Tag Archives: PCB Fabrication

PCB FABRICATION SUBSTRATES

PCB FABRICATION SUBSTRATES

What is PCB substrate?

Every home is required to have a solid foundation. A substrate is also required for every printed circuit board. The actual substance that contains the traces and elements is known as the PCB Fabrication substrate. The first step in creating a high-quality PCB is selecting the correct substrate. Structure and shape are required for a PCB. It also requires a platform or canvas on which to place all of its other components. The PCB’s performance is influenced by the substrate’s properties. A stiff substrate, for example, can improve the PCB’s strength and endurance. More design options are available with a flexible substrate.

The usage of a variety of substrates, ranging from solid fiberglass to flexible polymers, is becoming more common as the PCB industry evolves. Fiberglass has traditionally been the most prevalent type of substrate. It’s a low-cost, high-reliability material that gives the PCB a nice, stable foundation.

pcb board
pcb board

 Material of PCB substrate

It’s only reasonable that the materials you choose have an impact on your product’s performance. It’s the same with printed circuit boards, where selecting the correct PCB substrate materials can have a significant impact on the board’s performance, durability, and other characteristics.

printed circuit board
printed circuit board

Types of PCB substrate material

Following are the good material that we need for PCB substrate.

1. Copper foil:

PCB substrate materials are critical in defining the board’s endurance and quality. Manufacturers appear to be attempting to go towards fine lines and high density. You may be familiar with the term HDI PCB. This is the abbreviation of High-Density Interconnect Printed Circuit Board. To be classed in the HDI category ten years ago, a board had to have a line space (S) and line width (L) of less than 0.1mm. Today’s standards differ from one industry to the next. S and L on electronic devices are frequently set as low as 60m, and in advanced applications, they can even go as low as 40m. Once a thin copper foil substrate is applied, S and L can reach as low as 30m during circuit design development. The ideal thickness is between 9 and 12 meters.

The issue is that a thin copper-coated laminate can be costly and prone to flaws. It’s the most plausible explanation for why corporations use 18-meter-thick copper foil. However, if S and L are less than 20m, normal thickness copper foil may not be the best option.

pcborard
pcborard
 2. Dielectric Insulating Coatings:

The ability to build up is a key feature of HDI printed circuit boards. There’s a good probability you’ll be able to construct an appropriate circuit if you utilize resin-coated copper (RCC) or combine copper foil lamination with epoxy glass prepreg cloth. MSPA and SAP techniques have also been implemented by the manufacturers. By using an insulating dielectric film lamination with chemical copper plating, the copper conducting plane was created. The fundamental reason we can make acceptable circuits is because of the thin copper plane.

3. High heat protection and dissolution are required:

Electronic devices tend to generate more heat as the trend toward downsizing and high function continues; hence thermal management of electronic devices is becoming increasingly important. Thermal-conducting PCB research and development is one of the solutions to this problem. The main criteria for a PC Board to operate well in terms of heat resistance and dissipation are the substrate’s heat resistance and dissipation capacity. Improvements in thermal-conducting capabilities of PCBs are now being made through epoxy and filler additions; however this only works in a limited category. The most common way is to use IMS or metal core PCBs as a heating component. This system has several advantages over the typical radiator and fan, including a smaller amount and lower cost.

How to Select Substrate Materials for PCBs

You can choose between three distinct types of PCBs:

• Rigid
• Flexible
• Flex-rigid

The most important goal is to select a board that is ideal for your product. Many people strive for compact size and shape while overlooking performance. Polyimide film is a good choice since it is adaptable and can be used in a variety of applications, including black, white, and transparent. It also ensures a low coefficient of thermal expansion while keeping acceptable heat resistance. The Mylar substrate, on the other hand, is extremely flexible and resistant to external conditions. Furthermore, it is reasonably priced, which is why many consumers consider it. Flexible PCBs must attempt to achieve the same degree of frequency and speed performance as regular PCBs. Flexible boards can be made with advanced polyimide substrates and polytetrafluoroethylene.

