Monthly Archives: December 2018

Why Use a Multi-Layer PCB?

Although a multi-layer PCB is more expensive than a single or double-layer board of the same size, the former offers several benefits. For a given circuit complexity, the multi-layer PCB has a much smaller size as compared to that a designer can achieve with a single or even a double-layer board—helping to offset the higher cost—with the main advantage being the higher assembly density the multiple layers offer.

There are other benefits of a multi-layer PCB as well, such as increased flexibility through reduced need for interconnection wiring harnesses, and improved EMI shielding with careful placements of layers for ground and power. It is easier to control impedance features in multi-layer PCBs meant for high-frequency circuits, where cross talk and skin effect is more prominent and critical.

As a result, one can find equipment with multi-layer PCBs in nearly all major industries, including home appliances, communication, commercial, industrial, aerospace, underwater, and military applications. Although rigid multi-layer PCBs are popular, flexible types are also available, and they offer additional benefits over their rigid counterparts—lower weight, higher flexibility, ability to withstand harsh environments, and more. Additionally, rigid flex multi-layer PCBs are also available, offering the benefits of both types in the same PCB.

Advantages of a Multi-Layer PCB

Compared to single or double-layer boards, multi-layer PCBs offer pronounced advantages, such as:

  • Higher Routing Density
  • Compact Size
  • Lower Overall Weight
  • Improved Design Functionality

Use of multiple layers in PCBs is advantageous as they increase the surface area available to the designer, without the associated increase in the physical size of the board. Consequently, the designer has additional freedom to include more components within a given area of the PCB and route the interconnecting traces with better control over their impedance. This not only produces higher routing density, but also reduces the overall size of the board, resulting in lower overall weight of the device, and improving its design functionality.

The method of construction of multi-layer PCBs makes them more durable compared to single and double-layer boards. Burying the copper traces deep within multiple layers allows them to withstand adverse environment much better. This makes boards with multiple layers a better choice for industrial applications that regularly undergo rough handling.

With the availability of increasingly smaller electronic components, there is a tendency towards device miniaturization, and the use of multi-layer PCBs augments this trend by providing a more comprehensive solution than single or double-layer PCBs can. As these trends are irreversible, more OEMs are increasingly using multi-layer boards in their equipment.

With the several advantages of multiple layer PCBs, it is imperative to know their disadvantages as well. Repairing PCBs with several layers is extremely difficult as several copper traces are inaccessible. Therefore, the failure of a multi-layer circuit board may turn out to be an expensive burden, sometimes necessitating a total replacement.

PCB manufacturers are improving their processes to overcome the increase in inputs and to reduce design and production times for decreasing the overall costs in producing multi-layer PCBs. With improved production techniques and better machinery, they have improved the quality of multi-layer PCBs substantially, offering better balance between size and functionality.

What are Multi-Layer PCBs?

Most electronic equipment have one or more Printed Circuit Boards (PCB) with components mounted on them. The wiring to and from these PCBs determines the basic functionality of the equipment. It is usual to expect a complex PCB within equipment meant to deliver highly involved performance. While a single layer PCB is adequate for simple equipment such as a voltage stabilizer, an audio amplifier may require a PCB with two layers. Equipment with more complicated specifications such as a modem or a computer requires PCB with multiple layers, that is, a PCB with more than two layers.

Construction of a Multi-Layer PCB

Multiple layer PCBs have three or more layers of conductive copper foil separated by layers of insulation, also called laminate or prepreg. However, a simple visual inspection of a PCB may not imply its multi-layer structure, as only the two outermost copper layers are available for external connection, with the inner copper layers remaining hidden inside. Fabricators usually transform the copper layers into thin traces according to the predefined electrical circuit. However, some of the layers may also represent a ground or power connection with a large and continuous copper area. The fabricator makes electrical interconnections between the various copper layers using plated through holes. These are tiny holes drilled through the copper and insulation layers and electroplated to make them electrically conducting.

A via connecting the outermost copper layers and some or all of the inner layers is a through via, that connecting one of the outermost layers to one or more inner layers is the blind via, while the one connecting two or more inner layers but not visible on the outermost layers is the blind via. Fabricators drill exceptionally small diameter holes using lasers to make vias, as this allows maximizing the area available for routing the traces.

