This document summarizes an advanced packaging presentation that covered topics like package-on-package (PoP), system-in-package (SiP), through silicon vias (TSV), and bottom terminated components. PoP provides benefits like less board area, better performance, and defined supply chain ownership. TSV and SiP enable further semiconductor integration challenges but require optimization for cost and reliability concerns like copper cracking.

1. Advanced Packaging
DfR Solutions Open House
December 14, 2011
Presented by: Greg Caswell
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2. Agenda
o Package on Package -3D(PoP)
o System in Package 3D (SiP)
o Through Silicon Via (TSV)
o Bottom Terminated Components
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o QFN
o LFCSP
o .3 mm pitch CSP
o Copper Wire Bonding

3. Roadmap vs Market Application
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4. Benefits of PoP
o The benefits of PoP are well known. They include
o Less board real estate
o Better performance (shorter communication paths
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between the micro and memory)
o Lower junction temperatures (at least compared to
stacked die)
o Greater control over the supply chain (opportunity to
upgrade memory and multiple vendors)
o Easier to debug and perform F/A (again, compared to
stacked die or multi-chip module or system in package)
o Ownership is clearly defined: Bottom package is the
logic manufacturer, the top package is the memory
manufacturer, and the two connections (at least for one-pass)
are the OEM

5. Benefits of PoP
o The benefits of PoP are well known. They include
o Less board real estate
o Better performance (shorter communication paths
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between the micro and memory)
o Lower junction temperatures (at least compared to
stacked die)
o Greater control over the supply chain (opportunity to
upgrade memory and multiple vendors)
o Easier to debug and perform F/A (again, compared to
stacked die or multi-chip module or system in package)
o Ownership is clearly defined: Bottom package is the
logic manufacturer, the top package is the memory
manufacturer, and the two connections (at least for one-pass)
are the OEM

6. Smartphone advancements aided by PoP technology
and cost of ownership benefits.
PoP addresses integration challenges to enable
semiconductor advancements . . .
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. . . to cost affectively deliver physical
world benefits.

7. Stacked Packages = PoP – 3D 101
PoP
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Double stack
Triple stack
Double stack
Courtesy: ASE

8. © 2004 - 200107
8
Thermal Comparison

9. PoP Assembly Process
o Assembly of PoP can be through
one or two reflows
o Most commonly single
reflow (aka, one-pass)
o Top package is typically
dipped before placement
o Flux (sticky) or solder paste
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9

10. 1st Generation PoP – Infrastructure Development
OEMs
Architecture
stacking
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12 major OEMs in Handset and DSC market adopting PoP
Industry
Standards
JEDEC – JC.11.2 Design guide, JC11.11 POD, JC-63 pin outs
Equipment Panasonic, Siemens, Fuji, Unovis, Assembléon, Hitachi
EMS / ODM 5 major EMS providers in production or development
Logic IDM 15 major IDMs adopted PoP
Memory IDM 8 major Memory suppliers adopted PoP
Amkor
Full service – Develop, Design, Model, Standards, bottom,
top PoP, Modules, pre-stacked engineering samples, BLR
Practical Components – stocks Amkor 12, 14 & 15mm bottom / top DC samples
www.amkor.com Design, stacking, test and Brd level reliability (joint study papers)

11. Design Factors Impacting Warpage
• Die
– Die size
– Die Thickness
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o Mold
o Material property
o Shrinkage
o Thickness
• Laminate Substrate
– Properties
– Thickness
– Cu ratio
– Routing
• Die attach
– Material property
– Thickness

12. Package Warpage
o Due to mismatch in CTE between
the substrate, mold compound
and die
o Die attach can also play a role
o High Tg mold compounds are
used to balance CTE mismatch
between die and substrate
o Effect of mold compound
becomes negligible at reflow
temperatures
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12

13. Warpage and Yields
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13

14. Warpage and Reflow Profile
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14
Ramkumar, 2008 European Electronic Assembly Reliability Summit

