Question & Answer

EPR wants to be your partner in design, production and knowledge. We think that knowledge is most valuable when shared. That’s why you can ask us a technical question on every Monday through social media or by email. We aim to provide you with an answer to that question that same week.

Out of all those questions asked, we will highlight one question on our social media every Monday. The next day one of our professionals will answer the highlighted question. Click on the buttons below to find the question of the week or to check out the archive with an overview of all questions and answers discussed before.

Do you have a pressing question waiting for an answer? Please feel free to ask us! You can contact us through our social media or by sending your question to contact@eprpartner.com.

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Question of the week

Question

In a PCB design, do you need to remove silkscreen info above pads?

Answer

Many PCB manufacturers routinely strip (or ‘clip’) silkscreen to the mask opening and not just to the copper pad. However, doing so can render silkscreen text unreadable. Being able to catch such occurrences through a Design Rules Check, allows you to manipulate offending silkscreen text prior to sending the board to manufacturing.

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Archive

Here you will find an overview of all questions and answers discussed before.

Question

Is it possible to generate electricity directly from heat?

Answer

A Thermoelectric Generator (TEG) is a solid state device that generates electricity from temperature differences. The operating principle is called the Seebeck effect which is related to the better-known Peltier effect. The efficiency is relatively poor but good enough to power a smartwatch or a remote sensor.

Recent discoveries show that a significant increase in efficiency is possible by using nanostructured thermoelectric materials or by taking the advantage of quantum effects. In the near future it seriously could help turning waste heat into usable energy.

Question

What is a super capacitor?

Answer

A super capacitor or Goldcap is a high-capacity capacitor with capacitance values much higher than other capacitors (but lower voltage limits). They can store 10 to 100 times more energy per unit volume than electrolytic capacitors. They can accept and deliver charge much faster than batteries and tolerate many more charge and discharge cycles than rechargeable batteries. Super capacitors are low voltage components with a rated voltage between 2.5 and 2.7V and the capacitances achieved can be as high as 12000F. Large super caps can be used in electric cars to recover braking energy for later use. Small super caps are used as memory backup for static random access memory.

Question

What is SKEDD?

Answer

SKEDD is a new Through-Hole connection technology. With SKEDD you do not need any soldering tools. The component fits direct into your PCB and makes a reliable contact (direct plug-in). SKEDD is mostly meant for Wire-to-Board and Board-to-Board connectors like IDC, signal and power connectors. No counterpart connector might be needed. It is also easy to remove and it is reusable. So, SKEDD is an ideal component when you have a PCB with a lot of SMD components and you need only one or a few Through-Hole connectors. Or perhaps as a removeable one-time programming connector.

Question

What is the role of the Printed Circuit Board (PCB) designer in a project?

Answer

The PCB designer acts as the hub of board design: a liaison between all stakeholders , balancing demands so all requirements are met. Think of electrical- and mechanical function, routability, reliability, thermal issues, design for manufacturing, design for assembly and design for test.

Question

Do we need a silkscreen on the PCB board?

Answer

On modern high-density manufacturing, silkscreen is meaningless. It could only fit partly the small components anyway – at least in a readable way. It’s uncertain to read, and hence, serves no purpose of “clarifying the design intent” for automated Pick&Place. But for manual (through-hole) soldering of a large components, it’s useful.

Question

Why should you test for EMC in an early stage?

Answer

  1. To avoid unexpected delays:There are a lot of reasons why the first EMC tests are often performed very late in a project. Postponing the discovery of EMC issues until the end will put their correction into a phase in the schedule that is probably the worst time to introduce unexpected delays.
  2. The cost element:
    Making changes to a design as your product is almost ready for production is more expensive than doing so earlier in the process. The costs of early screening tests are much lower than those of certification testing. The earlier you discover problems, the cheaper they are to fix.

Question

What are MEMS?

Answer

Mems are Micro-Electro-Mechanical Systems. In general they are miniaturized mechanical and electro-mechanical elements. They are fabricated using integrated circuit (IC) batch processing tecniques and can range in size from a few micrometers to millimeters.

