How ESD Affects PCBs?

Written by Rush PCB Inc on . Posted in PCB

ESD or ElectroStatic Discharge damages both printed circuit boards (PCB) and electronic components. This happens when there is an accumulation of positive or negative charges on insulators or unconnected conductors. The amount of charge accumulating depends on the stored capacitance on the insulator or conductor with respect to nearby objects having a corresponding opposite charge. The charge is static as it is unable to equalize itself or be transferred by electromotive force, unless there is a decrease in the value of the capacitance between the objects, or there is a path for its discharge. The presence of a conducting path allows the charge to either bleed away slowly, or to discharge quickly depending on the resistance the path offers. The phenomenon of quick discharge, also called ESD, causes the most damage.

ESD PCB

Sources of Static Electricity

All materials can be sources of static electricity. However, some materials are susceptible to positive changes, while others to negative. For instance, positive charges accumulate predominantly on animal fur or human skin, while negative charges are more commonly found on synthetic material such as plastic cups and Styrofoam. The amount of electrostatic charge accumulating on an item depends on its capacity of storing it. For instance, the human body has a capacity of about 250 picofarads. This translates to a stored charge with an electromotive force of 25 kV.

ESD and Electronic Circuitry

Simply put, ESD is a tiny amount of lightning, similar to what happens during thunderstorms, only in a miniature form. According to the laws of physics, the electromotive force causes a massive amount of current flow through a path offering the lowest resistance. In most cases, the discharging current travels to ground via the metal chassis or frame.

For instance, while assembling a PCB, the electric charge stored in the operator’s body could discharge through the electronic circuitry via the grounded holder or metal chassis. While discharging, the ESD current may follow several available paths to reach the ground.

If the path available to the current is through the PN junction inside an integrated circuit, the current will burn through leaving visible holes. The burn comes from the I2R loss, where, even though the resistance (R) is low, the high electromotive force causes a high level of current (I) flow. The material is unable to dissipate the massive heat generated, and as a result burn.

As the amount of heat generated depends on the current flow caused by the electromotive force, the amount of accumulated charge actually governs the amount of damage that takes place. Sometimes, one ESD discharge may not be enough to totally disrupt the device, but only weaken it, causing it to subsequently fail when stressed during normal operations. Even smaller discharges, but repeated over time, may degrade the internal structure of a device.

Read More: Factors Affecting the Longevity of Copper Bond

Nature of ESD

ESD has different ways of manifesting itself. Most commonly, it occurs when humans touch sensitive devices. According to extensive studies, the human body and certain clothing can store anything from 500 to 2,500 V of static electricity during a normal workday. We do not realize this as the level is below the threshold of human perception, but the level is far above the level that can cause damage to electronic components.

Apart from the human touch, there are other ways also that ESD can damage PCB assembly. Some of these are:

  • Using ungrounded electrical equipment, such as an oscilloscope, to troubleshoot electronic circuitry.
  • Placing synthetic material, such as Styrofoam and/or plastic, on or near electronic circuitry.
  • Creating rapid movement of air near electronic assembly, such as when using compressed air to clean PCB assembly, blowing air on electronic assembly using fans, or handling electronic equipment near air handling systems.

In the above scenarios, static charge may accumulate without your knowledge, and an ESD may occur without the PCB assembly actually coming in physical contact with the charged object.

Read More: Advantages of Using a Consultancy for Circuit Board Manufacturing

Damage to PCBs by ESD

When a PCB assembly comes close to any object that has a charge, there is a possibility of an ESD. This depends on the electromotive force between the two and the distance separating them, with the greatest chance of an ESD taking place when the two touch.

Although manufacturers build different protection mechanisms within ICs, ESD can as much as totally ruin an IC. This damage may be of two types—latent or catastrophic.

When a device suffers latent damage due to ESD, it may be partly degraded, and continue to run. However, the device becomes unreliable as its lifetime reduces, and its operational behavior affected.

