Understanding PCB Prototyping and Fabrication Process Options

July 24, 2020 Cadence PCB Solutions

Key Takeaways

  • Why is PCB prototyping important?

  • What is rapid prototyping of PCBs?

  • What are the additive manufacturing processes for fabricating PCB prototypes?

  • How is additive-subtractive manufacturing used to fabricate PCB prototypes? 

  • What is required to facilitate the best choice for your rapid PCB prototyping and fabrication process execution?

Gazelle oblivious to a nearby lioness

Unaware of pending danger

Mother nature is wondrous, and one of the things that I find most fascinating is watching the interactions between animals in the wild. The suspense and pending danger of a predator, such as a lioness looking to provide sustenance for her young, approaching an unsuspecting gazelle is exhilarating. This is one of those times where the saying, “what you don’t know can’t hurt you” surely does not apply; however, “ignorance is bliss” may be applicable right up until the gazelle realizes it may be on the lioness’s menu. 

Lack of knowledge can also be a problem when designing PCBs for prototyping. For example, not knowing Design for Manufacturing (DFM) rules and guidelines that align with the equipment capabilities of your contract manufacturer (CM) can result in seemingly endless back and forths before a manufacturable design is achieved and an accurate quote can be obtained. Conversely, being knowledgeable of how your boards are built enables you to design for ease of fabrication.  Let’s take a look at the PCB prototyping and fabrication process options that are available to you and how you can design to facilitate their successful execution. 

Why is PCB Prototyping Important?

The essentialism of PCB prototyping is best understood by first clearly defining the circuit board development process, as shown below.

Printed circuit board development iteration flow chart

PCBA development cycle

IMG: PCB Prototype Iteration.jpg in Cadence | Software Images/Rapid Prototyping.

As illustrated above, developing circuit boards is typically cyclical and consists of numerous iterations. Each iteration is comprised of design, build, and test stages performed with the intent of improving the quality of the design. This technique of continually modifying the board until all errors have been corrected and the desired quality is achieved is known as PCB prototyping.  

The Role of Fabrication During PCB Prototyping

The build stage of development is where the physical embodiment of the design is constructed. During each iteration of the prototyping cycle, a new board is built or fabricated. Each new board, or set of boards, is then tested. During prototyping, testing is primarily done to validate functionality and operation. 

Bare board PCB

Fabricated PCB

The fabrication process will yield a PCB or bare board, as shown above, where no elements are attached. Although, the locations for electronic component placement or footprints and corresponding pads are laid out. Subsequently, the components are connected to the board using through-hole soldering, surface mount technology (SMT), or a combination of the two to yield the final PCB assembly (PCBA), ready to be tested. Depending upon board complexity and your CM’s manufacturing, this process can take days or even weeks to yield a prototype. 

To improve the overall speed of development, rapid prototyping techniques have emerged that employ additive manufacturing. These additive manufacturing fabrication processes are capable of building prototypes in less than a day. And there are many options available for your PCB prototyping, as discussed below. 

Building PCB Prototypes Using Additive Manufacturing Methods

Additive manufacturing is often used interchangeably with 3-D printing, which is a method of fabricating objects by successively adding layers of material. This method offers engineers and board designers the convenience of fabricating single or small numbers of PCB prototypes right at their desks.

3D printer and computer demonstrating the creation of a small globe

PCB prototype design and fabrication equipment at your fingertips 

Let’s take a look at some additive manufacturing techniques for PCB prototyping and fabrication.  

How to Fabricate Boards With Fused Deposition Modeling 

As its name implies, Fused Deposition Modeling (FDM) creates objects by stacking layers and fusing them together. Each layer is typically composed of a thermoplastic that can be fused through a heating and cooling process, such as the ones listed below:

FDM Materials

  • Acrylonitrile Butadiene Styrene (ABS)

  • Polyethethylene Terephthalate (PET)

  • Polyethylene Terephthalate Glycol (PETG)

  • Thermoplastic Polyurethane (TPU)

PCB prototypes can be created by combining FDM with stereolithography (SLA), Laser Direct Write (LDW), and other processes to add conductive materials and embedded components. 

Read this article for more explanation on the Fused Deposition Modeling process. 

The SLS Technique of PCB Prototype Building

Selective laser sintering (SLS) is one of the power bed fusion techniques that uses a laser to make nylon or polyamide parts. The process begins with a powdery substance, which is then heated to form different shapes without liquefication. 

More information can be found here on the selective laser sintering process in electronics manufacturing.  

