PCB is a copper laminated and non - conductive printed circuit board in which all electrical and electronic components are connected together in one common board with physical support for all components with base of board.
LIFE WITHOUT PCB :
at that time when pcb is not developed all the components are connected with a wire.
> which increases complexity .
> decreases reliability of the circuit.
like this we can't able to make large circuits .
It can found in many electronics devices like TV, MOBILE, CAMERA, COMPUTER PARTS ETC.
used in many fields like in medical devices, industrial machinery , automotive industries, lighting etc...
TYPES OF PCB:-
1). Single layer PCB.
2). Double layer PCB.
3). Multi-layer PCB.
4). Flexible PCB.
5). Aluminium backed PCB.
6). Flex - rigid PCB.
1). Single layer PCB:
> also known as single sided PCB.
> Easy to design and manufacture.
> one side of this pcb coated with a layer of any conducting material.
mostly copper is used as conducting material because it has very good conducting characteristics.
> A layer of solder mask is used to protect PCB against oxidation followed by silk screen to mark out all the components on the pcb.
> One side of the PCB is used to connect different types of electrical or electronics components.
> Used in low cost and bulk manufacturing.
2). Double layer PCB:
> In this type of PCB ,a thin layer of conducting material like copper is applied to both top and bottom sides of the board.
> consists via, which has two pads in corresponding position on different layers
> electrically connected by a hole through the board
> more flexible, lower cost, reduced size which makes circuit impact.
3). Multi-layer PCB:
> It has more than two layers.
> This type of PCB has at least 3 conductive layers of copper.
> Board glue is sandwiched b/w the layer of insulation which ensures that the excess heat will not damage any component of circuit.
> designing is very complex and used in very complicated and large electrical task in very low space and compact circuit.
> used in large applications like GPS technology, satellite system, medial equipment, file server and data storage.
LIFE WITHOUT PCB :
at that time when pcb is not developed all the components are connected with a wire.
> which increases complexity .
> decreases reliability of the circuit.
like this we can't able to make large circuits .
It can found in many electronics devices like TV, MOBILE, CAMERA, COMPUTER PARTS ETC.
used in many fields like in medical devices, industrial machinery , automotive industries, lighting etc...
TYPES OF PCB:-
1). Single layer PCB.
2). Double layer PCB.
3). Multi-layer PCB.
4). Flexible PCB.
5). Aluminium backed PCB.
6). Flex - rigid PCB.
1). Single layer PCB:
> also known as single sided PCB.
> Easy to design and manufacture.
> one side of this pcb coated with a layer of any conducting material.
mostly copper is used as conducting material because it has very good conducting characteristics.
> A layer of solder mask is used to protect PCB against oxidation followed by silk screen to mark out all the components on the pcb.
> One side of the PCB is used to connect different types of electrical or electronics components.
> Used in low cost and bulk manufacturing.
2). Double layer PCB:
> In this type of PCB ,a thin layer of conducting material like copper is applied to both top and bottom sides of the board.
> consists via, which has two pads in corresponding position on different layers
> electrically connected by a hole through the board
> more flexible, lower cost, reduced size which makes circuit impact.
3). Multi-layer PCB:
> It has more than two layers.
> This type of PCB has at least 3 conductive layers of copper.
> Board glue is sandwiched b/w the layer of insulation which ensures that the excess heat will not damage any component of circuit.
> designing is very complex and used in very complicated and large electrical task in very low space and compact circuit.
> used in large applications like GPS technology, satellite system, medial equipment, file server and data storage.
4).Flexible PCB: (Flex circuit)
> This type of pcb used for flexible plastic material like polymide, PEEK (Poly-ether ehter ketone) or transparent conductive polyester film.
> Circuit board is place in folded or twisted.
> complex type of PCB
> It also contains different range of layers like single sided flex circuit, double sided flex circuit.
> Flex circuit is used in organic LED, LCD fabrication, flex solar cell, automotive industries, cellular telephones, camera etc,.
5). Rigid PCB:
> Made out of solid material which don't allow PCB from twisting.
> same as flex PCB, rigid PCB also have different layer configuration.
> PCB can't be bent according to shape of base that's why this PCB is known as RIGID PCB.
> Lifespan of this type of PCB is very high.
> Multi- layer rigid PCB can be more compact by containing 9-10 layers.
6). Flex-rigid PCB:
> combination of flexible circuit and rigid circuit.
> Flex-rigid boards consists of multiple layers of flexible PCB attached to a number of rigid PCB layer.
Types of PCB's According to Mounting System
A modern PCB design has two main methods for mounting components onto PCB:
1). Through-hole Mounting.
2). Surface Mounting.
1). Through-hole PCB:
> Through hole mounting is the process by which components leads are placed into drilled holes on a bare PCB.
> In these holes, leads of components are mounted and soldered to pads situated on opposite side of PCB.
> Best used for high - reliability products that require stronger connections between layers.
> In single layer PCB , this mounting technology is east to implement, but in case of double layer and multi layer making hole is more difficult.
> In modern assembly facility , through - hole is considered as secondary operation.
> Through - hole component leads run through the board, allowing the components to withstand more environmental stress. That's why this technology most commonly used in military and aerospace products that may experience extreme accelerations, collisions, or high temperatures.
> This technology is also useful in test and prototyping applications that sometimes require manual adjustments and replacements.
> not all components are available as SMD packages and some through through hole components are less expensive
There are 2 types of components in through-hole:
- AXIAL :
Axial leads run through a component in a straight line (axially), with each end of the lead wire exiting the component on either end. Both ends are placed through two separate holes in the board, allowing the component to fit closer, flatter fit.
