Multi Layer PCB Designing and Assembly

Printed Circuit boards (PCBs) are the core building blocks of most of the electronic items today and the drive for innovation and improvement in the operation and reliability of the modern electronic circuits is more powerful today than ever before. PCBs are used in all major applications from simple to highly complex integrated circuitry. Looking at this large range of application and dependence of the electronic devices of the Printed circuit boards, it wouldn’t be wrong to say that they PCBs drive the world of today.

PCBs have reduced the size and weight of the conventional circuits while they have increased the design capabilities of the circuits manifold. They have paved the way for faster and more efficient processors to be built which require billions of transistors to be integrated on the board and work in unison. The high precision applications in aerospace technology and computer servers require the operation of integrated circuit of high density which has only been made possible through the advent of printed circuit boards.

Multi layer Printed Circuit Boards (PCB) has greatest and complex functional capability of all types of PCBs available today as they are used in wide range of consumer electronics i.e. smart phones and microwaves. Such devices tend to use Multi layer Printed Circuit Boards (PCB) for attaining less weight and small size. The multi layer PCBs are used in telecommunication devices such as transmission systems, GPS and satellite transmission systems. The reason behind using multi layer Printed Circuit Boards (PCB) in the telecommunication industry is the durability and high functionality provided by the multi layer Printed Circuit Boards (PCB).  Multi layer PCBs are also widely used in the medical industry due to the high density design capability made possible by them. In medical industry they are mostly used in x-ray machines, CAT scan, heat monitor devices and numerous other electronic devices used in the medical industry. Military and defense applications also widely use the multi layer Printed Circuit Boards (PCB) mostly in air traffic control systems, high power computers and servers operated in these environments, monitoring of sensors and wide range of military electronic devices.

The major reasons behind the wide use of Multi layer Printed Circuit Boards (PCB) is the high assembly density made available to the manufacturer. In Printed circuit board assembly it is given priority to choose the design such as to minimize the size and weight of the device, hence the multi layer Printed Circuit Boards (PCB) comes into play.  The multi layer Printed Circuit Boards (PCB) also allow for controlled impedance features, greater EMI shielding and overall design quality which makes them most suitable for applications where smart designs are required.

Multi layer Printed Circuit Boards (PCB) are like single or double layer Printed Circuit Boards (PCB) but in multi layer Printed Circuit Boards (PCB), the layers are substrate and copper coating exceed from two layers. The substrate of the multi layer Printed Circuit Boards (PCB) also range from glass epoxy resins to Teflon while the copper coating on the layers serves the purpose for drawing the conducting paths though the thickness of the copper coating can vary depending on the design and requirement of the application.

In Multi layer PCBs, the top and bottom layer contain the core between them which contain the inner layers stacked together. The different layers of the PCB are connected through via of various types depending upon the requirement. Some of the main types of via used in multi layer Printed Circuit Boards (PCB) are Plated through via, buried via hole and blind via hole.

    Plated through Via

Plated through via connects the top and the bottom layer of the multi layer Printed Circuit Boards (PCB). In order to spot a plated through hole, you can see if the light passes through it or it is possible to see through it. Plated through holes are the simplest kind of holes and they only need drilling or laser light to be drawn. Drilling of plated through holes is relatively cheap but they may take up more space as compared with the other types of via or the micro via.

    Blind via hole (BVH)

Blind via hole connects the outer layer of the PCB with the inner layers and it is not possible to see through the Blind via Hole (BVH) which is the reason why it derives its name. Blind via Hole is mostly used where the size and space utilization of the Printed Circuit Boards (PCB) is of importance. Blind via Hole are difficult to deal in as they require special attention to the depth of the hole to be made as anything imprecision in this regards can lead to severe design and operation complications. Due to the difficulty in handling them, the blind via Holes are not frequently used in the Printed Circuit Boards (PCB) assembly.

     Buried Via Hole

The buried via Hole connects the inner layers of the Printed Circuit Boards (PCB) while it does not pass through the outer layer. The buried via holes are made use of where space utilization is important and high density applications are to be supported. The buried via holes are commonly used in HDI technology. Buried via holes are extremely difficult to work with as they require more time as compared with the blind via hole and the plated through hole technology while special care is required in working with them.

