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Drill, Lamination, and Plating of PCB Design

Understanding Drilling

PC Board drilling involves different drilling machines which can make more than 30,000 holes in an hour. The machines have built-in systems for making precise holes and consist of spindles that can drill at a high speed of up to 110,000 RPM. An automated system and laser help manage drill bits to provide high-quality vias.

Drilling Of Through-Hole Vias

Standard PCBs have a through-hole where all PCB layers are drilled together under an NC machine. Then comes the plating of the holes’ inner and outer sides, and manufacturers use the same technique for all through holes, including the mounting holes.

Blind and Buried Via Drilling

The drilling of blind and buried vias occurs before lamination. The two-layered PCB goes through lamination after drilling. Whereas a multi-layer PCB is stacked and laminated after which it needs drilling and plating.

You can also make blind vias by drilling with a controlled depth where the drill machine works through the entire laminated board. Such a technique of making blind vias is cheaper than a sequential method, however, the hole size has some limitations. Besides, the routing of circuitry needs a specific technique.

Micro-vias Drilling

The drilling of micro-vias involves a laser machine because their size has to be small which is not easy to create through mechanical drilling. Micro-vias are ideal for thick PCBs, and you can connect them vertically by stacking them in layer pairs. Such as, in a traditional buried via, you can sequentially fabricate micro-vias whereas the buried vias need copper plating to connect the stacked vias.

When it comes to component holes, the through-hole technology works well. Such components are switches or standard connectors or mechanical components that need strong mounting that’s why the through hole suits them. Some common examples of devices having such holes include power regulators, resistors, op-amps, and capacitors, as they conduct heat and current.

How To Select A Drill

Though drilling is a basic function for a PCB Manufacturer, engineers use certain techniques to have precise drilling.

  • Sometimes a board needs lots of drills of the same size, which can cause changes in the bit during drilling. Such a change creates errors in terms of tolerance between hole diameters. So, engineers use drills of different sizes to avoid the quantity of the same-size drills.
  • Drilling diameter should be minimum, like in mechanical drilling, a six to eight mils drill is ideal for a 62-mils thick board. Whereas it is hard to use the small drill sizes in mechanical drilling, and its aspect ratio also makes plating difficult. So, engineers have to use laser drilling which is more expensive than normal drilling techniques. You have to use large drills for thick PCBs which are more than 62mils thick.
  • Use blind and buried vias when they are necessary otherwise avoid them. As their fabrication involves a sequential buildup method that increases the manufacturing cost of a raw board.

Different aspects affect the drilling methods and manufacturing cost of the PCB. Even the drill size affects the quality and cost of manufacturing. Too small holes highly increase a board’s cost, whereas too large holes can make assembly harder, increasing its cost. Engineers can avoid such issues by carefully designing a PCB, and having economical manufacturing.

PCB Plating or Metallization and Soldering

You need metal pads or lands to help components in mounting or soldering. You can’t solder the bare copper and have to plate it with an easy-to-solder material. In the past, lead-based tin was a common plating material. But, these days the environmental changes call for advanced materials like gold and nickel.

Unsoldered parts of the board need materials to resist soldering, such as polymer coating that prevents the bridging of traces. Moreover, it creates short circuits in the adjacent part leads.

Fabricating the External Layers

The above etching is ideal for circuits of external layers and the process includes drilling, metallization, and photoengraving. The final finishing happens after the external layers’ metallization. In general, the process includes soldering, silk screen application, testing, as well as packaging.

PCB Lamination

PCB lamination is crucial in terms of accuracy and creating a well-finished board. The process involves lots of stress, as you have to take care of the properties of PCB materials in terms of performance and production. PCB engineers and manufacturers have to work together to develop a functional product without sacrificing production.

Understanding the Lamination Process

The lamination of individual layers involves two main steps, such as:

Laying up:  It involves the stack-up of multiple layers. The manufacturer starts it from the bottom of the base substrate. Then comes the prepreg and internal etched layers. Then all layers are pinned together to make a final board without any disturbance. Laying up prepares the PCB before pressing.

