What should be included in a PCB fabrication drawing?

By | Date posted: | Last updated: December 17, 2022
PCB Fabrication Drawing

A PCB fabrication drawing is an extremely important file that contains the manufacturing details of the circuit board. The more diligently the PCB fabrication drawing is created, the better the chances of the circuit board matching your exact requirements. A fabrication drawing lays down the specifics of the circuit board such as the board outline, layer stack-up, drill chart and more. A fabrication drawing along with an assembly drawing together, comes in extremely handy in assembling the circuit board.

How does a PCB Fabrication Drawing differ from Assembly Drawing?

As their names suggest, a fabrication drawing provides essential details that are required for the manufacturing of the board. An assembly drawing on the other hand lays down details about how every component will be attached to the board.

What should a PCB Fabrication Drawing Include?

Some of the aspects that a PCB Fabrication drawing must include:

Dimensions

It is important to mention the dimensions of the board as that will determine how much PCB material is required. Typically, the areas that need to be mentioned include:

  • Length of the board
  • Its width
  • Thickness
  • Outline
  • Tolerances

There also needs to be a Board Outline, which includes the cut-outs, holes, radii, specific distances from the origin, and more

Drill Chart

There needs to be a detailed drill chart that offers the following information:

  • Which layers need drilling
  • Drill Sizes
  • Tolerance, and more.

The drill chart has specific symbols to do with the hole size. It offers information on whether the holes are plated or not and more.

Layer Stack Up

The layer stack up has a lot of influence on some of the other aspects of the project. It is therefore imperative to convey information such as:

  • Material
  • Thickness
  • Copper Weight
  • Surface Finish
  • Tolerances
  • Controlled Impedance

Basis the Controlled Impedance requirement, the manufacturer can then look at aspects such as the dielectric constant, spacing, trace width and more.

Title Block

The Title block consists of information such as:

  • Customer Name
  • Part Numbers
  • Fabrication Number
  • Measurement Units, and more.

PCB Fabrication Notes

In addition, it will help to include PCB Fabrication Notes with the following information:

  • Requirements of Controlled Impedance
  • Manufacturing specifications
  • Raw material specifications
  • Plating details
  • Details of Solder Mask
  • Gold fingers, if present
  • Any specifications related to hole positions
  • Presence of via-in-pad, if any
  • Blind/Buried via, if any
  • Tolerances, both in terms of board tolerance & plating & etching tolerance

The PCB Fabrication drawing can be created in a wide variety of software, including but not limited to:

Eagle EDA
This is one of the commonly used software where the process is fairly simple. The basic steps involved here include generating the PCB Gerber File. Next you need to go to the Layout Editor. This will enable you to use the drill symbols on the board. With all the information about the number of layers & board material compiled, the files can be sent to the manufacturer.

KiCAD
The basic steps here include adding the Title Block. You need to add all the dimensions of the board in the outline. Next you can use the Graphics Tool to draw the stack up. Information such as board thickness, layer thickness, tolerances etc. can be mentioned. On the fabrication layer information such as number of layers, IPC class of the board, solder mask color, type of pads and more can be added.

Altium Designer
You need to use a blank drawing format and then add the details to it. Fab Notes & Drill charts can also be added. The files are automatically linked to the design database of the tool

To Sum up

The PCB fabrication drawings provide a lot of critical, additional information that is not available by way of Gerber Files. With all the above information mentioned, you can make sure that there are no communication gaps remaining & the board is manufactured to the exact details required. Needless to mention that other than providing detailed PCB fabrication drawings, the choice of experienced electronics contract manufacturer can go a long way in ensuring that you receive quality boards. An experienced manufacturer is equipped with industry best practices that ensure that you do not need to reinvent the wheel.

With advanced methods of PCB fabrication, we give you the finest PCB fabrication services. The PCB fab services from our experts will take it to the next level by accepting every type of latest technologies.

Request a quick PCB Fabrication quote!

The Complete Guide on Printed Circuit Board Stiffener for Rigid-Flex & Flex Circuits!

