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Basic Die Bonding Process & Quality. Typical Die Bonding Sequence Wafer Collet at home position Die ready, Vacuum apply Ejector pin up Collet lower down.

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Presentation on theme: "Basic Die Bonding Process & Quality. Typical Die Bonding Sequence Wafer Collet at home position Die ready, Vacuum apply Ejector pin up Collet lower down."— Presentation transcript:

1 Basic Die Bonding Process & Quality

2 Typical Die Bonding Sequence Wafer Collet at home position Die ready, Vacuum apply Ejector pin up Collet lower down to pick position Ejector pin back to home Die is picked up Collet lower down to bond position Die is bonded onto L/F xx L/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

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  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 Dispensing Background Information of Epoxy

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

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

9  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 Dispensing Methodology Syringe with epoxy Vacuum Pressure

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  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 Dispensing Methodology Valve Chamber Piston Syringe

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 Epoxy disc rotation Stamping pin move in X & Z

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 4-point stamping2-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  Stamping pin  Nomenclature of stamping pin pin tip radius pin tip length Dispensing Application & Tools Tip length Tip radius Stamping pin tip

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

20 Effect of usage of Dispensing Method (Advantages & Disadvantages of Different Dispensing Method) Advantages of different dispensing method 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 Tungstein Carbide Collet Hi-temp Collet 4-sided Collet 2-sided Collet Rubber 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  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

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 dimensionSchematic 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 Disco K & S Teflon D company K company

30  Different type of wafer tape material  Mylar tape  UV tape  Waffle pack Pick & Place Wafer Tape Material 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 PlacementError 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Y X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 RotationError 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 CoverageInadequate CoverageExcessive 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  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 Die Epoxy not cover all the perimeter Epoxy Spread 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 Inadequate BLTExcessive BLT

45 Die Bonding Quality Specification Epoxy Build-up  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  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 Result Die size: 25 mil x 25 mil Die thickness: 9 mil Leadframe: SOT 23-3L Example of BLT Result Die size: 25 mil x 25 mil Die thickness: 9 mil Leadframe: SOT 23-3L 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 No Die Tilt Die Tilt

49 Die Bonding Quality Specification Die Tilt  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  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 mils 2 Minimum die shear strength (Fm) = 0.4 gf/mils 2 x Die area (A) mils 2, where A = length x width  Die area ≥ 6250 mils 2 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 F m Between 10% and 50% Measured die shear strength (F)  1.25 x F m Larger than 50%Measured die shear strength (F)  F m

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  Condition of reject: Any physical damage, such as scratch, found on die surface caused by die bonder.  Inspection Method: Visual inspection using Microscope (30X)  Mis-orientated die  Condition of reject: A bonded die is turned over. A bonded die is put upside down.  Inspection Method: Visual inspection using Microscope (30X) Crack Scratch found on die surface Die is turned over Die is put upside down Die bottom

53 Epoxy on lead Lead Pad Die Epoxy on die Die Pad Epoxy on pad Die Pad Epoxy Die Bonding Quality Specification Other 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.  Inspection Method: Visual inspection using Microscope (30X) Epoxy Outside Bond Area Excessive Epoxy

54 Die L T h b T = Die thickness b = Bondline thickness 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  Condition of reject: Two dice are bonded at the same bonding position with one stack on the other one.  Inspection Method: Visual inspection using Microscope (30X) 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)


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