Basics: Project 135p
Project name: Printed circuit board and terms used in connection with PCB design and manufacturing
Tags: KiCad, KiCad v5, terms, PCB design, PCB manufacturing, PCB, printed circuit board
We will learn about a printed circuit board (PCB) and terms used in connection with PCB design and manufacturing.
One of the key concepts in electronics is the printed circuit board or PCB. Printed circuit board is the most common name but may also be called “printed wiring boards” or “printed wiring cards“. A PCB supports mechanically and connects electrically electrical or electronic components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB.
PCB design software’s
The PCBs require design layout, but manufacturing and assembly is automated. The various electronic computer-aided design software’s are available to do the PCB design layout. You can find out more about it in here: Basics: Project 102a PCB design softwares
PCBs can be single-sided (one copper layer), double-sided (two copper layers on both sides of one substrate layer), or multi-layer (outer and inner layers of copper, alternating with layers of substrate). Let’s have a look at PCB composition.
(F.SilkS , B.SilkS)
|The silkscreen layer is applied on top of each soldermask layer. The silkscreen layers where the drawings of the components appear. That’s where you draw things like component polarity, first pin indicator, reference for mounting, text labels and so on that allow for easier assembly and indicators for users to better understanding the board. The silkscreen layer is normally white but any ink color can be used (black, gray, red, and even yellow). It’s normally one color silkscreen layer in use on a PCB board.|
|The layer below the silkscreen is called the soldermask layer. This layer gives the PCB its green, white, red, black, yellow or blue color. The common color in use is green. It is overlaid onto the copper layer to insulate the copper traces from accidental contact with other metal, solder, or conductive bits. This layer helps the user to solder to the correct places and prevent solder jumpers.|
All pads should appear on one of soldermask layers (Surface-mount technology) or both (for through hole) to prevent the varnish from covering the pads.
|The next layer is a thin copper foil, which is laminated to the board with heat and adhesive. On double-sided PCBs, copper is applied to both sides of the substrate but some low cost PCBs may have copper on only one side. When we refer to a double sided PCB we are referring to the number of copper layers (2). This can be a 1 layer or more than 16. The copper thickness can vary and is specified by weight, in ounces per square foot. The vast majority of PCBs have 1 ounce of copper per square foot but some PCBs that handle very high power may use 2 or 3 ounce copper.|
|Substrate (FR4)||The base material, or substrate, is usually fiberglass-reinforced epoxy laminate FR4. It gives the PCB its rigidity and thickness. There are also flexible PCBs built on flexible high-temperature plastic (Kapton or the equivalent). You will find many different thickness PCBs 0.4 mm and more. Cheaper PCBs and perfboards will be made with epoxies or phenolics materials those lack the durability of FR4 but are less expensive. These types of substrates are also typically found in low quality electronics. Phenolics have a low thermal decomposition temperature which causes them to delaminate, smoke and char when the soldering iron is held too long on the board.|
Electronic components mounting schemes
Surface-mount technology (SMT) is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referred to as a surface-mount device (SMD).
Through-hole technology (also spelled “thru-hole”), refers to the mounting scheme used for electronic components that involves the use of leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines.