Flexible boards are used in a variety of industries, including medicine, smartphones, and gadgets. As a result, the market has been implementing innovations in flexible and ultra-thin multi-layer boards (0.2-0.4mm). You can expect flexible boards to achieve speeds of up to 5Gbps at this time, but you’ll need to choose a substrate material with a low Dk/Df. It’s also a good idea to utilize conductors with a thickness of above 100m, as this will aid with current and power handling.

Best PCB substrate type

A substrate and printed wires are the two main components of a PCB (the copper traces). Substrates that divide the layers are required for multi-layer boards. The substrate works as physical support for the circuit components and printed wires, as well as providing electrical insulation between conductive portions. PCB Substrates are non-conducting materials. They act as a laminated electrical insulator between circuits for this purpose. An electrical insulator is a material that does not conduct electricity because its internal electric charge does not flow freely. As a result, plated through holes are used to connect traces on opposite layers on each layer of circuitry.

A substrate and laminate are commonly used as the foundation or base of a printed circuit board (PCB). The performance of the PCB is determined by the type of laminate and substrate used. As a result, choosing the proper types of PCB material for the job is crucial to getting the greatest results. Any PCB design guide should include such features:

 Working
 Durability
 Cost-effectiveness

The material you choose for your PCB can have an impact on its short- and long-term functionality, along with your contractor’s capacity to build it. You can’t blame the contractor if you buy substandard materials and they fail when your contractor tries to make the board. When maximum performance isn’t a must-have feature for a PCB, lightweight polyester material is typically a fine option. As long as lightweight polyester is utilized in conjunction with printed electronics (PE) technology, there are at least two reasons to choose it in these circumstances. Printed electronics with lightweight polyester have these features:

Cost-effective Lightweight polyester produces less waste, necessitates fewer manufacturing steps, and eliminates the need for desalination and purification.

Adaptability Flexible printed circuits (FPCs) are available, but the level of “bendability” that makes them so appealing is costly to accomplish. PE with lightweight polyester maintains flexibility at a far cheaper cost.

Traditional PCBs, on the other hand, is still the top choice for high-performance applications, and the materials used in their construction should be determined by the type of board required. For example:

 Manage frequencies ranging from 500MHz to 2GHz
 Allow for high power and, as a result, high temperatures
 Be “intense” and complicated
 Manage microwave and above-microwave frequencies

The board’s application decides the substrates and laminates to utilize to a considerable extent. There are five types of substrates, each with its own set of features for specialized purposes.

1. FR-4

Fiberglass substrates are comprised of woven fiberglass that has been impregnated with only a flame-retardant substance. The material is rigid and can be drilled, cut, or machined, although tungsten carbide tools are required due to the abrasive nature of the fiberglass. An FR-4 substrate is more resistant to cracking or breaking than an FR-2 substrate and is typically seen in higher-end devices.

2. RF
Low dielectric polymers are employed in RF substrates, which are used in printed circuit boards for high-power radio frequency applications. Despite its low mechanical qualities, the substrate exhibits remarkable electrical performance.

3. FR-2
This extremely low substrate is comprised of impregnated paper, also known as Phenolic, and is simple to the machine over a fiberglass substrate. Flame Resistant is denoted by the letter “FR.” This substrate is commonly encountered in lower-cost consumer devices.

4. Flex
Flex circuits are those that are meant to be very flexible or slightly flexible. As substrates, thin, flexible polymers are used. Although the manufacturing process is more complicated than utilizing rigid substrates, it provides benefits that rigid substrates cannot, such as reducing space by bending the circuit board to fit a specific place or where repetitive action is essential. A low-thermal resistance substrate is required for power electronics. A ceramic core or metalcore substrate has the essential properties to accommodate larger copper tracks and the high electrical currents that these circuit boards require.

