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A ShortWire Fixturing Technique EC-1 A ShortWire Fixturing Technique
EC-1 Sample High Point Count - Long Wire Fixture EC1 Shortwire*
Short Wire for: GR & Teradyne
Developed for :
Short Wire applications
High Pin Count applications
Small Target applications
Fine Pitch applications -
1mm centers -path to .8mm
* Patent Pending
Tester Interface
Unit Under Test
EC-1 Shortwire
-
What is so different ?
New Wiring technique
Shorter Wires
Faster wiring process
New wiring connection - crimped both
ends
New Probe technology - down to 1mm
centers now- migration to .8 mm
New receptacle concept - one size fits all Short
Distance
Between
Ground
Planes
Standoff
Gas-tight wire
termination process
Probes retained in
receptacles by 4
spiral detents
Cross-Section - Probe Plate and Interface Plate
EC-1 Shortwire
Innovative Fixture Technology
Ground plane
Ground plane
Short
Wire
G-10 interface plate
Probe Plate
Receptacle Plate Short
Distance
Between
Ground
Planes
Standoff
Gas-tight wire
termination process
Probes retained in
receptacles by 4
spiral detents
Cross-Section - Probe Plate and Interface Plate
EC-1 Shortwire
Potential for very short wires
Ground plane
Ground plane
Potential
for very
short wires
G-10 interface plate
Probe Plate
Receptacle Plate EC-1 Shortwire
Innovative Probe Technology
Recessed end that plugs into receptacle EC-1 Shortwire
Innovative Probe Technology
One Probe Size for 50ml, 75ml and 100ml
One probe size for 1mm
One Receptacle size for ALL Probes
ReceptaclesZero Probe walkout
Migration path .8mm probes EC-1 Shortwire
Innovative Receptacle Design
EC-1 Shortwire
Interconnect
4-Spiral Detents for
Probe retention
Improved Probe
Retention
One size fits all
No Wire Wraps EC1 Shortwire -
Recommendation for
when to use
High density test point fixtures
Higher percentage of .050 or 1mm center test
targets than 75s and 100s
Sub .050 center spacing requirements
1 mm available now
Small Test Targets - down to .018 diameter EC1 Shortwire -
Recommendation for
when to use (continued)
High Test Point count fixtures requiring
fastest possible delivery
Replacement for Wireless fixtures
Lower cost solution
More Copper per connection than wireless fixture traces
Wires are typically shorter than traces
Not reliant upon expertise of the PBC layout person
When you want short wires ! ShortWire Fixturing Technique
EC-1 Board Stress Analysis
(BSA)
and
Strain Gage
measurements What is a BSA A BSA (Board Stress Analysis) is a computer model that predicts the
stresses and deflections a PCBA will be subjected to when tested on a bed-
of-nails fixture. A BSA will give the results for several thousand or million points, dependent
only on the number of finite elements used in the analysis. Areas of concern
or interest can be scrutinized even further by increasing the total number of
elements in a given area. This analysis should be run before the fixture is built and is thus a proactive /
predictive method of controlling stresses in PCBAs, and minimizing
deflections. When the BSA process was initially developed (1988), the results were
verified & validated using direct measurement technology. The end result is a Test fixture can be designed & built that will not damage
the PCBAs it was built to test. 2D BSA
Generally speaking, the 2D analysis is simpler, requiring much
less set-up times and faster results.
2D BSAs model the PCB (bare board) without consideration of the
stiffening effects or surface mounted components.
The absence of components however, will exaggerate the stress
and deflection prediction that the board will be subjected to.
These results may be quite different from the actual condition of a
loaded PCBA, potentially causing a fixture designer to add more
PCB supports than necessary.
BSA output will quickly identify high stress or high deflection areas. Typical 2D outputs
Testing the Limits Plot showing contour & push finger locations
relative to component locations 2D Board Stress Analysis
Strength
Simpler analysis to run
Less (zero)set-up time
Faster results
Provides information for
the entire PCB
No CAD data required
(but highly
recommended)
Method has been
utilized for almost two
decades
Weakness
Results will somewhat
exaggerate stress and
deflection levels
Provides data for PCB
only
Radius of curvature
could be calculated for
PCB only. Not accurate
enough for components
Testing the Limits 3D BSA
Creates a CAD style Model of PCBA
Testing the Limits 3D BSA - Overview
The 3D analysis utilizes a more involved model of the PCBA.
It takes into account the component stiffening.
The analysis is also more complex, requiring tremendous computing power
as there could be hundreds of additional components on a fully loaded PCB.
The complexity of the 3D BSA stems from the interaction of individual board
components to the base PCB. Each individual component will carry its own
set of material properties, which behaves differently under given loading
conditions. Assignment of material properties is also not a straightforward
process. Many of the components are made up of several different
materials.
The 3D can model isotropic and non-linear materials used in PCBA.
The detail and complexity of the analysis requires that the 3D BSA should be
kept as a charge of the trained engineer.
Testing the Limits
BGA Cross Section Typical 3D outputs
Testing the Limits 3D Board Stress Analysis
Strength
Most accurate method
available when model is
accurate
Provides information for the
PCB and all components
Can prevent damage to
PCBAs when used properly
Radius of curvature
calculation is more accurate
with inclusion of components
Weakness
More difficult to run, requires
a highly trained engineer.
Very time consuming both
set-up and processing time.
Component data is not easily
accessible
Component material
properties may need to be
closest approximations for
multi-material components
Requires powerful computer
hardware and software.
Testing the Limits Strain Gage
(Direct Measurement) Technology
Strain
Gage
Measurement Recorder
Testing the Limits Sample specification for
Strain Gages
Strength
Concept is easier to
understand
Strain rate and strain
readings are available
Measurements are
actual rather than
theoretical
Weakness
Reactive - requires a completed
fixture and PCBA.
Analysis is limited to open areas
on PCB and subject to placement
of strain gauges.
Fixture may need to be modified
to find open real estate
High stress areas beneath
components can not be measured
Results may give false sense of
security since only finite number of
areas can be measured
Calibration/operator error
Testing the Limits Recommendations:
1)2D Board Stress Analysis for all fixtures
Provides immediate in-process feedback to the fixture
designer - problems addressed before fixture is built
Proven technology - fast & accurate results
No Cost only the benefit
2)Always utilize PCBA CAD and BOM data
when designing/building a fixture
the model must match the finished fixture.
3)Strain Gage testing for areas of concern
When BSA identifies high stress areas near sensitive
components - strain gages should be utilized Suggested References
The Finer Points of Test, Evaluation Engineering, PP 36, 38-41,
January 2006. Gary F. St.Onge.
IPC/JEDEC-9704, Printed Wiring Board Strain Gage Test
Guideline, June 2005, A standard Developed by IPC, Bannockburn, IL.
Mechanical Stress of BGA Solder Joints During In-circuit and
Functional Testing, Teradyne Users Group, Nashville TN, Jesse T.
Carpenter, ECT Test Fixture Division, May 2003
Adding 3-D to Board Stress Analysis, Evaluation Engineering,
PP78,80,82,89, August 2000. Gary F. St.Onge and Thomas Newhall.
Controlling Board Flex in Test Fixtures, Evaluation Engineering,
PP14- 18, September 1989. Gary F. St.Onge. Board Stress Analysis
(BSA)
and
Strain Gage
measurements
Gary St.Onge
518-877-3750
stongeg@ectinfo.com