conduction-cooled pcbs housing materials · test program by a high-reliability pcb manufacturer to...
Post on 25-Nov-2018
220 Views
Preview:
TRANSCRIPT
© Copyright 2014 DS&A LLC
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
David L. Saums, Principal* DS&A LLC, Amesbury MA USA
Robert A. Hay, Vice President, Business Development
MMCC LLC, Waltham MA USA Subsidiary of Parker Hannifin Corporation
Brian Edward, Senior Fellow and Systems Engineer RF
Saab Defense and Security USA LLC, East Syracuse NY USA
Peter Ruzicka, Sr. Mechanical Engineer Saab Defense and Security USA LLC, East Syracuse NY USA
* Corresponding and Presenting Author
IMAPS 23rd Advanced Technology Workshop on Thermal Management
Los Gatos CA USA October 28-30, 2014
Page 2 © Copyright 2014 DS&A LLC October 28-30, 2014
This presentation will describe:
Part I: Development and results for a thermal constraining core material for use in high-reliability, high density multilayer interconnect printed circuit board assemblies (PCBs), offering in a single material:
a. Selectable coefficient of thermal expansion (CTE);
b. Relatively high isotropic bulk thermal conductivity value;
c. Reduced density
d. Proven suitability for use in all standard PCB fabrication processes;
Part II: Application of high-reliability PCBs fabricated using this PCB technology to mount multiple high heat flux RF semiconductors.
Application of similar copper-graphite composite to manufacture a housing, providing heat transfer from the high-reliability PCBs to an ultimate heat sink.
Application of cast copper-diamond composite inserts, cast in-situ into the composite housing material at specific locations, to which the highest dissipating packaged semiconductor devices are directly attached.
Thermal modeling data for the devices, with demonstrated improvement in comparative thermal performance versus an identical housing manufactured from aluminum.
Development of Cu-graphite composite as a thermal core for PCBs was presented here in 2013.
Outline
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 3 © Copyright 2014 DS&A LLC October 28-30, 2014
Part I
Development of Constraining Core Thermal Materials for PCBs
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 4 © Copyright 2014 DS&A LLC October 28-30, 2014
Need: Single new material to replace heavy copper layer(s) for high-reliability PCBs as a
constraining core thermal material for PCBs:
Development of a thermal constraining core material for use in high-reliability, high density multilayer interconnect printed circuit board assemblies (PCBs), offering in a single material:
a. Selectable coefficient of thermal expansion (CTE);
b. Relatively high isotropic bulk thermal conductivity value;
c. Reduced density
d. Proven suitability for use in all standard PCB fabrication processes;
Test program by a high-reliability PCB manufacturer to determine that all standard PCB fabrication processes per IPC 6012 can be met.
Application of high-reliability PCBs fabricated using this PCB technology to mount multiple high heat flux RF semiconductors.
Market Requirements -- Constraining Core Thermal Materials for PCBs
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 5 © Copyright 2014 DS&A LLC October 28-30, 2014
Existing PCB Materials and Constraining Core Thermal Materials
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Material Type CTE
[ppm/°C, Room Temperature (typ.)] Thermal Conductivity
(W/mK)
Epoxy-coated E-glass1 4-6 0.4
Stablcor® ST-3251 4-6 X-Y: 175
Z: 1
20Cu-60Invar-20Cu2 X-Y: 6.0 Z: 7.7
X-Y: 164 Z: 22
MMCC Cu-MetGraf™ 7-3003 7 X-Y: 287 Z: 225
25Cu/50Mo/25Cu2 7.9 X-Y: 268 Z: N/A
DuPont (Arlon) Thermount™ woven/nonwoven aramid with thermoset resins1
8-10 0.3
Typical multilayer PCB1 15-17 0.5
Copper4 17 385
Aluminum1 25 150
Data sources: 1. J. Vesce, TTM Technologies, Inc., USA. 2. Pecht, M., Agarwal, R., McCluskey, F.P., Dishongh, T.J., Javadpour, S., Mahajan, R., Electronic Packaging Materials and Their Properties, CRC Press, 1998. 3. Pergande, A., Rock, J., “Advances in Passive PCB Thermal Control,” Proceedings of the 2011 IEEE Aerospace Conference, Big Sky MT USA, March 2011. 4. Rockwell Collins, Inc., USA.
