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
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Dr.Dr.---Ing.Ing. M. SchneiderSchneider---RamelowRamelow phone: +49 30 / 46 40 3-172, fax: -162 [email protected] 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: • 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 Wire Quality assurance Bonding metallization ! principle ! diameter ! quality test methods ! material, pretreatment ! parameters ! elongation, pull-strenght ! standards ! hardness, property ! bonding material ! hardness ! parameter control ! layer thickness/structure ! process kinetics ! surface topology ! product/application ! contamination etc. ! behavior during bonding requirements etc. etc. etc.
Influences due to the bonding process
Bonding machine Bonding conditions Bonding substrate Design ! bonding procedure ! personal know-how ! material, assembly ! layout ! bonding speed ! personal motivation ! vibration behavior ! functionality ! adjustment, accuracy ! production sequence ! layer adhesiveness ! simulation ! pattern recognition ! manuf. Infrastructure ! work holder ! compabibility to package system ! maintenance etc. and device standards etc. etc. etc.
sheet 3 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 proofproof:: selective parametersparameters:: - 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
RemarkRemark:: Visual inspection of bondpads before wire bondingbonding!!
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) loop high Ball Bond loop high Wedge Bond
loop length loop length influence to horizontal and neck and heel vertical deformation SEM – Figure of a typical Ball Bond
loop size and sweeping 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 -• Starke strong Verdrängung squeezing outder Chipmetallisierung of chip metallization while bonding durch die Drahtbonds -• Möglicherweise possible evidence Hinweis of aauf too zu softenweiche surface metallization Oberfläche
sheet 12 Wire Bonding Quality Assurance and Testing Methods
A W wire standard cutting edge D A B P W A B P W 100µm 125µm 125µm 45µm 50µm 75µm 75µm 38µm 1Mil .004in .005in .005in .0018in .002in .003in .003in .0015in B 125µm 150µm 200µm 75µm 90µm 125µm 140µm 70µm 2Mil .005in .006in .008in .003in .0036in .005in .0056in .0028in 180µm 200µm 250µm 125µm 120µm 170µm 150µm 112µm 3Mil .0072in .008in .01in .005in .0048in .0064in .006in .0045in D 200µm 280µm 280µm 130µm 150µm 220µm 190µm 130µm 4Mil .008in .0112in .0112in .0052in .006in .0088in .0076in .0052in wire Heavy wire PP D A B P W A B P W 250µm 300µm 350µm 150µm 175µm 250µm 250µm 150µm 5Mil .01in .012 .014in .006in .007 .01in .01in .006in A pad width W bond width 250µm 500µm 400µm 200µm 230µm 320µm 250µm 180µm 6Mil .01in .02in .016in .008in .0092in .0128in .01in .0072in B pad length P pitch 400µm 800µm 600µm 320µm 350µm 500µm 350µm 300µm 10Mil .016in .032in .024in .0128in .013in .02in .013in .012in D wire diameter 20Mil 800µm 1300µm1150µm 650µm 660µm 950µm 700µm 600µm .032in .052in .046in .026in .0264in .038in .028in .024in sheet 13 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 non- uniform • 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 Lead bond line finger
α Swept lead Integrated circuit chip L
Sweep % = α/L x 100%
sheet 17 Wire Bonding Quality Assurance and Testing Methods
MechaniMechanicalcal bbond ond contact inspection ((teststeststests))
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
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Quelle: Dage Firmenschrift sheet 19 Wire Bonding Quality Assurance and Testing Methods
Failure modes: 1, 5 Bond lift off from pad metallization (lift off) 2, 4 Wire break at bond (heelcrack or neck break when ball/wedge bonding) FR 3 wire break
1. Bond 3 2. Bond 1 2
4 5
sheet 20 Wire Bonding Quality Assurance and Testing Methods
