ASTM F1269-89(2001)
(Test Method)Test Methods for Destructive Shear Testing of Ball Bonds
Test Methods for Destructive Shear Testing of Ball Bonds
SCOPE
1.1 These test methods cover tests to determine the shear strength of a series of ball bonds made by either thermal compression or thermosonic techniques. Note 1Common usage at the present time considers the term "ball bond'' to include the enlarged spheriodal or nailhead portion of the wire, (produced by the flameoff and first bonding operation in the thermal compression and thermosonic process, or both,) the underlying bonding pad, and the ball bond-bonding pad interfacial-attachment area or weld interface.
1.2 These test methods cover ball bonds made with small diameter (from 18 to 76-µm (0.0007 to 0.003-in.)) wire of the type used in integrated circuits and hybrid microelectronic assemblies.
1.3 These test methods can be used only when the ball height and diameter are large enough and adjacent interfering structures are far enough away to allow suitable placement and clearance (above the bonding pad and between adjacent bonds) of the shear test ram.
1.4 These test methods are destructive. They are appropriate for use in process development or, with a proper sampling plan, for process control or quality assurance.
1.5 A nondestructive procedure is possible; although it may be contra indicated due to the possible interference with adjacent wire bonds and microcircuit components.
1.6 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F 1269 – 89 (Reapproved 2001)
Test Methods for
Destructive Shear Testing of Ball Bonds
This standard is issued under the fixed designation F 1269; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope F 458 Practice for Nondestructive Pull Testing of Wire
Bonds
1.1 These test methods cover tests to determine the shear
F 459 Test Methods for Measuring Pull Strength of Micro-
strength of a series of ball bonds made by either thermal
electronic Wire Bonds
compression or thermosonic techniques.
2.2 NIST Document:
NOTE 1—Common usage at the present time considers the term “ball
NBS Handbook 105-1 Specification and Tolerances for
bond’’ to include the enlarged spheriodal or nailhead portion of the wire,
Reference Standards and Field Standards, Weights and
(produced by the flameoff and first bonding operation in the thermal
Measures
compression and thermosonic process, or both,) the underlying bonding
IOLMClassM2-Circular547-1 PrecisionLaboratoryStan-
pad, and the ball bond-bonding pad interfacial-attachment area or weld
dards of Mass and Laboratory Weights
interface.
2.3 Military Standard:
1.2 These test methods cover ball bonds made with small
MIL-STD 883C, Method2010
diameter (from 18 to 76-µm (0.0007 to 0.003-in.)) wire of the
type used in integrated circuits and hybrid microelectronic
3. Terminology
assemblies.
3.1 Definitions of Terms Specific to This Standard:
1.3 These test methods can be used only when the ball
3.1.1 ball lift—a separation of the ball bond at the bonding
height and diameter are large enough and adjacent interfering
pad interface with little or no residual (less than 25% of the
structuresarefarenoughawaytoallowsuitableplacementand
bond deformation area) ball metallization remaining on the
clearance(abovethebondingpadandbetweenadjacentbonds)
bonding pad (that remains essentially intact). In the case of
of the shear test ram.
gold ball bonds on aluminum pad metallization, a ball lift is
1.4 Thesetestmethodsaredestructive.Theyareappropriate
defined as a separation of the ball bond at the bonding pad
foruseinprocessdevelopmentor,withapropersamplingplan,
interface with little or no intermetallic formation either present
for process control or quality assurance.
or remaining (area of intermetallic less than 25% of the bond
1.5 Anondestructiveprocedureispossible; althoughitmay
deformation area).
be contra indicated due to the possible interference with
3.1.1.1 Discussion—ntermetallic refers to the aluminum
adjacent wire bonds and microcircuit components.
gold alloy formed at the ball bond pad metallization interfacial
1.6 The values stated in SI units are to be regarded as the
area where a gold ball bond is attached to an aluminum pad
standard. The values given in parentheses are for information
metallization.
only.
3.1.2 ball shear (weld interface separation)—an appre-
1.7 This standard does not purport to address all of the
ciable intermetallic (in the case of the aluminum-gold system)
safety concerns, if any, associated with its use. It is the
and ball metallization, or both, (in the case of the gold-to-gold
responsibility of the user of this standard to establish appro-
system) remains on the bonding pad (area of remaining metal
priate safety and health practices and determine the applica-
or intermetallic greater than 25% of the bond deformation
bility of regulatory limitations prior to use.
area).
3.1.3 bonding pad lift (substrate metallization removal)—a
2. Referenced Documents
separation between the bonding pad and the underlying sub-
2.1 ASTM Standards:
strate.Theinterfacebetweentheballbondandtheresidualpad
metallization attached to the ball remains intact.
These test methods are under the jurisdiction of ASTM Committee F01 on
Electronics and is the direct responsibility of Subcommittee F01.07 on Wire
Bonding. Annual Book of ASTM Standards, Vol 10.04.
