Tutorial for Making Printed Circuit Board (PCB)

This tutorial is originally posted on https://blog.gwlab.page/making-printed-circuit-board-pcb-e222952864d5

PCB design
This is a Printed Circuit Board (PCB):


A Printed Circuit Board (PCB)

In this article, I will give you some basic ideas about how to make a PCB. A PCB usually contains several layers of copper foils working as wires and insulating substrates usually made by FR-4 fiberglass. To design the layout of these layers of copper foils, we can use PCB design software like Altium Designer or Eagle.

Parts selection
First of all, you need to have some ideas about what kind of circuit you want to make. When you are designing your circuit, you may face a problem with parts selection. At that time, Digikey or Mouser, which are online shopping websites for electronic components, are your best friends. For example, if you need an op-amp, you may search it on the Digikey database by setting your requirements. Then, click on each op-amp you found. You can find the datasheets of them, e.g., AD8421ARZ’s datasheet. By comparing the performance, features, and price…, you can find the one you want to use. Sometimes, if you can find example circuits designed by other people, they can be a good starting point to learn which model of ICs you can look into.

SPICE (circuit simulation)
Once you have some draft or prototype circuits, it’s a good idea to perform some SPICE analysis so that you can find the bugs of your circuit before you make the physical board. A powerful and free SPICE software is called LTspice.


LTspice — simulating circuit's behavior, an ac simulation gives you the frequency response of the circuit.Packages / Footprints

Then, you can draw the circuit diagram by using PCB design software in its Schematic View. At this stage, you have to decide the package of each component because the software will generate all the pads in the Board (Layout) View according to your circuit design, and it has to aware of what kind of pad (size) it should put on the layout. About the packages, usually, they are divided into two categories, Through-hole and SMD (Surface Mount Device). If there is no special requirement, SMD is preferred nowadays. Here is a nice review comparing the Through-hole device and SMD.


Through-Hole vs. Surface Mount Device

There are various packages of SMD. For most resistors and capacitors with a rectangular shape, their footprints or packages are usually named by their width and length, like 0603 representing 0.06 x 0.03 inches. For the integrated circuits (ICs) like op-amps, a popular package is called SOIC (Small Outline Integrated Circuit), like SOIC-8 being an eight pins SOIC package. An overview of SMD packages or footprints can be found here. Or you can find devices with package information directly on Digikey or Mouser.


Eagle (PCB Designer) — Schematic (Circuit Diagram) View

Design Rule
After creating your circuit diagram in the Schematic View in PCB design software, the software will generate many device footprints with connection guidelines in its Board (Layout) View. Before making the PCB layout, it is important to set the Design Rule for Design Rule Check (DRC). By setting up Design Rules, the software will make sure, for example, all the conduction lines will not getting too close to each other so that we can reduce the probability of manufacturing failure. A possible value for clearance between wire, pad, and via can be 10 mils, and the line-width of signal lines and power lines can be 12 mils and 20 mils respectively.

Routing, Via
When DRC is ready, you can start to drag and drop each component’s footprint to the right position on the PCB with the correct orientation. Then, use the routing tool to draw the desired copper lines or nets connecting devices together. In most PCB design software, the routing tool has auxiliary functions. It can tell you which pin of which IC should connect to which resistor. And it can also help you create two 45-degree angles instead of a single 90-degree angle when you change the direction of your routing, as you can see in the screenshot below. While avoiding a 90-degree angle in your layout routing is a good habit, the necessity of it is questionable when the target frequency of signals is not too high. There is an article discussing this issue. Sometimes, you may need to connect things existing in different layers in the PCB. In that case, we need to create a Via, a hole with copper, to connect wires in different layers.