A bare PCB may also suffer latent damage. For instance, there can be an electrical discharge from one neighboring track to another, if the latter is connected to ground. The discharge can char the top layer of the PCB insulation, causing a partially conducting path. This can affect the performance of the circuit after assembly.

Catastrophic damage occurs when the device is permanently damaged because of ESD. A performance test can usually detect such damage. As catastrophic damages are detected at early manufacturing stages, the effect is not as expensive as that from latent damages.

Products with latent damages can pass regular inspection and testing, but fail when operating in the field. Therefore, failure from latent damages can be extremely costly besides affecting the reputation of the company.

ESD Prevention by Design

Designers can follow standard practices during design that help protect PCBs from ESD. These include:

  • Use ground planes extensively, as these can help bypass ESD to ground, and prevent it from passing through the active parts of the PCB.
  • Reduce line lengths to reduce parasitic inductance. Parasitic inductance does not allow protection circuits to work fast enough to prevent damage from ESD.
  • Provide adequate spacing between traces carrying different voltages. If the voltage difference is high, the designer may have to introduce an air gap in the form of a slot or air gap in the PCB, as the PCB insulation material may not provide adequate insulation resistance.
  • Do not run tracks leading to IC pins near the extremities of the PCB. The edges of the board are more susceptible to ESD as operators handle PCBs more by the edges. It is preferable to run a broad ground track around the periphery of the PCB if possible.
  • Use surge protection diodes or transient voltage suppressors at input and output ports of the circuit as connecting or disconnecting a cable from a system may also cause ESD.
  • Use isolated pads or lands for metallic bodies of connectors.

ESD Prevention by Process

ESD prevention by process should follow a company-wide awareness and training of personnel at all stages involving PCB and component handling and storage. At all stages proper grounding of personnel and equipment is essential to prevent any static electricity buildup. Personnel must wear anti-static overalls, shoes, caps, and always carry their wrist bands, which they should connect to ground before they touch any PCB assembly.

Metal workbenches must be grounded to the electrical earthing system, and have grounded anti-static mats on top. All anti-static material grounding, including grounding wires for wrist bands have a high value resistor in series. This allows static charge to drain away, but protects personnel from inadvertent electrical shocks. For more information and recommended practices on static electricity, refer to NFPA-77.

It is necessary to establish a process of periodic checking of the grounding system to ensure proper working. Ground wires of tables and wrist bands have a limited life period, and must be checked and replaced periodically. The top surface of anti-static mats tends to wear off and this reduces their effectiveness. They too must be replaced periodically once their surface and volume resistivity changes. Compounds are available for treatment of carpets and floors to reduce the buildup of static charges.

Use of synthetic material must be curbed, especially at incoming material inspection, storage bins and facilities, PCB assembly and testing stages, and during packing and dispatch.

Dry air supports creation of ions and accumulation of static charges, whereas humid air helps to dissipate them. Areas with air-conditioning must include humidifiers to keep the air from becoming too dry.

Conclusion

If the above is not feasible for the entire shop floor, it may be prudent to establish an ESD Protected Zone with clear identification and demarcation. By linking all surfaces to the ground, it is possible to keep all objects, people, and ESD sensitive devices at the same potential. The area should be accessed only by trained personnel, and a periodic checking system established as above.

Trends in PCB Materials

Written by Rush PCB Inc on . Posted in PCB

With the field of PCB manufacturing evolving constantly, eminent manufacturers such as Rush PCB are continuously improving their technology, making innovations, and evolving better manufacturing methods. The pace of advancement is very high, such that methods commonly in use yesterday are considered as obsolete today. Keeping up with the new trends in the PCB industry is a tough challenge.

Complexity Increases but Thickness Reduces

The present trend in electronics is making gadgets more powerful but reducing their thickness. For instance, the latest generation of smartphones can do things that a few years back would look like science fiction. OEMs are in a race to provide more sophisticated functions and features in smaller and thinner gadgets. Consequently, the PCBs need to be smaller and with thinner substrates, while the trend towards greater complexity is increasing the number of layers. This trend is leading to increasingly complex computing systems being fitted into small and even smaller packages.