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 6 © Copyright 2014 DS&A LLC October 28-30, 2014
Market Requirements -- Constraining Core Thermal Materials for PCBs
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Parameter or Property Goal or Requirement
CTE Selectable, Lower value range appropriate for SiC, GaN
Packaged or bare die
Thermal Conductivity Relatively high versus existing CTE-matched materials
Requirement: > 250 W/mK Isotropic or near-isotropic if possible
Density Reduced versus existing CTE-matched materials
Requirement: 30+% reduction
Young’s Modulus Relatively stiff, with reduced or no warpage in fabricated PCB
Fabrication Demonstrated compatibility with standard PCB fabrication processes (per IPC)
“Drop-in-place” replacement of heavy copper layer Suitable for microdrilling, microvia processes
Manufactured Panel Size Requirement: 30.5cm x 45.7cm (minimum)
Manufactured Panel Thickness Initial requirement: 0.50mm (maximum)
Stretch requirement: 0.25mm
Manufactured Cost Reducible with future manufacturing process cost improvement program
Availability Suitable for IPC-standard PCB fabrication facilities globally
Not subject to legislative restrictions
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 7 © Copyright 2014 DS&A LLC October 28-30, 2014
Result:
The development program for a copper-graphite composite material manufactured in the required very thin sheets in large panel formats to achieve these goals was presented at La Rochelle in 2012 and 2013, as the program progressed.
MMCC Cu-MetGraf™-7 Copper-graphite composite sheet is now available in production in required 30.5cm x 45.7cm x 0.25mm thickness format.
Several PCB manufacturing facilities have received prototype quantities and demonstrated compatibility with IPC 6012 fabrication process standard for PCBs.
Initial programs and engineering design wins have been qualified for aerospace and defense procurement programs in the US.
Solution: Constraining Core Thermal Materials for PCBs
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 8 © Copyright 2014 DS&A LLC October 28-30, 2014
Solution: Constraining Core Thermal Materials for PCBs
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Parameter or Property
Goal or Requirement MMCC Cu-MetGraf™ 7-300
Value
CTE Lower value range, appropriate for SiC, GaN
Packaged or bare die 7.0 ppm/°C
Yes
Thermal Conductivity
Relatively high versus existing CTE-matched materials Requirement: > 250 W/mK
Isotropic or near-isotropic if possible
X-Y: 287 W/mK Z: 225 W/mK Near-isotropic
Density Reduced versus existing CTE-matched materials
Requirement: 30+% reduction 6.0 g/cc
Young’s Modulus Relatively stiff, with reduced or no warpage in fabricated PCB 75.8 GPa
Fabrication Demonstrated compatibility, standard PCB fabrication processes
“Drop-in-place” replacement of heavy copper layer Suitable for microdrilling, microvia processes
Yes Yes Yes
Manufactured Panel Size
Requirement: 30.5cm x 45.7cm (minimum) Yes, demonstrated
Manufactured Panel Thickness
Initial requirement: 0.50mm (maximum)
Stretch requirement: 0.25mm
Yes, completed Yes, completed
Manufactured Cost Reducible with future manufacturing process cost improvement program Yes, now underway
Availability Suitable for IPC-standard PCB fabrication facilities globally
Not subject to legislative restrictions Yes Yes
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 9 © Copyright 2014 DS&A LLC October 28-30, 2014
Result: A single new material to replace heavy copper layer(s) for high-reliability PCBs.
