Athira seminar

WELCOME

8/3/2013 DEPT ECE,SNMIMT,Maliankara 1

SEMINAR ON

PRESENTED BY

ATHIRA M JOSHY

ROLL NO:14,S8 ECE


CONTENTS

INTRODUCTION

MOISTURE MEASUREMENT INSIDE ELECTRONIC DEVICES

MOISTURE MEASUREMENT OF SKIN

BLOCK DIAGRAM

OVERVIEW

MOISTURE MEASUREMENT IN PCB

EXPERIMENTAL SETUP

MODELLING PTH AND NON-PTH IN COPPER PLANES

ADVANTAGES DISADVANTAGES

FUTURE SCOPE

CONCLUSION

REFERENCE


Moisture Measurement

Moisture is the amount of water in any form in a material

It is a component of molecular makeup for all material

Excessive or deficient moisture adversely impact the physicalproperties of a material

INTRODUCTION



BLOCK DIAGRAM Measurement

Primary

Air oven

Secondary

Destructive Non-Destructive

Interdigital capacitor Ultracapacitor



MOISTURE MEASUREMENT INSIDE ELECTRONIC DEVICES

USING ULTRACAPACITOR

Ultracapacitor:Electrochemical capacitor with relatively high energy density

Lack of dielectric permits packaging of plates with large surface area into a given volume

Formed of ordinary activated carbon electrodes



CONTD…

No liquid electrolyte exists inside the device

Electrodes are placed on both sides of a layer of porous silicon

Potassium hydroxide in powder form is embedded inside

porous silicon

Useful for monitoring moisture penetration inside small

electronic devices



CONTD…

As moisture penetrates the porous silicon layer, a liquid electrolyte starts to form

Presence of moisture causes:

• Conductivity of electrolyte increases

• Hence the capacitance of the ultracapacitor increases

• Results in high capacitance



CONTD…

Ultracapacitor (dry, without electrolyte) (with electrolyte)



CONTD…

8/3/2013 DEPT ECE,SNMIMT,Maliankara10

Capacitance with relative humidity

(5-80)% of MC causes (0-17) μF


MOISTURE MEASUREMENT OF SKIN

Importance: Needed for the identification and prevention of ECZYMA

Method adopted for skin moisture measurement:capacitancemethod(Interdigital Capacitor)

Mild case of eczyma



CONTD…

Stratum corneum is the outermost layer of the skin

It is composed of dead skin cells, a protein called Keratin, naturally secreted oils

Dry skin exhibits a lack of oils results in cracking of the stratum corneum



CONTD…


Stratum corneum


BLOCK DIAGRAM


INTERDIGITAL CAPACITANCE

CAPACITANCE MEASURING

CIRCUIT

MICRO

CONTROLLERDISPLAY


CONTD…

INTERDIGITAL CAPACITOR:

IDC is the core component in capacitance method

It contains thin strips of copper

Moisture is measured as proportional increase in capacitance



CONTD…

SCATTERFIELD EFFECT:

• Deviation of the linear path from one plate to the other

• Important concept in the design of an IDC



Interdigital capacitance

CONTD…

CAPACITANCE MEASURING CIRCUIT:

Circuit to measure the increase in capacitance is required

“Add on capacitance meter” is used for the purpose

Add on capacitance circuit is used to identify capacitors of therange 1pF to 100pF



CONTD…


Add on capacitance circuit


CONTD…


Circuit charges the test capacitor via a resistor selected by the rotary switch

Circuit charges the largest capacitor (in the range) in exactly 100 units of time

Voltmeter works only when the pin 6 of 74c14 IC is low

Voltmeter gives the reading corresponding to the test capacitance


CONTD…

MICROCONTROLLER :

Project incoporates AVR butterfly microcontroller

It has an ADC converter built in, labelled as Voltage V_in

Microcontroller takes data from the ADC port (V_in) and performs the conversion

It produces a value of 0 on the display when the device is turned on and IDC is exposed to air



CONTD…


AVR butterfly microcontroller kit


RESULT

SKIN TYPE VALUE DISPLAYED ON LCD

Moist skin 10-12

Normal skin 4-9

Dry skin 1-3


CONTD…


Complete circuit of moisture sensor


MOISTURE MEASUREMENT IN PCB

EFFECTS OF MOISTURE IN PCB :

