Wire Bonding Quality Assurance and Testing Methods
Visual and mechanical testing methods of wire bonds
• Light- and scanning electron microscopical examinations
• Pull test
• Shear test
β
β
β β
Dr.Dr.-Ing. M. SchneiderSchneider-Ramelow phone: +49 30 / 46 40 3-172, fax: -162
martin.schneiderramelow@izm.fraunhofer.de
Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (IZM)
Gustav-Meyer-Allee 25, D-13355 Berlin
sheet 1
Wire Bonding Quality Assurance and Testing Methods
Wire bonding and quality assurance: General requirements
Global formulation:
•
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low cost technology
easy to realize and flexible during application
strong mechanical stability
thermal stability (in regard to further processing steps) and
good long term stability
low contact resistance
as much as possible great welding area between wire and metallization
no physical and chemical interactions with other materials
Test methods:
• visual inspektion MIL-STD 883 method 2010, 2017
• pull test MIL-STD 883 methode 2011 (destructive), methode 2023 (non destructive)
• shear test ASTM F 1269-89
sheet 2
Wire Bonding Quality Assurance and Testing Methods
Bonding methods
! principle
! parameters
! bonding material
! process kinetics
etc.
Wire
! diameter
! elongation, pull-strenght
! hardness
! surface topology
! behavior during bonding
etc.
Bonding metallization
! material, pretreatment
! hardness, property
! layer thickness/structure
! contamination
etc.
Quality assurance
! quality test methods
! standards
! parameter control
! product/application
requirements
etc.
Influences due to the bonding process
Bonding machine
! bonding procedure
! bonding speed
! adjustment, accuracy
! pattern recognition
system
etc.
sheet 3
Bonding conditions
! personal know-how
! personal motivation
! production sequence
! manuf. Infrastructure
! maintenance
etc.
Bonding substrate
! material, assembly
! vibration behavior
! layer adhesiveness
! work holder
etc.
Design
! layout
! functionality
! simulation
! compabibility to package
and device standards
etc.
Wire Bonding Quality Assurance and Testing Methods
Bond pads on chip:
• Multiple imprints of test probes or deep very imprints
• Strong adverse effects of surface quality
• Influence on bondability
sheet 4
Wire Bonding Quality Assurance and Testing Methods
Visual inspection MIL-STD 883 method 2010, 2017
to proof:
proof:
selective parameters:
parameters:
- geometry of bond contacts
- wire deformation
- loop geometry
- snap off behaviour
- placement of bond contacts
- position and welded area
- predetermined quantity of loops
- adhesion of metallization
- short circuits
- missing bonds or loops
Remark:
Remark: Visual inspection of bondpads before wire bonding!
bonding!
sheet 5
Wire Bonding Quality Assurance and Testing Methods
Ball and wedge bond
lift offs of wafer
metallizations while
TS-Au-B/W-Bonding
Wafer metallization lift offs
while TS-Au-W/W-Bonding
sheet 6
Wire Bonding Quality Assurance and Testing Methods
SEM-View (BSE): PCB metallization lift off and
undersurface of a lift off bond (wedge)
sheet 7
Wire Bonding Quality Assurance and Testing Methods
Quality Tests (Visual Methods)
Ball Bond
loop high
loop high
Wedge Bond
loop length
loop length
influence to
horizontal and
neck and heel vertical deformation
loop size and
sweeping
SEM – Figure of a typical Ball Bond
position of bonds
on the pad
Geometrical Parameters during Wire Bond
SEM – Figure of a typical Wedge Bond
sheet 8
Wire Bonding Quality Assurance and Testing Methods
Ball bond failures
sheet 9
Wire Bonding Quality Assurance and Testing Methods
Visual inspection of wire bonds
sheet 10
Wire Bonding Quality Assurance and Testing Methods
