Printed Circuit Boards - Essay Example

?Printed Circuit Boards Introduction Printed Circuit Boards (PCB) are flat-boards upon which various electronic components are placed for mechanical support and connected through desired electrical connections to develop conductive circuits. PCBs are found in virtually all electronic devices and help in implementing any functionality based on the arrangement and connections among the different electronic components. Components can be connected on the PCB through conductive paths or etched copper wiring on a non-conductive substrate such as plastic. A PCB that has been assembled with such electronic components through appropriate connections is known as a Printed Circuit Assembly (PCA) (Khandpur, 2007). PCBs are relatively cheap and are known for their durability and reliability. While finding the material for the substrate and the conductive paths, much effort needs to be spent on defining a proper layout as well as the nature of the connections among various circuit elements. For example, a proper layout is necessary to accommodate all the required components and ensure proper connections among them to produce the desired output. Jawitz (2008) says that care needs to be taken when determining the type of connections (like point-to-point or wire wrap) besides ensuring that no unwanted contact is established due to crossing wires or faulty connections. Post this layout phase, production of PCAs in high volumes is relatively easier and can be accomplished by an automated assembly line. The design and construction of PCBs is governed by a number of standards that are set and revised regularly by the Association Connecting Electronics Industries (IPC). PCBs, with the etched copper pathways, are insulated from any contact with dust or moisture (thereby avoiding undesired electrical connections and short circuits) using green-colored solder. Some PCBs are also coated with blue and red colored solder. In fact, Bosshart, 2003 says that the choice of the solder, technically a dielectric known for very high resistance and lack of electrical conduction, can vary depending on the purpose of the circuit being developed. Some of the popular and widely used dielectrics include FR-1, CEM and Teflon. The underlying substrate that makes up the flat-board can be made from a combination of cotton paper, polyester, epoxy and glass. Dimensional stability combined with lack of expansion on exposure to heat qualifies these substances as highly suitable for PCB production. The average thickness of a PCB can range anywhere from 1 to 2mm (Montrose, 2009). Components can either be assembled on 1 side of the board or configured on both sides depending on requirements and space considerations. Types of PCBs PCBs come in many types based on a number of factors ranging from the number of sides utilized to the kind etching technology adopted for providing the interconnects. PCBs can also consist of multiple layers of the substrate and the interconnecting copper pathways and can thus be highly complex in construction. The following points describe some of the types into which most PCBs can be categorized. Single-sided PCBs These are the most basic type of PCBs and can be constructed even from a regular plastic board. A single sided PCB consists of electronic components soldered on one side while the pathways and interconnections are provided on the other side of the board. The term single-side arises from this segregation among components and pathways and their restricted location to a single side of the PCB (Robertson, 2004). Single-sided PCBs have a number of deficiencies in terms of routing and circuit connections whereby no two wires can cross each other. Thus, single-sided PCBs may consumer more wire or copper for the necessary interconnects and are thus relatively resource intensive than other PDB types. As such, they are preferred for the construction of primitive circuits and cannot be used for developing advanced circuitry. Double-sided PCBs As the name suggests, these PCBs have the pathways etched on both sides of the board. Pathways on individual layers are also connected to circuits from the other side of the board through bridges (also known as vias) (Williams, 2004). The simplest bridge is a hole in the PCB that is filled with a conducting metal to create a connection between pathways on both sides As the area available for the pathways is double that available for single-sided PCBs and since there is provision for connection between both sides through the vias, double-sided PCBs are more suited for the construction of advanced circuits. Flexible PTH Two individual PCB layers are combined using a dielectric intermediate that provides a broader scope for routing and interconnects. Once again, vias can be drilled into the boards to provide inter-layer connections (Varteresian, 2008). PCBs generated using this method are etched and bond encapsulated prior to further treatment and component assembly. Flex to Rigid It is possible to reinforce flexible mini-circuits into the PCB wherever necessary using aluminum or polyimide. These chemicals facilitate board fixing, component placement and heat sinking. This method provides both static and dynamic behavior to the PCB thereby improving its functionality (Brooks, 2003). Single-sided Flexible PCBs While conceptually similar to Single-sided PCBs, techniques like CNC machining facilitate the creation of anti-tear holes. These holes allow connections through the dielectric material thus allowing a better and wider use of the space available on the PCB (Brooks, 2003). Flying Tail PCBs PCBs of this type can have either one or both sides etched and consist of thicker pathways. A thicker interconnect qualifies such PCBs for use in high-power applications where the voltage and energy flows are much higher (Brooks, 2003). A Flying Tail PCB provides a broad array of fixing alternatives which are extended further by the use of thicker, heat-resistant pathways. Advantages of PCBs Using PCBs for developing electronic circuits has several advantages from an economic and technical perspective. While most of the effort in designing a PCB-based circuit is devoted towards defining a proper layout, such an exercise is extremely important especially where they will be produced through a mass-production mechanism (Khandpur, 2007). A proper layout helps preserve the desired electronic characteristics for the circuit besides preventing the occurrence of any parasite capacitance. Besides, mass production can be achieved easily using automation and appropriate machinery whereby the whole process of assembling the required components on to the layout and connecting them through soldering can be programmed and operated without much human involvement. According to Harper (2001), most of the PCAs used in modern electronic gadgets like televisions, radios, refrigerators etc. are produced through mass production. Besides, the use of equipment for the manufacturing process and the automated task of placing and soldering components simplify the task of troubleshooting and maintenance. Thus, the incidence of incorrect wiring on short circuiting