Terms used in connection with PCB design and manufacturing
|Perfboard||Perfboard is a material for prototyping electronic circuits (also called DOT PCB). It is a thin, rigid sheet with holes pre-drilled at standard intervals across a grid, usually a square grid of 0.1 inches (2.54 mm) spacing. These holes are ringed by round or square copper pads, though bare boards are also available. Inexpensive perfboard may have pads on only one side of the board, while better quality perfboard can have pads on both sides (plate-through holes). Since each pad is electrically isolated, the builder makes all connections with either wire wrap or miniature point to point wiring techniques. Discrete components are soldered to the prototype board such as resistors, capacitors, and integrated circuits. The substrate is typically made of paper laminated with phenolic resin (such as FR-2) or a fiberglass-reinforced epoxy laminate (FR-4).|
|Annular ring||A copper ring attached to the surface of a pad around a connecting hole wall. An Annular Ring Width = (diameter of the pad – diameter of the hole) / 2|
|Drills||The places on a PCB board made in the pads.|
|Drill hit||The place on a PCB design where a hole should be drilled, or where it’s actually was drilled on the PCB board. Inaccurate drill hit caused by dull bit is a common issue during PCB manufacturing.|
|DRC||Means Design Rule Check. An electronic computer-aided design software checks PCB design to make sure that it does not contain errors such as traces that incorrectly touch, traces too narrow or drill holes are too small.|
|Layers||PCB layers (copper layers). The number of copper layers can be from 1 to 16 layers.|
|Track spacing||Minimum width of any conductors, distance between any two adjacent traces|
|Gold fingers||Gold fingers are the gold-plated columns that you see along the connecting edges of printed circuit boards (PCBs). The purpose of gold fingers is to connect a secondary PCB to the motherboard of a computer.|
|Mouse bites||An alternative to v-score for separating boards from panels. A number of drill hits are clustered close together, creating a weak spot where the board can be broken easily after the fact.|
|The tooling holes placed on a PCB or a panel of PCBs for registration and hold-down purposes during the manufacturing process. Often tooling holes are non-plated through, meaning that they remain isolated from any electrical components or traces on the board.|
|Tooling rails||Tooling Rails are the ‘holding frame’ for the array. They provide stability and make it easier to handle the arrays throughout the assembly process|
|Fiducial (Fiducial markers)||Fiducial marker or fiducial refers to the reference point on a printed circuit board (PCB). Through fiducials it is possible for solder paste printer, automatic placement machines and optical inspections systems to precisely measure the circuit structure. The best to have 3 fiducials, as each of them serves a purpose.|
The first fiducials helps the machine recognize where the PCB is in its space in the X and Y dimensions. The second fiducial helps the machine recognize what orientation the PCB is in and also how skewed the PCB is in the clamps. Finally, the third fiducial helps the machine compensate for any shrink or stretch of the PCB.
|V–Groves||V–Groves are cuts, usually on both sides of a PCB and generally in a straight line. They are made with a cutter with a cut angle of 30° or 45°. You need tooling rails along the two longest sides and there should be no space between the boards.|
|Pad||A portion of exposed metal on the surface of a board to which a component is soldered.|
|Panel||A larger circuit board composed of many PCB boards which will be broken apart before use. Automated circuit board handling equipment frequently has trouble with mini PCB boards, and by aggregating several boards together at once, the process can be speed up significantly.|
|Half-cut / Castellated Holes||Half-cut holes or Castellated Holes or Castellations are plated through holes or vias located in the edges of a printed circuit board. Castellations are cut through to form a series of half holes. These half holes serve as pads intended to create a link between the module board and the board that it will be soldered onto.|
|A variable level elevation can be milled at the edge or within a circuit board. This is called Z-axis milling.|
|Solder Paste Stencil||A thin, metal (or sometimes plastic) stencil which lies over the board, allowing solder paste to be deposited in specific areas during assembly.|
|PCB Edge Plating|
|Sideplating is the metalization of the board edge in the PCB filed. Edge plating, round-edge plating, border plated, plated contour, side metal, these words can also be used to describe the same function. Possible applications of sideplating: improvement of EMC performance by shielding the inner region of multilayers (eg for HF circuit boards), cooling function with the edge as additional cooling surface, where an active heat dissipation can be used, housing connection, board-on-board connection (see plated half-holes).|
