence

Wafer

Colletat homeposition

Die ready,Vacuum apply Ejector pin up

Collet lower down to pick position

Ejector pin back to home

Die is picked up

Die is picked up

Collet lower down to bond position

Die is bonded onto L/F

x xL/F

Epoxy dispensed on L/F

Pad

Vacuum to hold substrate

Epoxy dispensed from syringe

L/F index to bond position

Vacuum to hold substrate

Mylar delaminate from die

Typical Die Bonding SequenceTypical Die Bonding Sequence

B/A lower to pick level and position

Ejector rises up and B/A lift up the die by vacuum

B/A swings to bond level and position for bonding

Die Attach Process ElementsDie Attach Process Elements

Dispensing Materials: Epoxy, Substrate, Control system, Tools e.g.

nozzle, pin.. Process: selection of methodolgy, parameter setting for

different materials and quality requirements

Pick and Place Materials: Die, Mylar & frame, Ejector pin & cap, Collet Process: selection of tools and bonding platform

Bonding Quality Aspects: Die placement, Rotation, Tilting, Bond Line

Thickness….

PropertyAblestik

Ablebond 841-LMISR4QMI

QMI 509Hitachi

Hitachi 4730Sumitomo

Sumitomo CRM-1575CFiller Silver Silver Silver SilicaViscosity 8000 cps@25C 9000 cps@25C 89 Pa.s@25C 22 Pa.s@25CThixotropic Index 5.6 3.5 5.1 2.8Work Life 18 hours@25C 48 hours@25C N/A 48 hours@25CConductivity Conductive Conductive Conductive Non-conductiveRecommended Cure Cycle 1 hour@175C 15mins@150C 60sec@200C 3mins@150CDie Shear Strength 3500psi@25C

(for 80 sq. mils)36 kgf@25C

(for 300 sq. mils)11.39 Mpa@200C (for 80 sq. mils)

15.7RT@200C

Epoxy Type

DispensingDispensingBackground Information of EpoxyBackground Information of Epoxy

Function of epoxy Adheres the die on substrate

Commonly-used epoxy Typical Property

Paste Die Attach in Plastic Packages Adhesive Properties Handling Properties

RheologyCure Condition

Assembly PropertiesBleedOutgassingAdhesion

Reliability PropertiesVoidsThermal / Electrical ConductivityIonic ContaminationStress

Why handling is important

DispensingDispensingBackground Information of EpoxyBackground Information of Epoxy

DispensingDispensingSubstrateSubstrate

Common substrates used PCB Leadframe BGA Ceramic

Considerations Wetting properties Pad to die ratio

Dispensing MethodologyDispensing Methodology

Time-Pressure-Vacuum System Volumetric Dispensing Rotating Disc

Time-Pressure-Vacuum System A process of the application of compressed air

in a preset period for the fluid dispensingApply Vacuum for removing the

compressed airMaintain the pressurePrevent dripping & suck back


Syringe with epoxy

VacuumPressure


Time-Pressure-Vacuum System Draw Backs

Air compressibility Difficulty in regulating the dispensing consistently Internal pressure (Pi) changes with epoxy level

Different epoxy level changes air volume inside the syringe

Time for vacuum suction and compress air refilling is changing

Ease of dripping & sucking-in of air bubbles

Volumetric Dispensing Process Principle

Positive Displacement System (Piston Pump)Apply compressed airPull up the piston to feed

epoxy into the chamberSwitch the valve portPiston is pushed to

dispense epoxy


Valve

Chamber

Piston

Syringe


Volumetric Dispensing Advantages

True positive displacement dispensing No dripping Inconsistency comes from piston position error and

epoxy compressibility only High accuracy

Draw Backs Slow epoxy feed-in rate Complicated design and longer time & costly

maintenance


Rotating DiscDisc holding

epoxy rotated with a stationary spreader

Level of epoxy thickness in disc can be adjusted

Epoxy disc rotation

Stamping pin move in X & Z

Dispensing Dispensing Application & ToolsApplication & Tools

Shower Head Dispensing A process for

dispensing the epoxy onto the leadframe with a fixed dispensing pattern according to the shower head size

Adopted to certain range of die size (30 x 30 ~ 150 x 150 mils)


