1. Particles & Fields Data Processing Unit (PFDPU)
Electronics Box Mechanical Evaluation
Bill Donakowski, SSL
David Pankow, SSL
Paul Turin, SSL
Scott Tucker, et.al., LASP
NOTE: Maven has requested in depth review support from GSFC on this topic. Our point of contact is Seke Gordo (code 542). This review is ongoing and still has some open items.

2. PFDPU Mechanical Evaluation
Evaluation Approach
Experience has shown that the largest components offer the greatest risk
Ceramic substrates are quite stiff as compared to flexible circuit boards
Most likely failure mode is (KOVAR) fatigue of corner leads on large components
Fatigue strains are dictated by the accumulated flexures of the PCB.
Steinberg’s methods predict max. board deflection for infinite fatigue life
He’s fitted his accumulated PCB test data to provide useable empirical relations
These results may also be applied to yield & finite fatigue life predictions
Infinite life is appropriate for many terrestrial applications, while the typical NASA launch vibration (& testing) exposure is very brief.
PCB (four sided) edge support naming conventions
Pinned – edges constrained in translation, but not in rotation
Fixed – edges constrained in both translation and rotation
Working Reference
Steinberg “Vibration Analysis for Electronic Equipment” 3rd Ed. J.Wiley, 2000

3. Summary of Evaluation Relations (after Steinberg)
PFDPU Mechanical Evaluation
Summary of Evaluation Relations (after Steinberg)
First Mode of a given PCB design (fixed edges):
Fn = (2p/3) (D/r)½ [3/A4 + 2/A2B2 + 3/B4]½ • D = Eh3 / [12 (1-m2)] • r = W/g / [AB]
A & B – PCB dimensions • h – PCB thickness • W - weight
Max PCB deflection for Infinite Fatigue Life:
Z∞ = B / [C h r √L] • C – component factor (table) • r - position factor (table)
L – component length
Maximum PCB test deflection of a given PCB design:
Z3s = 36.8 √P / Fn5/4 • P - ASD test level (G2/Hz) near Fn
Accumulated fatigue damage using “Miner's Rule”:
Rn = (Fn ST) [0.683/N1s /N2s /N3s ] • Nns = [Z∞/Zns]b x 1E7 cycles
ST – accumulated exposure time
Yield Strength Fraction:
Fy = (Se / Sy)(Z3s / Z∞) • Se - endurance strength • Sy – yield strength

4. PFDPU Mechanical Evaluation
OBSERVATIONS
GSFC-STD-7000 (GEVS) and NASA-STD-5001 pose two design constraints
1.6 min. safety factor on metallic yield in vibration from GEVS table 2.2-3
4X exposure time calculations to account for scatter in typical life data
Designing for “Infinite Life” is an admirable goal, but overly restrictive
Accepting modest fatigue damage (perhaps < 25%) poses minor risks
Plot below illustrates design reserves for retesting & programmatic unknowns
1.6 min. GEVS yield safety factor → 62% of yield (red line)
Finite life only in the box level PFM test
Subsequent tests are at lower levels
FM Level
Req’d PFM Level

5. PFDPU Mechanical Evaluation
PFDPU Box Construction
Each PCB is bonded into a ledged aluminum frame
Eleven slices stack together & bolt to base plate
Internal stacking connectors provide “backplane”
Two threaded “skewers” hold top corners together

6. PFDPU Mechanical Evaluation
PFDPU PCB Artwork
MAG PCB
DFB PCB
REG PCB – no concerns
DAP PCB
NOTE: No large components on BEB board

7. PFDPU Mechanical Evaluation
IIB Board:
includes two perpendicular daughter boards w/ frame
(and no large components)
DCB Board:
includes a partial daughter board on standoffs

8. Original PCB Evaluation Results
PFDPU Mechanical Evaluation
Original PCB Evaluation Results
COMMENTS
* The DCB board has a daughter card and many other features that make a proper (FEM) evaluation questionable. Having the EM board previously shown, the plan of action was to measure this board frequency, and make adjustments to obtain a first mode of > 200 Hz
• These evaluations assume good workmanship practices in building these PCBs.

