Underfill Training Report
ContentFlip Chip Technology
Underfill Process
Underfill Machine
Underfill Epoxy
Underfill Failure Mode Analysis
Applied Component and Foreground of Underfill
1.Flip Chip Technology
Component
Substrate
P r o c e s s
An IntegratedTechnology!
It is a chip connection technology which interconnects an IC chip to its next level
of packaging in such manner that IC’s active side faces to substrate.
DIE
Substrate
Bump
Adhesive
1.1 What is flip chip
1.Flip Chip Technology
Shrinking electronic devices
Packaged IC
Chip-On-Board
Flip Chip / CSP
Flip Chip bump configuration
DIE
Substrate
EutecticUBMPassivation
final pad
1.2 The component-Flip chip
1.Flip Chip Technology
Coverlayer /Base Layer
Lamination Adhesive 1Copper Trace Lamination Adhesive 2Stiffener (Metal/Polyimide)
Dynamic Area
Rigid Area Rigid Area
Pad cross-section
Flex structure
1.3 Flex lamination layer(Cross section)
XX--RayRay
CC--SAM SAM (C-mode Scanning
Acoustic Microscopy)
Curing
Cleaning
Reflow
Final QC
Solder PrintingPre-baking Chip Mounting Bonding
Function Test
Underfill
1.4 Process Flow
1.Flip Chip Technology
1.5 Why Underfill ?
Significance:
• Reduce stress due to thermal expansion
• Increase lifetime of connections
• Protect connections mechanically
• Reduce chance of contamination
Underfill is required to encapsulate under the die to neutralize the effects of
CTE mismatch.
1.Flip Chip Technology
CTE mismatch of varies components in Flip Chip package will cause high stress at the interconnection.
Underfill reduce Stress by distributing such stress over the entire chip area so the stress will not concentrated at the interconnections.
1.Flip Chip Technology
1.5 Why Underfill ?
2.1 Relative process flow of underfill
Reflow Reflow Inspection Pre-heater(In underfill machine)
Cen-heater(In underfill machine)
Post-heater(In underfill machine)
Touch up
Curing
Process control point: Underfill pattern Epoxy temperature
Substrate temperature Curing condition
1.Underfill Technology
2.2 Control point in underfill processUnderfill pattern selection
2.Underfill Technology
2.2 Control point in underfill processEpoxy temperature when dispensing
We select low viscosity temperature to insure epoxy can be dispensed out fluently
and flow fast.
Temp
Viscosity
Temp 1 Temp 2
Epoxy’s viscosity profile
2.Underfill Technology
2.2 Control point in underfill processSubstrate temperature when underfill
Dispensing temperature control is let the temperature stable when the pallet in Cen-
heater(Temp 3 to Temp 5).
Temp
Time
Reflow
Reflow Insp
Pre-heaterCen-heater
60sec 30sec 40sec
140℃
95℃
110℃
Temp 1
Temp 2
Temp 3 Temp 4 Temp 5
. . . .
. Desired Temperature Profile When Underfill
2.Underfill Technology
2.2 Control point in underfill process
Curing condition
120 150 170 2005% 1.1 0.1 0.0 0.050% 14.5 1.1 0.2 0.090% 18.1 3.6 0.8 0.199% 96.1 7.2 1.6 0.2
99.9% 144.2 10.8 2.3 0.399.99% 192.2 14.4 3.1 0.499.999% 240.3 18.0 3.9 0.5
Temperature(oC)Reaction rate(%)
Namics U8437-2 epoxy
Time of reaction rate X% at each temperature (min.)
Insure the reaction rate surpass 99.99% is our control specification.