Shower Head Nomenclature of

shower head Holes Hole diameter Needle length

4-point stamping2-point stamping

Dispensing Application & ToolsDispensing Application & Tools

Epoxy Drum Stamping A process for

dispensing the epoxy onto the leadframe with a dispensed epoxy dot according to the stamping pin size

Adopted to small die only (7 x 7 ~ 20 x 20 mils)

Stamping pin Nomenclature of stamping pin

pin tip radiuspin tip length

Dispensing Application & ToolsDispensing Application & Tools

Tip length

Tip radius

Stamping pin tip


Writing A process for

dispensing the epoxy onto the leadframe with a selectable dispensing pattern according to the die size

Adopted to wide range of die size (30 x 30 ~ 1000 x 1000 mils)

I.D. 0.33mm I.D. 0.21mm

I.D. 0.51mm


Writing pin Nomenclature of writing

pin writing pin length outer diameter inner diameter

Cross Double-Y-Horizontal Double-Y-Horizontal

Effect of usage of Dispensing MethodEffect of usage of Dispensing Method(Advantages & Disadvantages of Different Dispensing Method)(Advantages & Disadvantages of Different Dispensing Method)

Advantages of different dispensing methodAdvantages of different dispensing method

Disadvantages of different dispensing methodDisadvantages of different dispensing method

Higher Dispensing speed Consistent dispensed pattern Ease of BLT & die tilt control Programmable dispensed pattern Small dot dispensingEpoxy Writing Die size dependent Good Good Able UnableEpoxy Drum Stamping Able Acceptable Acceptable Unable AbleShower Head Dispensing Able Not Good Not Good Unable Unable

Ease of tailing occurrence Epoxy contamination Needle Blockage VoidEpoxy Writing Most stable No Accpetable Most stableEpoxy Drum Stamping Easy to occur Yes No NoShower Head Dispensing Acceptable (viscosity dependent) No Easy to occur Easy to occur

Effect of usage of Dispensing MethodEffect of usage of Dispensing Method

Common problems Dripping

Tailing

Inconsistency

Void

Void Area

Photo taken by X-ray







Thickness….

Pick & PlacePick & PlaceDie Picking Tools - ColletDie Picking Tools - Collet

Pick-up tools - Collet In contact with die surface;

apply vacuum and pick up die from Mylar

Selection depends on die features e.g. size, adhesion method

Tungstein Carbide Collet

Hi-temp Collet

4-sided Collet 2-sided ColletRubber Collet

Pick & PlacePick & PlaceDie Picking Tools - ColletDie Picking Tools - Collet

Different configuration of collet rubber collet

commonly-used, for normal die bonding

2-sided & 4 sided collet for die with a special surface coating eliminate the possible contamination by the contact

between die and collet

hi-temp collet for eutectic bonding able to sustain the high temperature of leadframe

tungstein carbide collet for small die bonding (size range 20 mils below) aim to prevent the suck-back phenomenon after bonding longer lifetime

Pick & PlacePick & PlaceDie Picking Tools - Die Picking Tools - Cap / Chuck / PinCap / Chuck / Pin

Cap Act as platform

for holding the die

Holes for vacuum

Chuck Holding the pin

Pin Eject the die from

the Mylar

Ejector Chuck & Pin

Ejector Cap

Ejector Assembly

Pick & PlacePick & PlaceDie Picking Tools – Die Picking Tools – Cap / ChuckCap / Chuck

Ejecting tools selection It is base on die dimension

die width x die length

Definition of die dimension Schematic diagram of chuck

Pick & PlacePick & PlaceDie Picking Tools - Die Picking Tools - PinPin

Ejector Pin Notation Ejector pin is notated by the dimension of pin

tip radius Examples

R5 ejector pin ( for both sharp & round pin) tip radius = 0.125 mm = 5 mils

R3 ejector pin tip radius = 0.075 mm = 3 mils

R8 ejector pin tip radius = 0.200 mm = 8 mils

Pick & PlacePick & PlaceDie Picking Tools - Die Picking Tools - PinPin

Selection of ejecting tools (con’t) sharp pin & round pin

It is mainly purposed for small die (range below 20 mils) contact surface area between die and pin relatively small

compared to round tip prevent failure of pick-up

round pin It is mainly purposed for die with size greater than 20 mils able to prevent die crack since the tip is round and

pressure exerting on die back will not be too large may cause failure of pick-up

Sharp pin Round pin

Pick & PlacePick & PlaceWafer HandlingWafer Handling

Different type of wafer ring / frame / wafer cassette Wafer cassette

Disco K & S

Wafer ring Disco K & S Teflon

D company K company

Different type of wafer tape materialMylar tapeUV tapeWaffle pack

Pick & PlacePick & PlaceWafer Tape MaterialWafer Tape Material

Blue Mylar Tape

Colourless UV Tape


Factors determine the degree of uniformity of wafer tape Die size

Large die size have a better tackiness

Surface finish of the wafer back Smooth surface of wafer back have higher tackiness