|Pick-and-place||The machine or process by which components are placed on a circuit board. A pick and place (PNP) machine is a robotic assembly device that uses a vacuum to lift a component off of a piece of tape, rotate it to the right orientation, then place it on a circuit board. It takes a few hours to setup a machine to build the assembly, but once everything is running, it is very fast.|
|Press-fit holes (plated through holes)||Press-fit holes are plated through holes with tighter tolerances than the standard +/-0.10mm. Press-fit holes fit the leads of connectors that will not be soldered but pressed into the holes. To accommodate lead and hole to tightly fit together, the tolerances are well defined and more tight than standard.|
|Copper pour (Ground Plane)||The copper pour refers to an area on a printed circuit board filled with copper (the metal used to make connections in printed circuit boards). The copper pour is commonly used to create a ground plane. Another reason for using copper pour is to reduce the amount of etching fluid used during manufacturing. PCB designers today almost invariably use completely solid areas of copper pour that completely cover the remaining area outside those tracks, pads, and stand-off regions. Many early PCBs have a “hatched copper pour”, sometimes called a “cherry pie lattice”. While solid copper pour provides better resistive characteristics, hatched copper pour is used to balance the heat and dilatation on both sides of the board in order to avoid warping of certain substrate.|
|Pogo pin (spring-loaded pin)||A pogo pin or spring-loaded pin is a type of electrical connector mechanism to make a temporary connection for test or programming purposes.|
|Reflow soldering||Reflow soldering is the most widely used method of attaching surface mount components to printed circuit boards (PCBs). The aim of the process is to form acceptable solder joints by first pre-heating the components/PCB/solder paste and then melting the solder without causing damage by overheating.|
|PCB Slots (cutouts)||Any hole in a board which can be round or oval. Slots may or may not be plated. Plated slot means this slot is plated with copper which can be used for electrical connection.|
|UL Marking||UL stands for Underwriters Laboratories, an organization that has been around for more than 100 years. UL is a global leader in testing, inspection, certification, auditing and validation. The UL Mark is the single most accepted Certification Mark in the United States. UL is similar to the CE marking organization.|
|Peelable Soldermask||A peelable soldermask is screen printed and used in order to protect selected solder holes against plugging during mass soldering. A peelable soldermask can also protect carbon elements and gold plated contacts during mass soldering.|
|PCB panelization||PCB panelization is a manufacturing technique in which smaller boards are manufactured en-masse connected together as a single array, making it easier to move through an assembly line. The individual boards can easily be depanelized or removed from the array for packaging or installation into a product.|
|Halogen-Free||The halogen-free material is a material that does not contain a group of halogen elements (fluorine, chlorine, bromine, iodine, and astat). These fire elements release substances that are toxic to humans in the form of toxic fumes but also cause corrosion of metals.|
|Impedance control||For high frequency analogue or digital circuits, it is essential to protect the signals that propagate on the PCB from being damaged. In fact, signals above 100Mhz are impacted by trace impedance which, if not properly taken into account, can cause unexpected errors that are especially difficult to analyse. Luckily, impedance control allows designers and PCB manufacturers to manage the phenomenon.|
|Carbon contacts||Carbon contacts are made of carbon ink and can be used for keyboard contacts, LCD contacts and jumpers. The printing is performed with conductive carbon ink.|
|Differential pair||Electromagnetic Interference or (EMI) can significantly impact the signal integrity on your boards; however, there are routing options that can help minimize this impact. The use differential pair routing can help protect sensitive signals on your board since they’re mostly immune to common mode noise and reduce the current flowing through the ground plane. However, differential pairs come with their own set of disadvantages, so you’ll have to manage trace widths, copper weights, impedances and current flows to avoid spreading EMI on the PCB and causing timing mismatches in the pairs themselves.|
|Solder pot||A pot used to quickly hand solder boards with through hole components. Usually contains a small amount of molten solder into which the board is quickly dipped, leaving solder joints on all exposed pads.|
|Solder jumper||A small, blob of solder connecting two adjacent pins on a component on a circuit board. Depending on the design, a solder jumper can be used to connect two pads or pins together. It can also cause unwanted shorts.|