Solution: Constraining Core Thermal Materials for PCBs
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Parameter or Property Molybdenum1 Cu-Mo-Cu1 20Cu/60 Invar/
20Cu2 Cu-Graphite
(Cu-MetGraf 7-300) 25Cu/50Mo/
25Cu2 Cu1
CTE (ppm/°C)
5.0 6 X-Y: 6.0 Z: 7.7
7.0 7.9 17
Thermal Conductivity (W/mK)
X: 140 Y: 142
170-182 X-Y: 164
Z: 22 X-Y: 287 Z: 225
X-Y: 268 Z: N/A
385
Density (g/cc)
10.2 9.9 - 10.0 8.5 6.1 9.6 8.9
Young’s Modulus (GPa) 330 280 135 75.84 220 120-130
Notes: Constraining core materials for high-reliability PCBs. Sources: 1. Rockwell Collins Inc., USA; 2. Pecht, M., Agarwal, R., McCluskey, F.P., Dishongh, T.J., Javadpour, S., Mahajan, R., Electronic Packaging Materials and Their Properties, CRC Press, 1998. ISBN 0-8493-9625-5.
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 10 © Copyright 2014 DS&A LLC October 28-30, 2014
Part II
Application of Conduction-Cooled Constrained Core PCBs and Composite Aerospace Housing
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 11 © Copyright 2014 DS&A LLC October 28-30, 2014
Need: Development and application of a conduction-cooled composite housing in an open-architecture format supporting commercially-available RF devices and thermal management technologies. mounting multiple high heat flux GaN RF devices
Development of a commercially-sourced set of component RF devices will enable significant development and procurement cost reductions.
Development of commercially-sourced constrained-core PCBs will enable cost reduction goals, eliminating traditional proprietary module packaging technologies.
Use of CTE-matched commercially-available thermal management technologies enables:
Limiting component operating temperatures to enhance system reliability and enable increases system availability with high performance devices
Improvements in thermal management with CTE-matched materials for (a) component mounting and (b) local conduction cooling allows use of eutectic solder of GaN MMICs directly to Au-plated Cu-diamond composite inserts.
Cu-diamond composite inserts transfer local device heat load to the transceiver base plate.
Market Requirements – Conduction Cooled Housing
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 12 © Copyright 2014 DS&A LLC October 28-30, 2014
Proposed:
The same casting and finishing processes used to manufacture MMCC Cu-MetGraf™-7 Copper-graphite composite sheet;
Manufacture cast copper-graphite composite housing to support PCB;
Incorporate high thermal conductivity, CTE-matched slugs cast within the composite housing at locations where high heat flux semiconductor devices would be located;
Enable reduced procurement cost assembly.
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 13 © Copyright 2014 DS&A LLC October 28-30, 2014
Proposed:
Same casting and finishing processes as used to produce MMCC Cu-MetGraf™-7 Copper-graphite composite sheet to be used to cast composite housing;
GaN RF die mounted to pockets machined in surface of thermal core PCB.
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Plan View Exploded View
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 14 © Copyright 2014 DS&A LLC October 28-30, 2014
Proposed:
Same casting and finishing processes as used to produce MMCC Cu-MetGraf™-7 Copper-graphite composite sheet to be used to cast composite housing;
GaN RF die mounted to pockets machined in surface of thermal core PCB.
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Plan View Exploded View
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 15 © Copyright 2014 DS&A LLC October 28-30, 2014
Proposed copper-graphite composite housing with copper-diamond inserts cast in-situ:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Multi-channel electronics unit housing – Cu-MetGraf™ 7-300 Copper-graphite composite
housing with Cu-Diamond Inserts
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 16 © Copyright 2014 DS&A LLC October 28-30, 2014
Constrained-core PCB:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Constrained-core PCB with Cu-MetGraf 7-300 layers (2) and thermal vias for heat spreading and transport
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 17 © Copyright 2014 DS&A LLC October 28-30, 2014
Proposed copper-graphite composite housing with copper-diamond inserts cast in-situ:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Cross-section schematic of as-cast hybrid composite frame structure for composite housing
As-Cast Frame Structure Design
Copper Diamond Inserts
Finished Frame Outline
Oversize Copper Metgraf Structure
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 18 © Copyright 2014 DS&A LLC October 28-30, 2014
Proposed:
Same casting and finishing processes as used to produce MMCC Cu-MetGraf™-7 Copper-graphite composite sheet to be used to cast composite housing;
Copper-diamond composite inserts cast as mounts for high heat flux devices:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Example of porous diamond particulate preforms manufactured via low pressure injection
molding. (Gates and sprues will be removed and recycled prior to copper infiltration.)
