Today, Alice from JHDPCBA will edit an article about PCB and the basic process of PCB assembly(the article is being edited and has not been completed yet)
The PCBA is a rigid body that holds various electronic components on it, the PCB when components are assembled is called PCBA or Assembled PCB.
The PCB is composed of a substrate that is made of fiber glass, the components, the copper layer that makes the traces, holes in which components are fitted and layers that can be inner layer and outer layers.
The pcb substrate and components are insulated with solder mask and held together with epoxy resin. This solder mask can be green, blue or red in color as commonly found in PCB colors. The solder mask will allow the components to avoid short circuit with tracks or other components.
The copper traces are used to carry electronic signals from one point to the other on the PCB. These signals can be high speed digital signals or discrete analog signals. These traces can be made thick to carry power / electricity to power up components.
Alice introduces the four main components of the PCB circuit board:
1- Substrate: It is the rigid board made of FR-4 material onto which the components are “stuffed” or soldered. This provides the rigidity to PCB.
2- Copper Layer: The thin copper foil is applied on top and bottom of the PCB to create top layer and bottom layer copper traces.
3- Solder Mask: It is the layer that is applied on top and bottom of PCB. This is used to create non-conductive region of PCB and it isolates the copper traces from each other to protect short circuit. The solder mask also avoids soldering on unwanted parts and assures that solder goes on that area that is meant for soldering like holes and pads. The holes will attach the THT components on PCB while the PADs are used to hold SMT components.
4- Silkscreen: The white labeling which we see on PCB fabrication for components designator, like R1, C1 or some sort of description on PCB or company logo it is all made of silk screen layer. This silk screen layer provides the vital information about that PCB.
Alice will introduce two common types of PCB circuit boards (in our PCB assembly factory, the first type is more common)
1- FR-4:
The PCBs are the majority of PCBs we see all around us in various types of devices. These are hard, rigid and solid PCBs with various thickness. The main material is the fiber glass or simple “FR4”. FR4 means “Fire Retardant – 4”. The self extinguishing property of FR-4 makes it favorable for use in many hard core industrial electronic devices. The two sides of FR-4 is laminated with thin layer of copper foil also known as copper clad laminates. Main applications where FR-4 copper clad laminates are sued in are power amplifier, switch mode power supplies, servo motor drives etc. On the other hand another type of rigid PCB circuit prototype substrate commonly used in home appliances and IT products is known as Paper Phenolic PCB. They are light weight, low density, cheap and easy to punch process.
2- Flexible PCBs:
The flexible PCBs are made of the substrate material like Kapton that can withstand very high temperatures while the thickness is as low as 0.005 inch. The can bend easily and are used in wearable electronics, connectors of LCD displays or laptops.
Alice gave an example of the two most common ways of installing electronic components onto PCB circuit boards (our JHDPCBA company was engaged in SMT assembly services when it was founded, and later slowly started PCB assembly)
1，SMT: SMT stands for “Surface Mount Technology“. The SMT components are very small sizes and comes in various packages like 0402, 0603, 1608 packages for resistors and capacitors. Similarly for Integrated circuits ICs we have SOIC, TSSOP, QFP and BGA.
The SMT components assembly is very difficult for human hands and can be time taking process so it is mostly done by automated pick and place robots.
2，THT: THT stands for “Through hole Technology”. The components with leads and wires, like resistors, capacitors, inductors, PDIP ICs, transformers, transistors, IGBTs, MOSFETS are example.
The component has to be inserted on one side of PCB and pulled by leg on other side and cut the leg and solder it. The THT components assembly is usually done by hand soldering and is relatively easy.