Current edition approved Dec. 29, 1989. Published March 1990. Available from the National Technical Information Service, 5285 Port Royal
Panousis, N. T., and Fischer, M. W., “Nondestructive Shear Testing of Ball Rd., Springfield, VA 22161.
Bonds’’, International Journal of Hybrid Microelectronics, Vol 6, No. 1, 1983, p. AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
142. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 1269
FIG. 1 Ball Shear Failure Modes
3.1.4 cratering—bonding pad lifts taking a portion of the itself. If cratering occurs, chemically etch off the ball bonds
underlying substrate material with it. Residual pad and sub- and bond pads of untested units and microscopically check for
strate material are attached to the ball. The interface between
cratering. Cratering caused prior to the shear test operation is
the ball and this residual material remains intact.
unacceptable.
3.1.4.1 Discussion—Itshouldbenotedthatcrateringcanbe
Variousaspectsofthefailuremodedefinitionsareillustrated
caused by several factors including the ball bonding operation,
in Fig. 1.
the post-bonding processing, and even the act of shear testing
F 1269
NOTE 1—Schematic diagrams of the ball shear test. (A) Horizontal sample and horizontal ram. (B) Horizontal sample and vertical ram. (C) Vertical
sample and vertical ram. The bonded (welded) area may be less than the interfacial contact area (area of intimate contact as observed optically.) Typical
dimensions with 25-µm (1-mil) diameter wire are: ball diameter 75 to 110 µm (3.0 to 4.5 mil) and ball height 25 µm (1 mil) or less.
FIG. 2 Ball Shear Test Configurations
ram be placed further above the substrate, but in all cases the ram should
4. Summary of Test Methods
be located below the ball’s horizontal centerline. The distance below the
4.1 The microelectronic device with the ball bond (wire
center should be at least half the distance between the center line and the
bond(seePracticeF458andTestMethodsF459))tobetested
substrate.
is held firmly in an appropriate fixture. A shearing ram is
NOTE 3—Besides ball separation from the substrate, other modes of
positionedparalleltothesubstrateandapproximately25µm(1
failure are possible and will be described in Section 6.
mil) above the substrate metallization. A typical shearing
configuration is shown in Fig. 2. The ram is then moved into 5. Significance and Use
the ball until the ball separates from the substrate. The force
5.1 Failure of microelectronic devices is often due to the
appliedtotheram,inordertocausethefailureoftheballbond,
failure of an interconnection bond. A common type of inter-
is recorded. The mode of failure (for example, ball lift,
connection bond is the thermo compression or thermosonic
weld-interface separation, cratering, etc.) is observed and
gold wire bond.Avery important element of this interconnec-
recorded.
tionisthefirstbondorballbond.Thesetestmethodscanassist
NOTE 2—Bonds made with larger diameter wire may require that the in maintaining control of the process for making ball bonds.
F 1269
FIG. 3 Ball Shear Interferences
Theycanbeusedtodistinguishbetweenweakandnonadherent or both, (chip) and cause inordinately high shear strength as
ball bonds, of both, and bonds that are acceptably strong. well as potentially damage the shearing ram.
5.2 These test methods are appropriate for on-line use in
6.3 Shearing gold ball bonds on gold metallization pads or
process control, for process development, for purchase speci-
substratescanleadtofrictionreweldingasillustratedinFig.4.
fications, and for research in support of improved yield and
As a strongly welded gold bond is sheared, the ball tends to tip
reliability. Since the ball shearing method tests only the first
away from the ram and contact the substrate as it moves. The
bond in a microelectronic wire bond interconnection system, it ball smears against the pad metallization and rewelds itself
6,7
mustbeusedinacomplementaryfashion withthewirebond
often several times before it finally clears the metallization.
pull test.
6.4 In bonding systems in which excessive intermetallic
growthhasformedaroundtheballbond,theshearingrammay
6. Inferences
contact the intermetallic rather than the ball bond and thus the
shear readings can be in error (that is, weak ball bond shear is
6.1 The most common interference is wire shear in which
maskedbytheshearstrengthofthestrongintermetallicwreath
the ball is sheared too high or offline. Only a minor fragment
surrounding it.
oftheballisattachedtothewire.Themajorportionoftheball
remains on the pad with the bond-pad weld interface region
7. Apparatus
intact. Wire shear is illustrated in Fig. 1, View B.
6.2 Many of the common interference modes (such as wire
7.1 Ball Bond Shearing Machine—Apparatusformeasuring
shear)arecausedbyimproperpositioningoftheramduringthe
the ball bond shear strength are required with the following
ball shear operation as shown in Fig. 3. Rams that are too high
components:
(Fig. 3, View B) or angled upward (Fig. 3, View D) result in
7.1.1 Shearing Ram—Various shearing tools or rams have
lower than normal shear strength values. Rams that are angled
been recommended in the technical literature, but the ones that
downward (Fig. 3, View C and Fig. 4) or positioned too low
appear the most effective have a flat chisel shape with a
(Fig. 3, ViewA) will strike the bonding pad and the substrate,
shearing edge dimension equal to approximately 1 to 2-ball
diameters as shown in Fig. 5. For 25.4-µm (1-mil) diameter
wire this dimension would be approximately 0.152 mm (6
mils).