    Micro Via

Micro via are another type of via used in the Printed Circuit Boards (PCB). They are via of very small size less than few micro meters and are used in highly sophisticated application. Micro-via are commonly used in flexible Printed Circuit Boards (PCB) or rigid flex Printed Circuit Boards (PCB).

Multi layer PCBs can be slightly costly as compared with the single layer PCBs which is only fair considering the high level design capabilities they are capable of supporting. They are also more complicated as compared with single layer PCB and skilled designers are required to work with them. 

Quality tests for Printed Circuits Boards

Quality tests for Printed Circuits Boards

The Printed Circuit Boards (PCBs) are very sophisticated and complicated items which are of utmost importance in the smooth operation and sustainability of the electronic machinery and it would not be an overstatement to say that even the slightest of faults in a PCB can bring the working of fundamental machinery to a standstill. In this scenario, it is of vital to have approved standards of quality control for the manufacturing, development and operation of the Printed Circuit Boards (PCBs). Some of the standard tests performed in order to ensure the quality of the Printed Circuit Boards (PCBs) are as follows,

    1)      100% Electrical Test

    2)      100% Visual Inspection

    3)      Dimensional Inspection

    4)      Micro Section

    5)      Solder Ability Test (245+-5C) , 10 sec

    6)      Thermal Test (288+-5C)

    7)      Tape Test

    8)      Peel Test

    9)      Impedance Test

    10)  Ionic Contamination Test

     1)    100% Electrical Test

Electrical testing is of utmost importance for a PCB which involves the electrical testing of various aspects of the Printed Circuit Boards (PCBs). In electrical testing every “Node” on the PCB board is tested. Short circuit tests are performed to be if any part of the PCB is short circuited. Clam shell tests are performed to obtain the simultaneous testing of both sides of the PCB in case of double sided Printed Circuit Boards (PCBs). Continuity tests are performed to check if the resistance between the tests points is within specified limit.  Some of the other tests performed in Electrical testing of the Printed Circuit Boards (PCBs) are flip test, high pot test, impedance control test, leakage test, opens test and optimized net list tests.

     2)    100% Visual Inspection

Visual tests are performed using AOI machines to check if all the components after the Printed Circuit Boards (PCBs) assembly process are there where they are supposed to be. The AOI machines use high resolution cameras aided with software Gerber and drill files to make the comparison on the Printed Circuit Boards (PCBs).

3)    Dimensional Inspection

Dimensional inspection is necessary because the size and dimension of the Printed Circuit Boards (PCBs) is specified as per the design of the device in which the PCB has to be used in. The dimensional test compares the physical dimensions of the PCB against the software provided design of the PCB.

    4)    Micro Section Testing

The micro testing of the Printed Circuit Boards (PCBs) is performed in order to check the drill via on the PCB. Via are micro sized in PCB and have to be carved with greatest care as slight offset in via can be of serious design and operation faults. 

    5)    Solder Ability Test

It is our understanding that components are soldered on the PCB during the Printed Circuit Boards (PCBs) assembly process therefore it is necessary to check the durability of the solder through the solder ability test. The solder has to withstand high temperatures and extreme working conditions without showing any signs of deterioration. The solder tests are performed up to 245C for 3 seconds to check the response of the solder. If the able to withstand such conditions, only then it passes the solder ability test.

     6)    Thermal Ability Test

During the working of Printed Circuit Boards (PCBs), extreme conditions can arise which can lead to heating of the inner core. In such cases, the Printed Circuit Boards (PCBs) should be able to withstand the extreme heating. Thermal ability tests are performed by subjecting it to temperatures up to 288 for about 10 seconds to check its performance.

7)    Tape Test (adhesion test)

Tape tests are performed to check the adherence of the copper foil on the PCB. The tape is applied to the Printed Circuit Boards (PCBs) and peeled off in order to check if any copper foil residue adhered to the tape. The Printed Circuit Boards (PCBs) is only passed for further processing if no copper residue adheres to the tape.

     8)    Impedance Test

Impedance testing is done in order to check the impedance between different nodes and the components of the Printed Circuit Boards (PCBs). The impedance should not be offset to the specified limits.

     9)    Ionic Contamination Test

The Printed Circuit Boards (PCBs) during manufacturing and developing process can be contaminated with ionic impurities which can lead to the decrease in the impedance of the Printed Circuit Boards (PCBs) which can cause operational ambiguities. In order to avoid any unforeseen circumstances, the ionic contamination tests are performed.