can be reduced and the entire process can be monitored at all times. Jawitz (2008) says that over the years, the size of electronic components has reduced drastically thereby facilitating the construction of highly complex circuitry on PCBs of smaller sizes. Many electronic components like transistors and capacitors are capable of producing high electrical noise or interference that is capable of affecting the operation of other electronic devices in the vicinity. A good PCB layout is one that places all such components in such a manner that the net interference is minimized and there are no residual currents flowing out of the layout (Bosshart, 2003). PCBs also provide the distinct advantage of labeling every component for their type and any other attribute like polarity or capacity. This helps in an easier analysis of the system for any desired parameters like voltage, resistance or net inductance across a segment. Diagnosis of these paths is done by using signal paths, which are provided by PCBs in an organized and efficient manner (Montrose, 2009). Connecting very small electronic components without a PCB is virtually impossible without avoiding unwanted electrical contacts. A PCB allows these components to be arranged in a compact fashion. In fact, components that perform a specific sub-routine like modulation or noise reduction can be grouped on the PCB for easier analysis and diagnostics (Robertson, 2004). Besides, the form factor of the circuits is kept at a minimal level thus helping build smaller efficient devices. Moreover, PCBs consist of components that are placed in a firm designated position using solder flux. Thus, Williams (2004) argues that PCBs can be placed on moving objects including cars and aircrafts to provide the necessary services. Effects including movement and shaking have a negligible impact on the operation of the PCBs in comparison to the effects from electrical or magnetic interference. The smaller size does not alter the shape of the components in any way when subjected to sudden mechanical forces (unless in direct contact with a rigid object) thereby avoiding any short circuits. Disadvantages of PCBs Although using PCBs has several advantages, there are many disadvantages to this method of developing electronic circuits and components. The design of any particular circuit is a laborious exercise and generates a final layout that satisfies all required parameters. Hence, such a design is final and ready to be delivered for production. Varteresian (2008) mentions that any change in design due to sophistication of available technology or change in required specifications requires a complete redesign of the circuit layout that consumes a considerable amount of time, effort and money. Detecting the faults in a damaged or dysfunctional PCB is not a job for the layman and requires the services of an expert. Thus, consumers may have to spend more to have their PCBs rectified depending on the severity of the defect and the complexity of the concerned circuit. While the design and development of a PCB can be compared to software development (due to the huge initial investment and effort outlays involved), the task of upgrading them is much simpler in the case of the latter. Any upgrades to software programs can be easily identified and implemented by changing the relevant sections of the code. However, upgrading a PCB is generally possible once it is printed. Unlike software, a PCB cannot be altered without compromising some of the existing functionality (Brooks, 2003). From an environmental perspective, the process of developing PCBs from plastic substrates and the use of etching to develop the metal conductive pathways relies on a number of chemicals that are harmful to the environment if not treated properly (Harper, 2001). The tasks of etching and soldering are also very delicate procedures that must be carried out without any errors. Overheating the flux or the substrate can spread the material beyond a desired area and create potential short circuits that may be very difficult to detect. Personnel involved in the design and manufacture of PCBs must also endure the rigors of a high learning curve and must be trained in electronics, software development (in hardware languages like VHDL), layout and design engineering (Jawitz, 2008). Establishing a PCB manufacturing unit requires a huge up-front investment and considerable marketing efforts since the competition in this market is predominantly high. Competition also reduces the bargaining power of PCB manufacturers and they must maintain a steady balance between pricing and profitability by the introduction of innovative techniques into PCB manufacturing (Williams, 2004). Conclusion The preceding sections have discussed some of the important features of PCBs and their utility in the development of electronic circuits. PCBs consist of electronic components assembled on a flat board which are then connected through appropriate wiring or using pathways etched with copper. One of the primary advantages of using PCBs is that the entire process of manufacturing them can be automated and carried out on an assembly line (Bosshart, 2003). This facilitates the use of components of similar quality and maintains uniformity in the PCBs produced. While manufacturing PCBs is relatively cheap, the major component of their conception is the design phase. Designing an appropriate layout for arranging the various circuit elements, minimizing the resources used (wires, connection distances, board size etc) and ensuring complete functionality requires elaborate time and effort. Thus, a PCB designer needs to be trained in many skills including electronics, programming and testing methodologies in order to produce efficient PCBs. Gaining programming skills for designing PCBs is necessary in the modern day as much of this phase is now simulated using computer programs before the actual components are laid out on a real PCB (Khandpur, 2007). In any case, the task of manufacturing PCBs has revolutionized our world. PCBs are used in virtually every gadget and machine associated with electronics and will continue to be used and improved in the future. Further, the process of assembly-line style line of manufacturing has reduced costs and made electronic goods affordable for the common man (Varteresian, 2008). References 1. Bosshart, W., 2003. Printed circuit boards: design and technology. London: Routledge. 2. Brooks, D., 2003. Signal integrity issues and printed circuit board design. Boston: Prentice Hall. 3. Harper, C., 2001. High performance printed circuit boards. New York: McGraw Hill. 4. Jawitz, M., 2008. Printed circuit board materials handbook. New York: McGraw Hill. 5. Khandpur, S., 2007. Printed Circuit Boards. New York: McGraw Hill. 6. Montrose, M., 2009. EMC and the printed circuit board: design, theory, and layout made simple. Chicago: John Wiley. 7. Robertson, C., 2004. Printed circuit board designer's reference: basics. Boston: Prentice Hall. 8. Varteresian, J., 2008. Fabricating printed circuit boards. London: Newnes. 9. Williams, A., 2004. Build your own printed circuit board. New York: McGraw Hill. Read More