Category Archives: Circuit Boards

What is a PCB Via and How is it Made?

Vias are actually holes drilled into PCB layers and electroplated with a thin layer of copper to provide the necessary electrical connectivity. Three most common types of plated through via are in use—plated through holes, blind holes, and buried holes—with plated through holes running through all the layers of the PCB. These are the simplest type of holes to make and the cheapest. However, they take up a huge amount of PCB space, reducing the space available for routing.

Blind vias connect the outermost circuit on the PCB with other circuits on one or more adjacent inner layers. As they do not traverse the entire thickness of the PCB, they increase the space utilization by leaving more space for routing.

Buried vias connect two or more circuit layers in a multi-layered PCB, but do not show up on any of the outer layers. These are the most expensive type of vias and take more time to implement, as the fabricator has to drill the hole in the individual circuit layer when bonding it. However, designers can stack several buried vias in-line or in a staggered manner to make a blind via. Therefore, buried vias offer the maximum space utilization when routing a PCB. Fabricators of high-density interconnect (HDI) boards usually make use of buried vias, most often using lasers for drilling them.

Drilling a Via

At positions for the vias, the fabricator drills holes through the PCB using a metal drill of small diameter. He or she then cleans the hole, de-smears it, and de-burrs it to prepare it for plating. Rather than removing copper as is normally the case with the etching process, the fabricator then adds a thin layer of copper to the newly formed hole through a process of electroplating, thereby connecting the two layers. For a two-layer board, the fabricator then etches circuit patterns on both sides. Via usually have capture pads on both layers.

The process of drilling a via hole using a laser is somewhat different. In general, fabricators use two types of lasers—CO2 and UV—with the latter able to make very small diameter via holes. UV laser-drilled via holes are about 20-35 µm in diameter. As the laser beam is able to ablate through the thin copper layer, capture pads with a central opening are not necessary. Most fabricators program a two-step process for drilling a hole with a laser beam.

In the first step, a wider-focused laser heats the top copper layer, driving the metal rapidly through the melt phase into the vapor phase prior to gas-dynamic effects expelling it from the surface. The laser repeats this for all via positions on the PCB layer.

In the next step, the program focuses the beam tightly and controls the depth the laser can burn. For blind vias, It allows the laser to burn through the intervening dielectric and stop when it has reached the bottom copper layer, before moving on to the neighboring via position.

The same process of electroplating as above deposits a thin layer of copper along the walls of the holes left behind by the laser beam, thereby connecting the two layers. The rest of the process for etching the circuit pattern on the two sides remains the same.

How useful are PCB Vias?

Designers use a plated through via as a conduit for transferring signals and power from one layer to another in a multi-layer printed circuit board (PCB). For the PCB fabricator, the plated through via are a cost-effective process for producing PCBs. Therefore, vias are one of the key drivers of the PCB manufacturing industry.

Use of Vias

Apart from simply connecting two or more copper layers, vias are useful for creating very dense boards for special IC packages, especially the fine-pitch components such as BGAs. BGAs with pitch lower than 0.5 mm usually do not leave much space for routing traces between neighboring pads. Designers resort to via-in-pads for breaking out such closely spaced BGA pins.

To prevent solder wicking into the via hole while soldering and leaving the joint bereft of solder, the fabricator has to fill or plug the via. Filling a via is usually with a mixture of epoxy and a conductive material, mostly copper, but the fabricator may also use other metals such as silver, gold, aluminum, tin, or a combination of them. Filling has an additional advantage of increasing the thermal conductivity of the via, useful when multiple filled vias have to remove heat from one layer to another. However, the process of filling a via is expensive.

Plugging a via is a less expensive way, especially when an increase in thermal conductivity does not serve additional value. The fabricator fills the via with solder mask of low-viscosity or a resin type material similar to the laminate. As this plugging protects the copper in the via, no other surface finish is necessary. For both, filled and plugged vias, it is important to use material with CTE matching the board material.

