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1st November 2021

PCB Types, Layer Counts, and What You Should Consider 

Printed Circuit Boards (PCBs) come in a variety of materials and layer counts. These allow you to maximise certain product strategies.  

For example, if you are producing at high volume, cost reduction will be important for Return on Investment (ROI). Whereas if your product’s appeal is based around minimised space then your considerations will be different. 

The Ignys Team have a lot of experience with electronics design services. Read more about PCB types and the pros and cons below.

PCB types and when to use them 

Here are the typical PCB types and some tips on when to use them. Each product is unique in some way. With that in mind if you are struggling to decide set up a discovery call with our engineering team. 

First, we’ll tackle the number of layers and then we’ll explore rigid versus flexible PCBs. 

PCB layers Pros and Cons 

Single sided PCB design 

These simple level circuit boards have copper on just one side of the board. 

Pros of single sided PCBs 

  • They are simple to design and manufacture 
  • They are extremely cost effective when mass produced due to their simple construction 
  • They are easier to test during the production stage 

Cons of single sided PCBs 

  • You can only use a certain number of components 
  • Complexity is low and may not be suitable for some products and devices 

Example of when to use a single sided PCB 

If you are selling in huge volumes, then product cost reduction becomes very important. Every penny (or cent), added to the cost per unit adds up significantly over your full volume. This effects profit margins on every product.  

If your product is focused on a simple concept that appeals to a mass market, then single sided PCBs can be a cost-effective way to design quickly and avoid the complications of double sided or multi-layer PCBs. 

Double sided PCBs 

In this case copper is present on both sides of the board and tracking can be done on both sides. Connectivity between the top and bottom of the board is achieved using vias which are small, drilled holes plated with copper.  

Pros of double-sided PCBs 

  • There is effectively double the amount of space and usable surface area when compared to a single layer board of the same size.  
  • You can add complexity to the design whilst maintaining the same physical space as a single layer board. 
  • Still relatively cost effective to produce. 

Cons 

  • More expensive than a single layer board. If you are only using a few components on one side, you may want to consider using a single layer board 
  • Manufacturing and production testing is more complex than single layer boards 
  • The complexity is more limited than multi-layer boards 
  • The board layer count can make EMC (electromagnetic compatibility) more difficult due to limited options on power and ground planes and routing restrictions. 

Example of when to use a doubled sided PCB 

Where you have a mass market and want to create a medium complexity device, but space is not too much of a premium. This way you can save costs, keep space low and add some extra features.  The lowest cost double sided pcbs have components on one side of the board and use the other for more complex interconnections.  This keeps the component population costs low. 

Multi-layer board design 

Multi-layer boards have layer counts of three or more. Due to the manufacturing process, pcb layer counts are most commonly an even number with 4,6,8,10,12,14,16 and more layers. These higher layer counts allow electronics engineers to design more complex products . 

Using a multi-layer board allows you to use a wide range of high-speed and radio-frequency design techniques and to have robust power distribution and ground returns. Modern, dense device packages such as Ball Grid Arrays (BGA) force the requirement for multi-layer printed circuit boards simply to gain access to each of the signals. 

Pros of multi-layer board design 

  • You can control impedance. Manufacturers can produce a PCB stack-up that matches the design engineer’s specification.  
  • You can produce a high-speed layout that wouldn’t be possible on a single or double layer PCB because the impedance isn’t as easily controlled. 
  • well-designed multi-layer PCB will generally have a better EMI signature than the same design on a two-layer board. Electro Magnetic Compatibility (EMC) can be a significant contributor to the development cost of a product, so any risk reduction here can be a big cost saver.  
  • Your printed circuit board can be smaller 
  • Fun fact: Our electronics engineers at Ignys have tackled up to 25 layers and have experience from previous jobs of up to 40 layers. 

Related: Ignys PCB Layout Services

Dan Engineer at Ignys

Cons of multi-layer board design 

  • The costs increase as the layers go up – Therefore extra layers should be used when needed only. Added parts, manufacturing costs and development challenges all add up to money. Make sure this is part of your product’s ROI plan and pricing strategy. 
  • Extra design complexity – Complex electronics design means a lot of testing and a lot more than can go wrong. 
  • Test accessPrototype bring up testing can require access to all signals on the board for debug.  High layer count pcbs with BGA, LGA and QFN component packages can mean the signals aren’t accessible or modifiable on the early prototypes. 

