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What is the importance of PCB silkscreen and solder mask in PCB design and prototyping?

By Mer-Mar Electronics | Date posted: | Last updated: September 19, 2022
Solder Mask vs Silkscreen

When it comes to PCB design and eventual prototyping, two aspects that are very important, but may not get the discussion they deserve are Solder Mask & PCB silkscreen. Let us look at the difference between solder masks and silkscreen and each of them in detail.

Silkscreen VS Solder Mask

What is solder mask in PCB?

Also referred to as a solder resist, a solder mask is a thin polymer. When applied to the surface of the PCB it helps seal the copper from environmental conditions. Essentially a solder mask performs two essential tasks. First, it helps prevent oxidation & second it ensures that solder bridges are not formed. If oxidation does happen it impacts the electrical property of copper. In turn, this affects the functioning of the PCB.

A solder bridge refers to an electrical connection between two conductors. When a solder mask is used it prevents this from occurring. A solder mask becomes particularly important for mass-produced boards where the soldering is done automatically by way of reflow or wave solder techniques.

A solder mask is available in a wide variety of colors. Additionally, it also comes in different media ranging from epoxy liquid to liquid photo imageable solder mask inks as well as dry film photo imageable solder masks. LPSM can be either sprayed on the PCB or silkscreened. When it comes to DFSM, it is typically vacuum laminated on the PCB followed by developing it.

Function of Solder Mask in PCB Design

To sum up, the functions of a solder mask layer include:

  • Ensuring that the conductor circuit doesn’t break physically.
  • Ensuring that there is no short circuit from the bridge connection during the process of soldering.
  • Ensuring that oxidation doesn’t happen on the copper layer.
  • Ensuring that there is no short circuit between conductive lines and solder joints.

Silkscreen

While a silkscreen is often seen as a not so important layer at first glance since it does not impact the electrical functionality of a PCB, the fact remains that it provides valuable information that can make or break the functioning of the PCB.

A silkscreen in PCB is typically used to transmit the following information:

  • It states the location of the parts with the use of reference designators.
  • It helps identify test points.
  • It offers identification numbers unique to each board.
  • It offers warning symbols.
  • Ensures polarity of parts.

When a PCB is being assembled, the information provided by the silkscreen is invaluable as among other things, it ensures that the components are correctly placed. In cases where a silkscreen is not available an assembly drawing becomes imperative.

The silkscreen also plays an important role in PCB testing as it provides the engineer with the location where measurements are to be taken, during the process of testing. This can go a long way in finding out the causes of potential failure. Some of the markings of the silkscreen used for testing include:

  • Test points – These indicate the location on the board where the desired values are known.
  • Warning symbols – These warning markings come in handy as they indicate areas such as a high voltage point.
  • Part numbers – In case a datasheet is not present it provides device information.

How silkscreen applied on PCB?

A silkscreen is applied on the PCB in three ways:

  • Manual Screen Printing (MSP)
  • Liquid Photo Imaging (LPI)
  • Direct Legend Printing (DLP)

How to ensure accuracy of silkscreen?

The importance of a silkscreen in ensuring PCB accuracy is undisputed. What is important is that the silkscreen should be accurate. Some tips to be followed that ensure accuracy of a silkscreen include:

  • Using fonts that work for the PCB contract manufacturer.
  • Using colors that are readable.
  • Following the dimension guidelines so that the silkscreen is not covered by components.

To sum up, both solder masks & PCB silkscreens play important roles in ensuring that the functioning of the PCB isn’t affected, albeit in different ways.

To get quality-based PCB design and manufacturing, contact us at sales@mermarinc.com or call us at (760) 244-6149. We provide PCB manufacturing services with a quick turnaround time. You can fill out the form below to initiate your PCB prototyping and PCB designing according to your requirement.