9. PFDPU Mechanical Evaluation
PFDPU Box Evaluation
Steinberg calls for an octave (2X) separation between boards and box
Charts below show potential board – box resonant interactions (using Miles Eq’n)
Lead fatigue is governed by board displacements shown in the right chart.
The 2X criterion reduces box-board mode interactions to quite modest levels
Acceleration
Displacement

10. PFDPU Mechanical Evaluation
MAVEN PFDPU
Design Details
2X Skewer Rods
11 X Individual Frames
(Al 6061 T6, .100” thick)
SolidWorks model
of PFDPU
Attach Frame
Bolted to S/C
Each frame interlocks with adjacent

11. PFDPU Mechanical Evaluation
MAVEN PFDPU FEM Analysis Details
Fixed Constraint at Box Base
(no other constraints in model)
11 x Individual PCBs/11 Individual Frames
Exploded View

12. PFDPU Mechanical Evaluation
Top of Box Frames Bonded
(Skewer Rods hold frames together)
FEM software
SolidWorks ‘Simulation’ 2011
SolidWorks Premium 2011 x64, SP 1.0
Includes FEM Simulation 2011 x64 SP 1.0)
Analysis Details
2-D Shells and Mesh
All 11 Frames and PCBs modeled
Frames fixed at bottom (mounting to S/C Deck)
Frames bonded to each other at Top (skewer rods)
Bottom of Frames Fixed
(PFDPU Base Plate not included - mounts to spacecraft)
Material Properties
Component
Material
Density
(#/in3)
Modulus
(psi)
Poison’s Ratio
Frames
Al 6061 T6
.100
10,000,000
.33
PCBs
Modified FRF
.225
70,000,000
.14

13. PFDPU Mechanical Evaluation
First Mode
(side view of PFDPU)
Second Mode
(top view of PFDPU)
Numerical Results
Mode
Frequency (Hz)
Description 1
581
Out-of-plane to PCBs, shear in relation to fixed bottom 2
684
Flexing of Side Walls 3
687 4
695
(modal mass was ~68% of total mass)
(many similar modes)

14. PFDPU FEM Modeling Discussion
PFDPU Mechanical Evaluation
PFDPU FEM Modeling Discussion
Box Modes (only) are the desired results in this effort
Software can provide up to 25 modes starting from the lowest value
Using actual PCB physical properties will only yield a plethora of board modes
PCB modulus (E) was increased 20X to avoid the box modes (i.e. very stiff boards)
Higher order box modes were frame flexing or (Al) end panel diaphragm flexing
A subsequent test run with the actual E(pcb) did not provide any box modes
This did provide a useful result where PCBs clustered around 176 Hz vs. 185 Hz
The 5% decrease in Fn is from the “less than rigid” nature of the stacked frames
This is a conservative result because stiff boards contribute to the modal mass
Actual ‘floppy’ boards will contribute less to the modal mass at these frequencies
PCB modes can be increased to ≈300 Hz before interactions are a concern

15. Review of, and Modifications to
PFDPU Mechanical Evaluation
Part 2:
Review of, and Modifications to
STEINBERG’S APPROACH
Issues to be considered:
EM – DCB board test results
Validation of PCB frequency predicts
PCB mode shape vs. fatigue amplitude discussion
PCB material damping

16. EM-DCB BOARD TEST (¼ G sine sweep)
PFDPU Mechanical Evaluation
EM-DCB BOARD TEST (¼ G sine sweep)
The partial daughterboard & many connectors defy proper analysis
TEST RESULTS
Fn = 211 Hz (185 Hz Steinberg predict for a nominal – single board)
Qmax = 46 (measured near the board center) • Qcg = 4/p 2 Qmax
A measured Q at some arbitrary point is not meaningful, Qcg is needed
Qcg = 18.6 (14.5 predict using Steinberg’s QSt = √Fn)

