PCB assembly and welding technology

 PCB assembly and soldering construct a complete physical circuit by selecting components, placing and soldering them onto the circuit board.

In through-hole technology, electronic devices with pins or plugins are soldered onto a circuit board to form a circuit.

Wave soldering is the most commonly used technique in THT and SMT PCBA

Printed circuit boards (PCBs) are an important component of electronic products; Without PCBs, most electronic devices are just boxes that cannot be used. PCB is usually made of fiberglass and fixed together with epoxy resin. The PCB assembly and soldering process involves selecting components, placing and soldering them onto the circuit board to construct a complete physical circuit. The inspection, testing, and feedback after PCB assembly and soldering ensure that the PCB can be successfully manufactured. In this article, we will discuss the PCB assembly and soldering process.

PCB assembly and soldering

The PCB assembly and soldering process turns a circuit board into a functional prototype. The PCB assembly (PCBA) stage includes device placement, soldering, inspection, and finally testing. The PCBA process can be manual or automatic, depending on the manufacturer's decision at each stage.

PCBA Process Overview

PCB design starts from the schematic diagram. Design a PCB layout based on the schematic diagram. PCB layout defines the electrical connection paths (called wiring) in a circuit and the placement of components. Once the PCB layout design is approved, printing will proceed.

The pre made PCB is made of fiberglass material sheets fixed together with epoxy resin. The wiring made of copper is laid on the circuit board. The device is fixed on the circuit board through the soldering process. The welding process uses a material called solder to fix the device in a designated position. The PCB with soldered components forms the assembled PCB. After attaching the device to the PCB, it can be tested.

Three technologies were used in the PCBA process, which will be discussed one by one in the following text.

PCB assembly technology

In the PCBA process, there are three key technologies:

1. Through hole technology (THT) PCBA process

In through-hole technology, electronic devices with pins or plugins are soldered onto a circuit board to form a circuit. The leads or terminals of the device are inserted through holes or pads on the PCB and soldered on the other side.

2. Surface Mount Technology (SMT) PCBA Process

There are two types of pads: through-hole and surface mount. In PCBs using surface mount pads, surface mount devices (SMDs) are soldered to form circuits. The welding surface is also the surface of the device placed using solder paste.

3. Mixed technology PCBA process

As circuit design becomes more complex, it is not possible to insist on using only one type of device in a circuit. In the implementation of complex circuits in PCBs, there are both plugins and surface mount devices. This type of PCB that utilizes hybrid devices is called a hybrid technology circuit board, and its assembly process uses the hybrid technology PCBA process.

Steps for PCB assembly using through-hole technology

The order of PCBA process varies depending on the mounting technology used. Now let's explore the steps of PCB assembly using through-hole technology.

1. Device placement: In through-hole technology PCBA, engineers first place the device in the corresponding position provided in the PCB design file.

2. Inspection and calibration: After all components are placed, the circuit board should be inspected. When checking, check whether the components are placed accurately. If inaccurate placement of devices is found, such issues should be immediately corrected through calibration steps. Inspection and calibration must be completed before the welding process.

3. Welding: The next step in this process is welding, fixing the placed components onto the corresponding solder pads.

4. Testing: After completing the PCB assembly and soldering process, the circuit board can be tested. Every PCB circuit board used in electronic devices must go through this process and pass the test.

There are various welding techniques, and the following will explore several of them.

welding technique

Regardless of the mounting technology used, all PCBA processes involve the welding process. There are many different types of welding techniques that can be used to connect electrical components to PCBs, including:

Wave soldering: the most commonly used technique in THT and SMT PCBA

In wave soldering, the PCB moves on a liquid thermal solder that resembles waves, causing the solder to solidify and secure the device.

Brazing: The highest temperature results in the strongest welding effect

In brazing, metal components are attached by heating. However, this technology melts the metal at the bottom to accommodate the filler metal.

Reflow soldering

The reflow soldering process uses heated solder paste to attach the device to the circuit board. The solder paste in the molten state connects the pads and pins on the PCB.

Soft soldering: a popular technology used to secure compact and fragile devices onto printed circuit boards

In soft soldering technology, a metal space filler made of tin lead alloy is heated with an electric soldering gun or gas to fix the device onto the circuit board.

Hard welding: The welding effect is more firm than soft welding

Hard welding is used to bond metal components such as copper, brass, silver, or gold at a temperature of approximately 600°F.

In the process of PCB assembly and soldering, if there are Design for Manufacturing (DFM) errors in the PCB design, designers will have to return to the layout process to solve these problems. And this may occur multiple times, and after multiple iterations, it will lead to significant design delays and waste of time, money, and manpower. A good DFM design helps to maximize the smoothness of the entire design process, avoid accidents, and ensure the predictability of construction costs.