15. 1st Gen PoP Technologies limit PoP I/O and Bottom Stacked
Die Density – Requiring New Technology
o Die stacking in bottom package requires thicker mold cap
o New memory architectures require higher I/O interfaces
o Higher Semiconductor density requires package size reduction
o Thin form factors and increased battery size require thinner PoP stacks
o Improved warpage control required when go thinner with higher density
o A new bottom PoP technology is needed to continue growth
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0.50mm pitch Multiple die in bottom package

16. Thru Mold Via Technology (TMV®)
o Enabling technology for next generation PoP reqmts
o Improves warpage control and PoP thickness reduction
o TMV removes bottlenecks for fine pitch memory interfaces
o Increases die to package size ratio (30%)
o Improves fine pitch board level reliability
o Supports Wirebond, FC, stacked die and passive
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integration

17. Construction and package stack-up for the TMV PoP
Test Vehicle
Reference : "Surface Mount Assembly and Board Level Reliability for High
Density PoP (Package on Package) Utilizing Through Mold Via
Interconnect Technology - Joint Amkor and Sony Ericsson", Paper
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18. CCaatteeggoorriieess ooff SSiiPP –– eexxaammpplleess ooff 33DD
Horizontal Placement
Stacked
Structure
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Interposer Type
Interposer-less
Type
Wire Bonding Type Flip Chip Type
Wire Bonding
Type
Wire Bonding +
Flip Chip Type Flip Chip Type
Terminal Through Via Type
Embedded Structure
Chip(WLP) Embedded
+ Chip on Surface Type
3D Chip Embedded
Type
WLP Embedded + Chip on Surface Type

19. © 2004 - 200107
SiP: from Die to Package to Hybrid Stacking
The Road to 3D Packaging
~2010 2011 2012 2013
die stacking
8 dies
4 dies
TRD PoP
PIP FCCSP
aMAP PoP
aWLP PoP
aMAP PoP
(Cu pillar)
Bare-die FC PoP
3D IC PoP
Exposed-die aMAP
PoP
2.5D IC SiP
CoC FBGA
Hybrid FCCSP
ASIC
EDS PoP
aEDSi PoP
Courtesy: ASE

20. TSV Development
Courtesy:ASE
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21. Silicon Interposer
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Chip 1 Chip 2
Si Interposer
65 nm ASIC
Si Interposer w/ TSV
Substrate
Courtesy ASE

22. © 2004 - 200107
XBit: Aug 17, 2011:
Samsung announcement
of 32 Gbit Memory with
TSV
Samsung TSV Implementation

23. Through-Silicon-Vias
o Through Silicon Vias (TSV) are the next generation
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technology for system in package devices
o Similar to plated through holes in a PCB
o Promised advantages include
o Thinner packages
o Greater level of integration between active die.
o Process still being optimized and cost must be reduced
for widespread adoption.

24. TSV (cont.)
TSV is rarely justified by just miniaturization alone
More cost-effective to thin, stack and wire bond
Cost can be 2X-4X price of flip chip ($200/wafer is the goal)
and 5X-10X the price of wire bonding
TSV will be justified by
performance
Increase in inter-die I/O
Increase in bandwidth
Decrease in
interconnect length
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24
http://www.intel.com/technology/itj/2007/v11i3/3-
bandwidth/6-architectures.htm (August 22, 2007)

25. TSV Processes
o Via First, before Front End of Line (FEOL)
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o Vias etched in bare wafer prior to fab
o Not likely
o Back End of Line (BEOL)
o Via First, before BEOL
o Via Last, after BEOL
o Vias can be created at various stages of the process
o By the wafer provider, IC manufacturer, or packaging house

26. TSV Process – BEOL
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27. How Can Through Silicon Vias (TSV) Fail?
o Three primary failure mechanisms
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o Cracking of the Copper Plating
o Cracking of the Silicon /Change in Resistance of Silicon
o Interfacial Delamination of Via Wall from Silicon
o Challenges
o The exact process and architecture (materials, design) for TSV
has yet to be finalized
o Can lead to large changes in stress state

28. TSV Design
o Via walls can be straight (etch) or tapered (laser)
o Vias can be filled (likely) or not filled (aka, annular)
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29. TSV Design
o Depending on Via First or Via Last design layout, TSV
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can have a ‘floor’ of copper
o Also known as Carpeted or Nailheading
S. Barnat et. al., EuroSIME 2010