Final Thoughts

Every substrate has its uniqueness and you get to know almost every substrate detail in this write-up. Interested to know more about our facilities at PNC? Contact us at sales@pnconline.com

Embedded software development along with PCB Assembly

Embedded software development along with PCB Assembly

No company can excel at every aspect of new product development and trying to do everything can dilute an organization’s focus on the tasks that are essential to its success. For example, most companies have long ago outsourced the PCB design and fabrication steps of new product development. This same need to focus on the essential is true of software development too. It is difficult for a software company to excel at every type of software development because of the ever expanding universe of software languages, operating systems, and architectures.  A cloud based SAAS or PC based application is very different from embedded software running C on a 16-bit processor, and it takes very different software development skills to develop that kind of embedded application.

Unlike cloud based or PC based applications, embedded software is optimized to run on a specific custom hardware platform with limited processing power and memory.  It often runs on a real time operating system or no operating systems at all, and the interface of an embedded device may consist of only a small display, or just a few buttons and LEDs.

The unique challenges working with embedded systems is why many software companies outsource their embedded software projects to experts like PNC.  Here are three reasons why they do.

The embedded system is not the organization’s primary product line.

Many products on the market require options or accessories that are important to the customer, but not are not similar technically to the primary product. A cable set top box remote is a good example.  Customers expect a cable set-top box to have a remote, but the low power microcontroller embedded in the remote is likely to be completely different from the high power processor and OS driving the set-top box functions.  Similarly, Industrial or commercial equipment may have optional modules to provide additional functionality like a cellular modem.   These optional modules have independent processors and embedded software which is unrelated to the primary product software.

In these cases, software companies will choose to focus their development resources on the primary product, recognizing that it is more cost effective to outsource the software development for the ancillary embedded products to a company that is familiar with embedded microcontrollers and the constraints that come with low power operation. If that company can design the hardware and perform SMT assembly too, it becomes an even better value.

Embedded software development along with PCB Assembly
Embedded software development along with PCB Assembly

The software is deeply embedded and invisible to the user

Successful software companies are highly focused on the customer experience with their product. They are constantly refining the look and feel of the industrial design and user interface to make the product more attractive, and easier to use.  But what if the product doesn’t have a user interface?   What if it is a router or a motor controller?  Products like these need a simple interface for initial configuration, but they typically operate in the background, invisible to the customer.  In this case the goal is to optimize for cost and performance rather than user experience.  Deeply embedded applications without a sophisticated customer facing interface  are ideal to outsource to a company like PNC because the product requirements are centered on the embedded functionality – there is no need to maintain the same look and feel as the company’s customer facing products.

The application requires specialized expertise

 Sometimes a software company needs embedded expertise that it just doesn’t have in-house.  For example, they may need a Zigbee or Bluetooth RF stack, or expertise with digital signal processing on low power Digital Signal Processors DSP.  In some challenging embedded applications, a company may need a partner with the expertise to  iterate the design of both the hardware and software simultaneously to arrive at an optimized embedded solution.  In that case you need a full service provider like PNC.

PNC offers the full solution to developing embedded products

When it comes to product development, PNC is not just a PCB manufacturer.  The engineers at PNC can work with you to design and manufacture the product hardware, and then develop the embedded software to run on that hardware.   If you have a challenging embedded software or hardware project, contact PNC today and find out how they can help.

Minimizing Crosstalk in PC Board Layout

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

solderpaste

Basics of Solder Paste selection for PCB Assembly

INTRODUCTION

Solder pastes are amorphous putty-like soldering materials used to solder surface-mounted components to the Printed Circuit Board. The effect of solder paste on the PCB’s structural and functional integrity is the paramount factor to consider when deciding on selection of solder paste for application. Many factors which contribute towards the strength of the solder joint and its conduction efficiency need to be addressed as well. This is not just a discussion on what measures and precautions to take during PCB assembly and reflow, but also to put into question what a PCB design engineer should consider when designing a PCB and how the layout should adapt to the corresponding solder paste properties to yield the best result. It is a very brief introduction towards an expansive topic like solder pastes which will be discussed in further detail in future posts.

