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Electronics Packaging Society
Chris BaileyPresident
1
Reliability Challenges for the Aerospace Sector and the Use ofCommercial Off‐The‐Shelf Components (COTS)
Chris Bailey
University of Greenwich, London, UK
Computational Mechanics and Reliability Group
• Established in 2004• Staff: 3 Profs, 5 Post Doc’s, 7 PhD’s• Research Mission
To develop and apply CAE technologies to predict the physical behaviour, performance, reliability, and maintainability of complex engineering components/systems.
12
Content
• COTS
• Modelling <-> Metrology
• Refinishing Processes
▪ Hot Solder Dip
▪ Reballing
• Board Assembly & Reliability
▪ QFN’s
▪ uBGA’s
• Conclusions
Commercial off-the-shelf Components (COTS)
• Avionics Systems
• Components
▪ Leaded components
▪ BGA’s
▪ QFN’s
▪ etc
• Use of commercial components for high reliability application
• Lead-free solders still an issue
Reliability Challenges
• Ruggedising components
• Refinishing components
▪ Hot solder dipping
▪ Deballing/Reballing
• Impact of assembly materials
▪ Solders
▪ Conformal coatings
▪ Underfills
▪ Compliant PCB’s
▪ ….
Solder Dipping Deballing/Reballing
Conformal Coatings
Content
• COTS
• Modelling <-> Metrology
• Refinishing Processes
▪ Hot Solder Dip
▪ Reballing
• Board Assembly & Reliability
▪ QFN’s
▪ uBGA’s
• Conclusions
Reliability Predictions:Physics of Failure
17
Modelling
Metrology →Modelling• COTS need to be chacterised (usually limited data available)
• SEM/EDX, CSAM, SEM/EDX, Tomography, etc…
• Data to feed into models – Geometry, Materials Data
Computational Intelligence and Machine Learning for Predictive Modelling
• Similarity-based reliability qualification approach• Optimisation of product qualification processes• Technologies: self-organising maps (SOM), support vector
machines, neural network, state-space models, etc
S. Stoyanov, C. Bailey and T. Tourloukis (2016), Similarity approach for reducing qualification tests of
electronic components, Microelectronics Reliability, Vol. 67, pp. 111-119
S. Stoyanov, C. Bailey, et al (2019) Predictive analytics methodology for smart qualification testing
of electronic components, Journal of Intelligent Manufacturing, Vol. 30 (3), pp. 1497–1514
New PART
Part Characterisation (geometry, materials,
integrity)
Sufficiently similar part?
Part Qualified or Failed
Experimental Qualification Tests
Yes
No
Database
previously
qualified parts
Cluster coordinate X
Clu
ster
co
ord
inat
e Y
Part No.Normalised Attribute Value
a1 a2 a3 a4 a5
Part No. 1 0.427 0.318 1.000 1.000 0.240
Part No. 2 0.284 0.000 0.068 0.615 0.200
………..............................................................................
Part No. 35 0.873 0.373 0.731 0.065 0.832
Part No. 36 0.211 0.263 0.353 0.458 0.524
Similarity Approach to Qualification
Normalised attribute #1
No
rmal
ised
att
ribu
te #
2
Normalised attribute #1
No
rmal
ised
att
ribu
te #
2
Cluster coordinate X
Clu
ster
co
ord
inate
Y
Normalised attribute #1
New Part B
No
rmali
sed
att
ribu
te #
2
Similarity based predictions
Electronic Parts and Data
ProcessSOM Similarity Model Development
Content
• COTS
• Modelling <-> Metrology
• Refinishing Processes
▪ Hot Solder Dip
▪ Reballing
• Board Assembly & Reliability
▪ QFN’s
▪ uBGA’s
• Conclusions
Refinishing (Hot Solder Dip) Process
• Undertaken by Micross Components Ltd
• Double dip hot solder refinishing process
• Robot arm automated
Refinishing components for High-Rel Apps• Remove lead-free finishes (Tin Whiskers)
• Standard: ANSI/GEIA-STD-0006
• Impact of process on reliability
3D-CT Scans
Thermal
Stress/Damage
COTS Package
Temperature (⁰C)
Heat Transfer Process from
Model
Model Validation on Optimised Process
Refinishing Step
Temperature at Die Centre
( ⁰C )
Experimental
Thermo-couple
Readings
Model
Prediction
End of First pre-heat 105.6 125.0
End of First Solder Dip 127.7 128.0
Prior to second pre-heating 121.1 108.3
End of Second pre-heat 118.9 119.4
End of Second Solder Dip 119.6 120.6
End of forced air cooling 87.6 86.7
End of water rinse 65.8 66.1 HSD Normalised Time0 1
S. Stoyanov et al., Modelling methodology for thermal analysis of hot solder dip process, Microelectronics Reliability, 53, 2013, 1055-1067
1
-20
-13.333-6.667
06.667
13.33320
26.66733.333
40
SEP 14 2011
11:26:05
Example of Modelling Stress Response1
-6
7.66721.333
3548.667
62.33376
89.667103.333
117
SEP 2 2011
17:58:32
NODAL SOLUTION
STEP=31
SUB =1
TIME=64
S1 (AVG)
DMX =.039098
SMN =-17.73
SMX =277.488
1
-6.52
7.20120.923
34.64548.367
62.08975.811
89.533103.255
116.977
SEP 2 2011
17:53:24
NODAL SOLUTION
STEP=31
SUB =1
TIME=64
S1 (AVG)
DMX =.009946
SMN =-6.52
SMX =116.977
1
-20
-13.333-6.667
06.667
13.33320
26.66733.333
40
SEP 14 2011
11:27:13
Die Stress
Response
Peel stress at
wire bond
interface
Can we predict delamination?