Some examples of MEMS are:

  1. Pressure sensors
  2. Magnetic field sensors
  3. MEMS microphones
  4. Digital mirror devices used in a DLP projector
  5. Accelerometer used as airbag sensor

Question

How to route a small pitch Ball Grid Array Intergraded Circuit?

Answer

The problem with a small pitch BGA is that it is not possible to place vias between the pads of the BGA. Nor is it possible to route between the pads out of the BGA chip. The solution for creating a fanout for this type of BGA chip, is to place capped/blind vias inside the pads of the BGA. If you look from the top to the BGA, you will see normal pads. But beneath this pad is a via that makes it possible to route the BGA to the inner layers of a PCB. And this is the way to create a fanout for a small pitch BGA.

Question

What is Voltage Rating for a capacitor?

Answer

All capacitors have a maximum voltage rating and when selecting a capacitor consideration must be given to the amount of voltage to be applied across the capacitor. The maximum amount of voltage that can be applied to the capacitor without damage to its dielectric material is its working voltage. If the voltage applied across the capacitor becomes too high, the dielectric will break down (known as electrical breakdown) and arcing will occur between the capacitor plates resulting in a short-circuit. The working voltage of the capacitor depends on the type of dielectric material being used and its thickness.

In practice, a capacitor should be selected so that its working voltage either DC or AC should be at least 50 percent higher than the highest effective voltage to be applied to it.

Question

The Industrial Internet of Things is mainly about monitoring assets using remote wireless sensors. Does this mean that we’re facing an increased amount of battery operated electronics?

Answer

Batteries are an easy and cheap power source in remote sensor designs, but can be expensive to replace in terms of labor. Especially if the device is placed in a hard to reach location, self-powered wireless sensors are preferred. Depending on the situation different forms of energy harvesting technologies can be chosen: solar, RF, thermal or piezoelectric. Thanks to ultra-low-power MCUs and power management ICs specifically targeting energy harvesting applications, remote wireless sensors without a battery have a bright future.

Question

What happens if you do not specify a manufacturer part number (MPN) for capacitors in the bill of material (BOM)?

Answer

If you do not specify a MPN, then EPR will choose a type which will match form and function. But then it is very important for you that you have to specify at least the value, size, tolerance, voltage and dielectric. Let’s say you describe a generic capacitor with the value of 100nF, 0805, 20%, 50V, X5R. Then EPR is free to choose a capacitor from any brand and MPN that will match these values. We even may choose a better tolerance (10%), higher voltage (100V) or a better dielectric type (i.e. X7R or X8R). This will make us more flexible with the current shortage on the market of components these days! But keep in mind that if you do specify a MPN we will always use the one you have specified. And if that one is unavailable at on the market, we will come back to you to propose an alternative which you have to approve.

Did you know the only difference between X5R and X7R is that the X7R has a wider temperature span at a capacitance change of +/-15%? X5R ranges from -55 to +85 and X7R from -55 to +125 degrees. Please ask us if you would like to know more about dielectric types and classes.

Question

Why still use through-hole mounting instead of surface mounting components?

Answer

The great benefit of surface mounted components is that there is the possibility to place the components using a pick and place machine, whereas through-hole mounted components often need to be placed by hand. However, some applications demand the use of through-hole components. For example, the use of a connector. The use of a through-hole connector will create a much stronger connection with your PCB, which will make your product much more reliable. In addition, for applications that cause a lot of stress on a PCB or in situations with fast accelerations, through-hole is still used quite often. That’s also the reason that the military still uses this technology for many applications.

If you would like to read more about the use of through-hole mounting or surface mounting technology, read our blog “Basic principles of PCB assembly: Through-Hole vs Surface Mounted” from July: https://bit.ly/2v3orCm.

Question

Component placement, how is it done and what are the requirements? 

Answer

Component placement can be done manually or automatically. EPR prefers automatic placement because of the higher rate of component placement and accuracy. There are situations were it is not feasible and/or efficient to use pick and place equipment, for instance when only one Surface Mount Device (SMD) is used.

