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ACCULOGICACCULOGIC
Design forDesign for Flying ProbeFlying Probe
TestingTesting
DFT Seminar Series 20091 www.acculogic.com
DFT Seminar Series 200
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ACCULOGICACCULOGIC Agenda
Introduction
The DFT Concepts
Mechanical DFT Issues
Circuit DFT Issues
DFT Seminar Series 20092 www.acculogic.com
y ng ro e es ys ems Discussions
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ACCULOGICACCULOGIC Glossary of Terms
DFT Design forTestability
DFM Design forManufacture
DFx Design forExcellence = DFT+DFM
SMT SurfaceMountTechnology SMD SurfaceMountDevice
JTAG JointTestActionGroup
TAP TestAccessPort
DFT Seminar Series 20093 www.acculogic.com
ICT InCircuitTest FPT FlyingProbeTest
MDA Manufacturing Defect Analyzer
PCA LoadedPrintedCircuitAssembly
PCB BarePrintedCircuitBoard
UUT UnitUnderTest
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ACCULOGICACCULOGIC Why is DFT required in today's designs?
Design ComplexityIncreasing
Part Sizes Decreasing Part Pin Out Increasing
System On Chip
1100+ Pin BGA
900 mm2
400 mm2
225 mm2
QFPQFP
TABTAB
COBCOB
15 mm
20 mm
30 mm
DFT Seminar Series 20094 www.acculogic.com
uBGA Fan out issues
Part Placement DensityIncreasing
Complex Fault Isolationwithout DFT
100 mm2Flip ChipFlip Chip
Source: IBM
10 mm
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ACCULOGICACCULOGIC Mechanical DFT Issues
PCA Handler Issues
PCA Alignment System
Tall Part Test Limitations No Fly Zones
Test Accessibility Near Card Edges
DFT Seminar Series 20095 www.acculogic.com
Types of Test Access Point Test Point Dimension Recommendations
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ACCULOGICACCULOGIC PCA Handler Issues 3 mm rule
Edge Clearance on two Parallelsides of the UUT are required 3
mm
Best along the longest edges ofthe UUT to prevent sag
Predictable leading edgedimension required for boardstopping position on systems with
Good Layoutfor conveyor
3mm edge clearance
DFT Seminar Series 20096 www.acculogic.com
automatic conveyors 3mm edge clearance
In the case with odd shapedboards two solutions exist
Use break away rails thatcomply with the above
Use a custom or universalcarrier to move the UUT intothe machine.
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ACCULOGICACCULOGIC PCA Alignment and Fiducials 3 FID rule
3 Board FID points are required on bothtopandbottomofthe UUT Placed near the perimeter of the UUT
Must be free from solder after production Must not be identical from top to bottom
Must not be near similar graphics, etches, silk screens.
Must be clear from the 3 mm edge clearance
DFT Seminar Series 20097 www.acculogic.com
Should be in the CAD as a part or easily identifiable entity.
3 Fiducial points place properly
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ACCULOGICACCULOGIC PCA Alignment and Fiducials FID Qualities
According to the IPC-SMEMA Council FiducialLocating marks should have the following
characteristics: Size: 1 mm to 3 mm in diameter (40 118 mils)
Clearance Area around the FID: - 1-2 times the radius of thesize
DFT Seminar Series 20098 www.acculogic.com
Some samples are below, most commonly used is thecircle in circular clearance area.
Sample FID PatternsClearance Area
1 to 2 times Radius
FID Mark
1-3 mm
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ACCULOGICACCULOGIC PCA Alignment of Panelized UUTs
Panels should have panel FIDPoints that follow singleboard requirements
Clear from the edge, 3 top, threebottom, 1-3 mm is size and 1-3mm clearance
DFT Seminar Series 20099 www.acculogic.com
Must be in CAD or MechanicalDrawing and accurately
referenced to individual UUT.
This does not remove therequirement for Single Board
FIDs, these are still required
In the case when real FID points are not available mostIn the case when real FID points are not available mostsystems can capture another image and use it as asystems can capture another image and use it as a
locating, but probing and placement accuracy goes downlocating, but probing and placement accuracy goes down
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ACCULOGICACCULOGIC No Fly Limits and Part Selection
As robotic systems, flying probe machinesneed to move over parts to go from place toplace. Given that they are to contact the
board under test and they are not infinitelyhigh from the surface of the UUT some UUTmechanical limits will exist depending on thesystem you have, or plan to use.