Metal Core Printed Circuit Boards

Metal Core Printed Circuit Boards

Printed Circuit Board (PCB) can be classified into three categories if the criteria of classification were to be made the core material of the PCB. The Printed Circuit Board (PCB) are available in ceramic based core material, FR-series or fire retardant series of the core material and the Metal core Printed Circuit Board (PCB) or most commonly known as MCPCB. The most commonly used Printed Circuit Board (PCB) is standard FR4 boards which have various fire retardant material as their core. FR4 or FR-4 is a NEMA used for the glass reinforced epoxy laminate material which is commonly used in standard Printed Circuit Board (PCB) used in the PCB industry.

Ceramic Printed Circuit Board (PCB) or CPCBs

The second type of PCB is the ceramic Printed Circuit Board (PCB) or the ceramic core PCBs. The ceramic PCBs are used for high temperature, pressure, frequency operations. They provide greater insulation and are highly reliable as compared with other type of the PCBs. The ceramic Printed Circuit Board (PCB) are mostly used for minor volume production of the electronic devices as for high volume production it is more economical to use the standard FR-4 type PCBs. The composition of ceramic Printed Circuit Board (PCB) is usually alumina aluminum nitride and beryllium oxide. The conducting material used in ceramic Printed Circuit Board (PCB) is either copper or silver palladium. 

Metal Core Printed Circuit Board (PCB) or MCPCBs

The third type of the Printed Circuit Board (PCB) is the Metal Core Printed Circuit Board (PCB) or MCPCB. The metal core PCBs have some metal as their core which mostly range from Aluminum, Copper and steel alloy. All three metal cores have either own advantages and are used for their specialized purposes. The aluminum core has greater heat transferring and dissipating capabilities and it is also relatively cheaper as compared with copper and silver. Copper has better overall properties as compared with aluminum but it is more expensive. Steel is more rigid and provides greater stability to the core as compared with aluminum and copper but its conducting properties are inferior as compared with copper and aluminum. Making the comparison, it can be analyzed that aluminum is more suitable and economical to be used as compared with silver and copper, so most of the Metal Core Printed circuit boards make use of the aluminum core.

The metal core PCBs are also referred to as the metal backed PCBs, metal base or metal clad PCBs.

Advantages of Metal core Printed Circuit Board (PCB)

The main advantage of Metal core Printed Circuit Board (PCB) over ceramic and FR-4 type of Printed Circuit Board (PCB) is their ability to dissipate heat more efficiently away from the components on the circuit board, hence in turn saving the components from overheating and damage. In most LED applications, metal core Printed Circuit Board (PCB) is used because of its ability to dissipate heat generated in the LED circuitry. In this case if the heat were not properly dissipated, it would cause severe damage and output inefficiency for the system. In this case, the main purpose of the metal core is to dissipate the heat away from the board so as to protect the system.

The second advantage of the metal core Printed Circuit Board (PCB) over the other kind is their better coefficient of thermal expansion. Thermal expansion and contraction is the inherent nature of the material and most material suffer from it. The aluminum core Printed Circuit Board (PCB) on the other hand has greater ability to without such changes under severe circumstances.

The third bigger advantage of the metal core Printed Circuit Board (PCB) is their dimensional stability. Even at high temperatures and severe conditions, the size change of the metal core PCB is minimal as compared with the other type of the PCBs.

Applications of Metal Core Printed Circuit Board (PCB)

The metal core Printed Circuit Board (PCB) are used in major applications such as LED lights, cars, amplifier and audio systems, printers, switching electronic devices.

The metal core Printed Circuit Board (PCB) is also further divided into five categories depending on the location of the metallic core and the layers of the Printed Circuit Board (PCB). The five categories are named as single layer, chip on board, double layer, double sided and multi layer metallic core Printed Circuit Board (PCB). 