Visual inspection of wire bonds
sheet 11
Wire Bonding Quality Assurance and Testing Methods
Wedges on chip
Drahtbonds auf dem Chip
-•
-•
strongVerdrängung
squeezing out
of chip
Starke
der Chipmetallisierung
metallization while bonding
durch die Drahtbonds
possible evidence
of aauf
too
Möglicherweise
Hinweis
zusoften
weiche
surface metallization
Oberfläche
sheet 12
Wire Bonding Quality Assurance and Testing Methods
A
W
D
B
D
P
P
A pad width
W bond width
B pad length
P pitch
D wire diameter
sheet 13
standard
wire
A
B
P
cutting edge
W
A
B
P
W
1Mil
100µm 125µm 125µm 45µm 50µm
.004in .005in .005in .0018in .002in
2Mil
125µm 150µm 200µm 75µm 90µm 125µm 140µm 70µm
.005in .006in .008in .003in .0036in .005in .0056in .0028in
3Mil
180µm 200µm 250µm 125µm 120µm 170µm 150µm 112µm
.0072in .008in .01in .005in .0048in .0064in .006in .0045in
4Mil
200µm 280µm 280µm 130µm 150µm 220µm 190µm 130µm
.008in .0112in .0112in .0052in .006in .0088in .0076in .0052in
wire
Heavy wire
D
A
B
P
W
A
75µm 75µm 38µm
.003in .003in .0015in
B
P
W
5Mil
250µm 300µm 350µm 150µm 175µm 250µm 250µm 150µm
.01in
.012
.014in .006in .007
.01in
.01in
.006in
6Mil
250µm 500µm 400µm 200µm 230µm 320µm 250µm 180µm
.01in
.02in .016in .008in .0092in .0128in .01in
.0072in
10Mil
400µm 800µm 600µm 320µm 350µm 500µm 350µm 300µm
.016in .032in .024in .0128in .013in .02in
.013in .012in
20Mil
800µm 1300µm1150µm 650µm 660µm 950µm 700µm 600µm
.032in .052in .046in .026in .0264in .038in .028in .024in
Wire Bonding Quality Assurance and Testing Methods
Overbonded wedges (too much deformation), right: Detail
sheet 14
Wire Bonding Quality Assurance and Testing Methods
Results of a tilted glued or
soldered chip on bonding
process:
•
Surfaces of chip pads
aren´t horizontal
•
Bonding tool is touched
down tilted, too
•
Wedge is deformed nonuniform
•
Pad metallization or chip
could be damaged
sheet 15
Wire Bonding Quality Assurance and Testing Methods
Optical inspection of die tilting
tilted chip
IZM: Hillmann, Großer, Ghaharemani
sheet 16
Wire Bonding Quality Assurance and Testing Methods
Wire Sweep Definition
Normal
bond line
Integrated
circuit chip
α
Lead
finger
Swept lead
L
Sweep % = α/L x 100%
sheet 17
Wire Bonding Quality Assurance and Testing Methods
Mechanical
Mechanical bond contact inspection (tests)
tests)
to proof:
selected tests:
- mechanical stiffness of loops
- pull test
- ball bond strength
- shear test
- heavy wire wedge bond strength
- shear test
- simultaneous proofing of many bond contacts
- centrifugal test
- fatigue behaviour of loops
- vibration test
- crack initiation and growth
- mechanical shock test
- sweep off behaviour
- air jet test
sheet 18
Wire Bonding Quality Assurance and Testing Methods
Principle of pull test
β
β
β β
Quelle: Dage Firmenschrift
sheet 19
Wire Bonding Quality Assurance and Testing Methods
Failure modes:
1, 5 Bond lift off from pad metallization
(lift off)
FR
1. Bond
1
2
2, 4 Wire break at bond (heelcrack or neck
break when ball/wedge bonding)
3
wire break
3
2. Bond
4
sheet 20
5
Wire Bonding Quality Assurance and Testing Methods
load at chip:
Load/Force
Load/Force distribution while bond pull test
F1 = F2 =
F
= F 1+
2
2 sin Θ
d
2 1/2
F
Φ
2h
true for Φ = 0, both bond contacts at
one level and Θ1 = Θ2 = Θ
cos (Θ2 - Φ)
sin (Θ1 + Θ2)
load at substrate:
F2 = F
F1
h
Θ1
chip
H
d1
d2
d
sheet 21
F1 = F
cos (Θ1 + Φ)
sin (Θ1 + Θ2)
F2
Θ2
support
Wire Bonding Quality Assurance and Testing Methods
Quality criteria for pull testing
β
β
if
Characteristics
pull force
- average value (based on nondeform ed wire)
- standard deviation (based on average value)
- proportion of values < (based on standards) cN
β β
Conditions
laboratory
fabrication
>50 %
<15 %
0%
>50 %