Eagle (PCB Designer) — Board (Layout) View

NC Drill File and Gerber Files
Once you finished the layout, it’s time to export your work to the files that can be sent to the PCB manufacturers. In the industry, people use the Gerber Files, a vector image format, for making PCB layout and use NC Drill File for Vias and holes to be drilled on the PCB. When you export to the Gerber, you will find the software gives you about ten files corresponding to different layers in your PCB, including Copper, Soldermask (the green polymer preventing solder bridges), Silkscreen (white text and indicators for human) for both top and bottom… All of them are Gerber files. Different software gives you Gerber files with different extensions, but they are the same things. You may also check the Gerber files you exported by Geber Viewer like Cupru‪m‬ on macOS.


Cupru‪m‬ (Gerber Viewer) — Viewing Gerber files generated by Eagle


Content of NC drill file

BOM (Bill of Materials) File
After you submit your Gerber files and NC drill file to a PCB manufacturer, it is time to worry about purchasing electrical parts for PCB assembly (soldering). Usually, we will export a table called the BOM (Bill of Materials) file. It contains the name of each part on your PCB and its part number… This BOM file can help us ordering parts from Digikey or Mouser. Also, when we solder the components onto our PCB, we can refer to this BOM to know which parts should be soldered onto which place. If you want to send your PCB and electrical parts to a PCB assembly factory for automatic assembly, you also need to provide this BOM to them.


Example BOM file source:https://dcc.ligo.org/LIGO-D1003116/public

Soldering
After you received your PCB from the manufacturer, it’s time to solder the electrical parts onto it. Let’s discuss something about soldering.

Tools
- Sodering Station

There are various soldering stations on the market. Some of them are expansive, like JBC, while some are relatively cheaper, like Hakko. If you are based in Taiwan, I recommend a high C/P value model—Vectech SD-101 with excellent performance, which costs about 6k NTD. The most important feature of a soldering station is temperature control. When you purchase the soldering station, make sure that it is equipped with the temperature control function. Also, if you have some concerns about the Lead-free process or ESD (Electro-Static Discharge), make sure you were paid attention to them.

- Solder
Again, there are many different brands manufacturing solder like Kester (US) and Goot (Japan). If you are in Taiwan, I personally recommend the solder made by 新原金屬, which can be found in 光華電子商場 easily. When it comes to solders, usually they are divided into Lead and Lead-free solders. While Lead-free solder is non-toxic, eco-friendly, and RoHS compliant, which your institute or customer may require. Lead solder still has some unique features. For example, Lead-based solder can prevent whisker happened.

- Flux
Using flux can help heat conduction during soldering and can remove the oxidized material on the sodering surface. Although some solder already contains flux in it, putting extra flux on the soldering joint is always helpful.

Soldering
- Temperature

For Lead-based solder, the suggested temperature is 600°F / 315°C. For Lead-free solder, you need a little bit higher temperature.

- Tutorial Videos
There are many videos on YouTube talking about how to perform soldering. For example:


About the requirement of soldering, there is a 3C guideline:

  • Concave
    The surface of the solder joint must look smooth and being a shiny concave surface. Sometimes, we also call it wetting.
  • Contour
    With a proper amount of solder, the contour of wires or legs of the object being soldered should be visible. If it is fully covered by solder and invisible to you, you have put too much solder on the joint.
  • Clearance
    Keep proper clearance from insulating materials, bending point of legs, and nearby conductors are necessary when you do the soldering.
Besides, avoid non-wetting, and de-wetting solder joint is required. By using some flux, you can reduce the probability of being non-wetting and de-wetting. If they happened, they could be fixed during the rework process.

Here is a good article talking about soldering problems — 13 Common PCB Soldering Problems to Avoid. Also, NASA has a good reference website with many photos of sample solder joints on it and good slides.

Epilogue
Being a non-self-contained tutorial, I hope that this article is helpful to you. You may take this as a starting point and learn more about making PCB by watching YouTube, reading more articles, joining training class, and joining an experimental laboratory.


Reference

Medium Article


Youtube (Mandarin)
There are two tutorials I found on YouTube. Fortunately and unfortunately, they are in Mandarin. Here are the links:

  • 基本電路製造簡介與EAGLE Video(by王權)
  • 基本電路製造與EAGLE Part 2(by王權)

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