30. TSV Materials
o Will the via be filled?
o If yes, with what material?
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o Copper
o Tungsten
o Conductive
polymer
Why Tungsten?
Low CTE mismatch with
Silicon

31. Via Fill (Tradeoffs)
o Solid Fill (copper, nickel, tungsten, aluminum, etc.)
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o Most robust (fatigue)
o High stress in silicon
o Longest process
o Enhanced thermal performance
o Greater density (think filled microvias)
o Polymer Fill
o Still robust
o Reduced stress in silicon
o Shorter process, more expensive material
o No Fill (annular)
o Least robust
o Lowest stress in silicon
o Fastest process, lowest cost

32. Cracking of Copper TSV
o Will copper in TSV experience fatigue cracking?
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o Classic circumferential fatigue cracking of copper plating is
currently unlikely for two reasons
o Reason #1: Hole Fill
o Most TSV concepts seem to be moving to a solid plug design
(fully filled)
o A partial fill or plated barrel
likely a process defect
(pinch off due to non-optimized
leveler)

33. Example: Filled PCB Vias
o Filled PCB vias (copper, solder,
or conductive fill) do not fail
when subjected to temperature
cycling
o KEY EXCEPTION
o Partially filled PCB vias fail faster
due to the presence of a stress
concentration
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34. Cracking of Copper TSV (cont.)
o Reason #2: Unfilled Via and Compressive Stress
o Unlike in PCB, the ‘matrix’ (i.e., silicon) has a lower coefficient of
thermal expansion (CTE) than the barrel
o There is also a lower CTE mismatch
o PCB: 50ppm vs. 17ppm (33) / TSV: 2ppm vs. 17ppm (-15)
o If electroplated, stress free state should be at room
temperature
o Any increase in temperature, due to hot spots or change in ambient
conditions, will place the copper
plating under an axial compressive stress
o The tensile stress then arises circumferentially
o Could induce cracking along the length of
the via, but will not cause electrical failure
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35. Cracking of Copper TSV – Possible Exceptions
o Lu claimed very large stresses in the copper plating for
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annular TSV
Lu, Dissertation, UTexas, 2010

36. Cracking of Copper TSV – Possible Exceptions
o Liu measured (XRD) similar stress levels in filled TSV
Liu, ECTC, 2009
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Note zero stress state

37. Cracking of Copper TSV – Possible Exceptions (cont.)
o One publication seems to show stress-driven cracking
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of TSV, but little additional information is provided
J. McDonald, Thermal and
Stress Analysis Modeling for 3D
Memory over Processor Stacks,
SEMATECH Workshop on
Manufacturing and Reliability
Challenges for 3D IC’s using
TSV’s, 2008

38. Cracking of Silicon – Single TSV
o Stresses within the silicon can be computed using plane-strain
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analytical solution known as Lamé stress solution
Cylindrical
Cartesian
o sxx and syy are inplane
stresses
o B is modulus, T is thermal
mismatch strain, r is TSV
radius
o sr and sq are radial and
circumferential stresses
o E is modulus, eT = (af-am)DT
(thermal mismatch strain), Df
is TSV diameter, u is
Poisson’s ratio
Ignores elastic
Lu, Dissertation, UTexas, 2010 mismatch
Zhang, IEEE Trans. ED, 2011

39. Stresses in Silicon
Zhang, IEEE Trans. ED, 2011
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40. Stresses in Silicon (cont.)
o Are these stresses high enough to cracking
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semiconductor-grade silicon?
o Unlikely
o Fracture strengths of silicon wafers have been reported
between 1 – 20 GPa
Ritchie, Failure of Silicon, 2003
o Some debate about silicon and fatigue
o Dauskardt reports no fatigue behavior
o Ritchie reports fatigue behavior up to 0.5 fracture strength

41. Interfacial Failure of TSV
o This failure mechanism is the most likely failure mode of
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TSVs
o Very high stresses
o Very complex stresses
o Difficult to measure
material properties
o Key material properties
not controlled
(i.e., fracture strength)

