PCB: The Hidden Treasure

Most printed circuit boards are made from fiberglass or plastic, non-ferrous metal, and other recyclable materials. Gold is one of the most commonly found precious metals in integrated circuit boards, as it is an excellent conductor of electricity and is highly resistant to corrosion.

Additionally, printed circuit boards may also contain other valuable metals – silver, platinum, palladium, copper and nickel – that can be extracted from them and reused to make a variety of new products, including circuit boards.

Certified and credible e-waste recycling companies have emerged these years, they typically use internationally accepted methods of processing PCBs, which means they’re sent to specialized smelters to recover precious metals. So, you can take your electronic waste for safe recycling.

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Track Sizes

There is no recommended standard for track sizes. What track sizes you use mainly depend on the electrical requirements of the design, the routing space and clearance. Every design will have a different set of electrical requirements which can vary between tracks on the board.

All but basic non-critical designs will require a mixture of track sizes. As a general rule though, the wider, the better. That’s because wider tracks have lower DC resistance and therefore higher current capacity, lower inductance, can be easier and cheaper for the manufacturer to etch, and are easier to inspect and rework.

The lower limit of your track width will depend on the fabrication ability of your PCB manufacturer. Typically, figures are 10/10 and 8/8 for basic boards. The IPC standard recommends 4 thou as being a lower limit. The lower the track figure, the greater care the manufacturer has to take when aligning and etching the board, and this will cost you more. 

As a start, you’d better to use 25 thou for signal tracks, 50 thou for power and ground tracks and 10-15 thou for going between IC and component pads. Good design practice is to keep tracks as big as possible and then to change to a thinner track only when required to meet clearance requirements.

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Track Clearances

Electrical clearances are an important requirement for all boards. Too tight a clearance between tracks and pads may lead to hair-line shorts and other etching problems during the manufacturing process. These can be very hard to find once your board is assembled. At least 15 thou is a good clearance limit for basic through-hole design, with 10 thou or 8 thou being used for denser surface mount layout. 

As a rule of thumb, an absolute minimum of 8mm equals to 315 thou spacing should be allowed between 240V tracks and isolated signal tracks. The clearance varies based on whether the tracks are on internal layers and the external surface. They also vary with the operational height of the board above sea level, due to the thinning of the atmosphere at high altitudes. Conformal coating (a non-conductive spray often applied over the tracks to resist moisture, corrosion, etc) also improves these figures for a given clearance. 

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Snap Grid

A major rule of PCB design which always missed by beginners is to lay out your board on a fixed grid. This is called snap grid, as your components and tracks will snap into fixed grid positions. 100 thou is a standard placement grid for very basic through-hole work, while 50 thou is a standard for general tracking work. For even finer work, you may use a 25-thou snap grid or even lower. 

Why is a coarse snap grid so important? That’s because it will keep your components neat and symmetrical. Besides, it makes future editing, dragging, movement and alignment of your tracks, components and blocks of components easier as your layout grows in size and complexity.

Enough PCB layout practice is very crucial for your future. You’re required to start out with a coarse grid like 50 thou and use a progressively finer snap grid if your design becomes tight on space. Drop to 25 thou and 10 thou for finer routing and placement when needed. This will do for 99% of boards. Make sure the finer grid you choose is a nice, this means 50, 25, 20, 10, or 5 thou is a good choice.

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Safety Basics of Electrical Grounding

Safety basics of electrical grounding involve making sure all wires and cords are undamaged, checking that all circuits are performing well and none electrical fittings need to be replaced or repaired. Electrical grounding is the process of stabilizing an electrical current in order to limit the variation and volume of a machine's electrical current. 

When performing any electrical grounding work, workers should be sure to have a strong understanding of the process of grounding and the type of electrical current that is being worked with. Workers should also keep a first aid kit close by in case of injury. Workers should be aware of common symptoms of serious electricity-related injuries. Because of the high risk of electrical shock, it is also wise to only use non-conductive tools or tools with non-conductive handles and grips. Tools like these can absorb limited amounts of electricity and protect the user from serious harm.

