How to prepare your PCB before the industrialization
Nowadays technologies are driven by the development of both software and hardware. However, if software program writing is related to the programmers’ skills, hardware crafting requires more technical specifics to be optimised, especially concerning electronic hardware.
Thus, as the basis of electronic hardware, Printing Circuit Boards (PCBs) crafting necessitates particular processes to be efficiently performed.
This week, Rahul Khurana, microelectronics expert at Usine IO will explain the inner working of PCBs manufacturing :
In this article, I will be talking very much in surface, covering all the important steps involved in the electronic development process in order to make it understandable for all.
“My perception and experiences with PCB suppliers and manufacturers led me to determine an approach to craft my own PCBs in 3 phases : prototyping, design and industrialization.”
However, this article will be focused around the two first phases.
The 1st phase of PCB manufacturing is the Prototyping which is the most important base of electronic development. Any development starts with an emergence of new idea or improvement of some existing solutions / products.
In any case, you need to validate your idea in real time. The very first step is the choice of Electronic Development Board (EDB) and is followed by the associated components like sensors, actuators, power modules and connectors etc.
The choice of EDB usually depends upon the following parameters :
· Microcontroller or FPGA : this depends upon the choice of your architecture and also your comfort of working, price etc.
· IO Pins : The access to the outside peripherals, it depends on the number of peripherals you want to communicate with.
· Clock Speed : This is one of the factor which decides the processing speed.
· System on Chip (SoC) facilities (Eg. Bluetooth, Wifi etc).
· Kind of use/ application
· Availability of technical information and support
· Ease of embedded programming or Integrated Development Environment (IDE)
(Be more specific about the involvement of the parameters, you could draw up a list of question the engineer must ask to himself (e.g. In which case Microcontroller is better than FPGA? )
Once the EDB choice is done, the next step is to choose your components. Thus this is important to :
· Read the data sheet very carefully ; mainly supply voltage, communication protocol etc, so that you can easily interface the components with your EDB
· Be careful of the power consumption and/or operating current. For example, actuators often need more power than the EDB capacity. In that case, you need to use a separated power supply and some interfacing power transistors/ MoSFETs (e.g. TP120)
Electronic Prototyping mainly consists in the following two phases:
- The Functional Validation phase
- The Testing and Debugging phase
This simply means realizing in real time the hardware of your idea and make it work. In most of the cases, electronic circuits won’t work because of one specific parameter.
For example, voltage supply changing, radio noise/ interferences, over heat, embedded software performances or power consumption problems are factors that work in interaction with the others, which means you have to configure each component taking in account all the other components.
In that case you need to test and debug all these problems one by one and iterate the test methods until the final objective is reached.
Circuit design mainly consists in
· Schematic Design
· Simulation (Either partial or for full circuit)
· PCB routing and design.
Once your prototype is functional then it comes to circuit design. A basic electronic prototype includes :
· Bread Board
· Connecting wires
· Power Modules
· Wireless Modules
· Antenna Circuitry
(general but non-exhaustive list)
Now you need to transform all these into one single circuit. In order to do that we must start with the circuit of EDB and study in detail microcontroller or FPGA data sheet. Generally, in a EDB there are many electronic components which are not used for your circuit because these boards are designed for a generic use.
These components could be:
· Interfacing Modules
· Power Supply Modules (sometimes, as you might have to choose another depending upon the power consumption of your circuit)
· Passive Components
· Connectors/ Headers etc.
Most of the EDB are developed in open source, meaning you have access to its circuit schematics most of the time. On the other side, the CAD files are unavailable because the format is not standardized, hence the necessity to start by reading in detail the data sheet of the microcontroller.
For the circuit design phase, I would recommend you to divide your circuit into various blocks/groups before interfacing.
These blocks could be:
· Microcontroller and Passive Components : All details are explained in the Data Sheet.
· Power Supply Modules : Be very careful about the choice of the PS components. Using an inapt PS component may damage your entire circuit. Of course this step is done in prototyping stage, but some additional subtractions always appear.
· Sensors, Actuators and other components : Normally they are already qualified during the last step, but always be careful about their positioning in the circuit, as they will have to interact with the outside world so these components shouldn’t be hidden.
· Accessibility and Peripherals : This is the most important part which normally we don’t test during the prototyping phase. Once your circuit is designed, you need to test, program, debug, interface it. For this you will need some provisions, like JTAG, ICD, Test Points etc.
Based upon the above architecture, design the electronic circuit, using any of the CAD software convenient for the user.
The most commonly used electronic CAD software are KiCAD and Eagle.
KiCAD is totally in open source and free to use. However, Eagle is not in open source, but is free to use. The Eagle’s free version limits you in terms of board size, and single layer hierarchy designs. Single layer here doesn’t mean single layer of PCB but single layer schematic hierarchy.
However, in professional circuits, we use high end platforms like ADS, Altium, Proteus, Cadence, Upverter etc. apart from circuit design sophistications and big libraries, those software also have inbuilt spice (or other) simulator, which saves a lot of iteration time.
Some component manufacturers give access to their personalized simulation environment like Linear technology’s LT Spice or Texas Instruments’ TINA.
PCB Routing and Design
I would like to enlighten you about the second step : PCB routing and design.
This can be very simple and very complex in the same time depending upon the nature of your circuit. In general, I look this complexity in two ways:
· Circuit without Radio Signal / without Antenna
· Circuit with Radio Signal / Antenna.
The circuits without radio signal avoids the complexity of antenna, it matches network and many other associated complexities in routing. Electromagnetic guidelines for PCB is a very vast topic ( I should write a Medium about it later ! ).
But generally speaking the following factors are accountable for the complexity of PCB routing :
· Number of copper layers
· SMD / Through Hole / Single Sided / Double Sided Components
· Vias and Holes : For example micro vias below the smd components
· Connectors / Test points : Their positioning should be convenient of the ease of access.
· Signal Ground / Power ground in RF circuits : In RF circuit the PCB routing is complicated, so one needs to follow the proper guidelines.
Bill of Material Generation : Once your circuit design is done you can very easily generate your BoM. But in most of the cases you will need to customize or optimized it for components price and supplier’s reference.
Manufacturing the PCB : This is done by generating the Gerber File from your CAD software. Gerber is the machining file which is sent to the manufacturer. Depending upon the complexity of soldering, you can either go for PCB — B (Bare PCB) or PCB — A (Assembled PCB). But be careful that PCB — A is 5 to 7 times more expensive than PCB — B mainly because of production cost.
Test and Debug : Once your PCB manufactured, you must test and debug it. You will rarely success at the first try because a lots of mistakes may occur during the previous phases (especially during the schematic design of circuit). If the problems origins come from the hardware (and not the embedded), you will have to adapt all debugging techniques by using simple millimeters to high end oscilloscope.
Once your PCB is functional in normal conditions, then you should test it in abnormal conditions, to define the tolerance limits. These conditions could be :
- Continuous Power ON for long hours Conclusion:
Electronic prototyping and design are the basis of electronic development. Thanks to the development board one can start to play and innovate in electronics without being an electronics engineer. However fine tuning of hardware and embedded code need an expertise.
If you have an idea in electronics or a basic prototype or if you would like to develop one, then I would be happy to work with you.