PCB FABRICATION

The fabrication of a PCB includes four steps.

87

 Preparing the PCB pattern.

 Transferring the pattern onto the PCB.

 Developing the PCB.

 Finishing (i.e.) drilling, cutting, smoothing, turning etc.

Pattern designing is the primary step in fabricating a PCB. In this step, all interconnection between the components in the given circuit are converted into PCB tracks.

Several factors such as positioning the diameter of holes, the area that each component would occupy, the type of end terminal should be considered.

Transferring the PCB Pattern

The copper side of the PCB should be thoroughly cleaned with the help of alcoholic spirit or petrol. It must be completely free from dust and other contaminants. The mirror image of the pattern must be carbon copied and to the laminate the complete pattern may now be made each resistant with the help of paint and thin brush.

Developing

In this developing all excessive copper is removed from the board and only the printed pattern is left behind. About 100ml of tap water should be heated to 75 ° C and 30.5 grams of FeCl₃ added to it, the mixture should be thoroughly stirred and a few drops of HCl may be added to speed up the process. The board with its copper side facing upward should be placed in a flat bottomed plastic tray and the aqueous solution of FeCl₂ poured in the etching process would take 40 to 60 min to complete. After etching the board it should be washed under running water and then held against light .the printed pattern should be cleanly visible. The paint should be removed with the help of thinner.

Finishing Touches: After the etching is completed, hole of suitable diameter should be drilled, then the PCB may be tin plated using an ordinary 35 Watts soldering rod along with the solder core, the copper side may be given a coat of varnish to prevent oxidation.

88 Drilling: Drills for PCB use usually come with either a set of collects of various sizes or a 3-Jaw chuck. For accuracy however 3-jaw chunks aren‘t brilliant and small drill below 1 mm from grooves in the jaws preventing good grips.

Soldering: Begin the construction by soldering the resistors followed by the capacitors and the LEDs diodes and IC sockets. Don‘t try soldering an IC directly unless you trust your skill in soldering. All components should be soldered as shown in the figure. Now connect the switch and then solder/screw if on the PCB using multiple washers or spaces. Soldering it directly will only reduce its height above other components and hamper in its easy fixation in the cabinet.

Now connect the battery lead.

Assembling: The circuit can be enclosed in any kind of cabinet. Before fitting the PCB suitable holes must be drilled in the cabinet for the switch, LED and buzzer. Note that a rotary switch can be used instead of a slide type. Switch on the circuit to be desired range. It will automatically start its timing cycles. To be sure that it is working properly watch the LED flash. The components are selected to trigger the alarm a few minutes before the set limit.

The fabrication of one demonstration unit is carried out in the following sequence:

1.Finalizing the total circuit diagram, listing out the components and their sources of procurement.

2. Procuring the components, testing the components and screening the components.

3. Making layout, preparing the inter connection diagram as per the circuit diagram, preparing the drilling details, cutting the laminate to the required size.

4. Drilling the holes on the board as per the component layout, painting the tracks on the board as per inter connection diagram.

5. Etching the board to remove the un-wanted copper other than track portion. Then cleaning the board with water, and solder coating the copper tracks to protect the tracks from rusting or oxidation due to moisture.

6. Assembling the components as per the component layout and circuit diagram and soldering components.

7. Integrating the total unit inter wiring the unit and final testing the unit.

8. Keeping the unit ready for demonstration.

89 PCB FABRICATION DETAILS:

The Basic raw material in the manufacture of PCB is copper cladded laminate. The laminate consists of two or more layers insulating reinforced materials bonded together under heat and pressure by thermo setting resins used are phenolic or epoxy. The reinforced materials used are electrical grade paper or woven glass cloth. The laminates are manufactured by impregnating thin sheets of reinforced materials (woven glass cloth or electrical grade paper) with the required resin (Phenolic or epoxy). The laminates are divided into various grades by National Electrical Manufacturers association (NEMA).

The nominal overall thickness of laminate normally used in PCB industry is 1.6mm with copper cladding on one or two sides. The copper foil thickness is 35 Microns (0.035mm) OR 70 Microns (0.070 mm).

The next stage in PCB fabrication is artwork preparation. The artwork (Mater drawing) is essentially a manufacturing tool used in the fabrication of PCB‘s. It defines the pattern to be generated on the board. Since the artwork is the first of many process steps in the Fabrication of PCBs. It must be very accurately drawn. The accuracy of the finished board depends on the accuracy of artwork.