Pressing of layers: Pressing involves heat and pressure that melts prepreg to finish the etched copper layer, making the insulation layers essential for electronic layers which can work closely. Prepreg bonds the layers, getting hard after curing, and makes a PCB mold.

You need to consider different factors during pressing. Like, many PCBs can be pressed together to save time and production costs. However, manufacturers have to place a separator between the individual layers to bear high pressure and heat without changing the PCB shape.

The laminating press also needs a vacuum to prevent the PCB voids to hinder the dielectric property, affecting its structural strength. The environment after pressing also needs consideration to prevent the STP quenching due to weather conditions. Manufacturers should store the pressed circuit boards in a press to cool them down. Cooling of the boards prevents the thermal contraction of the board.

Lamination Styles

Two styles are common in this case, such as:

  • Foil lamination
  • Cap lamination

PCB Lamination with A Foil: the foil lamination is simple and involves less hassle, as you have to foil the base and top layer. After lamination, the layers go through etching just like internal layers.  Foil lamination is more advanced than cap lamination, but you have to select the foil layer with care to remove them easily later on. The technician should work in alliance with the designer and material manufacturers to ensure precise production.

Copper Clad or Cap Lamination: It is an original method that PCB manufacturers have been using for years. There is a layer clad with copper between the base layer, top layer, and first and last inner layer. Such lamination is suitable for blind vias, however, you need a special laminate between the external and nearby layers to enhance a PCB function.

Purpose Of Sequential Lamination

You can use sequential lamination for advanced vias where drilling and plating come after lamination. However, vias other than through holes should be made before lamination, leading to sequential lamination. Such a technique involves many precautions in terms of materials and design to have a successful lamination. For like, you have to consider the z-axis CTE, Tg or glass transition temperature, and copper retention. A copper filling helps reduce copper accumulation to have a well-managed uniform CTE expansion.

The selection of the materials for PCB lamination involves great care. Besides, you should use the latest design software.

Testing a Final Product

Remember that PCB testing is very important to check damaged connectors and short circuits. Optical testing consists of layer scanning to find defects, whereas electrical tests involve a flying probe to verify different connections. It is easier to detect short circuits or breaks through electrical testing.  Whereas the optical inspection can better detect poor clearances between the conductors.

Final Thoughts

Drilling, plating, and lamination are important processes of PCB construction.  PCB drilling involves machines that can make more than 30,000 holes in an hour. The machines have built-in systems for making precise holes and consist of spindles that can drill at a high speed of up to 110,000 RPM.

An automated system and laser help manage drill bits to provide high-quality vias.  The two-layered PCB goes through lamination after drilling. Whereas a multi-layer PCB is stacked and laminated after which it needs drilling and plating.

The drilling of micro-vias involves a laser machine because their size has to be small which is not easy to create through mechanical drilling. Micro-vias are ideal for thick PCBs. Plating of the holes is also essential to provide electrical connections.

PCB laminating press needs a vacuum to prevent PCB voids to hinder the dielectric property, affecting its structural strength. The environment after pressing also needs to be considered to prevent any damage due to weather conditions.

Would like to know more about the Drilling, Lamination, & Plating or smt assembly? Email us at sales@pnconline.com

What is Printed Circuit Board Copper Clad Laminate?

What is Printed Circuit Board Copper Clad Laminate?

Printed circuit boards come in different materials known as substrate, including copper-clad laminate or CCL. PCB substrates are either organic or inorganic, depending on their properties. The organic substrates come up in different materials known as the reinforced board, such as glass felt, fiberglass, fiber paper, fiber cloth, and so on.
PCB fabricators impregnate there in forcing materials with an adhesive called resin, making it dry, and then cover it with copper foil at high pressure and temperature. Such a substrate is CCL or copper-clad laminate that resides on either one or both sides of the board. So, CCL is either single-sided or double-sided.
Rigid PCB has a rigid CCL with a substrate, such as

  • Resin epoxy FR4
  • PTFE
  • Aluminum or copper
  • Ceramic

These materials help make different types of PCBs, including single, double, and multilayer PCBs.