17. VIABILITY OF PCB FREQUENCY PREDICTS
PFDPU Mechanical Evaluation
VIABILITY OF PCB FREQUENCY PREDICTS
NASA-SP-160 (1969) is one of the most complete analytic works available
<available on line by searching ntrs.nasa.gov>
A 5% frequency reduction is needed to reflect the less than rigid stacked frame FEM.
Minor corrections are needed for the EM – DCB test results
The test board had eight screws, but was not glued into it’s board frame
DCB test board was FR-4 while FMs will use higher modulus polyimide PCBs
Isola P95 is one example of a higher modulus board material

18. Steinberg on PCB Edge Conditions
PFDPU Mechanical Evaluation
Steinberg on PCB Edge Conditions
PCB mode shape descriptions
Pinned edge mode shape is a half sine wave: Z(x.y) = [sin(px/a) sin(py/b)]
Fixed edge mode shape is a full sine wave: Z(x,y) = ½ [cos(2px/a) -1] [cos (2py/b) -1]
Local curvature differs by a factor of two at the board center
In his text, on pages , this curvature difference is dismissed as small
Section 8.6 discusses edge wedge clamps (fixed edges)
His fatigue database presumably includes these types of PCBs

19. Steinberg on PCB Edge Conditions (con’t)
PFDPU Mechanical Evaluation
Steinberg on PCB Edge Conditions (con’t)
Pinned vs. fixed PCB edge comparisons – an even more conservative approach
Heavy solid lines are the mode shapes – dashed lines are the local (2nd derivative) curvature
Rust line is the |fixed to pinned edge curvature ratio|
Fatigue amplitudes are defined by curvature between any two chip ends (arbitrary positions)
Red 1.26 is the average of this curvature ratio between 20% & 80% of board dim’s
Large parts typically aren’t put in board corners (centered can be a smaller issue)
We introduce a modified (x , for x&y) location factor: r’ = 1.60 r(Steinberg)

20. PCB Material Damping Properties
PFDPU Mechanical Evaluation
PCB Material Damping Properties
Inherent PCB material damping is proportional to 1/Q test results
Damping is the least understood material property, subject to many factors
SDOF models assume viscid damping, while data often shows hysteretic trends
Test data often reflects a weak amplitude dependence
Actual DCB test result was close to Steinberg predict ( Q = √Fn)
Design margin predicts are tolerant of variations in Q (below)
test
predict

21. PFDPU Mechanical Evaluation
DCB Daughterboard has only a CCGA (ceramic column grid array) Actel
Considered a risk, but not as bad as the BGA (ball grid array)
Maven Thermal Expectations
Actel has provided an extensive thermal cycling test report
Typically 1000 cycles of +105 to -55C needed for failure
Coffin Manson predicts provided for other environments
PFDPU Thermal environments are expected to be mild
> 10C variation predicts for Martian orbits
CCGA Contacts Detail
Maven Vibration Expectations
Small (2.5” x 2.7”) pinned edge board
~ 1100 Hz first mode predict (DB only)
Z3s deflection ~ 0.004” predict
Z∞ deflection ~ 0.006” for infinite life
DB’s input will be rolled off ~ 12dB from the ~300 Hz first mode of its motherboard.
~ 0.007” deflection at DBs center [R] from MBs 300 Hz 1st mode (~ 0.003” under CCGA)

22. Revised Design Margins
PFDPU Mechanical Evaluation
Revised Design Margins
The revised results table below reflect:
Corrections based on the EM-DCB reduced vibration test data
Scaled DCB PCB frequency predicts
The 5% frequency reduction to account for the frame stacking
Enhanced location function (r’ = 1.60 r) accounting for larger board curvature