By | Date posted: | Last updated: February 14, 2022
pcb-stiffeners

A printed circuit board stiffener plays an important role when it comes to offering mechanical support to a PCB. They are particularly helpful for flexible circuit boards, that given their name, are flexible and in need of stiffness in certain places.

Stiffeners are particularly required when components are placed in a flex zone & the weight of these components stresses the flex material. They are also of use where a rigid printed circuit boards surface needs to be created to place SMT pad components. Also, connectors that need multiple insertions need stiffeners so that the stress of the pads is reduced. Let us look at the uses of stiffeners in some more detail.

What are the various uses of PCB stiffeners?

Simply put a stiffener is used where a certain area of the circuit needs to be hardened. Here are some of the common reasons for which a stiffener is used:

  • Supporting areas of the board that have SMT or PTH components.
  • Maintaining legitimate thickness of the flex circuit.
  • Supporting PCB connectors.
  • Ensuring better handling of the circuit board.
  • Ensuring that areas of the circuit board are kept stable.
  • Helping in routing and retaining arrays.
  • To help in strain relief as well as effective heat dissipation.

Broadly, flexible PCB stiffener requirements fall in the following usage categories:

  • Rigidizing Component / Connector areas
  • ZIF (Zero Insertion Force) Thickness Requirements
  • Localized Bend Constraint(s)

Component / Connector Stiffeners
Essentially, they create a rigid area where components and connectors are attached. They also protect solder joints by ensuring the flex doesn’t bend in the component area.

ZIF Stiffeners
They ensure that the thickness is increased at contact fingers to meet specific ZIF connector specifications.

Localized Bend Constraints
They restrict bend areas to specific locations in a flex design.

How to select the right PCB stiffener material?

Typically, PCB stiffeners are made up of FR4 or rigid polyimide. One of the oft-used polyimides in PCB stiffeners is Kapton.

The thickness of a typical stiffener ranges from 0.002″ to 0.059″. The thickness of the Kapton stiffeners range from 0.002” to 0.010” and the thickness of the rigid stiffeners range from 0.008” to 0.059”. Broadly, of course the thicker the PCB stiffener, the better support it offers. However, the requirement of each design is different.

Some use cases also necessitate the use of stainless steel or aluminum as PCB stiffeners. The disadvantage with using those, of course, is the prohibitive cost.

How to use printed circuit board stiffeners?

In case of plated through-hole components, the PCB stiffener is located on the same side of the flex as the components. With this, access to solder pads on the flex circuit is easier.

It is also possible to attach stiffeners to both sides of a part however, in such cases the PCB assembly needs to go through an array configuration review.

When an assembly array is required for flex circuit designs, it is recommended to use the FR4 stiffener throughout the array border. By doing this, you eliminate the need for any additional tooling plates. Besides, it allows the parts to run through the automated assembly much like a rigid circuit board.

When it comes to attachment of a stiffener to a circuit, heat and pressure is used. A pressure-sensitive adhesive can also be used to attach PCB stiffeners.

Two popular types of adhesives include:

  • Pressure Sensitive Adhesives
  • Thermally Bonded Adhesives

To make the right selection of adhesives, some of the factors that need to be taken into account include:

  • Thermal Exposure
  • Chemical resistance
  • Adhesive capacity when it comes to different materials.

PCB Stiffener Considerations

When using stiffeners, it is important to note that they should overlap bared coverlay by .030” to relieve stress. Also, when using multiple stiffeners, the same stiffener thickness should be maintained.

To sum up

The advantage of using a PCB stiffener when we need a rigid area in the circuit, in order to protect components or connectors, cannot be overstated. By doing so you can ensure that the circuit doesn’t bend and that the integrity of solder joints is protected. It is common to use FR4 as stiffener material for rigidizing specific areas of the circuit.

At Technotronix, we are fully equipped to handle your PCB manufacturing requirements. With over 4 decades of experience in rigid-flex PCBs with differing levels of complexities, our team of experts and state-of-the-art equipment ensure that all our PCBs meet the industry standards of quality and testing.

For more information, contact us via email at [email protected] or call us on 714/630-9200.

The Complete Guide on PCB Milling in Circuit Board Fabrication!