Design and Operation Optimization of a Solar Collector System

This thesis introduces the concept of Concentrated Solar Power utilization for the production of Electrical Energy. As the world economy grows and the technology growth booms, the dependability on more robust, ingenious and cost effective ways of generating electricity becomes essential. Solar Energy is currently striving to become a major player in fulfilling the energy needs of the modern world with environmental aspects guaranteeing a safer future for our generations. There are two main ways through which solar energy from sun is employed to produce electricity i.e. Photo-voltaic cells and Concentrated Solar Power. Little work has been carried out in the field of Concentrated Solar Power (CSP) but there is still room for significant improvement. Concentrated Solar Power has a lot of potential in our country considering the abundance of solar radiation throughout the year particularly in the southern region. The proposed design will be scalable to industrial level. This research project is one of its kind considering not much work has been carried out previously in this regard in Pakistan. The following report contains detailed design strategies for making a Heliostat. We carried out work on Heliostat design in our institute and significantly improved the previous designs of any such tractable heliostat thus enhancing the efficiency of the system.

Heliostat Design

1        Heliostat Design

The Design of the heliostat is a very important task. A good design can enhance the efficiency of the system significantly. It is also necessary in order to effectively withstand various static & dynamic loads that the heliostat will face.

Following are some of the aspects of Heliostat design and other parameters associated with or related to the design of heliostat.

•      Field Selection for Heliostats/Polar Field

•      Selection of Frame Arrangement/Horizontally rectangular main frame

•      Shape and design of the Mirror/Slightly tilted mirrors

•      Wireless And autonomous control

•      Tracking of primary axis

•      Wind Protection

•      Hail protection /Rain protection

Design Features of A Heliostat

1        Heliostat Field Selection

From case studies of different mega projects involving SCSs (solar tower) we observed that the heliostats were arranged in one of the following configurations

1.      Surround Field

2.      Polar Field

1.1      Surround Field

In this configuration the solar tower is completely surrounded by heliostats on all sides. This configuration has an added advantage that the total insolation remains relatively more uniform throughout the day. When the sun moves from one side of the tower to the other side then the heliostats on the opposite side start to reflect the sun rays more effectively hence maintaining a uniform profile.

It has been experimentally observed that the efficiency of the heliostats nearest to the tower is maximum & it decreases as the distance increases. In surround field configuration more heliostats can be placed inside this high efficiency region.

This type of field is used in Ivanpah (392 MW).

1.2      Polar Field

In this type of field all the heliostats are placed on one side of the tower.

This characteristic can be utilized in medium to large sized solar tower systems(STS). If the same number of heliostats is arranged in polar field instead of surround field then due to their increased efficiency more energy will be generated with the same initial cost

Due to above mentioned reasons we are going to use “Polar Field”.

1.2.1    Mechanical Design

The mainframe of the heliostat is designed to be rectangular with its length greater than its height. This arrangement will give us following benefits

1. Due to smaller height, the heliostat will cast a smaller shadow on the mirrors behind it as opposed to a vertically erect rectangular heliostat.
2. The distance between consecutive rings can be decreased due to smaller shadow of front row heliostat which will result in increased system efficiency.
3.   The center of gravity will be lower to the ground which will increase stability of the mechanical system while facing wind.
4.      Smaller height will result in smaller moment arm so the assembly can bear high forces without being overturned.
5. The frame will be rotated along the horizontal axis while the mirror will rotate along the vertical axis.

Mirror Manufacturing for Solar Concentrator

Selection of Reflective Mirror

In almost all of the STSs plane mirrors are used. The reason is that the cost of manufacturing curved mirrors is enormous which results in an increased amount of capital required to install the plant.

Despite the higher cost, curved mirrors were selected for this project due to following reasons

1.      Through literature survey we came to know that in terms of “Levelized Cost of Electricity” (LCOE) reduction, a design improvement that results in 1% performance improvement is equivalent to a design improvement that reduces solar field cost by about 2.3% i.e. the leverage of performance vs. cost on LCOE is better by a factor of about 2.3x

The exact improvement in efficiency due to this decision is unknown at this stage & it is possible that this improvement might not be able to balance out the increase in capital cost. Any and all results will be reported at the end of the project including the impact of this decision.

2.      There is another factor that inspired us to use curved mirrors. As the distance from the solar tower increases, the effect of scattering from dust particles becomes more and more pronounced. Thus the advantage of using a converging beam of light become more evident as this kind of reflected beam will be able to transfer a considerably more amount energy to the solar tower even after scattering.

3.      As the beam is converging therefore the area of the “wave front” formed at the receiver will be of small size. This enables us to design a receiver of smaller size which will reduce cost.

4.     Higher concentration of light due to converging beam will result in increased temperature which will result in increased efficiency of the system.