CCL Standards

Engineers define the CCL standard specification with ASTM D1867 and develop their circuit boards according to these standards. To cover twelve grades of CCL, ASTM needs the laminates to meet certain factors for peel strength, like

  • High temperatures
  • Volume resistivity
  • Water absorption
  • Flammability ratings
  • Dissipation
  • Dielectric breakdown
  • Permittivity
  • Lengthwise and crosswise strength

The PCB Manufacturer should also check the CCL for twist, warp, or blistering. CCL manufacturers often follow the IPC-410IC as a standard. Moreover, they use IPC-IM650 to test the fabricated CCL.

CCL Materials

FF4 CCL: As discussed above FR4 is a popular material for copper-clad laminate. The material is resin epoxy, and it is ideal for rigid circuit boards. You will see it on both sides and only one side of the board. The material is a combination of epoxy resin and fiberglass cloth. Resin makes the board fire resistant that’s why we abbreviate it as FR or flame retardant. However, it has to pass through testing to see if it is according to the UL94V-0 standards.

Copper base: like aluminum CCL, copper core CCL has a copper plate, copper foil, and dielectric layer for bonding. PCB’s thermal dissipation and dielectric bonding determine the overall thermal conductivity.
PCB with copper substrate has three types, depending on its design, such as copper without PTH, COB, or chip-on-board copper circuit board which is without the thermal pad insulation.
Aluminum CCL: Copper-clad laminate also has aluminum as a base material combined with a dielectric layer and copper foil. These materials are bonded through hot pressing and very high temperatures. The dielectric bonding determines the thermal conductivity of the aluminum core laminate. However, both copper foil and dielectric have high conductivity, and manufacturers often use ceramic to fill the dielectric layer.

What Is RF, Radio Frequency CCL?

The RF CCL is also known as the Microwave PC Board CCL as the board has microwave frequencies. Such a circuit board has certain characteristics to consider, such as

  • DK, dielectric constant
  • DF, dissipation factor
  • CTE, coefficient of thermal expansion
  • TCDR thermal coefficient of dielectric constant
  • Thermal conductivity

It involves high-frequency materials of which PTFE is a common practice. It is a synthetic material having great dielectric properties at high frequencies which are also known as microwave frequencies. A few companies develop the high-frequency PCB CCL, including Isola, Rogers, Taconic, and Panasonic.

What is Prepreg in CCL?

Prepreg or pre-impregnated CCL is a kind of fiberglass that is impregnated with a bonding material such as resin. The resin is not hard, however, it is dry and gets sticky when heated. In other words, the fiberglass is made strong through an adhesive just like FR4.
Prepreg materials come up in different thicknesses that determine their quality, such as standard resin, SR, medium resin, MR, or, high resin, HR. The PC Board manufacturer use the resin thickness according to the type of PCB they require.

What is Printed Circuit Board Copper Clad Laminate?
Printed Circuit Board Copper Clad Laminate

CCL PCB Applications

PCB with copper clad laminate is ideal for:

  • Electronics PCBs
  • Radars
  • High-speed communication devices, like 4G,5G, and LTE
  • Automotive products, such as ADAS radar
  • Avionics Radar
  • Automobiles
  • Welded tanks
  • Offshore platform shearing
  • Steam condenses
  • Pressure vessels
  • Heat exchangers
  • Missile components
  • Hydraulic bushings

The above applications related to communications are essential to communicate faster, such as 4G helps you download anything within seconds. Whereas 5G is much faster, in this case, and you can see it by comparing it with the old and low-speed communication devices.