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 19 © Copyright 2014 DS&A LLC October 28-30, 2014
Copper-diamond composite insert manufacturing:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Diamond preforms loaded into fiber preform
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 20 © Copyright 2014 DS&A LLC October 28-30, 2014
CTE-matched copper-graphite composite housing manufacturing:
Post-processing final machining steps for composite enclosure casting
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Finished back side of copper-graphite composite housing
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 21 © Copyright 2014 DS&A LLC October 28-30, 2014
Composite copper-graphite housing (copper-diamond inserts) and constrained core PCB:
Highest heat flux GaN RF devices mount directly through window in PCB to the copper-diamond inserts in enclosure casting:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Heat transport from the high power components into the copper MetGraf housing, immediate spreading by
the copper-diamond Inserts, and removal by the array structure.
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 22 © Copyright 2014 DS&A LLC October 28-30, 2014
Thermal model results for the copper-graphite housing and copper-diamond inserts. Temperature at the GaN device mounting interface is 59.6˚C:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Example of thermal model for reference copper-graphite housing
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 23 © Copyright 2014 DS&A LLC October 28-30, 2014
Thermal model results for a reference aluminum housing. Temperature at the GaN device mounting interface is 70.7˚C:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Example of thermal model for reference aluminum housing
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 24 © Copyright 2014 DS&A LLC October 28-30, 2014
Thermal modeling shows the following comparative results:
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Parameter or Property Aluminum
Housing (Reference)
Cu-Graphite Composite Housing w/Cu-Diamond Inserts
Temperature at GaN device mounting interface (°C) 70.7 59.6
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 25 © Copyright 2014 DS&A LLC October 28-30, 2014
CTE-matched copper-graphite composite housing manufacturing:
Post-processing final machining steps for composite enclosure casting
Solution: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Machining cavity side of copper-graphite housing
Finished multichannel electronics unit housing
manufactured as a cast copper-graphite
composite with in-situ copper-diamond inserts.
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 26 © Copyright 2014 DS&A LLC October 28-30, 2014
Composite housing and inserts:
Manufactured with the same casting and finishing processes
Comparison of material properties
Result: Conduction-Cooled Composite Housing and CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Parameter or Property Cu-Graphite Composite1
Cu-MetGraf 7-300
Copper Diamond Composite2 CuDia 65™
CTE (Average in-plane, 20-220°C) (ppm/°C) X-Y: 7.0
Z: 16 X-Y: 7.5 Z: 7.5
Thermal Conductivity (W/mK) X-Y: 287 Z: 225
550 Z: 550
Density (g/cc) 6.07 5.50
Material applications: 1. Constraining core layer for high-reliability PCB fabrication and for manufacture of CTE-matched system housing; 2. High thermal conductivity inserts for high heat flux device mounting locations.
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 27 © Copyright 2014 DS&A LLC October 28-30, 2014
Successful design and prototype manufacturing of conduction-cooled CTE-matched copper-graphite enclosure housing;
Initial thermal modeling results show the thermal design advanced on this program reduces the GaN device operating temperature in excess of 10˚C.
Thermal performance improvements result in:
Reduction in power amplifier operating temperature in excess of 10˚C.
This temperature reduction yields an order of magnitude (10X) amplifier MTBF increase
Accomplishes attendant performance improvements with respect to RF device and system output power, efficiency, and gain.
