1. Basic Die Bonding Process & Quality

2. Typical Die Bonding Sequence
Epoxy dispensed on L/F
Die is bonded onto L/F
L/F
L/F index to bond position x x
Wafer
Die is picked up
Pad
Collet lower down to pick position
Collet
at home
position
Collet lower down to bond position
Epoxy dispensed from syringe
Die is picked up
Mylar delaminate from die
Vacuum to hold substrate
Vacuum to hold substrate
Die ready,
Vacuum apply
Ejector pin back to home
Ejector pin up

3. Typical 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

4. Die 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….

5. Dispensing Background Information of Epoxy
Function of epoxy
Adheres the die on substrate
Commonly-used epoxy
Typical Property

6. Dispensing Background Information of Epoxy
Paste Die Attach in Plastic Packages Adhesive Properties
Handling Properties
Rheology
Cure Condition
Assembly Properties
Bleed
Outgassing
Adhesion
Reliability Properties
Voids
Thermal / Electrical Conductivity
Ionic Contamination
Stress
Why handling is important

7. Dispensing Substrate Common substrates used Considerations PCB
Leadframe
BGA
Ceramic
Considerations
Wetting properties
Pad to die ratio

8. Dispensing Methodology
Time-Pressure-Vacuum System
Volumetric Dispensing
Rotating Disc

9. Dispensing Methodology
Time-Pressure-Vacuum System
A process of the application of compressed air in a preset period for the fluid dispensing
Apply Vacuum for removing the
compressed air
Maintain the pressure
Prevent dripping & suck back
Vacuum
Pressure
Syringe with epoxy

10. Dispensing Methodology
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

11. Dispensing Methodology
Volumetric Dispensing
Process Principle
Positive Displacement System
(Piston Pump)
Apply compressed air
Pull up the piston to feed
epoxy into the chamber
Switch the valve port
Piston is pushed to
dispense epoxy
Syringe
Piston
Chamber
Valve

12. Dispensing Methodology
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

13. Dispensing Methodology
Rotating Disc
Disc holding epoxy rotated with a stationary spreader
Level of epoxy thickness in disc can be adjusted
Stamping pin move in X & Z
Epoxy disc rotation

14. Dispensing Application & 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)

15. Dispensing Application & Tools
Shower Head
Nomenclature of shower head
Holes
Hole diameter
Needle length
2-point stamping
4-point stamping

16. Dispensing 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)

17. Dispensing Application & Tools
Stamping pin
Nomenclature of stamping pin
pin tip radius
pin tip length
Tip radius
Stamping pin tip
Tip length

18. Dispensing Application & Tools
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

19. Dispensing Application & Tools
Writing pin
Nomenclature of writing pin
writing pin length
outer diameter
inner diameter
Cross
Double-Y-Horizontal
Double-Y-Horizontal

20. Effect of usage of Dispensing Method (Advantages & Disadvantages of Different Dispensing Method)

21. Effect of usage of Dispensing Method
Common problems
Dripping
Tailing
Inconsistency
Void
Void Area
Photo taken by X-ray

22. Die 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….

23. Pick & Place Die 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
Hi-temp Collet
Tungstein Carbide Collet
Rubber Collet
4-sided Collet
2-sided Collet

24. Pick & Place Die 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

25. Pick & Place Die Picking Tools - Cap / Chuck / Pin
Act as platform for holding the die
Holes for vacuum
Chuck
Holding the pin
Pin
Eject the die from the Mylar
Ejector Cap
Ejector Assembly
Ejector Chuck & Pin

26. Pick & Place Die Picking Tools – Cap / Chuck
Ejecting tools selection
It is base on die dimension
die width x die length
Definition of die dimension
Schematic diagram of chuck

27. Pick & Place Die Picking Tools - Pin
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 = mm = 5 mils
R3 ejector pin
tip radius = mm = 3 mils
R8 ejector pin
tip radius = mm = 8 mils

28. Pick & Place Die Picking Tools - Pin
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

29. Pick & Place Wafer Handling
Different type of wafer ring / frame / wafer cassette
Wafer cassette
Disco
K & S
Wafer ring
Teflon
D company
K company