How To Identify The Best CCL PCB

A few parameters help you find if the copper-clad PCB is the best or not, such as size, neatness or appearance, chemical properties, performance according to the environment, as well as a physical performance.

PCB Design Parameters Including Size: The size of the CCL matters a lot in PCB design as it’s the base material. The quality of the end product also depends on the thickness of the core material. At the same time, you have to consider other parameters, including length, width, wattage, and diagonal deviation. Each design parameter should meet the necessary standards to have an ideal product that performs well.

CCL Appearance: several issues happen during Printed Circuit Board manufacturing that can affect the appearance of the copper foil. Such as dents, pinholes, scratches, resin points, bubbles, wrinkles, etc. These issues also slow down the PCB CCL performance.

Environmental Compatible: Copper-clad laminate PCB should be compatible with the environment. Like, it should resist water and corrosion or its production will get slow, resulting in serious issues.

Chemical Function: The chemical properties of copper-clad laminate are also vital and should be according to the standards in terms of flammability. The Z-CTE or, Z-axis coefficient of thermal expansion, Tag, chemical resistance, and dimensional stability has to be considered.

Physical Function: Copper-clad laminate has to meet certain physical requirements, including the PS or peel strength, bending strength, dimensional balance, heat resistance, as well as punching. It should resist thermal stress.

Electric Property: Copper-clad laminate should electrically perform high, as it’s very important. As described above, copper-clad laminate PCB should strictly meet certain requirements, such as DF, DK, insulation resistance, CTI or comparative tracking index electric strength, arc resistance, and volume resistance.

How Many Types Of Copper Clad Laminate Are There?

You can classify the copper-clad laminate according to different factors, such as size, thickness, mechanical material, structure, insulation material, types of reinforcement, resin type, and CCL performance.
Copper-clad laminate is either rigid or flexible of which rigid CCL is further divided, depending on its combination materials. It is either single or double-sided, besides there are also special rigid CCL PCBs with a high-flame resistance and other properties.
Flexible CCL: It includes,

  • Non-flame retardant polyester
  • Flame retardant polyester
  • Polyimides with and without flame retardant
  • Fiberglass cloth of small thickness

Benefits of Flexible Copper Clad Laminate

  • The FCCL has many benefits, such as
  • It has great flexing power
  • It is ECO friendly
  • It is free from halogen
  • Better heat resistance
  • Great adhesive properties
  • it is a blend of different copper clad thickness

Special copper-clad laminate has ceramic and it’s also called ceramic CCL. It has different materials, such as aluminum oxide, aluminium it ride, silicon carbide, boron nitride, and beryllium oxide.

FAQs

What is the manufacturing process of CCL?
Copper-clad laminate has complex manufacturing, including rolled copper foil that acts as a conductive material. PCB fabricators impregnate the reinforcing materials with an adhesive called resin, making it dry, and then cover it with copper foil at high pressure and temperature.

What Are The Uses Of CCL PCB?
Copper-clad laminate is fiberglass mixed with resin and glass and it is on either one or both sides of the glass fabric. Engineers use it to develop radios, mobile devices, televisions, computers, digital devices, and other multiple electronics.

What Is Copper Foil In CCL?
Copper foil in CCL is a cathodic electrolytic material that lies on the metal foil in a PCB. The material is easy to bond with the insulating layer to provide a protective covering. It is also easy to corrode to make a circuit protector.

What are CCL Standards?
Copper-clad laminate standard specifications are defined with ASTM D1867 and engineers develop their circuit boards according to these standards. To cover twelve grades of CCL, ASTM needs the laminates to meet certain factors for peel strength.
The fabricators should also check the CCL for twist, warp, or blistering. Copper-clad laminate manufacturers often follow the IPC-410IC as a standard. Moreover, they have to use IPC-IM650 to test the fabricated CCL.