Current work indicates system-level cost improvements:
a. Unit production costs will be reduced on the order of 50%;
b. Active array operation and maintenance costs, which are ultimately even more significant, can be reduced up to 50% also.
c. Overall improvement in development and Life Cycle Cost structure.
Next steps: Manufacture and assembly of complete test array for empirical data collection and system performance analysis.
Result: Conduction-Cooled Composite Housing with CTE-Matched Inserts
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 28 © Copyright 2014 DS&A LLC October 28-30, 2014
DuPont® is a registered mark of E.I. du Pont deNemours and Company.
MetGraf™ and Cu-MetGraf™ are trademarks of MMCC LLC, Waltham MA USA Website: www.mmccinc.com
Stablcor® is a registered mark of Stablcor Technology Inc., Huntington Beach CA USA Website: www.stablcor.com
Thermount™ is a trademark of E.I. du Pont de Nemours and Company.
Notes
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 29 © Copyright 2014 DS&A LLC October 28-30, 2014
1. “Future Trends in PCB Technologies for Space Applications”, ESA PCB Workshop, 22-23 October 2009. ESTEC, Noordwijk, The Netherlands.
2. Hay, R., “Copper MetGraf Composites for Printed Circuit Board Thermal Control,” IMAPS Advanced Technology Workshop on Thermal Management 2011, Palo Alto CA USA, November 7-9, 2011.
3. IPC 6012(C) “Qualification and Performance Specification for Rigid Printed Circuit Boards,” ISBN 1-580986-36-6, April 2010. Published by IPC, Bannockburn IL USA, www.ipc.org.
4. Pecht, M., Agarwal, R., McCluskey, F.P., Dishongh, T.J., Javadpour, S., Mahajan, R., Electronic Packaging Materials and Their Properties, CRC Press, 1998. ISBN 0-8493-9625-5.
5. Pergande, A., Rock, J., “Advances in Passive PCB Thermal Control,” Proceedings of the 2011 IEEE Aerospace Conference, Big Sky MT USA, March 2011, Manuscript 978-1-4244-7351-9/11.
6. Saums, D., “Developments in CTE-Matched Thermal Core Printed Circuit Boards,” Electronics Cooling Magazine, June 2011, pp. 10-11.
7. Soulier, J.-Y., “C-PCB: A EURIPIDES Initiative for Evaluating Carbon-drained Printed Circuit Boards for Airborne Applications”, EURIPIDES Forum, Berlin, Germany. 9-10 October, 2008.
8. Vasoya, K., Burch, C., Roy, D., “Solving Thermal and CTE Mismatch Issues in Printed Circuit Boards and Substrates,” Proceedings, IMAPS Symposium 2005, Philadelphia PA USA, September 25-29, 2005.
References
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
DS&A LLC David L. Saums, Principal Chestnut Innovation Center E: dsaums@dsa-thermal.com 11 Chestnut Street Tel: +1 978 499 4990 Amesbury MA 01913 USA Website: www.dsa-thermal.com
Business and product development strategy for electronics thermal management: advanced thermal materials, components, and thermal systems.
MMCC LLC Robert A. Hay, Vice President – Business Development 191 Clematis Avenue E: rhay@mmccinc.com Waltham MA 02453 USA Tel: +1 781 893 4449 Website: www.mmccinc.com MMCC is a subsidiary of Parker Hannifin Corporation Metal matrix cast composite design, development, and series production on a design-to-print basis for commercial, industrial, and military/aerospace markets. Saab Defense and Security USA LLC Brian Edward, Senior Fellow and Systems Engineer RF 5717 Enterprise Parkway E: brian.edward@saabusa.com East Syracuse NY 13057 USA Tel: +1 315 234 3754 Pete Ruzicka, Sr. Thermal Engineer E: peter.ruzicka@saabusa.com
Contact Information
Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
IMAPS 23rd ATW Thermal Management Los Gatos CA USA
Page 30 © Copyright 2014 DS&A LLC October 28-30, 2014
top related