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How to Identify the Special Size of the PCB
PCBs can be customized to any shape or size, depending on your application requirements.
This flexibility allows you to explore unique shapes and sizes that best fit your PCB project’s specifications.
For tailored circuit board manufacturing that meets the precise needs of your design, understanding the possibilities for PCB customization is key.
Special PCB Shapes
We see PCBs often coming in square or rectangle shapes. But you can make PCBs of any kind, such as:
- Round
- “L” shaped
- Polygon
- Oval
Indeed, there’s no end to ways you can give to your PCB. The different ways fulfill different purposes and fit in various enclosures.
You can use your PCB design tool to create PCBs of various shapes. Use the PCB editing window and choose a new design based on how you want to use it. You can also create your own form or edit current ones using the editor.
Special PCB Sizes
Just like PCB shapes, PCB sizes can also vary. Here, we are talking about PCB panel sizes. The standard PCB size for most manufacturers is 18 x 24 inches. You can also have other formats like 12 x 18 inches, 21 x 29 inches, and so on.
You should choose a size that is suitable for your application.
Now, we will explore different PCB materials.
Several Types of Special PCB Materials
You can make PCBs from a range of materials like epoxy, Teflon, and metal. Some of the unique materials include-
TG 150
TG refers to the glass transition temperature. The value refers to the heat resistance of PCB material. The higher the TG, the more is the heat resistance. TG 150 is a high heat-resistant material that you make from flame-retardant fiberglass reinforced epoxy. They are also known as FR-4 and can withstand high temperatures.
TG 170
TG 170 has a higher heat resistance than TG 150. You can use the material for high-temperature electronic applications. The content will withstand heat effectively and change to liquid over temperatures of 170 degrees C.
Rogers PCB
Rogers is a PCB manufacturing company specializing in high-frequency PCBs. The Rogers PCBs use FR-4 laminates and Teflon for higher-frequency properties. They can be more expensive than fiberglass but are resistant to losses in higher frequencies.
You should select material based on your project requirements.
In the next chapter, we will take a look at solder mask options.
In the PCB Assembly Special Solder Mask and Silkscreen
A solder mask is a permanent layer that you apply to PCBs. Solder mask safeguards copper traces and interfaces in the board. The coating prevents conductive solder bridging and eliminates short circuits.
What is a Liquid Ink Photoimageable Solder Mask?
Liquid Ink Photoimageable or LPI solder mask is an ink formula. You can spray LPI on PCBs and expose them to UV light to develop desired patterns.
What is a Dry Film Photoimageable Solder Mask?
It would help if, after development, you could solder parts on copper pads using the openings in the pattern. It would help if you used a vacuum to apply a Dry Film photo imageable solder mask. Then, you have the copper layer on the board, which you send for thermal curing.
What is Epoxy Liquid Solder Mask?
The epoxy liquid is the cheapest solder mask, and you apply it on PCB through silkscreen. Epoxy is a thermosetting polymer, and you use it for various electronic applications.
What is Silkscreen?
The silkscreen is the markings or letters that you use to identify PCB components and parts. Silkscreen uses inks of different colors, like white, red, black, or yellow. You can apply silkscreen using three processes-
- Manual screen-printing
- LPI (Liquid Photo Imaging)
- DLP (Direct Legend Printing)
Now comes the turn to explore PCB vias and drills.
Drills or Vias
Vias offers a conductive path for carrying an electrical signal in a PCB. Vias use plating holes to do their job and can be of different types. Here’s a breakdown of the special via processes-
Back drill/counterbore: Counterbore holes are standard screw holes drilled on the PCB. They can fit regular socket cap screws. Back drills negate transmission and connection to prevent reflection and scattering.
Plugged vias: You can fill vias using a mask or other non-conductive material. Before applying the cap, the hole is plated with copper.
Buried and blind vias: You use a blind via to connect inner layers with one outer layer. It doesn’t penetrate the whole board.
Buried vias connect at least two inner layers but are invisible from the outside. Both processes are ideal for space-restricted PCBs.
Inner hole: Inner hole is a type of process to make multi-layer PCBs.
Micro via: Micro vias are tiny holes drilled by a laser on a PCB. They create electrical connections in a multi-layer PCB.
Tenting vias: You can use Vias to the tent and cover the hole and annular ring with a solder mask. The process reduces the number of conductive pads that you can see otherwise.
Milling blind shot: Milling refers to removing copper from the board to create a PCB according to the layout. It is a chemical-free process, unlike etching.
Important Surface Treatment for PCB Assembly
You often find a surface finish on PCBs for protection and optimum solderability. Some of the joint surface finishes include-
Hard Gold
and gold is a suitable finish for keypads and edge connector fingers. Hard gold is very durable but is also expensive. It comes with a layer of gold that you apply over a barrier coat of nickel. The solid gold finish is labor-intensive and needs extra processing.
Nickel Palladium
Nickel palladium finish is that you apply on the PCB to make it resistant to abrasion. The process also improves conductivity and protects the copper layers. It is a simple process but not suitable for PCBs with higher density.
Immersion Tin/Silver/Gold
You can also use immersion tin, silver, and gold for the PCB surface finish. Immersion silver is ideal for fine traces and follows a simple finishing process. However, it is difficult to electric test and may have welding durability issues.
You use an immersion tin for lead-free soldering, which is suitable for SMT. However, the material needs careful storage and is not ideal for contact switches.
Immersion gold or ENIG is a standard surface finish and provides a flat surface for SMT. You can also use it for through-hole and high-thick panels. Immersion gold has a higher resistance to environmental attacks.
Gold Fingers
PCB connection points have to endure continuous plugging and unplugging. As a result, they can be vulnerable to malfunctioning. Connectors are plated with gold or other metals to strengthen edge connectors. It makes them endure wear and tear effectively.
Now, let’s check out the tooling implications for PCBs.
Electrical Testing-Important Steps to Detect the Function of the PCB
After the surface treatment, we need to detect the function of the PCB. Engineers perform mainly two types of tests- circuit continuity and isolation checks.
You will need to test the board to ensure there are no open circuits or short circuits. Electrical testing also determines the integrity of through-hole interconnections and tracks.
Sometimes, you also use flying probe testing. The process uses moving probes to check the electrical performance of each net on a bare PCB. It would help if you had electrical testing to ensure the quality and performance of your PCB batch.
Precautions
Tooling
Tooling is the process of creating PCBA; it’s the programming that you use to control pick and place mounting. You do tooling only once for a project, and you do not need any repeat orders.
Halogen Free
Some PCB materials that fall under the family of Halogen elements can be toxic and harmful to humans. Some halogen elements include-
- Bromine
- Fluorine
- Iodine
- Chlorine
- Astatine
Halogen-free PCBs have deficient levels of halogens to promote safety and health.
PCB Manufacturing–HF / CIT
You use the CIT technology to print copper on flexible substrates like PET. It is a low-cost process ideal for rapid prototyping.
HF or high-frequency PCB is typically made of PTFE material. They are suitable for high-frequency applications over 1 GHz.
Now, let’s check out the PCB electrical testing process.
Conclusion
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