Final Thoughts

PCB different materials known as substrate, including copper clad laminate or CCL. PCB substrates are either organic or inorganic, depending on their properties. The organic substrates come up in different materials known as reinforced boards, such as glass felt, fiberglass, fiber paper, fiber cloth, and so on.
PCB fabricators impregnate the reinforcing materials with an adhesive called resin, making it dry, and then cover it with copper foil at high pressure and temperature. Such a substrate is CCL or copper-clad laminate that resides on either one or both sides of the board.
Would like to know more about Copper Clad Laminate or prototype pcb manufacturer? Email us at sales@pnconline.com

High-Frequency PC Board

High-Frequency PC Board Applications, Specifications, and Challenges

Some electronic products need special signals for which you have to make a high-frequency PC Board. Such a circuit board can provide 500 MHz to 2 GHz frequency that is ideal for microwaves, a radio frequency, and certain mobile applications that involve high-speed designs.

Several electronic components and switches are complex and need to transfer signals at a fast speed which is provided by high-frequency PCBs. Such boards need special materials because ordinary materials can affect signal transmission due to a poor Er value. Designers have to consider certain factors while designing the high-frequency Printed Circuit Board that we will discuss below.

Understanding a High-Frequency PCB

PCB involves connections of different components through conductive paths to run a specific electronic item. Designers use copper to develop a conductive path in a PCB. Circuit boards also help in signal transmission in the case of Wi-Fi and other satellite systems. In other words, you need a high-frequency circuit board to connect multiple objects through signals.

High-Frequency PC Board
High-Frequency PC Board Applications, Specifications, and Challenges

Which Factors Affect The High-Frequency PCB?

The design of a high-frequency PCB is not that easy because certain factors influence it and you have to consider them. Such boards have complex fabrication due to high-frequency laminates. Besides, the circuit board has to manage different applications’ thermal heat transfer.
You can’t use any material for high-frequency PCBs because it influences signal transmission that can be fast or slow, depending on the material. Moreover, the change in a material’s Er value also affects a PCB’s impedance.
Similarly, the dielectric material also plays a role in the design of high-frequency boards. Manufacturers use different dielectric materials as mentioned below:
1. Roger’s
2. Teflon
3. FR4.
The Roger’s is not expensive, and its DF and DK values are also less than other materials. Besides, it is ideal for prototyping manufacturing and applications. Moreover, there is a minimum chance of signal loss due to this material.
Whereas Teflon is used due to its high frequency that is up to 5 GHz that enhances the speed of signals between different parts and objects.
On the other hand, the FR4 is ideal for RF applications that need a frequency from 1GHz to 10 GHz. But, the electric products having FR4 have certain drawbacks due to their limitations.
The best material for high-frequency PCBs is Teflon due to factors like water absorption, DK, and DF. Teflon is more expensive than other materials, but it is ideal for products that need more than 10 GHz frequency of signals.
What Are The Standard Specifications Of a High-Frequency PCB?
You have to consider certain materials to have a high-frequency board as mentioned above. Moreover, the change in a material’s Er value also affects a PCB’s impedance. PCBs are available in different frequencies and have certain specifications that we will discuss below.
PCB Size: It should be at least 6 mm x 6 mm, and can go up to 457 mm x 610 mm.
PCB Thickness: It ranges from 4 mm to 5 mm.
Type of Material. Generally, it should be RO4003C, Ro3003, RT5880, and Ro3010
Weight of Copper: It ranges from 0.5 oz. to 2 oz.
PP: It includes Domestic-25FR, Domestic-6700, and Roger’s 4450F.
Min Spacing: It should be at least 3 mils.
Solder Mask Colors: Some common colors, in this case, are yellow, red, white, green, and blue.
Sides of Solder Mask. They are according to the design files.
Silkscreen Colors and Size: The colors are mostly white, black, and yellow, whereas the sides are according to the files.
Impedance Clearance: It is either plus 10% or minus 10%, depending on the design.
High-Frequency PCB Finish: It can be immersion tin, gold, silver, or electroless nickel. All these finishes should be RoHS certified.
Annular Ring: It should be min 4 mil.
Diameter of Drilling Hole: It is a minimum of 6 mils.