<25 %
0%
0%
0%
<10 %
0%
lift offs
- pull lift off
- bond lift off
sheet 22
Wire Bonding Quality Assurance and Testing Methods
Minimum pull forces for destructive pull test (MIL STD 883, Methode 2011):
Minimum Bond Pull Limit [cN]
1000
1
2
3
1 Au (preseal)
2 Al (preseal)
Au (postseal)
100
3 Al (postseal)
10
25
250
wire diameter [µm]
sheet 23
Wires:
2500
Wire Bonding Quality Assurance and Testing Methods
Pull
Force
increasing quantity
of pull lift offs
increasing quantity
of heelcracks
optimum
sheet 24
increasing parameters
Wire Bonding Quality Assurance and Testing Methods
Principle of shear test
Source: Dage and „DVS-Merkblatt Drahtbonden“
sheet 25
1
2
3
4
5
Substrate/Pad
Interface Ball/Substrate
Au-Ball
Shear Tool
S Shear Heigth
Shear Level
FS Shear Force
Wire Bonding Quality Assurance and Testing Methods
1,6 16,7 10,0
1,4 6,7 5,0
0,9 0,0 0,0
0,8 0,0 0,0
0,9 0,0 0,0
1,0 11,5 0,0
1,2 20,0 0,0
bond lift offs [%]
s [cN]
10,5
12,0
14,5
15,0
14,5
11,5
8,5
pull lift offs[%]
average value
pull force [cN]
104/110
109/115
114/120
124/130
134/140
144/150
154/160
pull force
< 6 cN [%]
US power
1./2. bond [scale]
Standard report of pull test: Standard AlSi1 wire (30 µm)
5,0
1,7
0,0
0,0
0,0
0,0
0,0
Fehlerrate
error
rate
pull
force
Pullkraft
20,0
cN
16,0
100
%
80
12,0
60
8,0
40
4,0
20
number of tests:
n = 30
US time: 30 ms
bond force: 32 cN
tensile wire strength: 19 cN
sheet 26
average
pull[cN]
force [cN]
Pullkraft MW
Standardabweichung
[cN]
standard deviations[cN]
Pullkraft
6 cN
[%][%]
pull
force< <
6 cN
Pullabheber
[%]
pull lift offs [%]
Bondabheber
bond
lift offs[%]
[%]
0
104/
110
109/
115
114/
120
124/
130
134/
140
144/
150
US power 1./2. bond [scale]
scale]
154/
160
Wire Bonding Quality Assurance and Testing Methods
Failure modes while shear test
metallization
schear tool
ball
substrate (chip)
Ball shear
sheet 27
shear heigth
Ball lift off
Metallization cracking
Metallization lift off
Chip cratering
Wire Bonding Quality Assurance and Testing Methods
Quality criteria for ball shear testing (TS bonding)
bonding)
Conditions
laboratory
Characteristics
shear force
- average value (based on minimum shear force value)
- standard deviation (based on average value)
- minimun shear force (based on ball diameter after bonding)
fabrication
> 140 %
> 120 %
< 15 %
< 20 %
see beneath, no value < …
lift offs
0%
0%
0%
0%
> 80 %
> 50 %
no metallization lift off,
no cratering
- bond lift off
- shear lift off
- percentage off Au on pad
Minimum shear
value
shear force (cN)
sheet 28
50
15
ballbond diameter (µm)
75
100
30
45
125
75
Wire Bonding Quality Assurance and Testing Methods
Heavy wire wedge shear testing
Fshear
Pitch = W + S
W
Heavy wire: 400 µm
Pitch: 750 µm
sheet 29
S
Principle of shear test
Wire Bonding Quality Assurance and Testing Methods
Problems while evaluation of heavy wire shear test results
950
250 µm Al heavy wire on Al sheet
shear force [cN]
900
optimised parameters
850
800
750
very high parameters
700
650
Partial shear lift off
0
25
50
75
100
125
shear heigth [µm]
Questions: Where is the limit between shear lift off and shear through the
bond? What shear heigth should be choosen while shear testing?
sheet 30
Source: IZM Berlin
Wire Bonding Quality Assurance and Testing Methods
Load Cartridge Options:
1. Wire Pull
Maximum Pull Force
I Cartridge 1 I 100 g
I Cartridge 2 I
1 kg
I Cartridge 3 I 10 kg
2. Tweezer Pull/Peel
Maximum Pull Force
I Cartridge 1 I 100 g
I Cartridge 2 I
5 kg
Maximum Shear Force I Cartridge 1 I
250 g
3. Ball Shear
4. Shear
Maximum Shear Force I Cartridge 2 I
5 kg
I Cartridge 3 I 100 kg
Special Load Cartridges:
High Force Tweezer Pull up to 10 kg
Heated Bump Pull up to 10 kg
Stud Pull
Cold Bump Pull up to 5 kg
sheet 31