Charles, Jr., H. K., and Clatterbaugh, G. V., “Ball Bond Shearing—A
Complement to the Wire Bond Pull Test’’, International Journal of Hybrid
7.1.2 Shearing and Gaging Mechanism—Mechanism for
Microelectronics, Vol 6, No. 1, 1983, p. 171.
applying a measured vertical (or horizontal) force to the
Harman,G.G.“TheMicroelectronicBall-BondShearTest—ACriticalReview
shearing is needed. The mechanism shall incorporate a means
and Comprehensive Guide to its Use’’, International Journal of Hybrid Microelec-
tronics, Vol 6, No. 1, 1983, p. 127. for recording maximum force applied and shall be capable of
F 1269
FIG. 4 Gold-to-Gold Friction Rewelding
applyingtheshearforceatauniformrateoframmotion.Force 7.1.4 Device Holder— A clamping mechanism for rigidly
application rate can be variable (either continuously or in fixed
holding the device under test in either a horizontal or vertical
steps) to accommodate different shearing conditions and con-
position depending upon shear tester configuration is required
figurations,orboth.Innocaseshouldtheramspeedexceed6.0
(see 7.2).
mm/s.
7.1.5 Calibration Masses—At least five masses (weights)
NOTE 4—Ithasbeenshown thattheshearforceisindependentofforce with mass values known to an accuracy of 0.5% (or better,
application rate in the range from 0.25 to 6.0 mm/s.
such as NBS Class T or IOLM Class M2 (NBS Handbook
NOTE 5—Electronic-strain gage-force reading mechanisms are pre-
105-1 and Circular 547. IOLM) ) sized to cover the shearing
ferred; however, the dynamometer type mechanisms known as“ gram
and gaging mechanism range of force measurements and
gages’’ may be used satisfactorily providing careful calibration test
suitably configured so that they may be supported by the shear
procedures are employed.
mechanismforcalibration,areneeded.Inthecaseofhorizontal
7.1.2.1 Therangeoftheforcereadinggageshallbeselected
shearingrammotion,thetestermechanismshouldrotate90°to
sothatthemaximumscalereadingwillbenogreaterthanthree
allow the weights to be hung from the shearing ram. Other
times the expected average ball bond shear strength. Antici-
indirect methods of calibration may also be possible for this
pated force ranges for the various wire sizes and materials
configuration.
covered by these test methods are summarized in Fig. 6.
7.1.6 Shear Test Tolerances—The shear test sample holder
NOTE 6—The maximum scale range of the electronic strain gage with
orthesheartestrammustbeabletobepositionedtotolerances
digital readout may be larger than three times the expected average shear
strength providing the accuracy specified in 10.7.6 is maintained over the better than 610 µm (6 0.4 mils) and the X and Y directions
entire range of the load cell.
(plane of the bonding pad) and 5.0 µm (60.2 mils) in the Z or
the above substrate direction. The shearing rams over travel
7.1.3 Microscope and Light Source—Zoom microscope
(distance it proceeds from the point of ball contact) should be
with a light source for viewing the device under test is needed.
The minimum magnification shall be at least 603. limited to 2-ball diameters. Additional over travel may be
F 1269
FIG. 6 Shear Force Versus Diameter of the Bonded Area for
Various Wire Materials and Sizes
NOTE 1—Tool face is 1 to 2 ball diameters.
FIG. 5 Schematic Representation of Shearing Tool 25.4µµµ m
Diameter Wire
allowed in cases where the excessive ram motion does not
damage other bonds or the device under test.
7.2 TypicalsheartestconfigurationsareillustratedinFig.7.
Viewashowsahorizontaltestsystemwithhorizontalshearing
rammotion.Viewbpresentsaverticaltestsystemwithvertical
shearing ram motion.
8. Sampling
8.1 Since the shear test method is destructive, it shall be
performed on a sampling basis. The sample selected should be
representative of the ball bonds of interest. The size of the
sampleandthemethodofselectionshallbeagreeduponbythe
parties to the test. The sample space should be as large as
practical (nominally 35 bonds) to ensure the proper statistical
inferences from quantities such as the mean shear force (X)
FIG. 7 Shear Tester Configurations
and its standard deviation (s).
9. Calibration
9.3 Calibrate the shearing and gaging mechanism.
9.1 Calibrate the ball bond shearing machine at the begin- 9.3.1 For mechanisms or systems that incorporate a calibra-
ning and of each series of tests, or at the beginning and end of tion standard or mode, either calibrate the mechanism accord-
each day if the test sequence spans more than one day. ingtothemanufacturer’sinstructionsorinaccordancewiththe
9.2 For multifunction wire test machines, set up the test procedure in 9.3.2.
machineintheproperconfigurationfortheballbondsheartest, 9.3.2 For mechanisms without a built-in calibration
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