Week 8. Electronics Production
Image Courtesy: Photo by Vishnu Mohanan on Unsplash
To produce our PCB, we will be using a milling machine to remove the excess copper from the board, leaving only the necessary circuitry. We will then solder the components onto the board as per our design, including a microcontroller, which will serve as the central processing unit of our device. Once the soldering is complete, we will program the microcontroller to carry out the desired functions.
Assignment Tasks:
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Group Assignment: Characterize the design rules for the PCB production process in-house.
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Individual Assignment: Make and test the development board that was designed earlier in the week to interact with and communicate with an embedded microcontroller.
Learning Process
Printed Circuit Board (PCB)
A Printed Circuit Board (PCB) is a flat board made of insulating material, such as fiberglass or plastic, that serves as a platform for mounting and connecting electronic components. It is a non-conductive material with conductive lines printed or etched. Electronic components are mounted on the board and the traces connect the components together to form a working circuit or assembly.
Printed circuit boards provide mechanical support for electronic components so that a device can be mounted in an enclosure. A printed circuit board design must include a specific set of steps that aligns with the manufacturing process, integrated circuit packaging, and the structure of the bare circuit board.
Conductive features on printed circuit boards include copper traces, pads, and conductive planes. The mechanical structure is made up of an insulating material laminated between layers of conductors. The overall structure is plated and covered with a non-conductive solder mask, and a silk screen material is printed on top of the solder mask to provide a legend for electronic components. After these fabrication steps are completed, the bare board is sent into printed circuit board assembly, where components are soldered to the board and the PCBA can be tested.
Types of PCBs
Single-sided: This board only has components mounted on one surface. The back surface is typically fully copper (ground) and coated with a solder mask.
Double-sided: This type of circuit board has components mounted on both surfaces. Each surface is defined as a signal layer in the PCB stack-up, so the surfaces will contain traces that carry signals between components.
Multi-layer PCBs: These boards have conductors on internal layers that carry electrical signals between components, or the internal layers could be conductive plane layers. Multi-layer PCBs may be single-sided or double-sided.
Rigid PCBs: These boards are fabricated and assembled on rigid laminate material, such as FR4-grade epoxy resin-impregnated fiberglass laminate materials. Other types of rigid laminate materials are available as well, which provide different material properties for use in some specialized applications.
Rigid-flex PCBs: Rigid-flex PCBs use a flexible polyimide ribbon that connects two or more rigid sections in a printed circuit board assembly. A rigid-flex board might be used when the design must have some movable element, such as a folding or bending enclosure.
Flex PCBs: Fully flexible PCBs do not use any rigid materials and are made entirely of flexible polyimide ribbons. These boards can have components mounted and soldered on the, just like rigid and rigid-flex printed circuit boards.
Metal-core PCBs: These boards use a metal slab in the core layer (normally aluminum) in order to provide much greater rigidity and heat dissipation than in typical rigid printed circuit boards. The metal-core PCB design manufacturing process is quite different from the standard rigid PCB design manufacturing process, and there are a few design points to consider to ensure solvability. These boards are common in high-power lighting and some industrial applications.
Ceramic PCBs: These boards are less common and are used in applications that require very high thermal conductivity such that the board can dissipate large amounts of heat away from components.
The Parts of PCBs
Substrate: The first, and most important, is the substrate material, usually made of fiberglass. Fiberglass is used because it provides a core strength to the PCB and helps resist breakage. Think of the substrate as the PCB’s “skeleton”.
Copper Layer: Depending on the board type, this layer can either be copper foil or a full-on copper coating. Regardless of which approach is used, the point of the copper is still the same — to carry electrical signals to and from the PCB, much like your nervous system carries signals between your brain and your muscles.
Solder Mask: The third piece of the PCB is the solder mask, which is a layer of polymer that helps protect the copper so that it doesn’t short-circuit from coming into contact with the environment. In this way, the solder mask acts as the PCB’s “skin”.
Silkscreen: The final part of the circuit board is the silkscreen. The silkscreen is usually on the component side of the board used to show part numbers, logos, symbols switch settings, component reference and test points. The silkscreen can also be known as legend or nomenclature.
PCB Substrate
PCB substrate is the insulating material that forms the base of the printed circuit board. It is the material onto which the conductive traces and electronic components are attached to create a functional electronic circuit.
The substrate material should be able to withstand high temperatures, resist moisture, and provide sufficient mechanical strength to support the electronic components. Common materials used as PCB substrates include fiberglass-reinforced epoxy resin (FR-4), polyimide (PI), phenolic paper material (FR1).
FR4
FR4 is a widely used substrate material in the production of Printed Circuit Boards (PCBs). It is a type of woven fiberglass cloth that has been impregnated with a flame retardant epoxy resin.