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Pads

Pad sizes, shapes and dimensions depend not only on the component you are using but also the manufacturing process used to assemble the board. There is an important parameter known as the pad/hole ratio. It is the ratio of the pad size to the component lead hole size in that pad. As a simple rule of thumb, the pad should be at least 1.8 times the diameter of the hole or at least 0.5mm larger. This is to allow for alignment tolerances on the drill and the artwork on the top and bottom layers.

There are some common practices used when it comes to generic component pads. Pads for leaded components like resistors, capacitors and diodes should be round, with around 70 thou diameter being common. Dual in line (DIL) components like integrated circuits are better suited with oval shaped pads (60 thou high by 90-100 thou wide is common). Most surface mount components use rectangular pads with circular ends and the pads should not be any wider than the component itself. As a general rule, use circular or oval pads unless you need to use rectangular.
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Different Transformer Types

Some different types of transformers are power transformers, potential transformers, audio transformers and output transformers. A transformer transfers electrical energy from one electrical circuit to another without changing its frequency. 

Power transformers are used in electric power transmissions and electrical appliances to convert main voltage to low voltage. Laminated core and toroidal transformers are two power transformer types. Laminated core transformers have an insulated lamination that minimizes eddy current loss in the inner core, while compared to laminated core transformers, toroidal transformers have a lower external field and need less space. 

Potential transformers are used to monitor single-phase and three-phase power line voltages in power metering applications. There are three types of potential transformers: optical, capacitor and electromagnetic transformers. Optical transformers are designed for optical materials. The electromagnetic and capacitor transformers are both designed for higher voltage applications.

Audio transformers are used to carry audio signals in audio circuits. They provide impedance matching between high and low impedance circuits. Audio transformers are commonly used to interconnect professional audio systems components.

Instrument transformers are used to operate instruments from high current circuits or high voltage lines. Two instrument transformers types are current and potential transformers. Current transformers are used with an ammeter to measure current in AC voltages, while potential transformers are used with a voltmeter to measure voltage in AC.
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Necking

Changing your track from large to small and then back to large again is known as necking or necking down. This is often required when you have to go between integrated circuits or component pads. You can have nice big low impedance tracks with enough flexibility to route between tight spots.

In practice, your track width is designed according to the current flowing through it and the maximum temperature rise you are willing to tolerate. Every track will have a certain amount of resistance, so the track will dissipate heat just like a resistor; the wider the track, the lower its resistance. 

The calculations to figure out a required track width based on the current and the maximum temperature rise are a little complex. As a rule of thumb, a 10° Celsius temperature rise in your track is a nice safe limit to design around. In addition, the wider the track, the better.

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Advantages and Disadvantages of Parallel Circuits

The power remains at the same voltage as the voltage of a single power source is the major disadvantage of parallel circuits. Parallel circuits have more than one output device or power source, so electricity has more than one path to flow. Another disadvantage in parallel circuits is that the energy from the source is usually split across the entire circuit. Therefore, there are varying currents flowing in the circuit. As a result, where a constant current is desired throughout, parallel circuits cannot be effectively used. Similarly, the resistance in parallel circuits is much lower. 

Parallel circuits also have many important advantages. For example, the bulbs connected in parallel circuits tend to have brighter light than those connected in series circuits. In addition, when one bulb is turned off, it does not affect the others. So you can easily found parallel circuits used in houses, such as microwaves, refrigerators, heaters and television sets. This system is capable of providing each appliance with the full mains voltage, and a homeowner can turn on one appliance without necessarily turning on another.

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Grid Types

A snap grid and a visible grid are two main types of grids in PCB. The visible grid is an optional on-screen grid of solid or dashed lines, or dots. You can have a snap grid or visible grid set to different units (metric or imperial). Many designers prefer a 100 thou visible grid and rarely vary from that.

An electrical grid is also used in some programs. This grid is not visible but it makes your cursor snap onto the center of electrical objects like tracks and pads. This is extremely useful for manual routing, editing and moving objects.

One last type of grid is called component grid. It works the same as the snap grid but only for component movement. Component grid allows you to align components up to a different grid.

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