Model
CSAM
Model
CSAM
Deballing Process and Risk of Damage
Hot Nitrogen Deballing
• Heat dissipates through the top most metal layers of the BGA substrate
• Thermal effects are localised. Very little propagation of the temperature front from the pad towards the die and first-level solder joints
Stoyanov, Dabek and Bailey, Proc. International Spring Seminar on Electronics Technology, Dresden, Germany, 2014, pp. 1-6
Reballing Process and Risk of Damage
Tungsten
Nozzle
BGA
substrate
φ = ID nozzle
Solder
mask
Copper
padBT
core
N2
pressure
Silicon dieBased on PacTechjetting equipment
0
50
100
150
200
250
300
0.1 1 10 100 1000
Tem
pera
ture
(C)
Logscale time of laser re-balling for a single 2nd level joint
(ms)
P1 P2
P3 P4
Laser Re-balling : Local/Global BGA Level
Temperature (C) results from local model
Solidification time window
• Temperature front from laser re-balling does not propagate towards the 1st level solder interconnects (even in the case of direct signal path)
Stoyanov, Dabek and Bailey, Proc. Electronics System-Integration Technology Conference, Helsinki, Finland, 2014, pp. 1-6
Temperature (C) results from global model over 60 ms time interval
Solidification Process during Re-balling
TEMPERATURE
MIN
MAX
TIME
LIQUIDFRACTION
SOLID FRACTION
t = 6.5 ms t = 7.0 ms t = 7.5 ms t = 8.0 ms t = 8.5 ms t = 9.0 ms t = 9.5 ms t = 10.0 ms
t = 13.3 ms t = 16.6 ms t = 20.0 ms t = 23.3 ms t = 26.6 ms t = 30.0 ms t = 33.3 ms t = 36.6 ms
• Solidification of the solder material is extremely fast process
• Solder material of the deposited droplet solidifies within 36 ms
Stoyanov and Bailey, Microelectronics Reliability, Vol. 55, Issue 9-10, 2015, pp. 1271-1279
Tungsten
Nozzle
BGA
substrate
φ = ID nozzle
Solder
mask
Copper
padBT
core
N2
pressure
Silicon die
Content
• COTS
• Modelling <-> Metrology
• Refinishing Processes
▪ Hot Solder Dip
▪ Reballing
• Board Assembly & Reliability
▪ QFN’s
▪ uBGA’s
• Conclusions
Conformal Coatings• Protection to PCB’s
▪ contamination, salt spray, moisture, fungus, dust, and corrosion
▪ Mitigation to tin whiskers
• Materials
▪ Silicone, Urethane, Acrylic
P1 P2 P3 P4 C1
Yin, Stoyanov, Bailey, Stewart, Thermo-mechanical Analysis of Conformally Coated QFNs for High Reliability
Applications, IEEE Transactions CPMT, 9 (11), 2210-2218, 2019
Finite Element Model
Material Stress Free Temperature
Solder 180
Coating A 90
Coating B 22
PCB 170
All others 145
Development of Lifetime Model
Yin, C, Stoyanov, S, Bailey, C, Stewart, P, and McCallum, S, Reliability Assessment of QFN Components for Aerospace Applications,
IEEE 66th Electronic Components and Technology Conference, 1996-2002, 2016
Impact of Conformal Coatings
• Coating A increases damage for all cases
• Mixed situation for Coating B
• Damage reduced in smaller packages (P1, P2, P3, C1),
• Increased in the larger package (P4)
• Complex interaction• Package size, coating penetration & properties
Impact of Edgebond And Conformal Coating
Yin, Stoyanov, Bailey, Stewart, “Modelling the impact of
conformal coating penetration on QFN reliability”, IEEE ICEPT, 1021-1026, 2017
Damage Mechanism
◼ When conformal coating is not used
Shear stress/strain in solder joint due to global CTE mismatch between the PCB and component.