42. Interfacial Delamination (cont.)
o Analysis by Dudek identified risk of micro cracking and
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delamination problems at the upper via pad in a local
model.
o R. Dudek, et. al., Thermo-Mechanical Reliability Assessment for
3D Through-Si Stacking, EuroSimE, 2009
o Liu found that Cu/SiO2 interfacial cracks and SiO2
cohesive cracks are likely to initiate and propagate at
the corners of electroplated Cu pads, where large
stress gradients and plastic deformation exist
o X. Liu, et. al., Failure Mechanisms and Optimum Design for
Electroplated Copper TSV, ECTC, 2009

43. Interfacial Delamination
o Interfacial delamination of TSVs was found to be
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mainly driven by a shear stress concentration at the
TSV/Si interface
o Can result in TSV extrusion, fracturing the overlaying
dielectric material
P. Garrou, “Researchers Strive for Copper TSV Reliability,” Semi Int,
03-Dec-2009.

44. TSV Failures (Summary)
o Ability to predict TSV reliability still in its infancy
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o Hampered by little published test data (primarily simulation)
o Any prediction must taken into account changes in
interfacial material
o Don’t simulate/test nominal; investigate realistic worst-case
o However, there is no need to reinvent the wheel
o A significant amount of relevant material, especially in
regards to interfacial reliability can be found in studies on
fiber-reinforced ceramic composites

45. Manufacturability and
Reliability of 0.3mm Pitch Chip
Scale Packages and QFNs
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46. Reliability and Next Generation Technologies
o One of the most common drivers for failure is
inappropriate adoption of new technologies
o The path from consumer (high volume, short lifetime) to high
rel is not always clear
o Obtaining relevant information
can be difficult
o Information is often segmented
o Focus on opportunity, not risks
o Can be especially true for
component packaging
o Fine pitch CSP (Chip Scale Packages)
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47. Solder Wearout
o Design change: More silicon, less plastic
o Increases mismatch in coefficient of thermal expansion
(CTE)
BOARD LEVEL ASSEMBLY AND RELIABILITY
CONSIDERATIONS FOR LNCSP TYPE
PACKAGES, Ahmer Syed and WonJoon Kang,
Amkor Technology.
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48. Solder Wearout (cont.)
o Hotter devices
o Increases change in temperature (DT)
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
0 50 100 150 200
Change in Temperature (oC)
Characteristic Life (Cycles to Failure)
tf = DTn
n = 2 (SnPb)
n = 2.3 (SnNiCu)
n = 2.7 (SnAgCu)
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49. .3 mm CSP: Why Not?
o .3 mm CSP is a ‘next generation’ technology for non-consumer
electronic OEMs due to concerns with
o Manufacturability
o Compatibility with other OEM processes
o Reliability
o Acceptance of this package, especially in long-life,
severe environment, high-reliability applications, is
currently limited as a result
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50. Chip Scale Packages
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Wafer Level CSP
Lead Frame Chip Scale Package

51. Design and Fab Thoughts?
o Board Fabricators
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o A first step in adapting to .3 mm pitch(12 mil)
o 2 mil traces and spaces
o Why? Bond pad will be .15mm
o 2 mil trace is only size that will fit between
o Most likely use via in pad
o Copper Thickness
o Board fabricators introducing a reduction in copper foil thickness to
work with these smaller components
o Going down to .25 ounce copper – good for lateral etching,
trace width control, uniform trace width.
ISSUE IS REDUCED RELIABILITY DUE TO POTENTIAL FOR TRACE
CRACKING

52. Fine Pitch CSP Manufacturability: Bond Pads
o Non Solder Mask Defined Pads Preferred (NSMD)
o Copper etch process has tighter process control than solder mask process
o Makes for more consistent, strong solder joints since solder bonds to both tops and sides of
pads
o Use solder mask defined pads (SMD) with care
o Can be used to avoid bridging between pads, especially between thermal and signal
pads.
o Pads can significantly grow in size based on PCB manufacturer capabilities
NSMD
Images courtesy of Screaming Circuits
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53. Solder Paste
o Continued reduction in apertures and bond pad dimensions
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are driving toward Types 5 or 6 shown in the chart to
facilitate .3mm pitch components
o While changes in the solder paste is expected – this move
toward “nanosolder” - the increasing ratio of surface area
to volume in these small particle systems may start to
influence coalescence behavior and storage times as well.