23. PFDPU Mechanical Evaluation
BOARD BY BOARD SUMMARY
DCB 1&2 (UCB) stiffened by partial daughter board: 0.062” PCB with glued edges
Test measurement of EM DCB resonant frequency proved adequate
IIB (UCB) w/ 2 T daughter boards and no large parts: 0.062” PCB with glued edges
REG 1&2 (UCB) NO large parts: 0.062” PCB with glued edges
DAP 1&2 (UCB): one large part: 0.062” PCB with glued edges
MAG 1&2 (GSFC) one large part: Considering (CAD-FEM) a local board stiffener
Fallback Option: ” PCB with glued edges
BEB (LASP) NO large parts : ” PCB with glued edges
DFB (LASP) Investigating (CAD-FEM) a local board stiffener
Fallback Option: 0.093” PCB with glued edges, or DFB-BEB-end plate partial skewer
PCB Edge Bonding (gluing) Plan
All board frames have a 0.080” wide shelf (all around) for good board support
Generous structural epoxy (Hysol EA-9309) fillets on both sides, before conformal coating

24. APPENDIX LASP’s Board Stiffener

25. Structural Analysis/Redesign EUV Mechanical
Appendix: LASP’s DFB Stiffener
Digital Filter Board
Structural Analysis/Redesign
EUV Mechanical
David Normen / David Braun
Structural Analyst / Mech. Design Eng.

26. Appendix: LASP’s DFB Stiffener
LASP provides DFB and BEB board to Berkeley.
DFB
BEB

27. Appendix: LASP’s DFB Stiffener
DFB’s FPGA did not meet LASP’s criteria for infinite life.
Steinberg Analysis for Electronic Equipment
Trade study to improve the FPGA’s structural performance.
Improved mounting does not predict infinite life, but should be acceptable.
Board w/ CQ352
Board
Thickness
Max Board Disp
(inches)
Lead Wire Stress (ksi)
Board Freq
(Hz)
Steinberg
1/16”
.006
N/A
223.3
Initial Mounting.
(8 fasteners)
.013
92.7
176.1
Improved Mounting
14.5
394.3

28. Appendix: LASP’s DFB Stiffener
Convert EMI Shield to stiffen board.
Add a center support.
Add simple support around the edges of the board.
Mat’l = Al 6061-T6
FPGA add
Corner staking with Scotch Weld 2216.
Standard LASP lead wire forming.
Frame
Note change to 8 edge fasteners.
Board
No layout changes.
EMI Shield and Stiffener
Lead wire and corner stake elements

29. Appendix: LASP’s DFB Stiffener
CQ352 FPGA

30. Acceptance(RV + Acoustics) / 1. min
Appendix: LASP’s DFB Stiffener
Criteria: DFB/FPGA must survive all vibration tests + flight w/ margin. (≠  life)
≥ 9 minutes of vibration.
< 100% Cumulative fatigue damage.
Vibration
Test
# Axes
Level/Time per axis
# of runs
Duration
(min)
Lead Wire
Stress
(ksi, rms)
Cumulative
Damage (3)
Time to
Failure(2)
PFDPU Test
1(1)
Proto-flight/1. min 2 2.
14.5
1.3%
39.5
Space Craft Level 3
Acceptance(RV + Acoustics) / 1. min 6.
10.3
.0% 
Launch 1 1.
Total 5 9.
---
(1) Assume only vibration normal to the board causes damage to lead wires.
(2) Time to Failure includes a 4x uncertainty factor for fatigue life per GEVS
(3) Failure occurs when damage ≥ 100%. Alloy 42 lead wires, use Kovar properties.

31. Appendix: LASP’s DFB Stiffener
Stiffener and EMI shield are integrated as one part
DFB layout will use “EM” board-to-frame mounting hole pattern
LASP supplied Stiffener
LASP supplied DFB PWBA
LASP supplied Frame
Berkeley supplied Vent Assembly

32. Appendix: LASP’s DFB Stiffener
Fasteners pass through frame and PWBA and threads into stiffener
Stiffener sits within the 0.070” keepout of PWBA
EMI groove
Stiffener, chromated aluminum, 178g
PWB
Frame, chromated aluminum

33. Appendix: LASP’s DFB Stiffener
Copy of frame drawing so we can duplicate size and tolerances
Locate (2) clock signal connectors
Determine fix ~.050 height discrepancy of stackable connectors
Check on fastener head clearance between DFB & BEB