LoadLoad/Force/Force distribution while bond pull test load at chip: F Θ Φ cos ( 2 - ) 2 1/2 Φ F1 = F F = F d sin (Θ + Θ ) F1 = F2 = 1 + 1 2 2 sin Θ 2 2 h load at substrate: true for Φ = 0, both bond contacts at Θ Φ Θ Θ Θ cos ( 1 + ) one level and 1 = 2 = F2 = F F1 Θ Θ sin ( 1 + 2) h Θ 1
F2 chip H Θ 2
support d1 d2 d
sheet 21 Wire Bonding Quality Assurance and Testing Methods
Quality criteria for pull testing
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if β β Conditions Characteristics laboratory fabrication pull force
(based on nondeformed wire) - average value >50 % >50 % (based on average value) - standard deviation <15 % <25 % (based on standards) - proportion of values < cN 0 % 0 %
lift offs - pull lift off 0 % <10 % - bond lift off 0 % 0 % sheet 22 Wire Bonding Quality Assurance and Testing Methods
Minimum pull forces for destructive pull test (MIL STD 883, Methode 2011):
1000 1 2 Wires: 3 3 1 Au (preseal) 2 Al (preseal) 100 Au (postseal) 3 Al (postseal)
10 Minimum Bond Pull Limit [cN]
25 250 2500 wire diameter [µm] sheet 23 Wire Bonding Quality Assurance and Testing Methods
Pull Force
increasing quantity increasing quantity of pull lift offs of heelcracks
optimum increasing parameters
sheet 24 Wire Bonding Quality Assurance and Testing Methods
Principle of shear test
1 Substrate/Pad 2 Interface Ball/Substrate 3 Au-Ball 4 Shear Tool S Shear Heigth 5 Shear Level F Shear Force Source: Dage and „DVS-Merkblatt Drahtbonden“ S
sheet 25 Wire Bonding Quality Assurance and Testing Methods
Standard report of pull test: Standard AlSi1 wire (30 µm)
Fehlerrateerror rate pullPullkraft force 20,0 cN % 16,0
6cN [%] 6cN 100 [cN]
< pull lift offs[%] lift pull s pull force lift [%] bond offs US power power US [scale] bond 1./2. average value pull [cN] force 12,0 104/110 10,5 1,6 16,7 10,0 5,0 109/115 12,0 1,4 6,7 5,0 1,7 80 114/120 14,5 0,9 0,0 0,0 0,0 8,0 124/130 15,0 0,8 0,0 0,0 0,0 60 134/140 14,5 0,9 0,0 0,0 0,0 4,0 144/150 11,5 1,0 11,5 0,0 0,0 154/160 8,5 1,2 20,0 0,0 0,0 40
20 average pull force [cN] Pullkraft MW [cN] standardStandardabweichung deviation [cN] s [cN] 0 pull force < 6 cN [%] number of tests: n = 30 Pullkraft < 6 cN [%] pullPullabheber lift offs [%][%] 104/ 109/ 110 114/ 124/ Bondabheber [%] 115 134/ bond lift offs [%] US time: 30 ms 120 130 144/ 140 154/ 150 bond force: 32 cN 160 tensile wire strength: 19 cN US power 1./2. bond [[scale scalescale]] sheet 26 Wire Bonding Quality Assurance and Testing Methods
Failure modes while shear test schear tool metallization
ball shear heigth
substrate (chip) Ball lift offMetallization lift off
Ball shear Metallization crackingChip cratering
sheet 27 Wire Bonding Quality Assurance and Testing Methods
Quality criteria for ball shear testing (TS bondingbonding))
Conditions Characteristics laboratory fabrication shear force
(based on minimum shear force value) - average value > 140 % > 120 % (based on average value) - standard deviation < 15 % < 20 % (based on ball diameter after bonding) - minimun shear force see beneath, no value < …
lift offs - bond lift off 0 % 0 % - shear lift off 0 % 0 % - percentage off Au on pad > 80 % > 50 % no metallization lift off, no cratering
Minimum shear ballbond diameter (µm) value 50 75 100 125 shear force (cN) 15 30 45 75
sheet 28 Wire Bonding Quality Assurance and Testing Methods
Heavy wire wedge shear testing
Fshear
Pitch = W + S
WS
Heavy wire: 400 µm Principle of shear test Pitch: 750 µm
sheet 29 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 900 optimised parameters 850
800
750 shear force [cN] 700 very high parameters
650 0 25 50 75 100 125 Partial shear lift off 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?
Source: IZM Berlin sheet 30 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 3. Ball Shear Maximum Shear Force I Cartridge 1 I 250 g 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