As odd number of layers can be a cause of warping in PCBs, manufacturers prefer to make multiple layer boards with even number of layers. The core of a PCB is an insulating laminate layer with copper foils pasted on both its sides—forming the basic construction of a double-layer board. Fabricators make up further layers by adding a combination of prepreg insulation and copper layers on each side of the double-layer board—repeating the process for as many extra layers as defined by the design—to make a multi-layer PCB.

Depending on the electrical circuit, the designer has to define the layout of traces on each copper layer of the board, and the placement of individual vias, preferably using CAD software packages. The designer transfers the layered design output onto photographic films, which the fabricator utilizes to remove the excess metal from individual copper layers by the process of chemical etching, followed by drilling necessary holes and electroplating them to form vias. As they complete etching and drilling for each layer, the fabricator adds it on to the proper side of the multi-layer board.

Once the fabricator has placed all layers properly atop each other, application of heat and external pressure to the combination makes the insulation layers melt and bond to form a single multi-layer PCB.

Wireless Charging and Electric Vehicles

In our daily lives, we are increasingly using wireless products. At the same time, researchers are also working on newer trends in charging electric vehicles wirelessly. With more countries now implementing regulations for fuel economy and pushing initiatives for replacing fossil-fuel based vehicles with those driven by electricity, automotive manufacturers have focused their targets on development of electric vehicles. On one hand there are technological advancements on lithium-ion batteries and ultra-capacitors, while on the other, researchers are working on infrastructure and the availability of suitably fast charging systems that will lead to a smoother overall transition to the adoption of electric vehicles.

Charging the batteries of a vehicle requires charging systems using high power conversion equipment. They convert the AC or DC power available from the power supply sources into suitable DC power for charging. As of now, the peak power demand from chargers is of the order of 10-20 KW, but this is likely to climb up depending on the time available for charging, and the advancements made in capabilities for battery charging. Therefore, both governments and OEMs are gearing up for developing high-power charging systems to cater to the power needs of future electric vehicles.

Wireless charging systems transfer power from the source to the load without the need for a physical connection between the two. Commonly available schemes use an air-cored transformer—with power transfer taking place without any contact between the source and the load. Wireless power transfer technology is available in various ranges, starting from mobile power charger systems rated for 10s of watts, to high power fast chargers for electric vehicles rated for 10s of kilowatts.

Earlier, the major issues with wireless charging systems were their low efficiency and safety. The technology has now progressed to the stage where achieving efficiencies of over 80% is commonplace. Although this is on par with wired power charger systems, increasing the spacing between the primary and secondary coils allows the efficiency to drop exponentially, which means the efficiency improves as the spacing between the coils decreases. Researchers are also looking at adopting various other methods of constructing the coils to address the issue.

Likewise, smart power controls are taking care of safety, by detecting power transfers taking place spuriously and suspending power transmission directly. Manufacturers are ensuring safety at all stages by implementing regulatory guidelines such as SAE J2954.

Although several methods exist for wireless power transfer, most popular are the resonance and inductive transfer methods. The inductive method of power transfer uses the principles of the transformer, with the AC voltage applied to the primary side inducing a secondary side voltage through magnetic coupling, and thereby transferring power.

The inductive method of power transfer is highly sensitive to the coupling between the primary and secondary windings. Therefore, as the distance increases, the power loss also increases, reducing the efficiency. That restricts this method to low power applications alone.

Based on impedance matching between the primary and the secondary side, the design of a resonant method allows forming a tunnel effect for transferring magnetic flux. While minimizing the loss of power, this method allows operations at higher efficiency even when placing the coils far apart, making it suitable for transferring higher levels of power.

What is Raspberry Shake and BOOM?

The Earth below our feet is never still. Although we feel tremors only when they are substantially strong, such as during earthquakes, we can use the highly popular single board computer, the Raspberry Pi or RBPi to monitor what is happening just under us. This tiny seismograph, with an appropriate name of Raspberry Shake, is the smallest one can find.

Although small, Raspberry Shake can record earthquakes of all magnitudes, even those no human senses can detect. It is also capable of recording those huge destructive quakes that occur regularly around the globe. Raspberry Shake has a companion, the Raspberry Boom, and it detects infrasonic sounds given off when the Earth shakes.

During earthquakes, the Earth gives off low frequency sounds that are below the threshold of human hearing, but infrasound travels large distances. Other objects also generate such infrasound, including traffic, trains, airplanes, wind farms, weather systems, meteorites, and many more. The Raspberry Boom is the perfect companion to the Raspberry Shake for detecting and studying infrasound.