Depending on the application, fabricators may simply tent a via, covering it with solder mask, without filling it. They may have to leave a small hole at the top to allow the via to breathe, as air trapped inside will try to escape during soldering.

Trouble with Vias

The most common defect with vias is plating voids. The electro-deposition process for plating the via wall with a layer of copper can result in voids, gaps, or holes in the plating. The imperfection in the via may limit the amount of current it can transfer, and in worst case, may not transfer at all, if the plating is non-continuous. Usually, an electrical test by the fabricator is necessary to establish all vias are properly functioning.

Another defect is the mismatch of CTE between the copper and the dielectric material. As temperatures rise, the dielectric material may expand faster than the copper tube can, thereby parting the tube and breaking its electrical continuity. Therefore, it is very important for the fabricator to select a dielectric material with a CTE as close as possible to copper.

Vias placed in the flexing area of a flex PCB can separate from the prepreg causing a pad lift and an electrical discontinuity. It is important designers take care to not place any vias in the area where they plan the PCB will flex.

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.

What is the Automatic Test Equipment PCB?

Targeted towards verification of the functionality of a specific semiconductor chip, all major test activities use an automatic test equipment printed circuit board (ATE PCB) or simply a test board. Testing semiconductor chips with advanced functionality is necessary for manufacturers to ensure their reliability and functionality to OEM customers, and establish they operate according to their specifications.

In simple terms, the ATE PCB serves as an interface between the specific semiconductor chip and a large test system. The design and assembly of ATE PCBs allows testing an array of a large variety of semiconductor chips that includes field-programmable arrays, system-on-a-chip, memory chips, microprocessors, micro-controllers, and many more. As semiconductor chips are complex, the design and assembly of one ATE PCB makes it capable of testing only one particular type of chip set at a time.

Chipmakers employ a group of experienced project and program managers, along with highly trained engineering personnel for designing and assembling ATE PCBs to achieve the unique chip-testing quality. For this, conventional PCB assembly knowledge and experience is not adequate, and requires enhanced assembly line technical expertise along with highly disciplined administration management. Any misstep towards a successful completion of an ATE PCB can result in considerable loss of time-to-market along with a huge monetary loss.

Compared to conventional commercial and industrial PCBs, ATE PCBs are considerably different, and chipmakers usually differentiate them in three main ways—their larger size, number of layers, and the extra processes necessary. ATE PCBs are highly reliable and extremely robust, and their fabricators take special care to free them of assembly process residues and debris.

As the ATE PCB is so different, it is also difficult to make. This requires program managers associated with ATE PCB projects to have knowledge beyond that required for conventional PCBs, including all the nuances associated with ATE PCBs. They need to understand unconventional illustrations and diagrams, as these are the hallmark of projects involving ATE PCBs.

At the same time, technical personnel associated with the assembly of an ATE PCB need high-level knowledge and skill-set. This includes relevant hardware, tester orientation and configuration, stiffeners, cables, and other paraphernalia related to the ATE PCB. Both the assembly engineers and program managers must thoroughly understand the electronic format input required for designing a custom ATE PCB.

Unlike the netlist format conventional PCBs use, the input for ATE PCBs is usually in the form of map drawings, bitmaps, and ball maps. That means assembly engineers and program managers must be fully capable of creating the appropriate netlist after translating the original data from these unconventional methodologies.

As the ATE PCBs are large, typically measuring 12 x 10 inches or 14 x 14 inches, the pick-and-place systems for assembling these PCBs are also unlike those for populating conventional PCBs. They are capable of handling and populating large footprint boards, such as 20 x 24 inches to 26 x 30 inches.

These pick-and-place machines are extremely precise and highly accurate. Some of the latest machines can easily populate a board with 32 thousand components per hour at 21-µm fine-pitch repeatability. Such advanced machines also have the capability of selective or spot soldering.

Where Would You Apply Crowbar Protection?