54. Stencils
o The actual minimum area ratio tends to change for different
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solder paste types.
o For standard Type 3, the number tends to be 0.66, while pastes with
even smaller powder have minimum area ratios closer to 0.5.
Regardless, for a 0.15 mm (6 mil) bond pad, maintaining either of
these ratios would require stencil thicknesses of less than 4 mil.
o These stencil requirements can be problematic for larger or
non-fine pitch components, which can potentially experience
solder starvation or solder bridging or solder balls (if the
stencil aperture is widened to introduce more paste on
pad).
o All of these challenges are, of course, before attempting to
select the type of stencil technology (electroformed or laser
cut) or the process parameters (pressure, speed, etc.).

55. Manufacturability: Stencil Design
Datasheet says solder paste coverage should be 40-80%
Drawing supplied in same datasheet is for 26% coverage
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56. Reliability
o As usual, reliability is often the last issue to be
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considered.
o While minimum modeling or testing has been
performed, the relatively small volume of solder and
the non-uniformity of the interconnect geometry (0.15
mm bond pads on board and 0.075 mm bond pads on
package) could create unique scenarios in regards to
solder joint response to the application of stresses.
o This is in addition to the increasing introduction of
mixed mode (shear and tensile stresses) that are
greatly accelerating creep and fatigue damage
accumulation.

57. .3mm CSP Reliability Conclusions
o While the move to 0.3 mm pitch CSPs will be challenging,
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there is significant opportunity for leveraging the
experiences of other portions of the supply chain.
o Examples include wafer-level bumping, which has been stencil
printing 0.15mm pitch solder bumps for some time period,
o BGA substrates, which has been using 2 mil width and spacing on
advanced packages, and
o 01005s, which have bond pads only 7 mil wide.
Success will be ensured through adopting the information gained from
these other processes, being aware of the potential gaps in this
knowledge, and implementing industry best practices and physics of
failure to understand margins and interconnect robustness.

58. LFCSP Manufacturability: Bond Pads
o Can lose solder volume and standoff height through vias in thermal pads
o May need to tent, plug, or cap vias to keep sufficient paste volume
o Reduced standoff height reduces cleanability and pathways for flux outgassing
o Increased potential for contamination related failures
o Tenting and plugging vias is often not well controlled and can lead to placement
and chemical entrapment issues
o Exercise care with devices placed on opposing side of LNCSP
o Can create placement issues if solder “bumps” are created in vias
o Can create solder short conditions on the opposing device
o Capping is a more robust, more expensive process that eliminates these concerns
Images courtesy of Screaming Circuits
Thermal
vias capped
with solder
mask
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59. Bond Pads
o Extend bond pad 0.2 – 0.3 mm
beyond package footprint
o May or may not solder to cut edge
o Allows for better visual inspection
o Need X-ray for best results
o Allows for verification of bridging,
adequate solder coverage and
void percentage
o Cannot detect head in pillow or
fractures
o Note: Lack of good criteria
for acceptable voiding of the thermal
pad. Depends upon thermal needs.
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60. Manufacturability: Reflow Moisture
o LFCSP solder joints are more susceptible to dimensional changes
o Case Study: Military supplier experienced solder separation under LFCSP
o LFCSP supplier admitted that the package was more susceptible to moisture
absorption that initially expected
o Resulted in transient swelling during reflow soldering
o Induced vertical lift, causing solder separation
o Was not popcorning
o No evidence of cracking or delamination in component package
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61. Corrective Actions: Manufacturing
• Verify good MSL (moisture sensitivity level) handling and
procedure procedures
• Reflow Profile: Specify and confirm
• Room temperature to preheat: maximum 2-3oC/sec
• Preheat to at least 150oC
• Preheat to maximum temperature: maximum 4-5oC/sec
• Cooling: maximum 2-3oC/sec
6©1 2004 - 200107
• In conflict with profile from J-STD-020C which allows
up to 6oC/sec
• Make sure assembly is less than 60oC before any
cleaning processes