All the above species are standard and may change according to the board design. Besides, most circuit boards are customized and designed according to your needs. It is hard to recognize the best high-frequency circuit board, however, the material and specifications can help you in this case. You can also get professional help from a qualified PCB designer and/or a circuit board manufacturer.

Top Tips To Develop The Best High-Frequency PCB

As you know high-frequency PCBs have a high density and integration than other PCBs, they need a thoughtful design and fabrication. Such boards are more scientific than traditional circuit boards, and we have some tips to help you create a reliable PCB.

1. The pins that exist between various layers of a high-frequency PCB should have minimal leads as an alternate. Besides, the lead between different pins should be small.
2. When it comes to high-frequency devices, there should not be more bends between their pins.
3. Make sure that loops don’t develop while wiring.
4. The impedance of signals should be compatible.
5. The power pins of an integrated PCB should have a high-speed decoupling.

Meeting the Challenges of A High-Frequency PCB

No matter how well-designed is your high-frequency circuit board, you have to face some challenges during its fabrication and assembly. Let’s discuss some common issues in this case.

Consider Scaling

A professional fabricator knows that the thickness of internal layers decreases during the lamination of a multi-layered PCB made if FR4. So, the manufacturer should evaluate the percentage of such a loss. This helps printed circuit boards manufacturers get the right dimensions after the lamination process is over.
Besides, the laminate material is not hard like FR4, so it reacts differently. You should know the behavior of each material. Besides, you should scale each thickness separately or it will affect the registration from drill to pad and layer to layer. The fabricator should know all the statistics in this regard.

Preparing Different Layers

A board with several layers is complex, as you have to prepare each layer to have a strong bond, especially in the case of Teflon. Soft material can get deformed during the aggressive preparation of a surface. Such a deformation results in wrong registration, turning a PCB into a scrap.
Replacing the Teflon becomes expensive and causes delays in fabrication. So, you must prepare the surfaces carefully to avoid such challenges.

Preparation of Holes

You need to prepare the hole before plating. Like, it should be free from debris or epoxy attached to its walls. A smooth surface helps have a well intact copper plating. However, ceramic or Teflon involves a different kind of hole preparation.
This process involves a lot of care like you should consider various parameters of the drill machine to avoid the smearing of the substrate. After drilling, the hole is treated through plasma that involves gases. Poor preparation of the hole before copper plating might result in poor signal transmission. Hence, a PCB should have clean holes to perform better.

Considering the CTE Rate

The designer also has to consider the CTE or coefficient of thermal expansion of different materials. Different materials have different expansion rates, besides this expansion can occur in any direction like x, y, or z, depending on the heat. You can have well-finished holes if the CTE is less.
The factor of CTE can cause issues during a hybrid PCB of several layers when you join the high-frequency materials with FR4. So, the CTE of the materials should be compatible, or different layers or materials will expand differently, creating an issue.
Other than layers, vias also have to face this issue. Hence, the plugging material of the vias should be compatible with other materials.

Compatibility

Some FR laminates are similar to the RF materials in terms of behavior, and you should understand it. For example, the ceramic impregnated boards are hard when you drill through the drill bits. The hit counts should be less, besides, the RPM and spindle settings should be customized.
Sometimes the holes have fingers, which are hard to remove, so the adjustment of drilling parameters is essential to reduce fiber.
So, you can meet all the above challenges if you design and fabricate a PCB carefully by approaching a prototype pcb manufacturer to verify your design.

Importance of a High-Frequency PCB

A high-frequency PCB is widely used in different industries, such as military, interchanges, gadgets, vehicles, PC, instrumentation, clinical, and other such fields. These circuit boards are more in demand than before, and 15% of circuit boards in the market come up with high frequency.