Crowbar is an appliance typically used by construction workers. It is a heavy steel rod with one of its ends pointed and the other shaped like a spatula – both very useful for digging or breaking up construction rubble. Normally, one would not associate such a crude instrument for use by engineers dealing in electronics, were it not for one unusual property of the crowbar. Throw it across a power line, whether accidentally or with a purpose, and the power line trips – a fail-safe arrangement to protect the load in case of an emergency.

In electronics, a crowbar protection is generally an electronic circuitry placed across the outputs of a power supply. It activates to protect the load against overvoltage. When it activates, it shorts the output terminals – the crowbar action. This serves to blow the fuse, trip the circuit breaker or to shut down some part of the circuit so that power to the load is cut off. Most power supplies, whether low- or high-voltage, employ this kind of protection.

The crowbar protection circuit has a sensor that monitors the output voltage of the supply, comparing it against a preset value. When an overvoltage occurs, it triggers the crowbar circuit, which in turn short circuits the output terminals, thereby cutting off power to the load.

Crowbar devices typically use one of two types of components as their main protection. These are the Silicon Controlled Rectifier or SCR, and the Metal Oxide Semiconductor Field Effect Transistor or MOSFET. The design of the monitoring circuit of the crowbar depends on the sensitivity of the load circuit to be protected. For instance, the reaction time of the monitoring circuit depends on how long the protected circuit can survive the excess voltage without damage, and the response time of the main protection device.

Several fault-conditions may lead to possible over voltages. These include a fault in either the power supply or the load, and operator error. Present day electronics are sensitive and often operate at very low voltages with small margin. That makes it imperative to ensure that the safe voltages are not exceeded, and sensitive and expensive equipment remain undamaged.

Although blowing the fuse is a popular method of protecting a circuit, it has its disadvantages. Recovery is only possible by manually replacing the fuse, once the fault condition is repaired. This is a time consuming affair, and not helpful for low downtime appliances. Therefore, most engineers prefer a fold-back type of crowbar protection.

In a typical crowbar protection, the entire load current is diverted from the load and directed to the short circuit across the output terminals. This is constant current limiting and puts the fuse under tremendous stress, causing it to blow, thereby protecting the power supply and its load. In contrast, with the fold-back crowbar protection, the load current through the short circuit reduces once the crowbar has activated and shorted the outputs.

The short circuit current reduces to the extent that the power dissipated by the supply can remain within its safe operating area. This prevents the fuse from blowing, and at the same time, the power supply keeps the load circuit safe because of the crowbar action. As soon as the cause of the overvoltage is repaired, the power supply resumes automatically.

What is Vapor Phase Reflow Soldering?

Vapor Phase Reflow Soldering is an advanced soldering technology. This is fast replacing other forms of soldering processes manufacturers presently use for assembling printed circuit boards in high volumes for all sorts of electronic products. Soldering electronic components to printed circuit boards is a complex physical and chemical process requiring high temperatures. With the introduction of lead-free soldering, the process is more stringent, required still higher temperatures and shorter times. All the while, components are becoming smaller, making the process more complicated.

Manufacturers face soldering problems because of many reasons. Main among them is the introduction of lead-free components and the lead-free process of soldering. The other reason is boards often can contain different masses of components. The heat stored by these components during the soldering process varies according to their mass, resulting in uneven heat distribution leading to warping of the printed boards.

With Vapor Phase reflow soldering, the board and components face the lowest possible maximum temperatures necessary for proper soldering. Therefore, there is no overheating of components. The process offers the best wetting of components with solder and the soldering process happens in an inert atmosphere devoid of oxygen – resulting in the highest quality of soldering. The entire process is environment friendly and cost effective.

In the Vapor Phase Reflow Soldering process, the soldering chamber initially contains Galden, an inert liquid, with a boiling point of 230°C. This is same as the process temperature for lead-free Sn-Ag solders. During start up, Galden is heated up to its boiling point, causing a layer of vapor above the liquid surface, displacing the ambient air upwards. As the vapor has a higher molecular weight, it stays just above the liquid surface, ensuring an inert vapor zone.