Fully-Automated Additive PCB Prototyping

One of the advantages of rapid prototyping techniques is the minimization of equipment or machinery needed for fabrication. Typically, only one machine, such as a 3D printer, is required and no tooling equipment, such as lathes or drills, that is used for conventional PCB fabrication is needed. Processes that exhibit this lack of tooling along with the absence of human intervention between the computer model and final product are examples of solid freeform fabrication or SFF. 

You can learn about targeted design for solid freeform fabrication here.

In addition to additive processes as discussed above, there are also additive-subtractive manufacturing techniques for PCB prototype fabrication. 

Additive-Subtractive Manufacturing Processes of PCB Fabrication

The opposite of additive manufacturing is subtractive manufacturing, where an object or product is created by removing or cutting away excess material from a larger solid. When both of these techniques are required, the process is additive-subtractive, which is also used to fabricate PCB prototypes as discussed below.  

Constructing PCB Layers by Laminated Object Manufacturing

Another rapid protyping technique is laminated object manufacturing (LOM). The LOM process is similar to the methods discussed in the previous section in that the object construction includes a bottom up process of adding successive layers. However, the layers, which may be paper, plastic, or even metal, are typically glued together, and the final product is formed by cutting away excess material using a knife or laser tool. 

Here you can find more information on laminated object manufacturing. 

How to Optimize PCB Stackup and Layout Fabrication

Although the use of rapid prototyping techniques is expanding, by far most PCBs are fabricated employing an additive-subtractive process. The PCB stackup, an example of which is shown below, is built by adding successive layers and using an adhesive to secure them, as is done for LOM. 

Allegro cross section editor

PCB layer stackup design with Allegro

As illustrated in the figure above, there are several conductor layers. Unless a conductor layer is a solid plane, excess copper must be etched away to create trace routes and component pads for the surface(s). This removal of copper, coupled with the drilling of holes that are not refilled, such as through-hole vias and mounting holes, is a subtractive manufacturing processes. 

Additional PCB Prototyping Considerations

In virtually all cases, fabrication yields a PCB or board without components. Therefore, component attachment or assembly is required to complete the prototype. As discussed previously, there are some inroads into embedding components for rapid prototyping. 

Additionally, a new additive manufacturing fabrication technology where certain types of components can be embedded during fabrication has been developed. Although not widespread, this and other technologies are advancing in popularity.  An additive-subtractive manufacturing example is component in flex (CIF) that seeks to maximize the use of internal board space by embedding components on internal layers. One thing that all of these PCB prototyping fabrication methods have in common is that they require you to have the proper design tools for the best process facilitation. 

Design Tools for PCB Prototyping and Fabrication

Not all PCB design software is developed with the capabilities that promote the use of additive manufacturing processes. For example, these methods require you to design a 3D model, as shown below, and export it in a format that your fabrication equipment can utilize. 

3D rendering of a side profile view of a mutilayer PCB

3D inspection of fabricated PCB prototype

In contrast to the contemporary PCBA prototype manufacturing process, where rework can be done to correct errors during assembly, 3D printed electronics do not lend themselves to repair. Therefore, the ability to eliminate potential issues that may result in manufacturing errors should be corrected during design. This is best achieved if your have the following design tools.

PCB Prototype Fabrication Design Tools

🔧    In-Design Analysis

The ability to check and make corrections as you design is a major advantage.  When combined with your CM’s rules and guidelines, this allows for real-time Design for Manufacturiing (DFM) verification that enables quicker designs and reduces or eliminates manufacturing delays and subsequent redesigns.

🔧    Comprehensive Constraint Management

Most PCB design packages include some degree of design rule checking (DRC). However, for rapid PCB prototyping, accuracy of specifications and dimensions is critical. And, robust constraint management is necessary.      

🔧    Design Manufacturability

The ultimate metric of your PCB prototyping process is whether it supports and aids manufacturability or not. This includes capabilities such as 3D file format exportation and design signoff to compare with your CM’s specifications. 

Being aware of the options available for PCB prototyping and fabrication, and the tools necessary to best design for them, will aid you in making the best choice for your project.

With Cadence’s industry-leading PCB Design and Analysis package, these recommended tools are inherent. Additionally, with Allegro PCB Designer you are able to design for fabrication, assembly, and test, as well as perform 3D inspections at any stage of design.  

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

 

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

Follow on Linkedin Visit Website More Content by Cadence PCB Solutions
Previous Article
Analyzing the Venturi Effect in CFD Simulations and Testing
Analyzing the Venturi Effect in CFD Simulations and Testing

With the right field solver, you can analyze the Venturi effect in CFD simulations for your electronics.

Next Article
Considering PCB Assembly Cost And Design Constraints
Considering PCB Assembly Cost And Design Constraints

PCB assembly cost is a crucial component of any PCB design project. Here are a few key considerations with ...