◼ When conformal coating is used, coating presence
◼Reduces CTE miss-match induced shear stress/strain in solder joint (positive role).
◼Constrains the out-of-plane movement in solder joint (negative).
Content
• COTS
• Modelling <-> Metrology
• Refinishing Processes
▪ Hot Solder Dip
▪ Reballing
• Board Assembly & Reliability
▪ QFN’s
▪ uBGA’s
• Conclusions
Micro-BGA Assembly and Scope of Study• mBGA COTS packages (High Rel. Apps)
▪ Small size package architecture
▪ A range of IC functions
▪ Increasingly available at lower cost
• Assembly variants assessment (temperature cycling)
▪ PCB’s: Rigid and Compliant
▪ Resins: Underfill and Edgebond
• All combinations of PCB types and resin optionswere tested and modelled
Critical balls with
redundancy
1
2
34
5
Assembly with underfill
Dual connection
redundancy
Micro-BGAEdgebond
PCB
Assembly Variants• Two multi-layer PCB variants
1. Rigid PCB: an all-rigid stack-up, with the top-most layer (#1) being a “rigid” dielectric material layer
2. Compliant PCB: same PCB stack-up but with a compliant material (lower elastic modulus) top layer
• Three resin variants3. No resin (Edgebond or Underfill)
4. Edgebond - typically penetrating to a line half-way through the second row of joints in the grid array)
5. Underfill - a complete fill of the gap between the package and the PCB
Conformal coating applied after resins applied
Reliability Test Programme: Setup and Results
• Daisy chains
▪ Continuously monitored
▪ Cross-section failure analysis
• Temperature cycle
▪ −25˚C to 100˚C
▪ Ramp times of 10 minutes
▪ 30-minute dwells
• Failure data statistically analysed
Tests Outcome
• Substantial improvement with resins,particularly with underfill
• Compliant PCB advantageous whenresin is used
Finite Element Modelling
• Finite element moles developed for all assembly variants
• Ansys APDL, element type SOLID 185, transient analysis
• Quarter symmetry assumption
FE Models for 6
Assemblies
S. Stoyanov, C. Bailey, P. Stewart, G. Morrison, Reliability Impact of Assembly Materials for Micro-BGA Components
in High Reliability Applications, Proc. IEEE ESTC, 2020, 1-7
Discussions
• Test data and the model results for solder joints damage in good agreement
• The linear regression line represents a powerlaw relation between characteristic life andmodel predictions for solder damage value 1,220 cycles
948 cycles
3,991cycles
8,855 cycles
>10,000 cycles
Life cycles
from Test
Solder Damage from Model
S. Stoyanov, C. Bailey, P. Stewart, G. Morrison, Reliability
Impact of Assembly Materials for Micro-BGA Components in
High Reliability Applications, Proc. IEEE ESTC, 2020, 1-7
Findings: PCB Impact on mBGA Reliability
• The rigid PCB topmost layer (CTE<15 ppm/C) gives better match to the package CTE (mould resin CTE ~7 ppm/C and Si die CTE ~4 ppm/C) compared with the compliant (CTE>20 ppm/C) layerThe better CTE compliance of the rigid material delivers higher reliability than the lower modulus but less CTE-matching compliant material
• But, the compliant PCB provides an improved reliability for assemblies with resinsThe compliant layer has both lower modulus and better CTE match to the CTEs of the resin and the solder compared with the rigid layer
PCB type Impact
Findings: Resin Impact on mBGA Reliability and Solder Joint Damage Mechanisms
• Higher damage in solder joint at the package side interface
• Solder damage (plastic work) due to global, in-plane CTE miss-match between PCB and mBGA. Clear shear deformation and notable movement of solder joints under thermal cycling
• No solder damage drivers at local joint level
• Higher damage in solder joint at the PCB pad side interface
• More uniform plastic work distribution across the joint
• Solder damage (plastic work) due to global, in-plane CTE miss-match between PCB and mBGA greatly reduced. Minimum shear deformation of joints, movement restricted
• Main contribution to solder damage from local level CTE miss-match: PCB resist - resin - solder