2.Underfill Technology
2.3 Process control in different underfill epoxy
Epoxy Temp Substrate Temp Curing Condition
Namics U8433L 55~65C 95+5C 65C/15mins+150C/60mins
Namics U8437-2 50~60C 85+10C 150C/60mins
Hysol FP4530 55~65C 85+10C 165C/15mins
Hysol FP4549 / 85+10C 165C/30mins
Emerson E-1159 30C 50+10C 120C/30mins or 130/15mins
ItemEpoxy
2.Underfill Technology
3.Underfill Machine
3.1 Develop history of dispense valveAir pressure time control
Now we use this for manual underfill
Ideal for use in low cost assembly areas
Very little maintenanceLow cost
Dispensed volume changes dependingon the fill level of the syringe
3.Underfill Machine
3.1 Develop history of dispense valveAuger pump
•Easy to Clean
•Used for small dots dispensing of silver / solder paste and encapsulants
•Accuracy 3 to 5 % typical in the 10 to 100mg range
DV-8K
3.Underfill Machine
3.1 Develop history of dispense valve
Linear pump(DP-3K)
3.Underfill Machine
3.1 Develop history of dispense valve
Dispense Jets
Dispenses adhesive material from a distance of 0.5 mm to 3 mm
Eliminates movement on the Z-axis between dots
Jet dispenser cycles every 10 ms ( 360,000 cycle/h )
DJ-2K
Standard Dove Tail Adapter
Integrated Temperature Control
Piston Stroke Adjust
MaterialFeed Tube
Nozzle/Seat Assembly
3.Underfill Machine
3.2 DJ-9K instruction
3.Underfill Machine
3.2 DJ-9K instruction
Needle
U-cup
Fluid chamber
O-Ring
Seat
Nozzle
TCA
Stroke adjustment knob
Spring
Load button
Needle
NozzleDispense Distance
Dispense Gap
3.Underfill Machine
3.2 DJ-9K instruction
a. Seat:15mil
b. Nozzle:6mil
b. Stroke length:15unit
c. Valve1 fluid air digital gauge: 15psi
d. Valve on/off time: 4/4msec
e. Needle heater temperature: 60C
f. Substrate temperature: 90~100(setting:135)
h. Dispensing gap: 55~75mil
i. Dispensing distance: 8~10mil
Parameter setting on Toshiba FPCA
M-620 X-1020
Dispensing Jet
Display
Power
Urgency Switch
3.Underfill Machine
3.3 Structure of Asymtek underfill machine: M-620 and X-1020
3.Underfill Machine
3.4 X-1020 machine
Vision / Lighting
Heating
Height Sense
Software
MFC &
CPJ
Algorithm 2_Multishot X_0712_X&Y Errors
-8-7-6-5-4-3-2-10123456789
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
X Errors (mils)
Y Er
rors
(mils
)
Motion Control
Help File
3.Underfill Machine
3.4 X-1020 machine
1.Teach fiducial mark in workpiece to establish all sample’s location (Two circular
metal point on pallet);
2.Create pattern and teach fiducial mark on samples;
3.Edit weight control line in pattern,this will establish underfill pattern,epoxy
volume,dispensing gap,dispensing distance and other parameter;
4.Edit how the program running and teach each sample’s location.
How to edit a program
For optimal Production, a Program should contain three elements:
1.A Program File (dispensing commands, process commands, etc.)
2.A Fluid File (contains all relative parameters like dispense gap,dispense
speed to each dot.)
3.A Vision File (saved automatically when teaching a program)
4.A Recipe File (above three elements, when saved and assembled, are
collectively called a Recipe.)
How to save a program
3.Underfill Machine
3.4 X-1020 machine
FKV 2A0-U-9K-M-H-01 Program
3.Underfill Machine
3.4 X-1020 machine
FKV 2A0-U-9K-M-H-01 Program
3.Underfill Machine
3.4 X-1020 machine
4.Underfill Epoxy
4.1 Epoxy datasheet (Namics U8437-2)ITEM UNIT U8437-2
Filler content wt% 55Density - 1.6Colour - Black
Viscosity Pa.s 40Gel time(150C) sec 40
Tg(TMA) C 137C.T.E(TMA) <Tg 32
>Tg 100Bending modulus Gpa 8.0Bending strength Mpa 130Young's modulus Gpa 7.0
Poisson ratio - 0.33Volume resistivity Initial >1.0X1015
(500V) after PCT >1.0X1013Moisture obsorption (after PCT) wt% 1.4
Dielectric constant (1MHz) - 3.5Dielectric loss tangent (1MHz) - 0.007 (0.7%)
Thermal conductivity W/m.K 0.67 Purity (after PCT) Cl 2
Na <1.0K <1.0
Alpha ray emision cont/cm2.hr <.001PCT: 121C 2atm 20hours
ppm/C
ohm.cm
ppm
4.Underfill Epoxy
HOW TO USE Standard dispensing condition Needle :18-23G Temperature : Curing condition :150Cx20min(Standard) :165Cx60min(High reliability temperature reflow) Storage condition :Below -20C For a 10CC syringe,over 1 hours is needed for the syringe to return to room temperature
POT-LIFE Double Viscosity at 25C:>72hours
ADHESION STRENGTH(2x2mm chip) Shear strength:30kgf (Si Chip vs FR-4)
FLUIDITY TEST Test condition Substrate :FR-4 Chip :Glass Gap :50um Temperature :70C
0 1 2 3 4 50 5.5 11 14.5 16.5 19
5
10
15
20
25
0 2 4 6 8
Time(min.)
Fluid Length(mm)
4.Underfill Epoxy
4.2 Property of process control
Viscosity
Epoxy’s viscosity affect the dispense method and machine parameter.
FP4530 epoxy viscosity chart
2000
4000
6000
8000
0 50 100 150 200 250 300 350 400Time(mins)
Visc
osity
(cps
)
Double viscosity time(Epoxy’s use life)
52# Spindle 50rpm at 30C
4.Underfill Epoxy
4.2 Epoxy property on process control
Gel time
Epoxy’s gel time is the time of epoxy from liquid to gel,underfill flow time
should short than gel time.