Normally, in industrial applications the artwork is drawn on an enlarged scale and photographically reduced to required size. It is not only easy to draw the enlarged dimensions but also the errors in the artwork correspondingly get reduced during photo reduction. For ordinary application of simple single sided boards artwork is made on ivory art paper using drafting aids. After taping on a art paper and phototraphy (Making the –ve) the image of the photo given is transformed on silk screen for screen printing. After drying the paint, the etching process is carried out. This is done after drilling of the holes on the laminate as per the components layout. The etching is the process of chemically removing un-wanted copper from the board.

The next stage after PCB fabrication is solder masking the board to prevent the tracks from corrosion and rust formation. Then the components will be assembled on the board as per the component layout.

The next stage after assembling is the soldering the components. The soldering may be defined as process where in joining between metal parts is produced by heating to suitable temperatures using non-ferrous filler metals has melting temperatures below the melting temperatures of the metals to be joined. This non-ferrous intermediate metal is called solder. The solders are the alloys of lead and tin.

90

5 . MEMS (MICRO ELECTRO MECHANICAL SYSTEMS)

The MEMS (Micro Electro Mechanical System) which consists of a 3-axis accelerometer which gives output based on three axis movement. This setup is fixed on the road vehicles and during normal movement (X-axis), the accelerometer output is nearly constant. When any accident occurs the MEMS sensor gives unbalanced or high axis output value (depends on vehicle position), and then the microcontroller reads the value and expects for the normal movement output value again on same axis (X-axis). If the output is not returning back to normal value within the specific time then the microcontroller commands the GSM modem and send a SMS about the accident to any predefined numbers such as ambulance or police or any other numbers to intimate the accident.

Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro fabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes).

MEMS promises to revolutionize nearly every product category by bringing together silicon-based microelectronics with micromachining technology, making possible the realization of complete systems-on-a-chip. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of micro sensors and micro actuators and expanding the space of possible designs and applications.

Microelectronic integrated circuits can be thought of as the "brains" of a system and MEMS augments this decision-making capability with "eyes" and "arms", to allow micro systems to sense and control the environment. Sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then process the information derived from the

sensors and through some decision making capability direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the environment for some desired outcome or purpose. Because MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits, unprecedented levels of

91 functionality, reliability, and sophistication can be placed on a small silicon chip at a

relatively low cost.

Accelerometers

MEMS accelerometers are quickly replacing conventional accelerometers for crash air-bag deployment systems in automobiles. The conventional approach uses several bulky accelerometers made of discrete components mounted in the front of the car with separate electronics near the air-bag; this approach costs over $50 per automobile. MEMS and Nanotechnology has made it possible to integrate the accelerometer and electronics onto a single silicon chip at a cost between $5 to $10. These MEMS accelerometers are much smaller, more functional, lighter, more reliable, and are produced for a fraction of the cost of the conventional macro scale accelerometer elements.

Current Challenges

MEMS are currently used in low- or medium-volume applications.

Limited Options

Most companies who wish to explore the potential of MEMS and Nanotechnology have very limited options for prototyping or manufacturing devices, and have no capability or expertise in micro fabrication technology. Few companies will build their own fabrication facilities because of the high cost. A mechanism giving smaller organizations responsive and affordable access to MEMS and Nano fabrication is essential.

Packaging

The packaging of MEMS devices and systems needs to improve considerably from its current primitive state. MEMS packaging is more challenging than IC packaging due to the diversity of MEMS devices and the requirement that many of these devices be in contact with their environment. Currently almost all MEMS and must develop a new and specialized package for each new device. Most companies find that packaging is the single most

expensive and time consuming task in their overall product development program. As for the components themselves, numerical modeling and simulation tools for MEMS packaging are virtually non-existent. Approaches which allow designers to select from a catalog of existing standardized packages for a new MEMS device without compromising performance would be beneficial.

92

µVision3 adds many new features to the Editor like Text Templates, Quick Function Navigation, and Syntax Coloring with brace high lighting Configuration Wizard for dialog based startup and debugger setup. µVision3 is fully compatible to µVision2 and can be used in parallel with µVision2.

What is µVision3?

µVision3 is an IDE (Integrated Development Environment) that helps you write, compile, and debug embedded programs. It encapsulates the following components:

 A project manager.

 HELLO is a simple program that prints the string "Hello World" using the Serial Interface.

 MEASURE is a data acquisition system for analog and digital systems.

 TRAFFIC is a traffic light controller with the RTX Tiny operating system.

 SIEVE is the SIEVE Benchmark.

 DHRY is the Dhrystone Benchmark.