DFT Seminar Series 200910 www.acculogic.com
Fly over heights range from 30 mm to 45 mm
Fly around heights range from 30 mm to85mm in systems that have this capability.
Fly Over or Fly Around issues can beminimized
Select low profile parts
Place tall parts after test
Place heat syncs after test
Tall
device
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ACCULOGICACCULOGIC Test Access Requirements
Test Point Types:
Dedicated Test Points
Via Holes as Test Points
Through Hole Pins as Test Points
Surface Mount Pads as Test Points
Virtual Test Points
DFT Seminar Series 200911 www.acculogic.com
Ideal DFT from an access point of view
Full access to every net on the board is ideal
One or more access point per connected net
One access point per unconnected net
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ACCULOGICACCULOGIC Dedicated Test Points
As named are entities in the design that are specificallymeant for test access. Two main types exist:
Copper areas that are free from solder resistive mask and otherimpediments.
Should be as close as possible to the source end of
DFT Seminar Series 200912 www.acculogic.com
.
Physical Parts that can be mounted/placed on the PCA
Ground/VCC Stake
Ground/VCC Clip
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ACCULOGICACCULOGIC Vias as Test Points
Four types of vias are common in PCB Layout:
Testable Vias
Standard Via accessible to both top and bottom and may beconnected to a mid plane layer
Annular ring aperture may differ from top to bottom
indicating the preferred side to probe
DFT Seminar Series 200913 www.acculogic.com
mid plane layer
Non-Accessible Vias
Buried Via not accessible to the top or bottom and only
connects mid plane layers to one another. Tented or Masked Via can belong to all of the above
categories and has a solder resist mask or other coating that
prevents it from allowing electrical contact.
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ACCULOGICACCULOGIC Through Hole Device Leads as Test Points
Soldered Through Holes
Connector, socket, resistor, etc device leads that are solderedthrough holes in PCB can be ideal test access locations.
Flying probe will typically require that the actual contact pointbe offset from the center of the leg as its position is notabsolutely fixed in x, y or z planes.
Standard ractice is to have the robe oint offset to the rin
DFT Seminar Series 200914 www.acculogic.com
where the leg is solderedICT/MDA will use the leg centers and a crown probe type
Press Fit Through Hole
Usually connectorsUsually connectors
Flying Probe must be targeting to the annular ring ofthese access points
care must be taken not to stick the probe into the connector hole and jamif from retraction for systems that do not have z-axis feedback.
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ACCULOGICACCULOGIC SMD/SMT Pads as Test Points
The accuracy and repeatability of certain FP machines will allowyou to use these leads at viable test access locations.
0603 easy for most machines 0402- easy for some machine
0201 getting harder
01005 - difficult
DFT Seminar Series 200915 www.acculogic.com
IC Leads depends on pitch
PAD exposures need to be meeting the minimum targeting requirementsof the system used.
RF and other special circuits are burying pads underthe parts
cannot probe what cannot be seen
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ACCULOGICACCULOGIC Some SMD Packages from Wikipedia
DFT Seminar Series 200916 www.acculogic.com
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ACCULOGICACCULOGIC TYPICAL 0402 LAND PATTERN
43 mils
20 mils20 mils
S
O
L
S
O
L
DFT Seminar Series 200917 www.acculogic.com
m s
31 mils31 mils 20 mils
m s
drawing not to scale
Probe target
D
ER
D
ER
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ACCULOGICACCULOGIC
Provided there is enough spaceProvided there is enough space
Some part pads can be used
OK
DFT Seminar Series 200918 www.acculogic.com
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ACCULOGICACCULOGIC Manufacturing Issues that Impact Test
Clean or No Clean Process
If the UUT has flux residue or other non-conductivesubstance this can cause:
False failures of all test types
False passes of shorts tests
Lead Free or Leaded Solder
DFT Seminar Series 200919 www.acculogic.com
Lead free is harder and can provide worse contact over timewith probe tip aging
Through Hole Part Placement
Drift in hand placement can prevent use as viable test points
location Can damage the machine and parts if not consistently placed
SMD Device Flow Variance
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ACCULOGICACCULOGIC DFT Recommendations
Ensure that output enable pins are not tied to ground or VCCdirectly. Use pull-up/pull-down resistors that can be driven such that the device when
powered will be tri-stated.
Ensure that each device that has a disable pin is independentlycontrollable
DFT Seminar Series 200920 www.acculogic.com
As an example, if you have a bank of buffers that are used in conjunction
with a memory data but, the buffers and memories will need to be controlledfrom two nets so that we can effectively and discretely test each of theindividual parts.