Top PCB layout tips and tricks to relieve the swelling of post-assembly rework

By Mer-Mar Electronics | Date posted: | Last updated: May 25, 2022
PCB Layout Tips

Once the PCB components are placed on the board and routed, any requirement that calls for a sizeable amount of rework, can prove to be extremely cumbersome. Not only does it take time that in turn impacts go-to-market and impacts your competitive advantage, it also comes at a cost. Additionally, if your board hasn’t been designed to support rework, it makes the job even more difficult. In such cases, rework can also impact other sensitive parts in the vicinity and lead to further complications.

Fortunately, there are some handy PCB layout tips and tricks, which if followed, can go a long way in reducing the amount of rework required.

Before we look at these tips, it will be worthwhile to examine what are some of the PCB rework issues that are typically encountered:

Typical PCB Rework Issues

Part Replacement – Sometimes a wrong part may have been initially specified. A seemingly small lapse, it leads to wasted time, effort and costs.

Defects in Assembly – A big part of the rework is required when parts haven’t been soldered correctly during assembly. Sometimes these PCB soldering issues can be on account of improper DFM clearances or incorrect component locations.

Inaccessible Parts – Sometimes it is hard to replace parts or rework them, on account of the fact that the parts are either too close to other parts or sometimes even hidden. If the part is positioned in a manner that tools cannot reach them, it can be a big issue that can impact rework.

Damage – Parts that are placed very close to the components that need rework can also be damaged. The damage can happen on account of heat of soldering reaching these parts or any physical damage while replacing other parts. The rework process therefore may lead to reworking on these collateral damages too.

Needless to mention that rework also becomes a deterrent when you are chasing a deadline and also trying to keep things under budget.

PCB layout Tips to reduce post assembly rework

Here are top handy layout tips that when implemented well can go a long way in avoiding or minimizing rework issues:

  • Accurate BOM – Now this is a gold standard when it comes to avoiding rework. Sometimes the part information in the design isn’t updated or the schematic isn’t synchronized with the layout. In turn, it leads to reworking incorrect parts. It is imperative, therefore, that the BOM is totally in sync with the PCB design and layout.

  • DFM guidelines – A lot of the rework related to parts being placed in the wrong location or parts not soldered correctly can be avoided if the DFM guidelines are clearly specified and are followed accurately.

  • Room for rework – High density of parts is a function of miniaturization of devices. The components also need to be placed tightly together to ensure signal integrity. However given these constraints it is important to allow some room for rework. The PCB contract manufacturer will be in the best position to offer recommendations to be able to incorporate room for rework within the constraints.

The need to choose the right PCB contract manufacturer

As the complexity of a printed circuit board increases, so does the potential for rework. The right contract manufacturer given his expertise and access to industry best practices will be able to minimize the potential of rework. That said, even with all the precautions there will be some PCB assembly defects that can occur which an experienced PCB manufacturer will be able to cater to.

While potential rework situations need to be taken into account, what also need to be planned for are aspects such as:

  • Some printed circuit boards need additional testing.
  • Sensitive components need room for access. This may include additional vias for probing or header pins for test access.

An experienced and skilled PCB contract manufacturer can easily identify areas of the board that may need more room for rework or for extensive testing. Besides, a skilled PCB contract manufacturer will also have the engineering prowess that will be of utmost importance when it comes to meticulous rework in the least amount of time and with minimal added costs.

At Mermar Electronics, we have 4 decades of solid experience in assembling printed circuit boards, PCB design and PCB assembly rework and repair service through innovative tools and technologies. If you have any requirements or inquiries related to PCB manufacturing, Get a quick quote, or simply drop an inquiry at sales@mermarinc.com

RF Circuit Board Design – Top Challenges, Solution and Tips for smooth process!

By Mer-Mar Electronics | Date posted: | Last updated: February 9, 2022
RF Circuit Board Design

RF circuit board design is seeing increased usage whether it is in medical, industrial or communication devices. Simply put, RF signals are high-frequency analog signals. The RF frequency range is usually from 300 kHz to 300 GHz. This is as opposed to Microwave frequency range, which is anything above 300 MHz.

