PCB Strain Measurement 巨克富科技 Chief-SI

Professional System Integrator

Agenda „ „ „ „ „ „

Why need strain gages? IPC/JEDEC-9702/9704 Standard Fundamental of strain gauge Strain measurement requirement Report function Demo

Why need strain gages? „

Board flexure induced solder ball cracking, trace damage, pad lifting

Trend of PCB „ „ „

Finer pitch of chip Thickness of PCB Lead free (RoHS) … Brittle

BGA CSP

Who should be concerned „ „ „ „

Component suppliers Test-fixture vendors PCB assemblers System manufactures

IPC Standard „ IPC/JEDEC-9702

Monotonic Bend Characterization of Board-Level Interconnects …

June 2004

„ IPC/JEDEC-9704

Printed Wiring Board Strain Gage Test Guideline …

June 2005

IPC-9702 „

Topics …

„

Monotonic Bend Test

Equipment …

Universal tensile tester … Strain measurement instrument … Continuity monitoring strain & resistance instrument

„

Recording data … … … … …

strain vs. time strain-rate vs. time strain vs. strain-rate force vs. time resistance vs. time

IPC-9702 „

Universal tensile tester … Control

„

board deflection rate

Measurement Instrument … 500

Hz min. … Simultaneous recording strain & resistance 2008 Q1 will ready

Copy from IPC

IPC-9702 „ „

Daisy-Chain

Test board Daisy-chain Uni-axial strain gage … 1.5

mm*1.5 mm … Principal strain angle ~ longitudinal „

Load span

Test speed … Strain

rate:5000 με/s

PCB

Package type

Global PWB Strain

Strain gage

IPC-9704 „

June 2005

Topics … Test

setup and equipment requirements … Strain measurement … Report format „

Surface mount device … BGA

(Ball Grid Array) … SOP (Small Outline Package) … CSP (Chip Scale Package)

IPC-9704 „

Process need strain measurement … SMT „

assembly

Component/connector install

… Board „

test processes

ICT, Function test

… Mechanical „

assembly

System assembly

… Shipping

Environment

Copy from IPC

IPC-9704 „

Strain Measurement Instrument …

Simultaneous sampling … 500 Hz min. for impulse event „

…

ICT, Drop, …

100 Hz min. for assembly processes … 3-wire gage with low level excitation (typical 2V) … Low Pass filter … More than 3 channels (12 or more recommend)

IPC-9704 „

Analysis …

Principal strain … Peak value … Strain rate … Time history „

Test Frequency … … … … …

Before any test or assembly fixture is brought online. Whenever there are modifications to a test fixture that might alter the strain profile. Whenever there are modifications to an assembly process that might alter the strain profile. In-process stiffener design validation. Enclosure design validation prior to hard-tooling

Fundamental of strain gage

Copy from Vishay

What is strain?

＝μin/in ＝με

Copy from TML

Principle of strain gage

Copy from TML

Strain gage types Axis:

Uniaxial

Measure direction

Rosette(Tee)

Rosette(Rectangular)

Resistance：120Ω、350Ω、1000Ω Material：Steel、Aluminum、Plastic、Compound… Temperature：Room temperature、High temperature(500℃) Application：Residual stress、Crack detection、Shear

Gage (IPC 9704) „ „

Rosette Stacked Rosette Strain Gages with preattached wires Planar

Stacked

Gage position (IPC 9704)

Strain gage Attachment

Common question of Strain measurement 1. 2. 3. 4. 5. 6.

Strain要如何量？ Strain Gage要如何貼？ Noise如何克服？ 主應變如何計算及其物理意義？ 準不準？如何校正？ 要買那一家的設備？

How to measure strain?