Related Topic: The importance of test points

Example of when to use multi-layer boards 

These are great for more complicated projects where many features are needed, and a high level of engineering is required. These are often produced for a premium cost bracket product or a high sales volume product meaning the costs of development can be easily recouped. 

PCB Types 

Rigid PCB Designs

This is the most traditional form of PCB that most people immediately think of when they think of a PCB.  

An FR4 core is usually sandwiched between the conducting copper layers. FR4 is a fibre glass resin material, and is the most common PCB substrate, although a wide variety of other materials are also available. Compared with flexible and flex-rigid boards, rigid PCBs are generally less expensive to manufacture. If space isn’t a consideration but costs are, then rigid PCB could be the way to go.  

Super low cost designs may use FR1, FR2 or FR3 materials instead.  These have different properties for heat resistance, electrical strength, and thermal properties. These bring manufacturing issues and quality control concerns and should be used with care for a handful of use cases. 

At the other end of the spectrum are higher cost materials used for very high speed electronics as they have superior performance.  FR4 brings signal degradation issues at around 2-1GHz and is generally unsuitable beyond 20Ghz.  This is where ceramic or PTFE based boards are required. 

Applications which generate significant heat, such as LED lighting, often use aluminium pcbs which act as heatsinking. 

Flexible boards 

These are manufactured with a flexible substrate, often polyimide, rather than a fibre glass substrate. 

Pros of flexible PCB designs 

  • Allows the PCB to conform better within a complex product housing 
  • You can utilise a curved space within in a product and can use alongside rigid PCBs where needed 
  • Less susceptible to damage when the device is dropped 
  • More tolerant to high vibration and high heat environments 
  • Less affected by thermal cycling  
  • Multi-layer flexible PCBs are possible, so you don’t have to rely on a simple design 
  • Lighter weight than rigid PCBs.  

Cons of flexible PCB designs 

  • These are more expensive and difficult to manufacture 
  • There are more design guidelines that need to be considered when developing a flexible PCB 

Examples of when to use a flexible PCB 

There are two use cases where a flexible board design is ideal. 

1) Your product’s appeal relies on a small enclosure being used. Making less space available. To appeal to your target audience, you need your electronic device to not be cumbersome. 

2) Your product is expected to deal with bending during its lifecycle. For example, within a wearable smart watch device you can use flexible circuitry within it. To both avoid damage and make it functional for the set purpose.  

Rigid-Flex PCB designs 

These PCBs take the best of both worlds. Of course this comes at a cost! This hybrid option allows you to utilise the merits of both rigid and flexible PCBs.  

Pros of Rigid-Flex PCB design 

  • You can connect multiple rigid boards together using sections of flexible PCB. This means a multi-board design could be manufactured as a single assembly.  
  • You can use a rigid-flex PCB instead of connecting rigid boards together using traditional connectors. This eliminates the possibility of connectors coming apart when a product is subject to vibration. 
  • Great for small spaces, especially where a design is particularly space constrained, and you don’t have space for connectors within your enclosure. 

Cons of Rigid-Flex PCB design 

  • Additional manufacturing steps are required over both rigid and flexible boards, making this the most expensive option. 
  • A wide number of material options are available for both the rigid and flexible portions of the board. It is therefore essential to collaborate closely with your manufacturer, especially if controlled impedances are required. 

What to read next

How to Design For AvailabilityChip shortages and design

Cost or Investment? – Product development investment

Engineering Blog Authorship 

This blog was written with the knowledge of Toby Lane and with direct input from the Ignys engineering team. 

Toby Lane  

Toby Lane is one of our Ignys hardware engineers and joined us this summer (2021) following the completion of his master’s degree at the University of Sheffield. Toby also undertook a year’s placement at a product design and development consultancy, during which he assisted with projects utilising rigid-flex PCBs. His skillsets include analogue circuit design, electronics engineering and Altium Designer. This blog was produced alongside the marketing manager Hannah Ingram who has worked within tech sectors including electronics design and telecommunications.