By | Date posted: | Last updated: November 30, 2021
PCB Milling

PCB Milling also sometimes referred to as isolation milling or seclusion milling is an important process that is required to ensure high quality PCB boards.

Simply put, PCB milling is an eliminative process that involves the removal of copper tracts from the PCB substance. This ensures that pads are reproduced and configurations established on the PCB design. While milling is similar to etching, in that both are eliminative processes, milling, unlike etching does not involve the use of any harmful chemicals. It is therefore an ideal choice for anyone without a proper lab environment for etching. Also, etching chemicals are usually corrosive and produce harmful fumes when they react with copper traces.

Advantages of PCB Milling

PCB Milling offers a number of advantages when it comes to prototyping as well as some special PCB designs. The biggest advantage, of course, is that it does not involve the use of harmful chemicals. With etching of course not only do you need proper chemical handling but also a proper disposal method in place. The wet process is also unsuitable for high resolution boards.

With a CNC PCB milling machine you can create quick PCB prototypes without worrying about the chemicals. Also the CNC machine can undertake both drilling as well as milling and in some cases also the cutting.

It is important to remember, however, that both milling and etching are preferred under different circumstances. If the requirement is for mass production, for instance, etching is preferred.

PCB Milling Design Parameters

Below is a detailed guide on the design parameters involved in PCB Milling:

  • The regular diameter of the PCB mill device is 2 mm while
  • the lowest diameter is 0.8 mm.
  • The internal or external silhouette of the PCB can be milled as per requirements.
  • The borders of the rectangle need to be circular. It is also important that the connected milled area is pierced at every intersection.
  • The skeleton and separations of the PCB are milled as in its absence the strength of the PCB board may be impacted. Also, the internal and external silhouette of the PCB board needs to have a layer width of 1 micrometer.

PCB milling process

It essentially involves two systems, namely the hardware and software systems.

Software system

There are two types of software:

  • Raster
  • Vector

Raster typically does not have high resolving power as compared to Vector.

Hardware system

The hardware system is the numerically controlled milling machine. The system has either a serial or a parallel port that is connected to the main controller. On receiving the signals, the controller drives the positioning system which adjusts the milling head speed.

The movement around the X/Y axis is controlled by stepper motors. The Z-axis drive is also powered by a non-monitored lead screw.

Tips for CNC PCB Milling

Some of the tips to ensure effective printed circuit board milling include:

Leveling

This is crucial as you need to ensure that a uniform level is achieved when subtracting the metal layer off the board. Leveling can be achieved in two ways, physical leveling and computer leveling. Physical Leveling is done using a floating head CNC machine. The milling tool is maintained at a fixed distance from the board. Computer Leveling offers yet another possibility of achieving a uniformly milled PCB. In this leveling, the distance from the board is adjusted through a software.

Track clearance

It is important to pay due attention to the track clearance. Typically a 0.5 mm track clearance is used.

G-Code files

If you are using a machine that can undertake cutting, drilling as well as milling, it is important to have a G-code file for every operation

Coating

It is important to apply a solder mask as once milled the exposed copper can erode.

Safety

When drilling fiberglass you will be subject to dust. It is important that the dust isn’t inhaled. For this purpose, a vacuum cleaner should be used. You can also avoid this issue by using non-dusty FR1 and FR2 copper clad boards.

To sum up

PCB Milling offers a cost effective solution to make strong boards. It is imperative however to follow these tips to ensure that the process is effective.

Technotronix is one of the leading PCB manufacturers based in the USA. We have adopted advanced methods and technologies, which can give you the finest PCB fabrication services. We are adhering to strict high-quality standards and compliant with the RoHS (Restrictions of Hazardous Substance) directives.

If you have questions or queries related to any kind of PCB manufacturing services, email us at [email protected] or call us on 714/630-9200.

Top EMI and RF Shielding Methods for Custom Flexible PCB!

By | Date posted: | Last updated: November 11, 2022
custom-flexible-pcb

Custom Flex PCBs are subject to both Electromagnetic as well as Radio Frequency Interference. In turn, this can lead to a whole lot of consequences including but not limited to an increase in error rates.