A printed circuit board and components introduced in this inert vapor zone faces the phase change of the Galden vapor trying to cool back its liquid form. The change of phase from vapor to liquid involves the release of a large amount of thermal energy. As the vapor encompasses the entire PCB and components, there is no difference in temperature even for high-mass parts. Everything inside the vapor is thoroughly heated up to the vapor temperature. This is the biggest advantage of the vapor phase soldering process.

The heat transfer coefficients during condensation of the vapor ranges from 100-400Wm-3K-1. This is nearly 10 times higher than heat transfer coefficients involved in convection or radiation and about 10 times lower than that with contact during liquid soldering processes. The excellent heat transfer rate prevents any excessive or uneven heat transfer and the soldering temperature of the vapor phase reflow process stays at a constant 235°C.

There are several advantages from the Vapor Phase Reflow Soldering process. Soldering inside the vapor zone ensures there can be no overheating. As the vapor completely encompasses the components, there are no cold solders due to uneven heat transfer and shadowing. The inert vapor phase process precludes the use of nitrogen. Controlled heating up of the vapor consumes only one-fifth the usual direct energy consumption, and saves in air-conditioning costs.

As the entire process is a closed one, there is no creation of hazardous gasses such as from burnt flux. Additionally, Galden is a neutral process fluid and environment friendly.

What are Wearable PCBs Made of?

The Internet of Things market is growing at a tremendous speed. Among them, wearables represent a sizeable portion. However, there are no standards governing the small size PCBs or Printed Circuit Boards for these wearables. The unique challenges emerging in these areas require newer board level development and manufacturing experiences. Of these, three areas demand specific attention – surface material of the boards, RF or microwave design and RF transmission lines.

Surface material of the boards

PCB materials are typically composed of laminates. These can be made of FR4, which is actually fiber-reinforced epoxy, of polyamide, Rogers’s materials of laminates, with pre-preg as the insulation between different layers.

It is usual for wearables to demand a high degree of reliability. Although FR4 is the most cost-effective material for fabricating PCBs, reliability is one issue the PCB designer must confront when going for a more expensive or advanced material.

For example, with applications requiring high-speed and high frequency operation, FR4 may not be the best answer. While FR4 has a Dk or dielectric constant of 4.5, the more advanced Rogers series materials can have a Dk of 3.55-3.66. The designer may opt for a stack of multilayer board with FR4 material making up the inner cores and Rogers material on the outer periphery.

You can think of the Dk of a laminate as the capacitance between a pair of conductors on the laminate, as against the same pair of conductors in a vacuum. Since there must be very little loss at high frequencies, the lower Dk of 3.66 for a Rogers’s material is more desirable for high frequency circuits, when compared to FR4, which has a Dk of 4.5.

Typical wearable devices have a layer count between four and eight. With eight layer PCBs, the layer structuring offers enough ground and power planes to sandwich the routing layers. That reduces the ripple effect in crosstalk to a minimum, while significantly lowering the EMI or electromagnetic interference. For RF subsystems, the solid ground plane is necessarily placed right next to the power distribution layer. This arrangement reduces crosstalk and system noise generation to a minimum.

Issues related to fabrication

Tighter impedance control is an important factor for wearable PCBs. This results in cleaner signal propagation. With today’s high frequency, high-speed circuitry, the older standard of +/-10% tolerance no longer holds good and signal-carrying traces are now built to tolerances of +/-7%, +/-5% or even lower. This influences the fabrication of wearable PCBs negatively, as only a limited number of fabrication shops can build such PCBs.

High-frequency material such as Rogers require to have a +/-2% of Dk tolerance and +/-1% is also a common figure. In contrast, for FR4 laminates it is customary to have Dk tolerances of +/-10%. Therefore, Rogers’s material presents far lower insertion losses when compared to FR4 laminates.
In most cases, low cost is an essential factor. Although Rogers’s material offers low-losses with high-frequency performance at reasonable costs, commercial applications commonly use hybrid PCBs with FR4 layers sandwiched between Rogers’s material. For RF/microwave circuits, designers tend to favor the Rogers’s material over FR4 laminates, because of their better high-frequency performance.