Final Words

Sometimes the electronic components and switches are complex and need to transfer signals at a fast speed which is provided by high-frequency PCBs. Such boards need special materials because ordinary materials can affect signal transmission due to a poor Er value.
You can’t use any material for high-frequency PCBs because it influences signal transmission that can be fast or slow, depending on the material. Moreover, the change in a material’s Er value also affects a PCB’s impedance. PCBs are available in different frequencies and have certain specifications.
Would like to know more about high-frequency PCB applications or pcb assembly services? Email us at: sales@pnconline.com

Minimizing Crosstalk in PC Board Layout

In this ongoing series on PCB layout from the design team at PNC, previous posts have looked at some of the initial steps to turn a circuit schematic into a manufacturable, reliable PCB. These posts have looked at  component placement, selecting appropriate trace widths, and BGA routing.   In this post we are going to take a deeper dive into methods for reducing crosstalk in the PCB design. After the power and ground have been routed, the next task is to route high speed signal traces, and the traces that could either generate or receive crosstalk.

 What is Crosstalk?

Crosstalk occurs when the signal on an aggressor trace on a PCB appears on a nearby victim trace, due to capacitive and inductive coupling between the two traces.  Typical aggressor signal traces are:

● High speed digital signals, especially clock signals
● Noise from switching power suppliers
● High frequency RF.

Victim signal traces, on the other hand, carry high impedance signals like op amp input lines or reset lines, or low impedance signals with long loops.   Low amplitude signals such as a sensitive analog measuring circuit traces are also susceptible.

Crosstalk occurs when aggressor trace and victim trace are close together and run in parallel for a distance.  The aggressor and victim(s) can be side to side on the same layer or on top of each other on adjacent signal layers. Coupling between traces on adjacent layers separated by just a thin section of laminate is called broadside coupling.

Minimizing Crosstalk in PC Board Layout
Minimizing Crosstalk in PC Board Layout

 

 

 

 

 

Printed Circuit Board Design guidelines to reduce crosstalk

There are several design rules to reduce crosstalk between signal traces.  Before applying these rules, the first step is to use the general guidelines described above to identify and flag any potential aggressor signal traces and their potential victims.

Since crosstalk occurs between two traces running in parallel, try to reduce the distance that the aggressor and victim traces run in parallel. Unfortunately, this may be difficult if the signals originate and terminate from the same locations.  To minimize broadside coupling try to orient the signal traces east-west on one layer and north-south on the second layer.

It is essential to have a broad contiguous ground plane directly under (or over) the signal layer.  A ground plane located between two signal layers can prevent broadside coupling. However, make sure that ground planes located on adjacent layers but not electrically connected do not overlap.  The overlapping ground planes separated by a dielectric form a capacitor, which can transmit noise from one ground plane to the other. This can defeat the purpose of separate ground planes if they were created to isolate the noisy elements of a circuit from the noise sensitive ones.

Increasing trce spacing

The most effective method of reducing crosstalk is to increase the spacing between the aggressor signal trace and the potential victim traces.  Like all electromagnetic radiation, electrical or magnetic coupling between the two traces drops with the square of the distance between them.  The amount of spacing required between the traces is dependent on the height of the traces above the ground plane.   The formula defining this relationship is from Douglas Brooks “Crosstalk Coupling: Single-Ended vs. Differential”   The coupling between two traces is proportional to:

Where S is the spacing between traces, and H is the distance from the trace to the ground plane.  Once H is defined by the lamination stack-up, the relative change in coupling can be easily plotted as a function of S.  Douglas Brooks looks in detail at the coupling between traces under several scenarios.  For those looking for some general guidance, a spacing of 5H is considered conservative.  The PC Board design team at PNC can assist designing a PCB stack up that will minimize the spacing needed between coupled traces, ensuring that crosstalk is minimized while maintaining routing density.

