Benefits of PCB Prototyping

What is a PCB prototype?

A PCB prototype is essentially an early sample of a product that is used to test design concepts and their feasibility. While most prototypes are created for testing basic user functionality, a PCB prototype should also have some level of functionality, as it is made to test the overall design.

During the PCB prototyping process, engineers can experiment with different PCB design and manufacturing specifications to find the most effective one.

What are the benefits of PCB prototyping?

Shortens time and saves cost

PCB prototyping helps speed up the entire design and manufacturing process by allowing PCB design engineers to quickly and accurately test design issues. Without this, discovering design flaws would take more time and potentially lead to customer dissatisfaction and revenue loss.

Better communication with customers

Providing a prototype as an aid helps customers better understand the design, which can minimize communication time and customer requests for redesign.

Minimizes rework

PCB prototyping testing can help identify and fix circuit board issues before production, reducing rework. Defective products that go into production will take more time and cost more money to fix.

Helps with smoother manufacturing and production

When using a third-party PCB prototype manufacturing service, it is important to have a good communicator. There are several things that can lead to errors during the design process, including too many revisions without proper communication, design blind spots, and design rule checking (DRC) limitations. Some prototype manufacturers have methods for avoiding these issues, making PCB prototypes more suitable for the testing process.

Early testing and viewing of product functionality

Accurate and reliable PCB prototypes make it easier to solve design problems throughout the entire development process. High-quality prototypes represent the final product’s functionality, allowing engineers to test and evaluate aspects such as PCB design, functionality, and operational conditions.

Testing individual components

Engineers often use PCB prototypes for testing, particularly for single components and functions. This type of testing can help verify design theory, decompose complex designs, and reduce manufacturing costs by discovering design flaws earlier.

PCB Prototype Manufacturing Specifications

Size

This is simply the size of the PCB. The cost of a PCB is proportional to its surface area, so it is important to use space efficiently and minimize costs. Irregularly shaped PCB designs can result in material waste during the manufacturing process, while smaller rectangular PCBs can be more expensive.

Layers

The number of layers in a PCB is a basic indicator of complexity. The additional copper layers in a PCB can be thought of as stacked highways. When the electrical connections between components and pins overlap, electronic flow can be routed in them.

Material Type

Standard multilayer PCBs are made up of several layers of copper-clad boards stacked together. The most commonly used PCB material type is glass epoxy resin or the more well-known FR-4, where FR stands for flame retardant and the number represents its flammability.

However, care must be taken when designing high-speed or RF boards, as the dielectric properties and thickness of the material are very important.

PCB Thickness

Depending on the number of copper layers, the PCB manufacturer will choose the PCB core size to produce the required PCB thickness. If the PCB is enclosed in a tight space, a thickness of 1.0 mm or less may be required. Manufacturers can usually accommodate thicknesses as low as 0.4 mm.

Surface Treatment

Solder pad plating is a technique in which the exposed copper surface of a PCB is coated with another metal material to improve the solderability of the pads during assembly. The most common plating technique is leaded or lead-free HASL (hot air solder leveling), which applies solder to the circuit board during PCB assembly. Another technique is ENIG (electroless nickel immersion gold) plating. This is a more expensive plating technique, but it provides improved oxidation resistance and surface flatness, making it an excellent choice for large BGA components and exposed contact pads or test points.

The left PCB is plated with ENIG, while the right PCB is standard HASL. We can see from the picture the HASL pad is uneven, while the ENIG pad is completely flat.

Impedance Control

If there is radio equipment (Wi-Fi, Bluetooth, etc.) on the PCB, impedance control may need to be specified. Impedance control means that a group of specified traces (usually RF networks) presents a known resistance to all signals transmitted therein.

Impedance is influenced by a variety of factors, including the dielectric of the prepreg material, trace width, and solder mask layer. Controlling impedance is critical for optimizing wireless antenna performance. For example, Wi-Fi antenna circuits are typically controlled to 50 ohms impedance. Impedance control requires expensive equipment, and not all manufacturers can guarantee impedance control. This may increase manufacturing costs, and if the tolerance for controlled impedance is relatively strict, the cost will be higher.

Minimum Width/Spacing

This is a measure of the minimum width of copper traces on the PCB and the minimum distance between each trace.

Hole Size

The size of holes and vias (perpendicular electrical connections established between copper layers) on the circuit board. Specifying small pads and vias on the PCB is a good way to save space, but it also makes manufacturing more difficult. Smaller holes mean tighter tolerances during drilling and generate more waste.

Solder Mask

The solder mask helps prevent solder bridges and potential shorts and is typically applied to the copper traces on the PCB. In addition to the standard green, you can choose red, yellow, blue, black, or white.

The image above shows a pre-production sample where occasional discoloration can occur during high-temperature reflow soldering and wave soldering steps.

Discoloration of pink on white solder mask (left) caused by residual chemicals during PCB manufacturing and high temperatures during reflow and wave soldering. Normal sample on the right.

Silkscreen

The silkscreen is used to record and annotate text, graphics, and symbols on the PCB.

A more accurate alternative to silkscreen printing is LPI (liquid photo imaging) printing, which can create much higher resolution silkscreen printing at a slightly higher cost.

Comparison of LPI (left) and traditional silkscreen legend printing (right) at the same magnification.

Minimum Spacing

In the PCB field, “spacing” refers to the distance between adjacentcomponents or pads. Minimum spacing is an important specification to consider to ensure that there is enough clearance between components to avoid shorts or overlaps. It is also important to consider the spacing between different nets to ensure that there is no interference or crosstalk between signals.

Panelization

Panelization is the process of grouping multiple PCBs on a single panel for manufacturing. This can help reduce manufacturing costs and speed up production time by allowing multiple boards to be manufactured simultaneously. Panelization also provides more efficient use of materials and reduces waste.

Copper Weight

Copper weight refers to the thickness of copper on the PCB. The standard copper weight is 1 oz per square foot, but it can be increased to 2 oz or 3 oz for increased current-carrying capacity. However, increasing copper weight also increases the cost of the PCB.

Finish

The finish is the final coating applied to the PCB after manufacturing. The most common finishes are leaded or lead-free HASL, ENIG, immersion silver, and OSP (organic solderability preservatives). Each finish has its advantages and disadvantages, and the choice of finish will depend on the specific requirements of the PCB.

In summary, when specifying the manufacturing specifications for a PCB prototype, it is important to consider factors such as size, layers, material type, thickness, surface treatment, impedance control, minimum width/spacing, hole size, solder mask, silkscreen, minimum spacing, panelization, copper weight, and finish. Each of these specifications can impact the functionality, cost, and manufacturability of the PCB, so careful consideration is essential to ensure a successful prototype.