34. Appendix: LASP’s DFB Stiffener
CQ352 Package on Board
Board or CQ352 Mountings
Board
thickness
Max Board Disp
(inches)
Lead Wire Stress
(ksi, rms)
Mode Freq
(Hz)
Q.S. Acceleration
(Gs, rms)
Time to
Failure
(min)
Method of Analysis
Steinberg Assumptions (Simple Support on 4 sides )
1/16”
.0055
N/A
223.3
---
Steinberg
Current Mounting.
(8 fasteners)
1/8”
.0127
.0106
.0039
.0042
92.7
88.4
66.4
70.0
176.1
409.1
416.5
23.4
44.2 RV
Q.S. – Miles
Current Mounting, Corner Staking: Uralane
86.5
176.2 0.
Q.S. - Miles
Current Mounting, Under-Fill: Nusil CV-2942
.0108
81.5
183.8
24.2
Current Mounting, Corner Staking: S-W 2216
.0104
27.6
181.9
24.0
Current Mounting, Nusil under-fill
and Corner Staking (S-W 2216)
.0107
26.4
191.1
25.0
Current Mounting, Under-fill, 2216 Staking,
simple edge support, 8 Fasteners
.0098
.0034
.0037
25.3
28.2
27.5
207.2
480.5
26.5
49.8
Current Mounting, Add idealized center support, Q =19.1
.0061
18.6
364.8,…
52.4
DFB stiffener 01, Center Support, Q = 19.8
.0057
14.5
394.3,…
39.5 min
Board damping is assumed to be fn (Steinberg) unless otherwise noted.
Time to failure is 1/4th of the predicted per GEVS.

35. BACKUP MATERIAL

36. PFDPU Mechanical Evaluation
MAVEN Zone 2 –Fwd Deck Vibration Levels
(derived from Atlas 5 acoustic levels)
Steinberg’s KOVAR Fatigue Plot
Sy ≈
≈ Se

37. EM-DCB BOARD TEST RESULT (¼ G sine sweep)
PFDPU Mechanical Evaluation
EM-DCB BOARD TEST RESULT (¼ G sine sweep)
Partial daughterboard & the many other features defy proper analysis
Original result assumed a single uniform density board

38. DAVE STEINBERG’s ON-LINE PROFILE MAJOR PUBLICATIONS (books)
PFDPU Mechanical Evaluation
DAVE STEINBERG’s ON-LINE PROFILE
Dave S. Steinberg is a well-known author and internationally recognized authority on the mechanical design, analysis, testing and packaging of cost effective sophisticated electronic equipment that must work with a high degree of reliability in harsh thermal, thermal cycling, vibration and shock environments. He has been involved in these areas related to commercial, industrial and military applications for many years. He recently retired from Litton Industries, where he was the manager of the Engineering Department for 15 years.
Mr. Steinberg is a visiting professor at the University of Wisconsin and for the past several years at UCLA where he has been presenting full semester post-graduate courses on similar electronic subjects related to the reliability of electronic equipment.
Mr. Steinberg has worked on many aircraft/missile/space programs, ships' electronic systems, automotive electronics and computers. These include the F-14, F-15, F-16, F-22, cruise missile, AMRAAM, ALCM, TALCM, SLCM, Titan 2 and 3, space shuttle, Mercury, Gemini, Apollo, communications satellites, DD963 destroyers, and the USS Forestall aircraft carrier. Typical companies include Lockheed, IBM, Litton, Intel, GM, Ford, Boeing, Wright Patterson AFB, Northrop, Cisco, Harris, United Aircraft, Hamilton Standard and Motorola, just to name a few.
MAJOR PUBLICATIONS (books)
“Vibration Analysis for Electronic Equipment” 3rd Ed. J.Wiley & sons, 2000 : 2nd Ed. 1988
Cooling Techniques for Electronic Equipment, 2nd Ed. J.Wiley & sons, 1991
Preventing Thermal Cycling and Vibration Failures in Electronic Equipment J.Wiley & sons, 2001