The average thickness of printed circuit boards at present is closer to 0.4 mm, and very soon Rush PCB may decrease this to 0.3 mm. Although the decrease may not seem much, but it opens up a whole new realm of technical possibilities as we move towards the era of IoT and wearables.

3-D Integration and Embedded Components

With the growing complexity of PCBs, one of the growing trends is 3-D integration. Not only does this allow for better miniaturization, but it also makes the boards denser, also fitting more into a smaller space. To facilitate this technology, Rush PCB offers its customers modern PCBs such as flexible PCBs, rigid flex PCBs, and High Density Integration or HDI PCBs. Along with 3-D integration, Rush PCB also promotes technologies such as embedded components.

Rush PCB can embed a variety of components, ranging from passive components such as resistors and capacitors, to active components such as chips and integrated circuits. Embedding components inside PCBs offers substantial advantages. While decreasing the board size and increasing its complexity, embedding allows improving the system performance, while reducing overall manufacturing costs.

The improvement is performance from embedded components comes from reduced EMI or electromagnetic interference and better signal integrity. Moreover, with embedded components directly under them, integrated circuits link to these components with reduced length of traces. This drastically reduced via inductance and parasitic capacitance.

pcb trend

Improvement in Substrate Materials

Although paper phenolic and glass epoxy PCBs were in use for decades, these substrate materials are no longer suitable for modern PCBs with their higher data transmission rates and higher processing speeds. Therefore, newer substrate materials have emerged for handling the rapidly advanced technologies. For instance, Rush PCB now offers exotic substrate materials such as Fluoropolymers, Polyimide, acrylic adhesives, epoxy adhesives, and liquid crystal polymers.

Liquid crystal polymers have good dielectric properties with very low loss and moisture absorption. Rush PCB uses LC polymers in both clad and bondply, just as they do with fluoropolymer and low-loss all-polyimide constructions. They also offer rigid boards for high-speed applications made of low-loss thermoset adhesives.

Rush PCB uses special substrates that meet the demands of newer technologies such as LED lighting. Although these light sources are highly efficient, the LED chips produce heat, which unless conducted away, will reduce the life of the component. For such applications, Rush PCB makes metal clad PCBs that have a metal backing on one side acting as a heat sink to dissipate the heat, and a thermally conducting substrate to carry away the heat from the LEDs to the heat sink.

With rising speed of operation in electronic gadgets. PCBs require to handle very high-speed digital signals without distorting them. At high speed and frequency, the substrate material has a significant contribution to signal integrity, skin effect, impedance matching, and more. Rush PCB uses different suitable materials for substrates that allow high-speed and high-frequency signals to perform adequately.

Read More: Guidelines for Component Placement in Professional Boards

Green Electronics Manufacturing

With mounting statistics for climatic change, governments, businesses, and consumers are pressurizing the industry to look into more eco-friendly solutions for manufacturing. One of the initiatives Rush PCB has taken up is manufacturing PCBs that comply with RoHS and WEEE directives, by restricting the use of hazardous materials that earlier were part of PCBs.

Rush PCB makes printed circuit boards to meet the rising awareness towards RoHS compliance by meeting the demand for lead-free products that not only protects the user, but also minimizes their own carbon footprint. Furthermore, Rush PCB is foremost in manufacturing halogen- and lead-free PCBs, as their demand is rising rapidly.

With the rapidly shrinking size of SMD components, it is imperative the PCB has to also grow thinner and smaller. That implies everything on the PCB, including traces, spaces, and vias become smaller. Regular inspection techniques do not work for these miniature products, and Rush PCB has had to improve their PCB testing and inspection techniques to meet the miniaturization, and improve the quality throughout the entire manufacturing process.
Read more: Why You Need an HDI PCB?