PROBLEM STATEMENT

A big concern for manufacturers arises when they need to select the right solder paste for SMT applications that is best suited to the PCB assembly and the manufacturing setup. A regular PCB has different types of components, all of which cannot always be compatible with the one solder paste applied across the board and thus, need some necessary compromises in solder selection. PCB designers should be educated about solder paste application and properties in SMT manufacturing to increase reliability of product yield.

SOLDER PASTE BASICS

Solder pastes are categorized based on the following characteristics: RoHS compliance (solder composition), flux type, grain size etc. RoHS (Restriction of Hazardous Substances) is a directive which mandates the exclusion of lead and other hazardous materials from solder pastes and manufacturing processes and aims to reduce environmental and occupational hazards related to electronics manufacturing. It has been adopted as a standard for commercial applications while only military applications can use leaded manufacturing processes. Many components now specifically require RoHS or non-RoHS procedures for PCB Assembly.
Flux is a chemical resin that is used to facilitate the soldering process. It is responsible for removing dirt and preventing oxidation of the component tips during reflow. They can be classified as either water-soluble fluxes or no-clean fluxes. Water soluble fluxes can be cleaned by using water while no-clean fluxes produced low levels of residue which are not necessary to clean but it is advised to clean with designated chemical wash to provide better result.
Solder pastes consist of solder grains which are available in different sizes which are given numerical designations from Type 1 to Type 8 based on descending order of solder grain sizes. Decrease in solder grain size also highlights the advancements in solder technology where Type 1 was adopted first, and Type 8 is the latest addition to minimum achievable solder grain size.

SOLDER PASTE

Since 2006, commercial solder pastes were manufactured and used without lead and other hazardous materials like cadmium and mercury in accordance with the RoHS directive. The directive also affected key PCB fabrication processes and successfully eliminated usage of hazardous materials for commercial applications. Lead in a traditional tin-lead alloy solder is responsible for lowering the melting temperature of the solder to approx. 183°C and it also helps slow down the rate of tin whisker growth in electronics. The process of finding replacements to maintain those advantages offered by lead is still ongoing. Lead-free solders have higher melting points and are more expensive than leaded solders.
The most popular lead-free solder currently being offered is tin-silver-copper alloy which has a melting temperature of approx. 217°C. This has also resulted in components like resistors, transistors being conformed to RoHS compliance. The main drawback of maintaining RoHS compliance for the product is that it is significantly more expensive than leaded processes and does not yield any benefits of switching to lead-free options. The effect of RoHS directive on component manufacturing and the larger effect on electronics manufacturing will be discussed in detail in future posts.
As of today, Type 3 solder is the most widely used solder paste. The following comparison consists of certain superficial characteristics which are a good point to start at before diving into a thorough discussion for each and exploring more complex properties and features of solder pastes. The reason behind comparing T3, T4 and T5 specifically is that T4 and T5 were recently adopted for mass usage for finer and smaller footprints in the PCB assembly industry while T3 has been the industry standard for a long time.

solder paste
solder paste

It is important to note that the sensitivity and reactivity of solder paste to temperature change increases as the solder grain size decreases. This is due to increase in the number of solder grains occupying the same area as the solder grain size decreases. Simply put, the greater the number of solder particles in a given area, the more reactive that particular area of solder will be. Therefore, from this we can conclude that T4 solder will melt at a lower temperature than T3, and T5 will melt at a lower temperature than T4. The advantages, disadvantages and the various effects of using small grain-size solders on component structure and performance will be discussed in further detail in the next post.