Even though RF PCBs have a wide range of advantages, compared to high-speed digital-signal board design, RF circuit board design also comes with its unique set of challenges. Let us look at these challenges in some detail as also look at effective tips that help designers mitigate these challenges effectively.

Challenges associated with RF Circuit Board Design

  • Sensitivity to noise – RF signals are highly sensitive to noise and lead to ringing and reflections. What is important is to ensure that the signal is properly terminated. It is also advisable to optimize the return path and ensure proper grounding is maintained.
  • Impedance Matching – Essentially frequency and tolerance are inversely related The higher the frequency, the smaller is the tolerance. If the total length of he trace is greater than the critical length i.e 1/16th of the wavelength of the signal, impedance control needs to be undertaken.
  • Return loss – It is imperative that return loss be minimized. In the absence of a good design, the return signal will go through power planes, or through multiple layers of the PCB. In such cases it will not be impedance controlled. For this reason, it is important that there are ground planes underneath the signals that can provide an impedance-controlled path. With ground planes, ground loop currents are minimized and also RF leakage into circuit elements is minimized.
  • Crosstalk – High Frequency designs also suffer from crosstalk. Crosstalk, in fact, is directly proportional to edge rates of the active line. Here the coupled energy from the active line is superimposed on the victim line. With board densities rising, so does the issue of crosstalk. To counter this, it is important that adequate space is left around the signal trace. Also it is important that traces are kept as small as possible. Also it is important that high-speed signals are routed as far apart. Reducing the dielectric spacing between the line and its reference plane, is yet another effective measure. Similarly, terminating the line on its characteristic impedance also limits crosstalk.
  • Other signal losses – Other signal losses include skin effect loss as also dielectric loss. PCB designers therefore need to look at laminate properties such as:
    • Dissipation Factor
    • Dielectric Constant Value

FR4 material for PCBs or laminate, for example, has a high dissipation factor. Insertion losses are therefore higher when using FR4. Also, the dielectric constant value of FR4 can vary up to 10 percent. In turn, this impacts impedance. High frequency laminates have more stable frequencies.

Coming to the Dk value itself, in microwave circuits the Dk value is linked to the size of circuit elements. It is therefore possible for a designer to reduce the circuit size by choosing a laminate that has a higher Dk value.

Effective Tips for RF Circuit Board Design

There are a number of effective tips that help in creating better designs and improving anti-interference. Some of these include:

  • Usage of inner layers as power ground layers. By doing this you will provide shielding and reduce spurious inductance. Reducing the length of the signal wire reduce cross-interference.
  • Turning the circuit layout 45 degrees. By doing this, high-frequency signal emission and coupling will be reduced. Short layout lengths work better for through holes. Also, the layout between layers should be vertical in order to reduce signal interference. It is also beneficial to increase copper on the ground layer.
  • Packaging important signal traces. This goes a long way in increasing the anti-interference ability of the signal. When it comes to signal traces it is also recommended to avoid loops and use a chrysanthemum link instead.
  • Bridging the decoupling capacitor. It is important to lay out the RF first and make the RF signal 50 ohms.
  • The importance of isolation cannot be overstated.

Incorporating these seemingly small suggestions can go a long way in creating far more effective designs and improving overall efficiency.

Mer-Mar Electronics is a certified and leading PCB manufacturer that gets things done in lesser turnaround time. We are committed to accurately reflecting your PCB design specifications as well as meeting the industry standards. We at Mer-Mar Electronics, assist our customers from initial design to mass production & delivery; as one of the leading electronics manufacturing services (EMS) providers. To know more contact us at sales@mermarinc.com or call us on (760) 244-6149.

Top 7 Must-Know Rules to Consider for Aerospace PCB Design!