But when a fine pitch component is used (e.g. BGA, WLCSP), we will use the pick and place machinery because the demanding accuracy. For manual placement of the components we only need a good readable assembly drawing and the bill of materials. For automatic placement we need component location report, bill of materials and a good readable assembly drawing. There also need to be copper features on the Printed Circuit Board (PCB), so called fiducials, for component alignment.

Question

When to use a FET vs Transistor for switching on/off?

Answer

It depends mainly on the current to be switched. Generic transistors are OK for low current loads. FET’s are the best choice but need a series resistor to prevent ”snub” ringing due to the gate’s capacitance.

Question

Repair or replace defective industrial electronics?

Answer

We all know that most consumer electronics these days have become quite cheap. Once a serious defect introduces itself and the warranty period is over, most people buy new.

Industrial electronic units or PCB’s can be very expensive and in case of defect, a repair will be the best choice. For the less pricy industrial parts like generic Small PLC’s, driver cards and SMPU’s, a replacement seems the way to go, but in some cases tool owners end up having them repaired as well. Usually when parts get obsolete, or implementation of an alternative unit will imply a lot of work.

EPR-partner has extensive experience with unit and PCB repairs. We can carry out a preventive maintenance as part of the repair process. Obsolete parts can often be replaced by an alternative solution using a little engineering. In this way we take the best care of your company, your product and our environment.

Together we can create a more sustainable future.

Question

What does a class-d amplifier do?

Answer

A class-d amplifier is an amplifier with a high efficiency up to 90%-95% which converts an analog signal into a PWM signal.

The analog input signal is converted into a digital PWM (Pulse Width Modulation) signal using an analog input stage and PWM modulator. To drive the output power transistors, the digital PWM signal is fed to a control and handshake block and to high- and low side driver circuits. This level shifts the low power digital PWM signal from a logic level to a high power PWM switching between the main supply lines.

The amplifier output signal is a PWM signal with a typical carrier frequency between 250 KHz and 450 KHz.  A second order LC demodulation filter on the output is used to convert the PWM signal into an analog audio signal that can be used to drive a loudspeaker.

Question

How to create a fanout for a 0.35 mm pitch BGA?

Answer

The problem with a 0.35 mm pitch BGA is that It’s not possible to place vias between the pads of the BGA. Nor is it possible to route between the pads out of the BGA chip. The solution for creating a fanout for this type of BGA chip, is to place capped/blind vias inside the pads of the BGA. If you look from the top to the BGA, you will see normal pads. But beneath this pad is a via that makes it possible to route the BGA to the inner layers of a PCB. And this is the way to create a fanout for a 0.35 mm pitch BGA.

Question

How do you protect your printed circuit board assembly (PCBA) against environmental influences?

Answer

After assembly and test of your PCBA we can apply a conformal coating that will protect the PCBA against moisture , chemicals, dust and more depending on the type used. Another option is to mount the PCBA into a case. This case can be an of the shelf IP65 rated case or a tailor made solution. It is also possible to encapsulate your PCB in resin. The resin provides good protection against harsh environments and mechanical stress. All options have their advantages and disadvantages. Which option suits the best for your product depends on the requirements.

Question

What is the smallest component EPR can assemble on a PCB?

Answer

EPR can place 01005 type of capacitor and resistor components which is metric 04mm by 0.2mm. For IC’s like BGA’s and WLCSP a pitch of 350um with a pad size of 220um by 220um is reliable to produce.

Question

Why should we consider using GaN technology instead of silicon MOSFETs in power conversion applications?

Answer

GaN offers several key benefits and advantages when it comes to power density:

  1. Lower RDS(on): GaN has half the RDS(on) per area compared to MOSFETs. This translates to 50% lower conduction losses. Therefore, you can use smaller heat sinks and simpler thermal management.
  2. Lower gate and output charge: GaN technology offers a lower gate charge enabling designs with much faster turn-on times and slew rates, while reducing losses. A lower output charge results in two advantages to each design. First, the switching losses drop by as much as 75%, which in combination with lower conduction losses, has a major and positive impact on power density. Second, the design can run at up to 10X higher switching frequencies (depending on the application). This significantly reduces the size of magnetics as well as the size and footprint of designs, while improving overall efficiency by as much as 15%.
  3. Zero reverse recovery: Silicon MOSFETs have a typ. reverse-recovery charge in the 40- to 70-nC range (depending on their size and characteristics). When a MOSFET turns off, the reverse-recovery charges (Qrr) in the internal diode will produce losses that add to the total system switching losses. These losses rise proportionally with the switching frequency. GaN has zero reverse recovery and no Qrr losses, making GaN FETs ideal for applications which use a high switching frequency.