Moisture absorption
Moisture absorption is the ability of epoxy absorb moisture,low moisture
absorption is good because more moisture in epoxy can cause epoxy can’t
be cured completely.
Curing schedule
Curing is made epoxy’s molecular structure from chain to net,after this,epoxy
become harden and firmed
4.2 Epoxy property on function
4.Underfill Epoxy
Filler content
Affect epoxy’s CTE,viscosity and bending strength
Tg
Epoxy’s glass transition temperature,high Tg avoid high temperature cause
defect because after the epoxy changed into glass state,its molecular distance
become big,it will cause CTE changed acutely and the epoxy become breakable.
C.T.E.
Underfill epoxy is filled to reduce the C.T.E mismatch of chip and FPC,so the
epoxy’s CTE should near to chip and substrate’s C.T.E.
4.2 Epoxy property on function
4.Underfill Epoxy
Bending strength
Bending strength
TempTg
Bending strength is the combine intensity between chip and FPC,it changed acutely when
the temperature achieved to epoxy’s Tg point.
4.2 Epoxy property on functionBending strength
4.Underfill Epoxy
LCD monitor
Force GaugeCamera
FPC Fixture
Console
Shear tester is used to test bending strength,shear knife go ahead with a
constant speed,if the epoxy was separate from FPC,the shear knife will stop and
a value will be showed on force gauge.
4.2 Epoxy property on functionThermal conductivityThermal conductivity is epoxy’s capability to transfer heat,to the hard disk driver,
high thermal conductivity epoxy is acceptable.
4.Underfill Epoxy
Volume resistivity
A concept in electrostatic,it shows material’s electric conduct capability.
Dielectric constant
A coefficient which express material’s insulating capability.To underfill epoxy,
the high dielectric constant value,the better to use.
4.Underfill Epoxy
4.4 Ideal epoxy in underfill process
High Tg/Low CTE/Low Modulus
Low stress,Improve thermal shock,temp cycle
+ Good adhesion to all different surfaces
High bonding strength
+ High Moisture Resistance
+ Fast flow
Productivity
+ Fast cure
Productivity
4.Underfill Epoxy
+ Low Shrinkage
Low warpage
+ Low pot life
Stable in process
+ No Void
Dispensability
+ No filler separation
Uniform flow
+ No toxicity
4.4 Ideal epoxy in underfill process
4.5 Defect analysis
4.Underfill Epoxy
VoidEpoxy Fatigue
Island EpoxyExcess Epoxy
Poor Epoxy
Function defect
Void
Epoxy Fatigue
Visual defect
Island epoxy
Excess epoxy
Poor epoxy
Others
4.5 Defect analysis
4.Underfill Epoxy
VoidVolatile void Capture void
General cause&solution in process
Substrate temperature is not matched for underfill
---- >> Refer to epoxy’s datasheet and select proper temperature
Dispense pattern is not suitable for die shape
---- >> Optimize underfill pattern
Dispense volume is not enough
---- >> Dispensing with sufficient epoxy volume
Viscosity of underfill epoxy is high
---- >> Use fresh underfill epoxy
4.5 Defect analysis
4.Underfill Epoxy
Volatile void
Underfill Curing
Cause & solution
Absorb moisture of FPC
-- >> Dispensing duly after reflow
Poor wetting parts on substrate by flux residue exists
-- >> Reduce flux residue
Moisture absorption changed profile
4.5 Defect analysis
4.Underfill Epoxy
Volatile void
4.5 Defect analysis
4.Underfill Epoxy
Capture void
The flow speed > The penetrate speed >>> Capture void
Cause & solution
Dispense pattern is not suitable for bump layout
-- >> Select proper dispense pattern
Die size is too big
-- >> Optimize dispense method and select proper epoxy
4.5 Defect analysis
4.Underfill Epoxy
Capture void
Underfill time too short in seal pass
Cause & solution
Underfill time too short
-- >> Waiting for epoxy penetrate the whole chip then do seal pass
Seal passDispensing
4.5 Relative test
4.Underfill Epoxy
C-SAM (SAM=Scaning acoustic microscopy)
Cross section
C-SAM is a test method which use ultrasonic scan to establish solder layer, underfill
layer is integrated or not.
Reflection of the ultrasonic beam at interfaces with impedance mismatch,,f.e. surface,
back wall,defects,layer interfaces…
Transverse section test, skive the sample to a surface (to void layer or filler delamination
layer and so on) and will get a view at the layer you want.
6.Flip Chip Applied Component
Microprocessor
Memory
25mmX25mm (Biggest)
Hard Disk Driver3mmX3mm