How to solder like a pro

Manual soldering is a skill that gets better with practice. For those who are starting out for the first time, manual soldering can be risky, unless they take proper care and follow safety instructions. Manual soldering involves application of heat locally by a soldering iron, whose tip may reach temperatures as high as 400°C. Soldering materials are sometimes toxic, especially if using lead based solders. Some very useful information about soldering can be found here.

One of the best tips to follow for both starters and experienced people is to don safety glasses before starting to solder. This is something that should become a habit for everyone who is soldering, because hot solder entering the eye can be dangerous. A wire, bent the wrong way, can easily flick hot solder into the air. When cutting a component leg, the cut piece can travel at high speeds. Safety glasses will save the eyes from all these flying missiles.

For most people, soldering skills will not be very good at first, but will certainly improve over time. There is no magic in making perfect solder joints every time, you will simply get used to how to hold things, when the iron is hot enough and the feel for how long you need to apply the heat on.

One basic question that comes up often is whether people ought to use leaded solder or unleaded solder. Leaded solder is composed of Tin (Sn) and Lead (Pb), typically in the ration 60:40, with lead being added to bring down the melting point of the composition to about 180°C. However, Lead being unsuitable to human health, has led to creation of unleaded or lead-free solders. The composition of lead-free solder varies, but in general, these have a higher melting point, nearer to 240°C.

The lower melting point of leaded solder makes it easier for soldering work, and beginners find it easier to practice with. Unleaded solder also has a more corroding effect on the tip of the soldering iron, so you need to change the tip more frequently if you are doing a lot of soldering with unleaded solder. For fine electronics soldering, it is preferable to use a thin gauge of solder wire such as 0.7mm in diameter. Thicker solder is intended for heavier electrical work.

For solder to melt and flow easily, a chemical compound is used; this is called Flux. Usually, the solder wire has a hollow core, in which flux is filled. As you heat the solder wire, flux melts first and helps solder to melt and flow. However, melting flux releases fumes that although not harmful in small quantities, it is advisable to avoid breathing in.

Soldering should preferably be done in a large, well-ventilated room. If that is not possible, a fume extractor or even a fan should be used to draw the fumes away. The tip of the soldering iron should be kept clean and well wetted with solder. This keeps the tip in good condition for a longer time, preventing pitting. For cleaning the tip, use a wet sponge or some wire wool. Wire wool can be used to clean the surfaces to be soldered, resulting in faster and better-soldered joints.

Solder Sucker for Desoldering – New product alert!

Solder Sucker

Solder Sucker

We’re always adding new electronic components, parts and supplies to our inventory. This week, one of our new products is a solder sucker, which is a ‘must have’ for anyone that works with electronics and solder.

Crafted in Germany by Amax, this solder sucker is a pump style solder remover. Use it on heated solder to remove the solder from your boards and components. It comes in the original manufacturer’s packaging with instructions for the use and care of your solder sucker.

Here are some basic desoldering instructions:
1. Heat your soldering iron. Push down on the plunger until it clicks to arm the soldering iron.
2. Clean your soldering tip. Place the soldering tip on the side of the old joint. Apply some fresh solder on the old joint to help the old solder soften.
3. Set the plunger on the solder sucker. Place the tip of the solder sucker on the old joint as close as possible to the soldering tip.
4. Release the plunger by pressing the button.
5. Repeat until much of the old solder is gone.
6. If any of the old solder is left in PCB holes, you can heat the old joint again and using the soldering tip on one side and a miniature flat screwdriver on the other, gently rock the joint back and forth lightly to loosen up the tiny leads on the components.
7. You may need to repeat this process again when there is a stubborn joint.
9. Remove your component carefully; taking care to not damage the board.