Duration of die adhesion to wafer tape The longer the die are on the tape, the more they

adhere


Factors determine the degree of uniformity of wafer tape Exposure to UV light

The longer the exposure to UV light, the less they adhere

Storage condition It should be stored in a moderate condition

temp : 10-25 C humidity : 60-70%

Tape mounting process amount of tension should be even in both X & Y

direction







Thickness….

Die Bonding Quality IssuesDie Bonding Quality Issues Die Placement Die rotation Tilted die Epoxy build-up (fillet height) Epoxy coverage Bondline Thickness Die shear Other common errors

Lost die Cracked die Damage on die surface Skip bond unit Misorientated die Epoxy spread Epoxy outside bond area Excessive Epoxy Epoxy tailing Epoxy void

Common Problems & Possible CausesCommon Problems & Possible Causes

Die Placement

Good Placement Error Placement in X-Y direction

Die Bonding Quality Specification Die Bonding Quality Specification Bond PlacementBond Placement

Die placement Position shifted from

the target bond position

Condition of reject: (AD898 as example)

X & Y is out of the range 1 mil at Cp 1 in X or Y direction

Inspection method: Measurement using

Profile projector with 200X

Reference X axis

Reference Y axis

Target bonding position

Actual die bonded position

Y

X


Die Placement - con’t Too high bond level Error adjustment in 3-point alignment Too small BH Table Pick Delay Too small Bond Delay Non-leveled bond anvil block


Die Rotation

Good Rotation Error Rotation

Die Bonding Quality SpecificationDie Bonding Quality SpecificationDie RotationDie Rotation

Rotated die Angle rotated

reference to the target bond position


Angle is out of the range 0.5° at Cp 1.33 when viewed from above

Inspection Method: Measurement using

Profile projector with 200X

Reference X axis

Reference Y axis

= Angle of rotation viewed from above


Rotation - con’t Error adjustment in 3-point alignment Error adjustment in bondarm 90 degree motion Collet vacuum is not enough Too high bond level


Coverage

Good Coverage Inadequate Coverage Excessive Coverage

Die Bonding Quality Specification Die Bonding Quality Specification Epoxy CoverageEpoxy Coverage

Epoxy spread Condition of reject: (AD898 as

example) Epoxy is spread out of 10

mils measured from the die perimeter.

Inspection Method: Measurement using Profile

projector with 100X

Epoxy coverage Epoxy coverage area after die

bonded reference to the die area

Condition of reject: (AD898 as example) Epoxy coverage is less than

100% of die perimeter. Inspection Method:

Visual inspection using Microscope (30X)

Die

L

Epoxy

DieEpoxy not coverall the perimeter

Epoxy Spread

Epoxy Coverage


Coverage - con’t Inadequate coverage

Too high bond level Too short bond delay Non-leveled bond anvil block Too low bond anvil block level

Excessive coverage Too low bond level Too long bond delay Too high anvil block level

Common Problems & Possible CausesCommon Problems & Possible Causes Bondline Thickness & Fillet Height

Good BLT

Good BLT

Inadequate BLT Excessive BLT

Die Bonding Quality Specification Die Bonding Quality Specification Epoxy Build-upEpoxy Build-up

Epoxy build-up Also called Fillet

Height This is the epoxy

quantity build up onto the die


h > (1/2 T + b)

Inspection Method: Visual inspection

using Microscope (30X)

h

TDie

b

T = Die thickness h = Epoxy build-upb = Bondline thickness

Die Bonding Quality Specification Die Bonding Quality Specification Bondline ThicknessBondline Thickness

Bondline thickness Thickness of the

Epoxy -- measured from the LF to the bottom of die

Condition of reject: b out of the range 1

0.5 mil

Inspection Method: Measurement using

Hisomet microscope (200X)