FLUX

Fluxes are infused in the solder paste and they are released during reflow. The flux is always released before the solder can melt to provide an oxidation-free environment. Its chemical profile consists of a natural or synthetic resin to coat the component pins and pads, activators to release the flux at the right temperature, solvents to facilitate deposition of solder on the joint, and additives to compensate for any modifications in flux composition. Water-soluble and no-clean fluxes are both used in various situations based on the amount of oxidation occurring during reflow, the level of reactivity of the solder, solder grain size, material of the board, and surface finish of the board.
solder_paste
No-clean fluxes are generally used for boards where the corrosion resistance of the surface is weak. It yields low residue on the printed circuit board assembly because the flux either burns off during reflow or it forms noncorrosive, localized residue around the solder joints. Contrary to its name, it does require cleaning post-reflow but less so than most other high-residue fluxes. No-clean solder pastes are used as an industry standard by most electronics manufacturing service providers because of its ease of use. The main drawback of using no-clean flux is that since it is less corrosive, it does not provide as much protection from oxidation as water-soluble flux but that has to be accepted as a trade-off for better quantitative results in large-scale production.
Water-soluble fluxes are generally used for precise action and give excellent results but the main drawback is that they require careful application and condition regulation due to their highly reactive and corrosive nature, and the difficulty in cleaning them post-reflow. Compared to no-clean flux, it produces more residue that cannot be removed easily from the board and due its high corrosivity, it may damage the PCB surface and component leads. Cleaning unwanted residue off the board requires additional machinery which occupies valuable space on the shopfloor. This limits its usage in the industry to only customer requests or specifications to use water-soluble solder pastes.

KEY CONSIDERATIONS FOR PCB DESIGNING

It is important to consider how solder selection will affect your PCB design. For simplicity, the effects will be divided based on solder paste composition, solder size and flux usage. Many of these considerations may overlap or may have to be used in conjunction for achieving the best result.

SOLDER PASTE COMPOSITION:

• Components used on PCB should be first checked to see if they are RoHS compliant or not, based on the solder paste used. Components with RoHS compliance usually have different leads which may or may not be compatible with leaded solders, and it may affect the solderability of the component to the copper pads, the solder joint’s mechanical strength, and component shelf-life and performance. It is also important to ensure the components operating and manufacturing parameters meet the solder paste properties, otherwise components may get burned or dysfunctional during the reflow process, leading to visible or latent component failure.
• Flux selection should be based on solder paste composition. Flux release at specific temperatures should be done in conjunction with the reflow profile for that specific solder paste. Solder melting and flux activation occur at different instances in the reflow process. Early activation of flux may cause surface corrosion, component failure, early burn-off which may lead to poor soldering and late activation may lead to increased oxidation during reflow process along with difficulty in cleaning.

SOLDER SIZE

• Solder grain size should also be considered when choosing component package and its corresponding design footprint on the Printed Circuit Board. Larger footprints do not require smaller grain-size solders. If the grain size is small, say T5, then based on its high reactivity, more number of particles per unit area and greater wetting ability, solder may flow too easily on melting resulting in solder defects which will affect component performance and product life-cycle. The reverse situation, where small footprints are used in conjunction with large grain-size solders, also leads to solder defects.
• Component package selection will also affect stencil aperture size, stencil thickness and solder deposition efficiency. Using large-size solders, say T3 solder, for micro-BGA or 01005-imperial sizes will result in gasketing and insufficient paste deposition; while using small-size solders, say T5 solder, for large footprints may result in bridging.
• The spacing between footprints of separate components, spacing between component leads of the footprint on the Printed Circuit Board should change based on the solder grain-size as using large grain sizes for small footprints, and vice versa, will lead to solder bridging which will in turn affect device performance and life-cycle.

FLUX COMPOSITION

• PCB thickness, material and coatings should be selected based on flux used for the reflow process. One should avoid using water-soluble fluxes for a thin PCB as they are highly corrosive in nature and may lead to excess surface corrosion. Corrosion resistant material and coatings should be used in accordance with the flux selected, as not using them will lead to corrosion and cleaning issues and using them when not needed(say a no-clean flux is being used) will increase cost of production.

All PCB’s should be designed keeping in mind the effects of solder paste, stencil design, flux, process used on
SMT assembly
PCB’s. Some of these topics and more will be added to the list and discussed in further detail in the future.

