Desing for Flying Probe Testing.pdf

8/17/2019 Desing for Flying Probe Testing.pdf

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ACCULOGICACCULOGIC

Design for Design for Flying Probe Flying 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


y ng ro e es ys ems Discussions


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ACCULOGICACCULOGIC Glossary of Terms

DFT – D esign for T estability

DFM – D esign for M anufacture

DFx – D esign for E x cellence = DFT+DFM

SMT – S urface M ount T echnology SMD – S urface M ount D evice

JTAG – J oint T est Action G roup

TAP T est Access P ort


ICT – I n C ircuit T est FPT – F lying P robe T est

MDA – M anufacturing Defect Analyzer

PCA – Loaded P rinted C ircuit Assembly

PCB – Bare P rinted C ircuit B oard

UUT – U nit U nder T est


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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 mm 2

400 mm 2

225 mm 2

QFPQFP

TABTAB

COBCOB

15 mm

20 mm

30 mm


uBGA Fan out issues

Part Placement DensityIncreasing

Complex Fault Isolationwithout DFT

100 mm 2 Flip Chip Flip 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


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


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 both top and bottom ofthe 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


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 Fiducial Locating 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


Some samples are below, most commonly used is thecircle in circular clearance area.

Sample FID Patterns Clearance 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


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 down locating, 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 UUT mechanical limits will exist depending on thesystem you have, or plan to use.


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


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


.

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

–


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


where the leg is soldered – ICT/MDA will use the leg centers and a crown probe type

Press Fit Through Hole

Usually connectors Usually 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


– 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



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ACCULOGICACCULOGIC TYPICAL 0402 LAND PATTERN

43 mils

20 mils20 mils

S

O

L

S

O

L


m s

31 mils31 mils 20 mils

m s

drawing not to scale

Probe target

D

E R

D

E R


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ACCULOGICACCULOGIC

Provided there is enough space Provided there is enough space

Some part pads can be used

OK



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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


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


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


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


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


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



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ACCULOGICACCULOGIC PCBA Carrier



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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


FE

Thyristor Triac

Other Devices: Other Devices: Bridges

Switches Relay Optocoupler

Boundary Scan AOI 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


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


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 …



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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


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 possible VIT+ makes testing U3 possible

Documents

Desing for Flying Probe Testing.pdf