Moisture reduces the quality of lamination and solder

Excessive moisture increases dielectric constant leading to changes in circuit switching speed

Ionic corrosion causes electrical open circuit or short circuit

High levels of residual moisture in PCBs causes delaminationduring soldering



CONTD…

Moisture enters the PCB when the partial pressure of themoisture is greater to that inside the PCB

Focused on capacitance measurements to follow theabsorption and desorption behaviour of moisture

Capacitance is dependent on permitivity (which is dependenton moisture)



DELAMINATED PCB



EXPERIMENTAL SETUP

Test boards are designed with capacitors situated on inner layers between external copper planes

It is placed in 85°C and 85 per cent relative humidity (RH) environment

Moisture removal at bake temperatures of 80, 110 and 125°C is monitered

Capacitance is periodically measured at a frequency of 100 kHz




(a)Test board showing plated and non-plated through holesat different densities (b) Illustration of the internal gridcapacitors

Dimensioned capacitor design


CAPACITANCE MEASURED


Effect of non-PTH hole density on average capacitance decrease for the test boards baked at (a) 80°C, (b) 110°C and (c) 125°C


CONTD…


Comparison of PTH and non-PTH on the capacitance decrease with bake time at 125°C for three hole densities


CONTD…

Average capacitance decreases more quickly for higher hole densities due to the increase in surface area

Capacitance decreases faster for boards with non-PTH such boards require shorter bake time

PTH boards have a smaller exposed surface area than non-PTH boards so moisture cannot escape so easily



MODELLING PTH AND NON-PTH IN COPPER PLANES

Modelling is done to compare different moisture desorption capability of PTH and non-PTH boards during a baking

Model boards are subjected to stimulated baking

Model consisted of a PCB with a 0.4 mm hole repeated infinitely in both x and y directions and with a pitch of 4 mm

Extra model was created to represent copper planes on inner layers only



CONTD…


(a) Non-PTH with copper plane on outer layers, (b) PTH with copper plane on ouer layers and (c) PTH with internal copper planes


MODELLED MOISTURE PROFILE :


Modelled moisture profile (a) non-PTH with copper plane on outer layers, (b) PTH with copper plane on outer layers and (c) PTH with internal copper planes


CONTD…

CONTD…

Dark blue colour represents saturation and light yellow as dry regions

Moisture exits non-PTH PCB model more quickly as moisture can escape more easily from the greater open surface area

For PTH board, rate of moisture loss is slower as moisture must diffuse a greater distance to find surface free from copper

For boards with internal copper planes moisture rapidly exists first,then becomes slow



CONTD…


Modelled effect of bake time on the mean moisture content in the centralregion (1 mm off the copper plane) in boards PTH and non-PTH boards.


ADVANTAGES

ULTRACAPACITOR SKIN MOISTURE SENSOR

Long life High accuracy

Low cost portability

Extremely low internal resistance inexpensive

High output power and Improved safety



DISADVANTAGES

ULTRACAPACITOR SKIN MOISTURE SENSOR

Highest dielectric absorption Difficulty in producing the device

Low maximum voltage Not a handheld device

High self discharge



FUTURE SCOPE

SCOPE OF ULTRACAPACITOR IN PACEMAKER:

Pacemaker helps to monitor and control your heartbeat

It consists of a battery, a computerized generator, and wires with sensors at their tips

Malfunction can occur if moisture happens to be inside the device

Ultracapacitor can be used inside the device to check the amount of moisture



CONTD…


Pacemaker implanted inside human body


CONCLUSION


Food

Medicine

Industry

RELEVANCE

CONCLUSION

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CONTD…

A processed material's MC will define its physical properties at

all stages of processing and final product existence

Non-destructive methods are preferred and each method

discussed has specific applications

Moisture analysis means testing at the point of

processing, and making adjustments before product integrity

is effected



REFERENCE

Design of a handheld skin moisture measuring device for application towards eczema, By Scott Truong

Moisture measurements in pcbs and impact of design on desorption behaviour , Chris Hunt,, National Physical Laboratory, UK

N.P. Avdelidis, P. I. Nicholson & P. Wallace, ”Pulsed thermography in the investigation of PCBs for defect detection & analysis”,

www.wikipedia.org

www.ecma-international.org



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