BGA-HDI

Better BGA routing on a Printed Circuit Board with High Density Interconnect

One of the technologies that have allowed electronic products to shrink in size and provide increasingly higher performance is the ball grid array (BGA) IC package. The BGA allows higher density PC Board layouts because of simple geometry. The number of pins that can be accommodated on the perimeter of a quad pack increases linearly with package size. The number of connections that can be accommodated on a BGA increases with the square of the package size. BGA packages now routinely exceed 1000 connections, and the ball pitch has shrunk from 1.0 mm to .8 mm to a growing number of devices now available in the micro-BGA format with a ball pitch of .65 mm, .5 mm and smaller.

The decrease in BGA ball pitch would not have been possible without the improvements in PCB fabrication. These improvements, collectively called High Density Interconnects or HDI, give companies like PNC the capability of creating traces as narrow as 0.0762 mm (3 mil) and vias with annual rings as small as .25 mm (10 mil) HDI PCB fabrication has given designers greater flexibility in routing BGA devices down to a pitch of .65 mm The HDI technology is essential for devices with ball pitches less than .65mm

Routing the hundreds of connections from a typical BGA is called BGA breakout, and it can be a major layout challenge. For this reason, many designers place the BGAs into the layout first and fan-out the connections from each pad to a stub trace. This allows the designer to adjust the routing of individual pins under the BGA without rerouting the entire PC BOARD. Another reason the BGA should be placed first is that the BGA breakout will likely dictate the number of layers needed in the PCB stack-up.

The breakouts are typically a repeating pattern, with the traces for each row of balls around the perimeter routed similarly. Most BGA manufacturers will provide sample breakouts, and some high-end tools will automate this breakout process. Most BGAs use similar fanout approaches, the fanout differing only in the package specific routings for power and ground. With standard PC Board fabrication technology there really are not a lot of fanout options. Here is the typical approach used for BGAs with pitches down to .65 mm highlighting some of the advantages of PNC’s HDI fabrication technology

Routing the first perimeter row of the BGA is easy; the traces come straight out from the pads.

The traces for the second row pass between the pads of the first row. If the ball pitch is greater than .8 mm an HDI PCB fabricator with the capability of creating 3mm pitch traces can fit two 3mm traces with 3mm spacing between the pads in the outer row. This allows the first three perimeter rows of pads to be routed on the top layer.

Subsequent rows are routed using a feature called a dogbone. The dogbone has a pad at one end and a via at the other, separated by short trace. This prevents the via from wicking solder from the ball pad, starving the solder joint. It is also recommended to cover or “tent” the dogbone via with solder mask. The dogbone is typically oriented at 45 ° so that the via can be located in the center of each four pad grid. The via takes the signal trace to the next level where it is routed out between the other vias, similar to what was done on the top layer.

the following number of board layers typical are needed for each perimeter row of pads

board layers
board layers

This table demonstrates that using an HDI Circuit board fabrication process, even for a 1.0 mm or .8mm pitch BGA can result in the need for fewer signal layers, because two traces can be passed between each pad. The HDI fabrication process also allows the dogbones to be placed in line with the grid instead of diagonally, which allows two traces to pass between vias on the 2nd and 3rd layers

For smaller pitch devices PNC’s HDI fabrication techniques become essential. For ball pitch spacing of .65 mm and .5 mm the only way to create a fanout is using the 3 mil traces and 10.68 mill dia. vias allowed by HDI. The 3 mil trace and 3 mil trace spacing allows a single trace to just fit between .5 mm pitch pads.

The latest micro BGAs used in devices like phones and smartwatches have pitch spacing below .4 mm. The pitch spacing is so close that traces no longer fit between the pads. BGA breakout requires via in pad techniques, with the filled microvias routing the signals straight down and then out. Depending on the number of perimeter rows, blind and buried vias may also be needed.

If you are using a BGA in your design, using HDI design rules for fabrication can simplify the breakout and reduce the number of PCB layers needed. PNC engineers can help you understand what is possible with HDI Printed Circuit board fabrication.
The last thing to know about designing with BGAs is that process yield, and reliability are very process dependent. When selecting a
Pga Capabilities
it pays to select PNC. PNC has the equipment and expertise to manufacture your most challenging BGA designs.