Ensure that all clock/oscillator/crystal circuits can be isolated orstopped from oscillating
Ensure that watch-dog timers can be disabled so that they arenot continually resetting the UUT during test vector execution
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ACCULOGICACCULOGIC Limited Access Test Products Flying Probes
Double-Sided Flying ProberScorpion 8xx/9xx series
DFT Seminar Series 200921 www.acculogic.com
Single-Sided Flying Prober
Sprint 4510
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ACCULOGICACCULOGIC
Enables Prototype , NPI & low volume PCBs to be tested
Test PCBs with minimal NRE
Greater Test Access with targets down to 4 mil (0.1 mm)
Benefits of using a Flying Probers
DFT Seminar Series 200922 www.acculogic.com
Enables testing of PCBs without traditional ICT test pads
Provide for greater test coverage with AOI capability
Implement same day testing
BOM verification
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ACCULOGICACCULOGIC FLS Configuration flexibility
DFT Seminar Series 200923 www.acculogic.com
2 Stators - Topside and Bottom-side
Up to 4 Shuttles per Stator
3 Probe Slots per Shuttle
Max Probes 11 Topside / 11 Bottom-side
Total Maximum Probes 16
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ACCULOGICACCULOGIC
DFT Seminar Series 200924 www.acculogic.com
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ACCULOGICACCULOGIC PCBA Carrier
DFT Seminar Series 200925 www.acculogic.com
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ACCULOGICACCULOGIC FLS Test Techniques
Passive Components:Passive Components:
Resistors (R) Capacitors (C) Inductors (L)
Discrete Semiconductor:Discrete Semiconductor: Diode Zener diode (to 100V) Transistors
Active analog and hybridComponents:
Comparator and Regulator
Operational Amplifier
Other Tests: Contact
Shorts
Power Up and Functional Test
DFT Seminar Series 200926 www.acculogic.com
FE
Thyristor Triac
Other Devices:Other Devices: Bridges
Switches Relay Optocoupler
Boundary ScanAOI on all shuttles
Vectorless Opens Test:
ChipScan
C-Scan
Network Analysis: BodeScan
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ACCULOGICACCULOGIC
Resistors
Capacitors
Semiconductors
Electrical Test
Bypass Capacitors
Mechanical parts
Vision Inspection
Complementary Vision Inspection
DFT Seminar Series 200927 www.acculogic.com
n uc ors
OpAmps
Transformers
LEDs
Switch/Relay contacts
Shorts/Opens
Connector orientationSockets
Capacitor orientation
Labels
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ACCULOGICACCULOGIC FLYING PROBER COMPARISON
TEST TECHNIQUE MDA FP-SS PON FP-SS MDA FP-DS PON FP-DS NOTES
Shorts Nets on one side only not detectable
Opens
Passives
Bypass caps Vision option on FP
Low value RLC Dedicated hardware at DUT; kelvin tests
Actives
Markings/Barcode Vision inspection; barcode on one side only
Switches Mechanical contact
DFT Seminar Series 200928 www.acculogic.com
Connectors Probe connector pin tip
LED colors
IC Opens Vectorless testing (TestJet, FrameScan)
Frequency Test
Voltage Test
IC Internal Logic
IC Programming Using B/S
Boundary Scan FP needs B/S chain
Test Target Largest target on either side for -2
Datalog 1 log for both sides
Test time Two pass testing on 1 sided FP
SS: Single Sided; DS: Double Sided; FP: Flying Prober
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ACCULOGICACCULOGIC Flying Fixture probing
DFT Seminar Series 200929 www.acculogic.com
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ACCULOGICACCULOGIC Stages of Boundary Scan Test
TAPIT Test Access Port IntegrityTest Class 6
VIT: Class 1, 2, 3, 4, Test VIT+:Boundary Scan and Non-
Boundary Scan Device Test Digital I/Os behind Flying Probes Digital I/Os at Carrier I/O Interface
VCCT: Cluster, Memor Test &
U1 U2
DFT Seminar Series 200930 www.acculogic.com
Programmin
Each stage is generated in SVFFormat and comes with Diagnostics
Usually, test Coverage on UUTincreases with each additionalstage
SVF is an Industry standard forgenerating serial and parallelpatterns in ASCII format file
TDI TDO
U3INPUT
VIT+ makes testing U3 possibleVIT+ makes testing U3 possible