It is popular due to its excellent mechanical and electrical properties, making it suitable for a wide range of electronic applications. It has high tensile strength, good dimensional stability, and good resistance to moisture, heat, and chemicals. It is also highly flame-retardant, which is an essential property for electronic devices that may be exposed to high temperatures or fire hazards. FR4 is commonly used for both single and double-sided PCBs and is also used in multi-layer PCBs. It has a low coefficient of thermal expansion (CTE), which means it can handle a wide range of operating temperatures without warping or cracking. Additionally, it has low dielectric loss, which makes it an excellent choice for high-frequency applications.
FR1
FR1 is a type of substrate material used in the production of Printed Circuit Boards (PCBs). It is a type of phenolic paper material that has been impregnated with a flame retardant resin.
It is a low-cost substrate material that is commonly used for single-sided PCBs or for low-end applications where electrical performance is not critical. It has lower mechanical and electrical properties compared to other commonly used substrate materials such as FR4, but it is still an effective material for basic electronic circuits. However, it is important to note that due to its limited performance characteristics, FR1 may not be suitable for more advanced applications where higher temperatures, moisture resistance, or better mechanical properties are required.
Individual Assignment - “PCB Manufacture & Program”
The assignment for this week is to build and test a development board that was designed on our electronic design week asssignment.
This week doesn’t feel like a fresh start because it was the continuation of our electronic design week. It appears that we are on a path towards being able to create things that were once only a dream.
Stages that we go through:
1. PCB design, which we made on earlier week.
2. Familiarize with the components and their placement on the board.
3. Learn about the milling machine and its operations.
4. Review safety guidelines and best practices for using the milling machine.
5. Set up the milling machine and prepare the board for milling
6. Inspect the board after milling.
7. Review the soldering process and best practices.
8. Solder the components onto the board.
9. Finally, program the microcontroller to carry out the desired functions.
PCB Design
As part of my electronic week’s assignment, I designed a PCB the previous week. We were instructed to do this week’s milling will also be done with the same design. Detail design process is documented in Week 6.
The intial design I made was this.
As per my instructor’s suggestions, I made some minor adjustments, primarily reducing the size of the board because my previous design was a little larger in size and had a lot of waste.
Familiarize with the components
Bill Of Materials(BOM), which is the very first stage of production. Here we need to list down the materials we gonna use in this production, which includes:
a. PCB Board - 50mm x 50mm (Minimum Size as per design)
b. ATTiny 412 microcontroller - 1 no.
c. Capacitor - 100nf - 1 no.
d. UPDI - 2x3 pin - 1 no.
e. Resistor R220 - 2 nos
f. Resistor R1k - 1 no.
g. LEDs - 2 nos
h. Pinhead 1x6 - 1 no.
i. Button Switch - 1 no.
Materials were obtained from our lab according to the BOM and arranged in a notepad with tape because all of these parts are very small and the chances of losing them while handling are very high. Therefore, it requires more caution when handling and storing the materials until soldering them to the board.
Learn about the milling machine
Once all the required materials have been procured, milling can start. But first, we must become familiar with the machine used to mill our PCB. In our lab we have got one Roland Modela machine.
Roland Modela MDX-20
The Roland Modela MDX-20 is a very old, 3-d milling machine that can mill a variety of materials, including wood, acrylic, and others. However, in our lab, we only use this one for milling PCBs. The machine has a working area of 203 mm x 152 mm x 60 mm. he machine is controlled by Roland’s SRP Player software, but here we uses mods.
Safety Guidlines
This machine, like all the others in the lab, has safety guidelines that must be followed. Due to its age, this machine lacks any sensors that could detect whether or not someone was working on it. Therefore, always make sure the machine is in the idle position while changing tools. Make sure the end mill is always firmly fastened inside the spindle. Before and after use, you must make sure the tools are in good condition. Make sure the user’s senses of hearing and sight are alert to operational conditions.
When cutting or scanning, we must avoid touching the cutting tool or probe with our hands. Since the machine has a security lock, never use it if the cover is broken. Therefore, if it breaks, we might not know whether the lock is on or off. Never touch or push the cutting tool’s tip against anything, as this can harm the tool. Never leave the machine running or even just on. And never do any work alone.
Work safely and have fun while you’re at it.
Set up for Milling
Since this is an extremely basic milling machine, it has only a few settings. The changing of tools is a significant setting, and the origin setting is another.
We begin by first changing the tool. Prior to that, it is important to become familiar with the milling tool we used here. We are using two different bits in this instance, measuring 0.4mm (1/64”) and 0.8mm (1/32”). The first one was used to trace on the board, and the second one was used to mill the board into the shape we have already designed.
Changing the Tool
Step1: Insert the tool into the spindle. Place it until the only thing visible is the taper on the outside.
Step 2: Now lower the spindle using the down arrow on the switch panel. It should drop to the maximum height possible and leave the smallest possible space so that it can come down while milling or tracing through the material.
Step 3: Lower the tool by loosening the screws and making sure it touches the material before tightening back up. We have set the Z-axis origin. X-axis & Y-axis can be set via software.