5.     Very high precision tracking is usually not feasible. The decreased wave front area of the reflected beam gives us an increased margin of tolerable error in our tracking.

Heliostat Tracking Techniques and Control Mechanism

1.1      Solar Tracker

The solar tracker is a device and a mechanism for orienting the solar concentrator in such a way that it reflects maximum sunlight on the receiver directly from the sun and the deviation angle is minimum throughout the tracking time. A highly efficient Solar tracking mechanism drastically enhances the efficiency of the solar concentrator since it can collect more sun light as compared to a passive mechanism.

Solar trackers are implemented using Astronomical equations, light dependent resistors, sun pointing sensors etc. coupled with other devices such as Stepper motor, Dc Motors, Servo motors, gas filled piston etc.  

1.1.1    Dual Axis Trackers

The dual axis tracker has both horizontal and vertical axis and hence can track the position of the sun and its apparent motion anywhere in the sky throughout the day. Dual axis tracker track the sun through both East to West and North to South, which gives it an added benefit of capturing more sunlight directly from the sun, which increases the added power output and the theoretical efficiency by approximately 40%.

It can be implemented with the help of sun pointing sensors or light dependent resistors, astronomical data or predicted trajectory of sun throughout the day.

1.1.1.1  Disadvantage

Dual axis tracking comes with greater complexity for the system. More motors are to be used to dual track which increases the difficulty level. It is also argued that it can be less reliable considering greater number of devices used in this mechanism which increases the maintenance and down time.

Design of Uninterruptible Power Supply/UPS

Problem Statement:

Design a 1kVA UPS powered by a single phase 220V/50Hz AC. You may consider one of the following design options:

a.         A rectifier as battery charger+ DC-DC Boost converter + Sinusoidal PWM Inverter

b.         A rectifier as battery charger + Full bridge DC-DC converter using pulse power transformer+ Sinusoidal PWM Inverter

c.         A rectifier as battery charger + Sinusoidal PWM Inverter + Step up transformer

Charging current of battery must not exceed 15A and you must take care of input power factor.

What is an Uninterruptible Power Supply?

An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup is an electrical apparatus that provides power to the system which it is connected to i.e household assembly of electricity run devices, offices, computer run etc when the power from the main grid gets disrupted or cut off and it can also provide emergency power to a load when the input power source, typically mains power, fails.

UPS is a device that provides battery backup when the electrical power fails or drops to an unacceptable voltage level. Small UPS systems provide power for a few minutes; enough to power down the computer in an orderly manner, while larger systems have enough battery for several hours. In mission critical data centers, UPS systems are used for just a few minutes until electrical generators take over.

Traffic Control System based on PLC and SCADA Techniques

This smart traffic control system uses Programmable Logic Controllers (PLC’s) and SCADA HMI for monitoring and controlling of traffic signals. This system is quite useful in high-traffic-density areas, toll gates and other high-end-parking areas.

Wikipedia quotes " A programmable logic controller (PLCPLC SCADA, or programmable controller is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.

They were first developed in the automobile industry to provide flexible, ruggedized and easily programmable controllers to replace hard-wired relays and timers. Since then they have been widely adopted as high-reliability automation controllers suitable for harsh environments. A PLC is an example of a "hard" real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result."

This is a centralized control of traffic system where it collects the several places traffic conditions remotely through communication medium and this information is monitored using SCDA HMI. Therefore, synchronizing the traffic at different junction roads is possible with this system. And, also depending on the traffic density at different junctions, it controls the traffic light through remote operation.

Radio Frequency Identification for Library

Background

CE 1.1) RFID (Radio frequencyIdentification) technology is one of the most evolved technique in our contemporary time with huge potential ranging from applications as simple as implementation a gate security system to as complex and exigent as automatic money transfer system. The project for designing and implementing a RFID system for libraries employs the broader use of radio frequency technique along with PLCs in algorithm for security control, access control and tracking system of the library.

CE 1.2) RFID technique is an upgrade from bar-code technique which has been previously employed for realizing the same task. The bar-code consist of images of lines affixed with varying spacing against which there is information stored for the particular product to which the specific barcode has been assigned. Unlike RFID, bar-code technique uses light transmission for communication between the ‘reader’ and the bar-code. The reader in this case gather the information from the barcode and converts it into digital data for practical use.