- RADIAL:
Radial lead components protrude from the board, as its leads are located on one side of the
component
both through hole component types are "twin" lead components, and both have their distinct advantages. while axial lead components are used for their snugness to the board, radial leads occupy less surface area, making them better for high density boards. Generally axial lead configuration may come in the form of carbon resistors, electrolytic capacitors, fuses and LED's.
Radial lead components are available as ceramic disk capacitors, Schottky diode.
2). Surface mounted PCB:
Process by which components are mounted directly onto the surface of the PCB.
Developed in 1960s.
Now a Days all electronic hardware is manufactured using SMT.
it has become essential to PCB design and manufacturing, having improved the quality and performance of PCBs overall, and has reduced the costs of processing and handling greatly.
Difference between SMT and through - hole mounting are:
a) SMT does not require holes to be drilled through a PCB,
b) SMT components are much smaller than through hole components,
c) SMT components can be mounted in both sides of the board.
the ability to fit a high number if small components on a PCB has allowed for much denser, higher performing, and smaller PCBs.
through hole component leads, which run through the board connect a board layers, have been replaced by vias small components which allow a condcutive connection between the different layers of PCB, adb essentially acta s a through hole leads. some surface mount components like BGAs are higher performing components with shorter leads and more interconnection pins that allow for higher speeds.
NOMENCLATURE:
too many terms that describe different aspects of SMT:
SMA (surface mount assembly) - module assembled using SMT.
SMC (surface mount components) - components for SMT.
SMD (surface mount devices) - active, passive and electromechanical components.
SME (surface mount equipment) - machines used for SMT.
SMP (surface mount packages) - SMD case forms.
SMT (surface mount technology) - the act and method of assembling and mounting electronic technology.
> The taxonomy of surface mount devices(SMD) is so expansive and ever changing that covering it in full would be impossible.
types are
-- MELF(Metal Electrode Face Bonded): Consisting of two terminals bonded to a cylindrical body, these SMD components are less expensive than flat chips but require special handling during assembly.
--SOT( small outline transistor)Transistors and diodes: these are usually like rectangular and easy to place, though they are a bit outdated. the most common SOTs are SOT 23, SOT 89, SOT 143, SOT 223. (SOT 23,89,143,ETCC all are different types of transistors each one has a unique specification).
Integrated Circuits:
Small outline IC (SOIC) - these are good SMT alternatives to the dual in line package (DIP), due to their dramatically reduced size.
in general , they take up 30 - 50% less space and 70% less thickness than an average DIP.
Thin small outline package (TSOP) - TSOPs are low profile packages with fine - pitch leads..
typically meant to accommodate large silicon chips in high density packages (RAM/ FLASH memory ICs), largely because of their low volume/ high pin count.
Quad Flat Pack (QFN) – QFNs are high lead count packages (44 – 304). Its leads are typically gull wing. There are many kinds of QFNs, and they are one of the most common surface-mount ICs.
Plastic Leaded Chip Carrier (PLCC) - Connections are made on all four edges of a square package with a relatively high pin count. PLCCs can have roughly 18 – 100 leads (usually J-leads). Many of them can fit into IC sockets and can be easily replaced in the field. PLCCs have long been a popular option.
Lead-less Chip Carrier (LCC) – Not to be confused with PLCC, LCCs have no leads. Rather, LCCs are soldered directly onto PCBs by their solder pads. These are usually designed for Mil Spec because, with no leads to damage, they're quite "rugged." LCCs are great for high temperature and aerospace applications.
Pin Grid Array (PGA) – PGAs are typically square or rectangular, with pins arranged underneath the package. They're design was highly influential on the now ubiquitous BGA.
Flip Chip – Flip chips are bare die packages, with small bottom-side solder bumps that act as leads. They are soldered directly onto the PCB.
Ball Grid Array (BGA) – BGAs are perhaps one of the best performing SMT packages in use today, due to their high densities. The BGA is a descendant of the PGA, yet instead of pins, it has solder balls that can be placed directly onto the PCB. Because of their high density, BGAs are typically used to house microprocessors.
Pad:
it is nothing but a piece of copper on which lead of components are mounted and on which soldering are done. Pad provides the mechanical support to the components.
Trace:
In pcb , components are not connected with the help of wires. all components are connected with a conducting material like copper. this copper part of pcb which is used to connect all components that is known as trace.
layers:
According to application, cost and available space of circuit, user can choose the layer of PCB. most simple in construction, easy to design and most useful in routine life in single layer pcb.
But for very large and complex circuit, double layer PCB or multi layer PCB is most preferred compared to single layer PCB. now a days in multi layer pcb, 10-12 layers can be connected and most critical thing is to communicate between the components in different layers.
Silk layer:
Used for printing line, text or any art on the surface of PCB. usually for screen printing epoxy ink is used. silk layer can be used in top and/ or bottom layer of pcb according to user requirement which is known as silks screen top and silk screen bottom.
Top and bottom layer:
in top layer of pcb all components are mounted in this layer of pcb . generally this layer is green colored. in bottom layer of pcb, all components are soldered through the hole and lead of the components is known as bottom layer of PCB. sometimes in top and/or bottom layer of pcb is coated with green layer which is known as solder mask.
Solder mask:
there is one additional layer on the top if the copper layer called as solder mask. this layer is generally has green color but it can be of any color. this insulating layer is used for to prevent accidental contact of pads with conductive material of PCB.