Question

What issues do you have to address when using an Li-ion battery?

Answer

Nowadays Li-Ion batteries are very popular as power source or even as back-up for electronics. Ni-MH and NiCad batteries are old.

The advantage of Li-Ion batteries is that the self-discharge is very low and the energy density is high. The disadvantage is that additional protection is needed to address hazardous situations. The battery needs over charge protection as well as under discharge protection. When more Li-Ion cells are put in a chain charging and discharging is becoming even more complex because of unbalance during longer operation time. A BMC (Battery management Controller) can be used to address these issues. The nominal voltage of a Li-ion cell is about 3,7 Volt. Completely charged a cell will be 4.2 Volt. An Over voltage Protection Circuit (OVP) will protect this. Also a Li-Ion cell may not be discharge completely. An Under voltage Protection Circuit (UVP) will protect this. Furthermore the Li-ion battery must be protecting from over current charging and discharging. Adding a temperature sensor will help as an indication for over current. All this means a lot of design choices and effort must be made. Lucky for us that there are a lot of manufacturers who do have special IC’s to address these issues!

Question

What is a proper way to route high-voltage tracks near the components?

Answer

Make use of proper design rules to be sure that distances are maintained.

If the design has voltages above 750V, the type of solder mask should be adapted too.

Question

Via in between differential traces – how bad is it?

Answer

In a high-speed printed circuit board (PCB), a via is notorious for degrading signal-integrity performance. However, using via structures is unavoidable. In a typical board, components are placed on the outer layers, while differential pairs are routed in inner layers where they lower electromagnetic radiation and pair-to-pair crosstalk. Vias must be used to connect components on the board’s surface to the inner layers. Vias generally look capacitive. minimizing the annular rings and increasing the antipad diameter will help make the via look transparent. a good rule of thumb is to avoid all asymmetries in a differential pair. Whatever you do to one trace, do the same to the other.

Question

Are you using tantalum capacitors on your design?

Answer

In the past tantalum capacitors where very popular in SMPS (Switch mode power supplies) designs because of Low ESR value combined with high capacity at small size. The downside is that they are expensive and are less reliable. In the past we’ve seen a lot of shortened and exploded tantalum caps! Probably due to surge currents.

Today there are a few alternatives like MLCC and the new Niobium Oxide (NbO)capacitors. Niobium Oxide exactly looks like the old tantalum, however they are will not burn at overloads and are thus more safer. The price is roughly the same. Multi-Layer Ceramic Capacitors (MLCCs) have no temperature derating, are non-polarized, do have a wider bandwidth and a lower ESR at high frequencies. At low frequencies you could better choose for NbO or aluminum electrolytic capacitors.

Question

How do you plan routing and what are the parameters you consider while routing?

Answer

Routing is the next step after placement of most of the components. During placement consider all the main signals. These signals can be restricted in width and clearance, driven by their maximum current or signal impedance. In the routing phase always keep your applications signal in mind. Including ground planes, supplies and traces with less importance.

Question

How do you verify schematic symbols or footprints?

Answer

Verifying schematic symbols can be done by using the datasheet of the component. But keep in mind that schematic symbols can be drawn on several ways. You can choose between European or US standard or use a mix. In principle it doesn’t matter as long as the schematic symbol is build-up in a logical way and the function is easy to understand. You may choose to split the power part and put them together with all the other power parts at the bottom of the schematic page. In order to perform electrical rule check (ERC) it is a good practise to define all the component signals like Input, output, passive, etc. It is wise to put no-connect signals on not used pins. This will not generate errors when inputs are not connected. Of course you have to check the datasheet if inputs might become floated.