62. Manufacturability: LFCSP Joint Inspection
Goal is 2-3 mils of post-reflow
solder thickness
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63. Manufacturability: Board Flexure
o Area array devices are known to have board flexure
limitations
o In circuit testing (ICT), board depanelization, connector
insertion, manual assembly operations, shock and vibration,
etc. are common causes.
o For SAC attachment, maximum microstrain can be as low as
500 ue
o Use IPC-JEDEC 9701 and 9704 specifications
o .3mm CSPs and LFCSPs have an even lower level of
compliance
o Limited quantifiable knowledge in this area
o Must be conservative during board build
o IPC is working on a specification similar to BGAs
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64. Pad Cratering
o Drivers
o Finer pitch components
o More brittle laminates
o Stiffer solders (SAC vs. SnPb)
o Presence of a large heat sink
o Difficult to detect using
standard procedures
o X-ray, dye-n-pry, ball shear, and
ball pull
Intel (2006)
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65. Solutions to Pad Cratering
o Board Redesign
o Solder mask defined vs. non-solder mask defined
o Limitations on board flexure
o 750 to 500 microstrain, Component dependent
o More compliant solder
o SAC305 is relatively rigid, SAC105 and SNC are possible
alternatives
o New acceptance criteria for laminate materials
o Intel-led industry effort
o Attempting to characterize laminate material using high-speed
ball pull and shear testing, Results inconclusive to-date
o Alternative approach
o Require reporting of fracture toughness and elastic modulus
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66. Reliability: Thermal Cycling
o Order of magnitude reduction in time to
failure from QFP
o 3X reduction from BGA
o Driven by die / package ratio
o 40% die; tf = 8K cycles (-40 / 125C)
o 75% die; tf = 800 cycles (-40 / 125C)
o Driven by size and I/O#
o 44 I/O; tf = 1500 cycles (-40 / 125C)
o 56 I/O; tf = 1000 cycles (-40 / 125C)
o Very dependent upon solder bond with
thermal pad
QFP: 10,000
BGA: 3,000 to 8,000
LFCSP: 1,000 to 3,000
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67. Electro-Chemical Migration: Details
o Insidious failure mechanism
o Self-healing: leads to large number
of no-trouble-found (NTF)
o Can occur at nominal voltages (5 V)
and room conditions (25C, 60%RH)
o Due to the presence of contaminants
on the surface of the board
elapsed time
12 sec.
o Strongest drivers are halides (chlorides and bromides)
o Weak organic acids (WOAs) and polyglycols can also lead to drops in
the surface insulation resistance
o Primarily controlled through controls on cleanliness
o Minimal differentiation between existing Pb-free solders, SAC and
SnCu, and SnPb
o Other Pb-free alloys may be more susceptible (e.g., SnZn)
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68. Reliability: Dendritic Growth / Electrochemical Migration
o Large area, multi-I/O and low standoff can trap flux
under the LNCSP
o Processes using no-clean flux should be requalified
o Particular configuration could result in weak organic acid
concentrations above maximum (150 – 200 ug/in2)
o Aqueous Cleaning processes will likely experience
dendritic growth without modifications like:
o Increase in water temperature
o Additions of saponifiers or solvents
o Changes to number and angle of impingement jets
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69. Cleanliness Controls: Ion Chromatography
o Contamination tends to be controlled through industrial specifications (IPC-
6012, J-STD-001)
o Primarily based on original military specification
o 10 μg/in2 of NaCl ‘equivalent’
o Calculated to result in 2 megaohm surface insulation resistance (SIR)
o Not necessarily best practice
o Best practice is contamination controlled through ion chromatography (IC)
testing
o IPC-TM-650, Method 2.3.28A
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*Based on R/O/I testing
Pauls
General
Electric
NDCEE DoD* IPC* ACI
Chloride (μg/in2) 2 3.5 4.5 6.1 6.1 10
Bromide (μg/in2) 20 10 15 7.8 7.8 15