30. Pick & Place Wafer Tape Material
Different type of wafer tape material
Mylar tape
UV tape
Waffle pack
Blue Mylar Tape
Colourless UV Tape

31. Pick & Place Wafer Tape Material
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

32. Pick & Place Wafer Tape Material
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 : C
humidity : 60-70%
Tape mounting process
amount of tension should be even in both X & Y direction

33. Die 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….

34. Die 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

35. Common Problems & Possible Causes
Die Placement
Good Placement
Error Placement in X-Y direction

36. Die Bonding Quality Specification Bond 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

37. Common Problems & Possible Causes
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

38. Common Problems & Possible Causes
Die Rotation
Good Rotation
Error Rotation

39. Die Bonding Quality Specification Die Rotation
Rotated die
Angle rotated reference to the target bond position
Condition of reject: (AD898 as example)
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

40. Common Problems & Possible Causes
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

41. Common Problems & Possible Causes
Coverage
Good Coverage
Inadequate Coverage
Excessive Coverage

42. Die Bonding Quality Specification Epoxy 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
Epoxy coverage is less than 100% of die perimeter.
Visual inspection using Microscope (30X)
Die L
Epoxy
Epoxy Spread
Die
Epoxy not cover
all the perimeter
Epoxy Coverage

43. Common Problems & Possible Causes
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

44. Common Problems & Possible Causes
Bondline Thickness & Fillet Height
Good BLT
Good BLT
Inadequate BLT
Excessive BLT

45. Die Bonding Quality Specification Epoxy Build-up
Also called Fillet Height
This is the epoxy quantity build up onto the die
Condition of reject: (AD898 as example)
h > (1/2 T + b)
Inspection Method:
Visual inspection using Microscope (30X) h T
Die b
T = Die thickness
h = Epoxy build-up
b = Bondline thickness

46. Die Bonding Quality Specification Bondline Thickness
Example of BLT Result
Die size: 25 mil x 25 mil
Die thickness: 9 mil
Leadframe: SOT 23-3L
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)
Die b
Epoxy
b = Bondline thickness under the die before curing

47. Common Problems & Possible Causes
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

48. Common Problems & Possible Causes
Die Tilt
Die Tilt
No Die Tilt
Die Tilt

49. Die Bonding Quality Specification Die Tilt
Tilt up of the die horizontal surface
Condition of reject: (AD898 as example)
D > 0.6 mil
Inspection Method:
Visual inspection using Hisomet Microscope (200X) D
D = Difference between highest and lowest corner of a die

50. Common Problems & Possible Causes
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

51. Die Bonding Quality Specification 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

52. Die Bonding Quality Specification Other 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
Any physical damage, such as scratch, found on die surface caused by die bonder.
Visual inspection using Microscope (30X)
Mis-orientated die
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

53. Die Bonding Quality Specification Other Common Errors II
Epoxy on lead
Lead
Pad
Die
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
Excessive epoxy is found on the bond area.
Epoxy on die
Die
Pad
Epoxy on pad
Die
Epoxy Outside Bond Area
Die
Pad
Epoxy
Excessive Epoxy

54. Die Bonding Quality Specification Other Common Errors III
Epoxy tailing
Condition of reject:
Vertical tailing :
h > (1/2 T + b)
Horizontal tailing :
L > 4 mils
Inspection Method:
Visual inspection using Microscope (30X)
Double Die
Two dice are bonded at the same bonding position with one stack on the other one.
Visual inspection using Microscope (30X)
Die L
Die T h b
T = Die thickness
b = Bondline thickness
Epoxy Tailing
Double Die

55. Die Bonding Quality Specification Other 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.
Inspection Method:
Visual inspection using Microscope (30X)
No die found on the bond unit & no mark
No die and epoxy found on the bond unit
Die
Epoxy

56. Die Bonding Quality Specification Other Common Errors V
Lost die
Condition of reject:
No die is present on the epoxy but a mark of die is observed.
Inspection Method:
Visual inspection using Microscope (30X)