• Edgebond achieves similar effect as the underfill but to lesser extent
Plastic work
Deformed shape factor 10 / displacement contours
Plastic work
No Resin With Resin
Solder
Copper
Moulding
Resin
Solder Resist
PCB
Solder
Copper
Moulding
No
ResinSolder Resist
PCB
No Resin
Resin (Edgebond or Underfill)
Conclusions• Ruggedised COTS
• Refinishing Processes
• Assembly and Reliability
▪ Conformal coatings
▪ Edgebond or Underfills
▪ Ridgid or Compliant PCB’s
• Worst option
▪ PCB without additional resins
• Best options:
▪ Compliant PCB and underfill is superior
▪ Compliant PCB with Reworkable Edgebond
Conclusions• Design for Reliability
▪ Modelling <-> Metrology
• AI/Machine will also play significant role in future
https://eps.ieee.org/technology/heterogeneous-integration-roadmap.html
PublicationsS. Stoyanov, C. Bailey, P. Stewart, G. Morrison, Reliability Impact of Assembly Materials for Micro-BGA Components in High Reliability Applications, Proc. IEEE ESTC, 2020, 1-7
S. Stoyanov, C. Bailey, P. Stewart, M. Parker, J.F. Roulston, Experimental and modelling study on delamination risks for refinished electronic packages under hot solder dip loads, IEEE Transactions on CPMT, 10 (3), 2020, 502-515
C. Yin, S. Stoyanov, C. Bailey, P. Stewart, Thermomechanical Analysis of Conformally Coated QFNs for High-Reliability Applications, IEEE Transactions on CPMT, 9 (11), 2019, 2210-2218
S. Stoyanov, M. Ahsan, C. Bailey, T. Wotherspoon, C. Hunt (2019) “Predictive analytics methodology for smart qualification testing of electronic components”, Journal of Intelligent Manufacturing, 30, 1497-1514
S. Stoyanov, C. Bailey and G. Tourloukis, Similarity approach for reducing qualification tests of electronic components, Microelectronics Reliability, 67, 2016, 111–119
C. Yin, S. Stoyanov, C. Bailey, P. Stewart and S. McCallum, Reliability Assessment of QFN Components for Aerospace Applications, Proc. IEEE ECTC, 2016, 1996-2002.
S. Stoyanov, P. Stewart and C. Bailey, Vulnerability Study of Hot Solder Dipped COTS Components, Proc. IEEE ISSE, 2016, 193-198
S. Stoyanov and C. Bailey, Modelling the impact of refinishing processes on COTS components for use in aerospace applications, Microelectronics Reliability, 55, (9-10), 2015, 1271-1279
C. Yin, C. Best, C. Bailey, S. Stoyanov, Statistical Analysis of the Impact of Refinishing Process on Leaded Components, Microelectronics Reliability, 55 (2), 2015, 424-431
S. Stoyanov, G. Tourloukis and C. Bailey, Similarity Based Reliability Qualification of Electronic Components, Proc. IEEE ISSE, 2015, 202-207
S. Stoyanov, A. Dabek and C. Bailey, Thermo-mechanical Impact of Laser-induced Solder Ball Attach Process on Ball Grid Arrays”, Proc. IEEE ESTC, 2014, 1-6
S. Stoyanov, A. Dabek and C. Bailey, Hot Nitrogen Deballing of Ball Grid Arrays, Proc. IEEE ISSE, 2014, 1-6
S. Stoyanov et al., Modelling methodology for thermal analysis of hot solder dip process, Microelectronics Reliability, 53, 2013, 1055-1067
C. Bailey et al., Assessment of Refinishing Processes for Electronic Components in High Reliability Applications, Proc. IEEE EPTC, 2013, 156-161
S. Stoyanov, A. Dabek and C. Bailey, Thermo-mechanical Sub-modelling of BGA Components in PCB Reflow, Proc. IEEE ISSE, 2013, 253-258
S. Stoyanov, C. Best, C. Yin, M. O. Alam, C. Bailey, P. Tollafield, Experimental and Modelling Study on the Effects of Refinishing Lead-Free Microelectronic Components, Proc. IEEE ESTC, 2012, 1-6
C.Y. Yin, C. Best, C. Bailey, S. Stoyanov, M.O. Alam, Statistical analysis of the impacts of refinishing process on the reliability of microelectronics components, Proc. ICEPT-HDP, 2012, 1377-1381
S. Stoyanov, C. Best, M. O. Alam, C. Bailey, P. Tollafield, M. Parker and J. Scott, Modelling and Testing the Impact of Hot Solder Dip Process on Leaded Components, Proc. IEEE ISSE, 2012, 303-308
S. Stoyanov, C. Bailey, P. Tollafield, R. Crawford, M. Parker, J. Scott and J. Roulston, Thermal Modelling and Optimisation of Hot Solder Dip Process, Proc. IEEE EuroSime, 2012, 1-8
Thank [email protected]