Tool Used for loosening & tighten up the screw
Setting up in the Software
Here we use Mods application to run our Roland Modela MDX-20. Open the mods application via server or local. I used locally.
Step 1: Open terminal and use code bash start-servers to run it locally.
Step 2: Once Mods is opened. Click right button in mouse to open the menu.
Step 3: Open Programs > Open Programs > PCB Under Roland MDX Mill in machines section.
Step 4: After the programme has been opened, we proceed to upload the png file of our design that we exported from our software. (Note: KiCAd can only export SVG formats; we’ll use Inkscape to convert them.)
Step 5: Upload PNG File
Step 6: Check the dimensions once again before proceeding. Check dpi as well.
Step 7: Once the file has been uploaded and checked, it’s time to select the tool. In this process, we have two stages. Making trace is the first step, followed by milling the board. Check the tool parameters and click the mill traces (1/64) button.
Step 8: Now proceed to the 2D Tracing section, click the calculate button, and then wait. Let the computer handle the rest.
Step 9: Yes, that is the tracing result. The machine is about to trace this on our board.
Step 10: Setting the origin for X & Y - Axis. To position the tool head where we need it, use the X and Y sections under the origin. Jog height is the clearance of the tool head when moving from one point to another while milling. This is significant because the spindle is moving during movement.
Step 11: Now is the time to send this file to the machine and let it do the rest.
Step 12: And the Result. The first stage is completed.
Step 13: The time has come to cut out our board into the desired shape. Repeat the procedure by exporting the Edge cut line from KiCAD as an SVG file, converting it in Inkscape, and uploading it to the Mods.
Step 14: Selecting the tool. Click mill outline(1/32) button.
Step 14: Repeat Step: 8 & wait computer to calculate the outline.
Step 16: Repeat Step: 11 and wait for the Final result.
With an excitement I said Final Result. But its not, actually its just the interval. The major process is yet to come.
Inspect the board
It is always better to inspect our board before moving on to the next process, because the next step is to solder our components to the board, and if an error occurs while milling, the components can be damaged by short circuiting. For inspection we use a multimeter and if we have enough time, check every connections.
We can use the magnifier lenses to inspect manually as well.
The Art of Soldering
The most important step in the entire process is soldering the components into their proper positions. We only use our bare hands to complete this. Therefore, accuracy is crucial in this situation. Soldering is a skill that requires practise. To master the art of perfect soldering, one must practise more.
I have got only a few experience in soldering. So it took me a while to solder the components here. My tutor Mr. Jojin helped me a lot in cracking the skill for soldering. I used an damaged board to try and finally some good results came out.
Tools We Used
1.Soldering Iron: I used Weller WSD 71 fro soldering
2.Lead:
3.Tweezers:
4.Vaccum Pump for Desolder:
5.Magnifier Lens with Stand:
6.Fume Extractor:
7.Cutting Plier:
Lets start the soldering process:
Step 1: As always, it’s the preparation. Make sure we have all the necessary materials, including a soldering iron, solder wire, flux, and all necessary tools. Also, make sure our work area is clean and well-ventilated.
Step 2: Check the position of the component onto the PCB board whether it places in the correct location.
Step 3: Apply a small amount of flux to the pad where you will be soldering the component (Optional).
Step 4: Tin the soldering iron tip by melting a small amount of solder onto it. This will help transfer heat to the pad and component.
Step 5: Bring the tip of the soldering iron into contact with the pad and component. old it there for a few seconds to allow the heat to transfer to the pad and component.
Step 6: Once the pad and component are hot enough, touch the tip of the solder wire to the joint. The heat from the soldering iron will melt the solder, allowing it to flow into the joint and bond the component to the pad.
Tip: In order to prevent the component from moving, solder one leg first, then attach the component to the position. The remaining components can then be soldered without the use of tweezers.
Step 7: After soldering, inspect the joint to ensure that the solder has flowed evenly and has formed a good bond between the component and the PCB pad.
Step 8: Repeat the process for all other joints that need to be soldered.
And its DONE. My first ever Development Board.
Programming
The board is ready, and in order to check it, we must run a simple program on it. To program and upload the same, we use the Arduino IDE. The ATTiny library needs to be installed for that.Git Document for ATTiny Library.
Once the Library is installed, AtTiny 412 is selected as the board by selecting the same from Tools section.
After the selecting the board, we will select the port as well.
The above steps can be done in single step by clicking the board section on top left corner as shown.
We will use an example from the existing Library. I used Blink example here.
In this board we need a programmer to upload our program. We will select our programmer from Tools section.
Once the program is compiled, it is uploaded to the board using programmer. The programmer we used was made by one of previous student Mr Saheen.
Now is the time. The real fun begins when you programme something real, upload it, and run it on our board.
The program run successfully. Tested on both the LEDs and it functioned.
Group Assignment
Detailed Study Report on our Group Assignment Page.
Downloads
Download PCB Milling PNG Files
Help Taken & References
Chat GPT used for doubt clearing and content helps.