Finally, for very high speed digital signal traces, consider the use of differential pairs.  For many designers, the most common applications for a differential pair is for a high speed serial bus like USB, SATA, or HDMI.  The design rules for the layout of differential traces is beyond the scope of this post.

The most important part of reducing crosstalk in your PCB design is to first recognize in which signal traces crosstalk is likely to occur, then follow the guidelines above to minimize it.  PNC’s Printed Circuit Board designers have experience with high speed digital and RF circuits and can help you select the correct PCB layer stack-up and review your designs for areas where crosstalk is likely and suggest ways to minimize it. Request a design review from PNC today

3d-printed-pcb-prototype

Accelerate your New Product Development with rapid PCB assembly prototyping

The time from concept to prototype has accelerated remarkably in the past decade. 3D printed prototype components in a wide variety of materials are available in hours. Machined or sheet metal components are available from rapid prototype shops in only one or two days.

Prototype Printed Circuit Board Fabrication and assembly companies like PNC have followed this trend towards faster prototypes and can now provide complete assemblies in less time than ever before. PNC can fabricate and deliver a bare 10-12-layer PCB in just three days, and a simple double-sided board in just 24 hours.

However, even with the streamlining of PCB fabrication, the fully assembled PCBA is often the longest lead component in prototype designs primarily because of the sheer number and variety of passive and active components to be purchased and the demands of accurately placing and soldering those components. Sourcing the components on a typical PCBA BOM can take days in the best case and weeks in the worst case. Setting up and running the assembly job can add another few days, especially for double sided PCBs, and PCBs with a combination of surface mounted and through hole components.

Fortunately, there are some things that a product development team can do to reduce PCB assembly lead time.

First, do everything possible to reduce the impact of long component lead times. Plan to order the components as early as possible in the circuit design process. Deciding when to order components requires balancing the costs of scrapping some components as the design matures vs. the benefits of reducing the lead time for an assembled PCBA by days or weeks.

Second, reduce the time required to set up and build the prototypes by working with a full-service company like PNC. PNC has the capability to both fabricate the bare PCB and assemble the components. This means that the PCB fabrication team and assembly team can save time by working in parallel. While the PCBS are being fabricated, PNC’s engineers can create pick and place data, solder paste stencils and program the assembly equipment. When the PCBs are finished and the components arrive, everything is ready to begin assembly immediately.

The third way to save time with PCB prototypes is to minimize the number of PCB prototype iterations. Saving a full printed circuit board assembly prototype cycle is the most effective way to reduce the time from concept to mature design.

One way to reduce design iterations is by testing circuit designs as early in the design process as possible by building “Works Like” prototypes. “Works Like” prototypes are usually combinations of development kits, large one or two layer PCBs with larger SMT components that can be soldered by hand and various types of breadboards. In addition to testing the circuit, a “Works Like” prototype gives software developers an early platform to start developing code and debugging the circuit design. The result of testing early with rough prototypes is that you fix problems before you have invested the time in the full layout and prototyping process.

In parallel, the mechanical engineers can optimize cable routing and connector placement by printing 3D models of the PCBs, then epoxying actual connectors to the board model. This is an effective way to quickly try different options for cable routing using actual cables and connectors, since it is difficult to simulate the way actual cables behave with CAD software.

Experienced electrical engineers know that it is often poor connector access or cable interference that drive Printed Circuit Board layout redesigns as often as issues with actual circuit performance.

Once the circuit has been tested with the “Works-Like” prototype, and the board layout has been tested with 3D printed models, the last way to save time is to work closely with the PCB manufacturer to make sure that the PCB fabrication files are clean and complete, and that the BOM is accurate and matched with the circuit and layout to avoid placement mistakes.

This is another reason to select a full-service prototype pcb manufacturer like PNC. PNC can be a partner during the layout and design process, though fabrication and assembly ensuring the final design can be translated into a working prototype in the least possible time.