(thermal pad or thermal relief pad)
|A thermal relief pad, thermal pad or simply thermal, is a printed circuit board (PCB) pad connected to a copper pour using a thermal connection. It looks like a normal pad with copper “spokes” connecting it to the surrounding copper.|
|Copper Thieving||Thieving, also known as Thieving Pad, Copper Thieving, or Copper Fill, is an outer layer only process, which means “copper squares” or “copper dots” are added to outer layers of a PCB board to create a uniform distribution of copper across the surface. Thieving is to make sure the copper plating in the holes is uniform. If the copper distribution in the artwork is not uniform, areas with little exposed copper will plate very heavy while areas with large amounts of copper, such as BGAs or connector pin fields will not plate properly. In copper plating process, “thieving” steals some of the plating current that would otherwise concentrate on features that are sparse and be spread thin in areas with areas that are dense with features. Copper thieving can be applied on FR4 PCB, flexible circuit and rigid-flex board.|
|Trace||A signal trace on a printed circuit board (PCB) is the equivalent of a wire for conducting signals. Each trace consists of a flat, narrow part of the copper foil that remains after etching. Signal traces are usually narrower than power or ground traces because the current carrying requirements are usually much less.|
(V-grooving or V-cutting)
|V-Scoring also named as V-grooving or V-cutting, it is a way to split circuit boards. It is cutting a “v” groove on the top and bottom of a circuit board while leaving a minimum amount of material in place to hold the boards together.|
|Via||A via is used to make an electrical connection between the layers of a Multi-Layer PCB. Connecting multiple layers of the board make it possible to reduce the size of the PCB. A via is constructed by placing copper pads on each layer of the PCB and drilling a hole through them. The hole is made conductive through electroplating or by placing copper cylinders directly in the drilled holes.|
The inner part of the via, is usually filled with a non-conductive material (air in most cases), while the outer layer of the cylinder has a conductive plating which is used to connect each layer of the PCB. It is always good to use multiple smaller vias than one large via since it reduces the inductance and also provides an additional path to the current flow if any of the via fails.
There are three main types of vias used in a PCB -through hole via, blind via and buried via.
Through hole via goes right through the PCB board from top to bottom and can be used to connect all the layers of a PCB. It is the most common via and is easiest to construct.
Blind Via connects the outer most layer of a PCB to the next layer. It can not be seen on the other side of the board and is therefore called blind via.
Buried Via can be used to connect internal layers of a PCB. It will not be seen on the surface of the board.
|Via in Pad||When the via is placed directly on the pad of a surface mount component. Once this is done, the via is filled with conductive or non-conductive epoxy, followed by capping and electrochemical plating to make it virtually invisible. Such type of arrangement results in buried via within the PCB surface that can be completely soldered as standard SMT lands. The Via in Pad can be filled using non-conductive epoxy, conductive epoxy, copper, or silver followed by electrochemical plating.|
|Wave soldering||Wave soldering is a large-scale soldering process by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly. The name is derived from the use of waves of molten solder to attach metal components to the PCB.|
|Countersink||A countersink is a cone-shaped hole that is cut into the PCB to allow the flat head of a socket cap screw to fit flush with the surface of the board. The chamber angles that are commonly used for countersinks are 82°, 90° and 100°.|
|Counterbore||A counterbore is a cylindrical flat-bottomed hole that is designed to house a hex head or socket head cap screw to be used to secure a PCB board. A counterbore has a 0° chamber angle but is vertical.|
|Stackup||A stackup is the arrangement of layers of copper and insulators that make up a PCB before designing the final layout of the board.|
|Electropolishing||Also known as electrochemical polishing, anodic polishing, or electrolytic polishing (especially in the metallography field), is an electrochemical process that removes material from a metallic workpiece, reducing the surface roughness by levelling micro-peaks and valleys, improving the surface finish. It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating|
We have learnt about a printed circuit board (PCB) and terms used in connection with PCB design and manufacturing.
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- See attachments on the beginning of this project description.