„

Bridge … Four

bridge arms … Excitation voltage … One Gauge system „ „

Two-wire circuit Three-wire circuit (Lead wire compensation)

The Wheatstone Bridge „

Full Bridge … Loadcell … Strain

type Accelerometer … Torque Transducer „

Half Bridge … Strain

with Thermal compensation … Weighting scale „

Quarter Bridge … Strain

Optimum Excitation Voltage „

Features … Large excitation, large signal output … Thermal consideration 2

V Power = V × I = R …

Quarter Bridge

Optimum excitation „ „ „

…

Configuration

Gauge grid area Gauge resistance Mounting surface

+2.5 VDC for StrainMap

Full Bridge

Resistance

Excitation Voltage

120Ω

0 to 6.250 V

350 Ω

0 to 10 V

1000 Ω

0 to 10 V

120 Ω

0 to 3.125 V

350 Ω

0 to 10 V

1000 Ω

0 to 10 V

Strain vs. Ω 4167 1Ω ~ ？ με

GF ≡

ΔR

ε

R

GF=2, R=120 Ω, △R=1 Ω ε=

ΔR

R = 1 / 120 = 0.004167 = 4167 μ GF 2

1με ≈

1 Ω = 0.00024Ω 4167

1με ≈

1 Ω = 0.0007Ω 1429

GF=2, R=350 Ω, △R=1 Ω ε=

ΔR

R = 1 / 350 = 0.001429 = 1429μ GF 2

Calibration(Shunt) „ „ „

Add Large Resistor Simulate Strain predetermined Example Ω Rshunt=100 kΩ ΔR=0.1438 Ω 599.3 με

… Rgauge=120

Shunt

Principal strain and Mohr’s circle ε x′ = ε1, 2 =

εx +εy 2

εx +εy 2

+

εx −εy 2

cos 2θ +

γ xy

⎛ ε x − ε y ⎞ ⎛ γ xy ⎞ ⎟⎟ + ⎜⎜ ⎟⎟ ± ⎜⎜ ⎝ 2 ⎠ ⎝ 2 ⎠ 2

γ xy tan 2θ p = εx −εy

ε1, 2 θp Known:

2

sin 2θ 2

γ 2 ⎛ − γ xy ⎞ ⎜⎜ ε y , ⎟ 2 ⎟⎠ ⎝

⎛ ε x + ε y γ max ⎞ ⎜⎜ ⎟ , 2 ⎟⎠ ⎝ 2

(ε 2 ,0)

:Principal strain :Principal direction

′

ε x , ε y , ε x ,θ = 45ο

(ε1 ,0) ⎛ εx +εy ⎞ ⎜⎜ ,0 ⎟⎟ ⎝ 2 ⎠

2θ p ⎛ γ xy ⎞ ⎜⎜ ε x , ⎟ 2 ⎟⎠ ⎝

ε

Example for 0-45-90 Rosette ε a = 650 ε b = −300 ε c = 480

y

εc

εb

45ο 45ο

εa

unit : με

x

ε 1 = 1434 ε 2 = −304 γ max = 1739 θ p = −42.2 ε1 = 889 ε 2 = −539 γ max = 1428

ε a = 800 ε b = 520 ε c = −450

θ p = 14.4ο

ε a = 520 ε b = 360 ε c = −80

ε1 = 551 ε 2 = −111 γ max = 662 θ p = 12.5

Strain Measurement Solution „

StrainMap …

Simultaneous sampling … ±3με noise level … 2k/ch(5k/ch for PCI bus) … 24~128 ch „

StrainMap Enhanced … … … … … …

Simultaneous sampling ±5με noise level 50k/ch USB 24~56 ch Vibration Module (Option)

Our Customer ASUS „ Compal „ Inventec „ Lenovo „ TSMC „

Intel „ Foxconn „ CHIMEI „ PTI „

StrainMap advantage „

Total solution …

„

Integrate Gage、measure & Training

Performance … …

accuracy：±3με Simultaneous sampling： 2k (5k for PCI bus） … Channel：up to 128 Chs … stability „

Analysis & report function … … …

„ „ „

Auto-calibration (Shunt) Mohr’s circle analysis Excel report

Easy wiring Short lead time & lower price Local service

Easy wiring

Software for IPC-9704 „ „ „

Graphical User Interface Easy Wizar Calculation … … …

Diagonal strain = e1-e2+e3 Principal Strain StrainRate

Report of StrainMap

StrainMap Enhanced Demo

Thank you Chief SI 何寬賢 03-5936268 0922855439