You only have to snap the Raspberry Shake and Boom on to an RBPi. The two together form a super capable Earth monitoring network. Plugging their output into a Station View then allows creating a powerful array for monitoring and discovering several fascinating events from around the world in real time.

The Raspberry Shake and Boom combine several technologies. The Raspberry Shake has a powerful processor on its main board, and a digitizer with built-in sensors including a geophone or super-sensitive motion sensor for detecting Earth movements. You can plug this Shake board right into the RBPi board, which will power it. The data from the Shake board uses miniSEED for processing, as this is a standard data format the industry uses. The output is also compatible with jAmaSeis, and that makes it easy to learn, monitor, and analyze.

Other advanced options on the Raspberry Shake allow experienced users to use it by programming their own protocols such as the IFTTT. They can also laser print their own enclosures. Other users, especially novices, can also use the Raspberry Shake easily, as the design of the devices allows them to be plug-n-play. Their design is professional and anyone can use them on home monitors.

Anyone can use the Raspberry Shake range. For instance, Educational facilities, consumer interest groups, professional institutes, makers, RBPi enthusiasts, citizen scientists, hobbyists, and more can simply plug into the network of Raspberry Shakes to start watching the planet vibrate.

It is very easy for any school or university to access data from any Raspberry Shake anywhere in the world, allowing them to monitor seismic activity of any active earthquake area as well as of quiet regions anywhere. They can view any event such as those demonstrated in IRIS Teachable Moments, including micro-tremors or other larger events.

The Raspberry Shakes are compatible with SWARM analytical software and jAmaSeis. This made the Oklahoma Geological Survey acquire 100 units for expanding their network. They rolled these units to schools and educational institutional facilities for raising the awareness and providing valuable educational tools.

What are RTUs – Remote Terminal Units?

Nowadays, small computers make up remote terminal units or RTUs and SCADA units. Users program controller algorithms into these units, allowing them to control sensors and actuators. Likewise, they can program algorithms for logic solvers, power factor calculators, flow totalizers, and many more, according to actual requirements in the field.

Present RTUs are powerful computers able to solve complex algorithms or mathematical formula describing external functions. Sensing devices or sensors gather data from the field, sending the signals back to the RTU. By solving the algorithms in it using the input signals, the RTU then sends out control instructions to valves or other control actuators. As scan periods in RTUs are very small, the entire activity happens very fast, hardly taking a few milliseconds, with the RTU repeating the process.

Regulatory agencies certifying RTUs prefer use of dedicated hardware for solving certain safety related functions such as toxic gas concentration and smoke detection. Therefore, they make sure of the reliability of detection for safety related functions.

The RTU operates in a closed system. Sensors measure the process variables, while actuators adjust the process parameters and controllers solve algorithms for controlling the actuators in response to the measured variables. The entire system works together based on wiring or some form of communication protocol. This way, the RTU enables the field processes near it to operate according to design.

Before the controller in the RTU can solve the algorithm, it has to receive an input from the field sensor. This requires a defined form of communication between the RTU and the various sensors in the field. Likewise, after solving the algorithm, the RTU has to communicate with the different actuators in the field.

In practice, sensors usually feed into a master terminal unit or MTU that conditions their input, changing it to the binary form from the analog form, if necessary. This is because sensors may be analog or digital types. For instance, a switch acting as a sensor can send information about its state using a digital one or +5 V when it is open and a digital zero or 0 V when it is closed. However, a temperature sensor has to send an analog signal or a continuously varying voltage representing the current temperature.

The MTU uses analog to digital converters to convert analog signals from the sensors to a digital form. All communication between the MTU and the RTU is digital in nature, and a clock signal synchronizes the communication.

The industry uses RTUs as multipurpose devices for remote monitoring and control of various devices and systems, mostly for automation. Although industrial RTUs perform similar function as programmable logic circuits or PLCs do, the former operates at a higher level as RTUs are basically self-contained computer units, containing a processor and memory for storage. Therefore, the industry often uses RTUs as intelligent controllers or master controller units for controlling devices that automate a process. This process can be a part of an assembly line.

By monitoring the analog and digital parameters from the field through sensors and connected devices, RTUs can control them and send feedback to the central monitoring station for industries dealing with power, water, oil, and similar distribution.