PCBs for the Automotive Industry

The automotive industry offers a unique challenge to PCB manufacturers. When operating, the inner regions of an automobile exposes the PCB and the electronics to extremes of temperature cycling, bending, vibrations, humidity, and other stresses. The PCBs within an automobile is expected not only to function under these conditions, but also perform reliably over its lifetime. This requires PCBs made of special material that can handle these stresses. Rush PCB produces PCBs for the automotive industry that not only meet the present and upcoming challenges, but also cover testing and reliability.

For instance, automotive PCBs require handling high currents of several 100 A, with up to 1000 V, and information processing ranging to several GHz, for a lifetime of greater than 1000,000 hours. Rush PCB offers products that operate at higher voltages at small volumes. Their new PCBs with organic substances are suitable for power electronics and high-speed applications of vehicle computers and radar.

Of late, Rush PCB is experimenting with the option of all-polymer bondply and coverlay. Initially they had developed it for high-temperature applications by combining it with all-polyimide clads. The low loss characteristics of the new bonding film places it in the same range as the best all-polyimide clads. However, the new bondply requires high-temperature laminations, but offers the best options for high-speed circuits that also require to operate at high temperatures.

Conclusion

Rush PCB offers several types of materials for high-speed, high-temperature, and flexible circuits. The decision as to which material is the most suitable for a specific application depends on a number of tradeoffs such as electrical properties, mechanical properties, flexibility, and ease of processing. Rush PCB has extensive knowledge of the new materials and their processing techniques.

PCBs for Wearables and Ubiquitous Computing

Written by Rush PCB Inc on . Posted in PCB, PCB Manufacturing

The surge in popularity of fitness trackers and devices in the last few years has led to eminent PCB manufacturers such as Rush PCB produce Flex PCBs for wearable technology. The huge demand for smaller and lighter products has brought more focus on fulfilling the technical requirements through flex PCBs.

Applications in the medical sector offer an understanding of the scale of this opportunity. According to a report from the Global Industry Analysis, the US market for wearable medical technology itself is projected to be around $4.6 billion in value by 2020. The report says the major contributors to this trend is not only the growing number of diabetic patients, but the recent and future developments in flexible electronics benefiting innovation in wearable devices—implying more capabilities from the flex PCBs.

wearable smartwatch

Flexible PCBs

For this reason, Rush PCB has been pushing its experience with flex PCBs—from selecting the most suitable materials to achieving lines and spaces that are finer. They understand the challenges to both the designer as well as the supplier of coming up with the perfect flex PCB for a wearable application, whether entertainment, medical, or for some other vertical. That is the reason for Rush PCB going all out to ensure their flex PCB will properly support wearables in the rapidly growing market.

In a recent interview, an expert on flexible circuits from Rush PCB talked about some of the top emerging use cases for wearables including those designed for medical professionals and military personnel. Apart from being used in heart monitors, the latest flex PCBs from Rush PCB were evolving for applications including advanced wristwatches that will keep tabs on the respiratory and circulatory system of the wearer, sending data back to the relevant cardiologist.

The above implies that as the common flex application grows smaller, the PCB inside grows correspondingly tinier. This is the major cause of the significant challenges the designer and manufacturers face.

As the devices shrink in size, they are challenging the manufacturers to go for fine lines and spaces, thinner base material, and thinner copper. The demand for very thin, very small form factors is pushing the PCB manufacturers to their limits.

In this connection, Rush PCB has been experimenting with non-mainstream copper for use in flex PCBs. This will allow working around some limitations of the traditional alloys traditionally used. For instance, copper can become brittle over time, even when bent in a decent radius, and develop microcracks. Rush PCB is also experimenting with buildup copper rather than rolled copper in which the direction of grain is defined. Apart from addressing the issue of microcracks, buildup copper also helps achieve finer traces and lines. However, Rush PCB is yet to decide which of the two type of copper is more robust.

Rigid Flex PCBs

Most electronic circuitry require a rigid plate such as a PCB for connection and operation. However, the human body is highly flexible. Therefore, wearable medical devices need a mix of the two, which Rush PCB fulfils with its Rigid-flex PCBs.

