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 physical
properties 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,Maliankara
10

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:capacitance
method(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
CONTROLLER
DISPLAY

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 the
range 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 delamination
during soldering

CONTD…
 Moisture enters the PCB when the partial pressure of the
moisture is greater to that inside the PCB
 Focused on capacitance measurements to follow the
absorption and desorption behaviour of moisture
 Capacitance is dependent on permitivity (which is dependent
on 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 holes
at different densities (b) Illustration of the internal grid
capacitors
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 central
region (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
7/2/2013 DEPTOF ECE,SNMIMT,Maliankara 42

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 andeach 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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