Example of BLT ResultDie size: 25 mil x 25 mil

Die thickness: 9 milLeadframe: SOT 23-3L

Example of BLT ResultDie size: 25 mil x 25 mil

Die thickness: 9 milLeadframe: SOT 23-3L

Die

b

Epoxy

b = Bondline thickness under the die before curing


Bondline Thickness - con’t Inadequate BLT

Too high bond level Too short bond delay Too low bond anvil block

Excessive BLT Too low bond level Too long bond delay Too high anvil block level


Die Tilt

No Die Tilt Die Tilt

Die Tilt

Die Bonding Quality Specification Die Bonding Quality Specification Die TiltDie Tilt

Die Tilt Tilt up of the die

horizontal surface Condition of reject:

(AD898 as example)

D > 0.6 mil


using Hisomet Microscope (200X)

D

D = Difference between highest and lowest corner of a die


Die Tilt Non-leveled bondarm Uneven flatness of substrate & collet surface Non-leveled bond anvil block Error adjustment in 3-point alignment Inadequate suck bond & bond delay Dispensing position accuracy Dispensing pattern Measurement tools

Die Bonding Quality Specification Die Bonding Quality Specification Die Shear ForceDie Shear Force

Die Shear Force The minimum force requirement

to shear a die Depends on the die size area

Shear Strength A force sufficient to shear the die

from its mounting or equal to twice the minimum specified shear strength shall be applied to the die using appropriate apparatus

AD898 as example Die area < 6250 mils2

Minimum die shear strength (Fm) = 0.4 gf/mils2 x Die area (A) mils2 , where A = length x width

Die area ≥ 6250 mils2

Fm = 2500gf Acceptance Criteria

Device is accepted only when the measured die shear strength force (F) with adhesion of die attach media residue falls into the following acceptance criteria:

Die

Force

Die attach media residue

Acceptance criteria

Less than 10 % Measured die shear strength (F) 2 x Fm

Between 10% and 50%

Measured die shear strength (F) 1.25 x Fm

Larger than 50% Measured die shear strength (F) Fm

Die Bonding Quality Specification Die Bonding Quality Specification Other Common Errors IOther Common Errors I

Cracked Die Broken die Condition of reject:

Any kind of crack seen on surface Side penetrating the inner portion of die

Inspection Method: Visual inspection using Microscope (30X)

Damage on die surface Caused mark on die surface Condition of reject:

Any physical damage, such as scratch, found on die surface caused by die bonder.


Mis-orientated die Condition of reject:

A bonded die is turned over. A bonded die is put upside down.


Crack

Scratch found on die surface

Die is turned over Die is put upside down

Die bottom

Epoxy on lead

Lead

Pad

Die

Epoxy on die

Die

Pad

Epoxy on pad

Die

Die

Pad

Epoxy

Die Bonding Quality Specification Die Bonding Quality Specification Other Common Errors IIOther Common Errors II

Epoxy outside bond area Epoxy on die / lead / pad Condition of reject:

Epoxy is found outside bond area

Inspection Method: Visual inspection using

Microscope (30X)

Excessive Epoxy Condition of reject:

Excessive epoxy is found on the bond area.


Microscope (30X)

Epoxy Outside Bond Area

Excessive Epoxy

Die

L

DieT hb

T = Die thicknessb = Bondline thickness

Die Bonding Quality Specification Die Bonding Quality Specification Other Common Errors IIIOther Common Errors III

Epoxy tailing Condition of reject:

Vertical tailing : h > (1/2 T + b)

Horizontal tailing : L > 4 mils


Microscope (30X)

Double Die Condition of reject:

Two dice are bonded at the same bonding position with one stack on the other one.


Microscope (30X)

Epoxy Tailing

Double Die

Die Bonding Quality Specification Die Bonding Quality Specification Other Common Errors IVOther Common Errors IV

Skip bond unit Condition of reject:

No die and epoxy is found on a bond unit

No die is present on the epoxy and no mark of die is observed.



No die found on the bond unit & no mark

No die and epoxy found on the bond

unit

Die

Epoxy

Die Bonding Quality Specification Die Bonding Quality Specification Other Common Errors VOther Common Errors V

Lost die Condition of reject:

No die is present on the epoxy but a mark of die is observed.



No die found but mark of die observed

Die

Epoxy

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Basic Die Bonding Process & Quality