70. Physics-of-Failure Approach to
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Copper Wire Bonding

71. Copper Wire Bonding – Market Status
o Initial marketing activities for fine pitched applications
initiated in mid-2000’s
o Replacement of gold wire bonding initiated in 2007-
2008 due to gold pricing,
but stunted due to
economic recession
o Rapid implementation
and replacement of
gold wire bonding
starting in 2009
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Current state of suppliers

72. Design Changes in Response to Copper Wire Bonding
o The major issues in regards to copper wire bonding are
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bonding force (and risk of silicon damage) and reduced
nobility (greater risk of corrosion)
o In response, some suppliers have been forced to
o Redesign the bond pad and underlying structure
o Modified the molding compound (lower pH, reduced halogen
content)
o Still unresolved
o Preferred bond pad material (Al and Pd)
o The need for Pd coating over copper wire bond
o Type of forming gas used in process (N2 or N2H2)

73. Major concerns identified by DfR
o Palladium (Pd) coating creates galvanic couple with copper
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o Studies have demonstrated thinning or loss of Pd coating during
bonding
o Uncertain if JEDEC test with acceleration factor based on Peck’s
equation (based on aluminum/gold galvanic couple) is still valid
o Push out of aluminum pad
o Could result in subsurface
cracking (metal migration?)
o Uncertain if existing JEDEC
temp cycling test is sufficient to
drive crack growth

74. Other Systems (Cu-Al)
o Copper-aluminum forms intermetallics at a much slower
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rate
o Most common activation energy of 1.26 – 1.47 eV
o Micron reported 0.63 eV
o Molding compound has little effect
HJ Kim, IEEE CPT, 2003
L Levine, Update on
High Volume Copper Ball Bonding
L. England, ECTC, 2007
C. Breach, The Great Debate: Copper vs. Gold
Ball Bonding

75. Other Systems (Cu-Al)(cont.)
Cu-Al
o Cu-Al shows improved performance over Au-Al
o Not to the extent expected based on intermetallic growth
o Different failure mode (gradual vs. sudden)
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Au-Al

76. Cu-Al and Elevated Temperature – Concerns
o Different intermetallics form at different temperatures
o Can a 150C/200C test be extrapolated to 85C?
o Some indications that oxidation of the wedge bond may
be a critical weak point
o Additional testing and modeling may be necessary
© 2004 - 200107

77. Copper Wire Bond and Temperature/Humidity
o Copper is not as noble as gold
o Noble coatings (palladium) can
come off during bonding
o Palladium (Pd) coating can also
create galvanic couple with
copper
o Studies have shown early
failures during temp/humidity
testing
o Some dependency on molding
compound (need lower pH, lower
halogen content)
o Uncertain if JEDEC test with
acceleration factor based on
Peck’s equation (based on
aluminum/gold) is still valid
© 2004 - 200107
Halogen-Free Molding Compounds
H. Clauberg, Chip Scale Review, Dec 2010

78. Copper Wire and Temperature Cycling
o Power module industry believes copper wire is more
robust than aluminum
o Changes being implemented for electric drivetrain
o Part of improvement is believed to be
due to reduced temperature variation
from improved thermal conductivity
o Part of improvement could be due to
recrystallization
o Can result in self-healing
o Part of improvement could be more robust fatigue
behavior
© 2004 - 200107
D. Siepe, CIPS 2010
N. Tanabe, Journal de Physique IV, 1995

79. Copper vs. Gold – Temperature Cycling
o Copper clearly superior
N. Tanabe, Journal de Physique IV, 1995
© 2004 - 200107
G. Pasquale, J. Microelectromech Sys.,, 2011

80. Aluminum vs. Copper – Temperature Cycling
o Copper clearly superior
100
10
106 107 108 109
© 2004 - 200107
N. Tanabe, Journal de Physique IV, 1995
J. Bielen, EuroSime, 2006

81. Thank you!
Any Questions?
Contact me:
gcaswell@dfrsolutions.com
www.dfrsolutions.com
© 2004 -–2200011070