To verify footprints is a more important story. Your product might become not or less producible when an error has been made. The IPC-7351 describes the requirement for SMD land patterns and IPC-7251 for through hole land patterns. To create your PCB shape you may use a IPC footprint wizard like Library Expert or if available use a build-in tool from your (EDA) lay-out program. Most likely you’ll also find the footprint in the datasheet of a specific component. We prefer to use the datasheet footprint if available.

You always want to double-check if your shape is OK. The best principle is a four-eyes check. Even when you download components from the internet. For a lot of components like connectors there are 3D-shapes available on the internet. A good verification point is when placing this 3D-shape over your footprint. At that moment you have a verification check as well.

On the market there are also DfM (Design for Manufacturing) tools like Valor, GC-, Vayo, that will check your fabrication output on footprints.

Question

What are the four main categories of signal integrity problems?

Answer

The first category is best described as: signal reflections. Signals are reflected and distorted whenever the instantaneous impedance the signal ‘sees’ changes, thus the solution to this issue is to provide a signal with a constant instantaneous impedance. In PCB design this can be achieved by controlling the impedance of the interconnects. The second category is what is referred to as cross talk or signal coupling. Signal coupling arises from the magnetic and electric coupling of adjacent signal paths, such as two traces and their respective return paths on a PCB. By minimizing the mutual capacitance and inductance between the signal paths, one can minimize the amount of coupled signal. Or more practically, space the signal paths apart sufficiently to minimize magnetic coupling and minimize coupled surface to minimize electric coupling. The third main source of signal integrity problems is electromagnetic interference or more commonly known as EMI. One can simplify EMI by looking at electronics as an antenna, in the perspective of both being a transmitter as well as a receiver. By minimizing signal loop surfaces one can minimize the amount of electromagnetic radiation the signal loop emits or can receive. More practically, in PCB design this can be done by placing decoupling capacitors as close to ICs as possible and minimizing the thickness of the dielectric to their ground plane. The last category refers to something which is commonly known as rail collapse. This issue occurs in the power distribution networks (PDN) of an electrical circuit. Interconnects are never as perfect as described in most circuit diagrams, but instead have an impedance. The current flowing through the PDN to feed all the elements in the network will cause a voltage drop across the power and ground rails, meaning a deviation in the actual voltage values of the rail. By lowering the impedance of the PDN one can minimize the so called rail collapse. One way of achieving this would be to keep supply and ground traces in a PCB as wide as possible.

Question

How do you incorporate Design for Excellence (DfX) in your engineering flow?

Answer

EPR Partner has many years of experience in engineering and assembly of advanced printed circuit boards for the semiconductor, medical and many more markets. One of our success factors is the implementation of Design for eXcellence (DfX) in our partner’s product lifecycle.

But how do we incorporate this in our engineering flow? The key to success is getting involved in an early stage of the development phase. Our NPI Engineers can advise on product requirements for example to improve yield by implementing Design for Manufacturing (DfM), Assembly (DfA) and Test (DfT). Often design for Logistics (DfL) is implemented during the design stage and led by product requirements such as physical restrictions. When all requirements are clear our engineers can help our partner with co-engineering to decrease time to market and get the design first time right! Design for Cost (DfC) and reliability (DfR) are implemented in several stages of the design and production process, ranging from component and material determination up to supplier selection. The design and implemented DfX are verified by our suppliers, manufacturers and customers, as well as through the use of tooling.

Question

What is more critical on a logic input: a pull-up or a pull-down resistor?

Answer

A pull-up resistor connects unused input pins (Logic gates) to the dc supply voltage (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins to ground (0V) to keep the given input LOW. The resistance value for a pull-up resistor is not usually that critical but must maintain the input pin voltage above VIH. The use of 10kΩ pull-up resistors are common but values can range from 1k to 100k ohms.

Pull-down resistors are a little more critical because of the low input voltage level, VIL(max)and the higher IIL current. The use of 100Ω pull-down resistors are the most common but they can range in resistive value from 50 up to 1k ohms.

The correct answer is: a pull-down resistor is more critical.