By Mer-Mar Electronics | Date posted: | Last updated: December 23, 2021
aerospace pcb design

When it comes to manufacturing printed circuit boards for aerospace electronics, they need to have an extremely high degree of reliability. More so, as these need to operate in harsh environmental conditions! Since such mission-critical operations do not allow for any scope for error and need to stick to strict operating standards, there are some stringent guidelines that need to be followed.

Rules to consider when it comes to aerospace PCB design:

1. High Quality Components

Now this clearly makes sense. Since you do not have any scope for malfunction and maintenance interventions aren’t a possibility, it is imperative to use high quality materials and components.

For instance, one of the materials that is recommended to be used includes anodized aluminum as it helps in heat dissipation. In fact, its thermal conductivity is far higher than that of traditional materials.

2. Thermal Management

With aerospace PCB design What is required is effective thermal management. Therefore, you need to ensure proper heat dissipation without using external heat sinks. This can be done in several ways, including:

  • Use of heavy copper technology that allows heat dissipation without needing any additional cooling systems.
  • Use of thermal vias.
  • Use of materials such as Pyralux AP, FR 408 and other such materials.
  • Ensuring there is a reasonable distance between components to allow for heat dissipation.

3. Strict adherence to reference standards

There are fixed reference standards to be followed when it comes to PCBs for the aerospace industry. These include:

  • IPC 6012DS that lays down the performance standard for rigid PCBs for aerospace as well as military applications
  • AS/EN 9100, which is a series of standards developed by IAQG specifically for the aerospace industry.

4. Use of Conformal Coating in Aerospace PCB Design

Given the harsh operating conditions for aerospace PCBs, conformal coating is a step that cannot be avoided. Some of the conformal coatings include:

  • Electrolytic Nickel Gold
  • ENIG
  • HASL
  • Lead-free HASL

Such conformal coatings offer protection against heat, humidity and more. Once the conformal coating has been applied, the use of an acrylic based spray is prudent, as it protects the PCB from contamination as well as short circuits.

5. Routing Guidelines

It is important to choose the size of PCB traces so that they can handle the current load as also to ensure effective heat dissipation. It is recommended that the angles on the traces are less than 45°, so that the signal transmission is uniform. Additionally, it is important to separate components that operate at low frequencies from the ones that operate at high frequencies. This will ensure that the signal quality isn’t compromised. Also, the clock signals need to have proper physical shielding. It is also important to follow the rules to reduce crosstalk.

6. Use of flex and rigid-flex PCBs

The use of flex and rigid-flex circuit boards is widespread when it comes to the satellite, aviation and aerospace industries. However, as compared to industrial applications they are made of polyamide as opposed to FR-4. The advantages that it offers include:

  • It can adapt to small spaces.
  • It is light.
  • It is heat resistant.
  • It has high durability.

In fact, flex and rigid-flex PCBs offer high resistance to vibrations and shocks besides offering great mechanical and electrical connections. In addition, they work well in limited space applications. With their use, secure connections can be managed offering polarity and contact stability.

7. Aerospace PCB Design Testing

Above everything, what is required is robust testing. In fact, you need to go through a whole lot of testing loops to ensure that the design is reliable and will work well in the aerospace environment, which means working in zero-gravity in a vacuum as also working in extremes of temperature, depending on whether they are working on a low-orbit or geostationary satellite.

To sum up

With aerospace PCB design and manufacturing, the aim must be to offer high reliability even in the most difficult operating conditions. To this end, right from design to selection of right materials can all ensure that the PCB offers a failure-free operation. A robust board will ensure that it can resist g-force vibrations, thermal issues and more.

Mer-Mar Electronics is one of the leading aerospace PCB design and manufacturing companies that specialize in building ITAR compliance aerospace PCB assembly. We are committed to accurately reflecting your design specifications as well as meeting the aerospace industry standards. We at Mermar Electronics, assist our customers from initial design to mass production & delivery; as one of the leading Aerospace electronics manufacturing services (EMS) providers.

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