The burgeoning wearable device market is increasing the demand for rigid-flex PCBs, as these combine the requirements of the flexibility and the rigidity of both the human body as well as the electronic components.

The healthcare industry is the largest segment of the market where wearable devices are making a mark. Apart from personal health use, wearable devices are being used for collecting several varieties of physiological data for study and diagnosis. For instance, wearables are available for monitoring muscle movement, ECG, glucose, blood pressure, heart rate, and more.

It has been the experience of eminent manufacturers such as Rush PCB that designers as well as fabricators face unique problems in flex and rigid-flex design and manufacture, most of which they do not face when working with rigid boards.

Need for 3-Dimensional Design

Although every PCB has three dimensions, flex and rigid-flex boards offer the ability of the entire assembly to bend and be folded to conform to the package of the product. Typically, the assembly requires the flexible circuitry to be folded so that it fits within the product package, occupying the space reserved.

This foldable design brings additional challenges, which go beyond connecting the rigid parts. The designer must arrange the bends precisely so that boards will line up to the location where the designer intends to mount them, while ensuring the connection points do not come under extra stress. Engineers at Rush PCB no longer use the traditional paper doll models for simulating the PCB assembly. Rather, they use modern Computer Aided Design (CAD) tools providing 3-D modeling of the rigid-flex assembly. The latter technique not only allows much higher accuracy, it also allows a faster design turnaround.

The new compact flex and rigid-flex design make the wearable small enough to attach directly to the patient with only a few necessary external links. They are now complex enough not only to collect a variety of data, but also provide some local analyses.

Complexity, Density, and Bending

Such additional requirements for making the wearable device unobtrusive enough to allow direct attachment to the patient, requires the flex PCB to be complex and its layout to be dense. Moreover, the board shapes often have to be either circular or of unusual shapes, which requires the designer make clever placement and routing. Engineers at Rush PCB use the latest PCB CAD tools optimized for rigid-flex designs to design such small and densely-packed boards, and it also makes it easy to handle the odd shapes.

Flexible circuitry is necessary where bending the flex gives final shape to the assembly. However, bending produces stresses in the flex, which the designers at Rush PCB avoid by using curves or piecewise-linear curves rather than using ninety-degree bends on traces. They also ensure traces on double-sided flex are staggered, and do not run on top of each other, to improve the flexibility. As flexibility of the substrate may lead to delamination over time, designers also use teardrop shaped pads rather than circular pads. The additional material provides greater strength to the pad, thereby avoiding delamination.

PCBs for Ubiquitous Computing

Ubiquitous computing is bringing the latest in lifestyle using mobile devices and inexpensive sensors. It is entering almost all aspects of human life, for instance, education, healthcare, personal communication, entertainment, and many more. With more than four and half billion active mobile phones all over the world, even the most mundane appliances can be transformed into smart devices.

Rush PCB makes prototype PCBs for ubiquitous computing, where their engineers examine the design, implementation, use and the usability of newer interfaces. These include human computer interface, privacy, and networking of devices and people, along with the physical characteristics and limitations of the devices. For this, they need to consider the form factor, power consumption, and heat dissipation.

For instance, research in electronic textiles (e-textiles) is considering integration of ubiquitous electronic and computational elements into fabric. The challenge is in the design, engineering, and construction of traditional hardware components such as flex PCBs to attach them to textiles. This requires design of fabric PCBs or iron-on circuits for attaching the electronic components directly to the fabric substrate.

The next challenge is to use electronic sequins for creating wearable displays and other artifacts, and using socket buttons for facilitating connecting pluggable devices to textiles.

Conclusion

Rush PCB has a long-term experience in manufacturing flex and rigid-flex PCBs used in wearables and ubiquitous computing for portable devices mainly used for carrying on the human body, in head-mounted displays, or in e-textiles. As wearable applications advance and become more widespread, Rush PCB is bound to keep pushing the envelope with their flex and rigid-flex PCBs.