To protect custom flexible PCBs against this interference, it is important to carry out EMI shielding. This can be done by way of copper layers, silver ink and shielding films, each of which comes with a distinct set of advantages and disadvantages.

Let us look at the process in some detail as also look at the selection parameters:

What is EMI and RF shielding?

It is a method that prevents electromagnetic and radio frequency interference from external signals.

In addition, it prevents high-frequency signals from leaking out. This is done by using metallic barriers. Essentially the shielding effect is based on a principle used in Faraday Cage, which is that the metallic screen surrounds the sensitive or transmitting electronics.

In selecting the type of EMI shielding, it important to consider the following two aspects, namely the bend requirements and the controlled impedance.

Bend requirements

The minimum bend capacity is a function of the thickness. It can, therefore, reduce the bending capacity of the PCB. It is important, therefore, to evaluate the minimum bend radius and bend type requirements for shielded designs. Another aspect to consider includes whether the bend required is static or dynamic. It is important to remember that the bending capacity of a dynamic flex circuit board is far higher than that of a static one.

Controlled impedance

In Flexible PCB Board, the controlled impedance signal requirements also impact the EMI & RF shielding approach. The shields need to have electrical properties that meet the necessary criteria to obtain the appropriate impedance values.

Types of EMI & RF shielding used in Custom Flexible PCB

EMI shielding is done using 3 types of materials, namely:

  • Copper Layers
  • Silver Ink
  • Shielding Films

In making the choice of material, some of the considerations include:

  • Shielding Performance
  • Mechanical Bend Capabilities
  • Suitability for controlled impedance

Copper Layers

Here the copper layers are used either as solid or cross-hatched planes. They are linked to the ground through stretched vias. The solid copper layers tend to provide a higher degree of shielding. Cross-hatched layers, on the other hand, are used where shielding is required without impacting the board flexibility.

The disadvantage of this shielding, stems from the fact that it increases the thickness which in turn affects the bending capacity. In fact a three-layer copper shielded flex circuit increases the thickness by nearly 125%.

Also, the fact that the shielding layers are connected to the ground plane through vias, tends to act as a mechanical stress concentrator.

Silver ink

As opposed to copper layers, silver ink has the advantage of offering greater flexibility at a lower cost. A silver ink shielded flex circuit is only about 75% thicker. Additionally, silver ink uses selected perforations in the coverlay. These perforations, in turn, allow for electrical interconnections.

Also, silver ink is relatively inexpensive as compared to other shielding material.

Specialized shielding films

These are suitable for dynamic bend applications and are suited for small structures. These also work well in sensitive applications.

Essentially it involves an electrically conductive adhesive, a metallic layer, and an insulating layer to be laminated. It is then bonded on the surface of the coverlay.

In terms of thickness, a 2-sided shielded film is only 15-20% thicker.

What are some of the design tips to avoid EM and RF interference in Custom Flexible PCB Boards?

  • Sharp bends need to be avoided as they lead to fluctuations in impedance and signal reflections.
  • It is important to isolate high-speed and low-speed signals.
  • It is imperative that the current return path be kept small
  • Vias should not be placed in differential pairs
  • If split ground planes are required, they should be connected at a single point

To sum up

To ensure that the shielding is reliable and cost-effective, it is important to undertake a thorough examination of all aspects of the electrical and mechanical design factors. This will help in arriving at the right shielding method that works well for your Flex PCB.

At Technotronix, we are fully equipped to handle your PCB manufacturing requirements. With state-of-the-art equipment, we deliver the highest quality boards that you can rely on. No matter how complex your requirement, you can count on us to deliver to your bespoke needs. Our stringent quality control processes ensure that the boards deliver to your benchmarks.

To get more insights into the PCB fabrication, multilayer PCB fabrication & quick turn PCB fabrication, please explore our PCB fabrication services. Also, you can drop an email to [email protected] to solve your queries or to get a quote for custom flexible circuit boards, rigid-flex PCBs, flexible printed circuit boards manufacturing, flexible PCB prototyping.