Soldering Assembly: Meaning, Types, and Process

PCB soldering is a crucial part of the PCB manufacturing process, where wire leads are soldered onto metalized contacts using semiconductor materials. The actual PCB manufacturing process covers several steps, from bare board fabrication to the final assembly and packaging.

There are several types of PCB solder used for this, each with mechanical components, safety features, and disposal issues. This article details what soldering is in electronics assembly, the types, materials used, and the processes involved.

What Does Soldering in Electronics Assembly Entail?

Soldering covers the soldering processes in the light of electronic assembly type, flux, solder, and cleaning requirements. The book, “Soldering in Electronics Assembly” by Mike Judd and Keith Brindley theoretically details every available process. This ranges from the basic hand soldering to zoned forced convection infrared machines, providing a detailed analysis of soldering action, among other things. Also, it provides a detailed analysis of the soldering process defects as well as its causes.

It is a practical guide for industries, detailing all the main current soldering processes, cleaning, faults, and troubleshooting and standards. It also considers and assesses the safety and quality of the solder process.

What Determines PCB Soldering Solidification?

There are different kinds of PCB soldering materials on the market, which can make choosing the best confusing and daunting. Engineers and designers use solders to make electrical connections between metal contacts by letting the soft alloy (molten solder) fuse. As the alloy cools down, it forms a eutectic that fuses the metals together. The mechanical strength of the solidification will depend on the blend of metals the soldered PCB comprises.

The materials also determine the required melting temperature and fumes put off during soldering. PCB soldering materials are differentiated by their soldering flux types, core material, and metallic constituents.

What Are Lead-Based Alloys?

Lead-based alloys or lead solder blends are soft solders used in the electronics industry. These types of solders have a melting point of about 180 to 190 degree Celsius and about two years shelf life. The most common lead solder blends include 60/40 Sn/Pb, 63/37 Sn/Pb, and 62/36/2 Sn/Pb/Ag; others are 10/90, 30/70, and 50/50. The primary base metal used in lead-based alloys is Tin; it is responsible for the alloy’s lower melting point.

Are Lead-Free Solders Good?

The European Union recently passed the RoHS (Restriction of Hazardous Substances) that restricts lead use in the electronics industry. As a result, the use of lead-free solders has become more prominent; they are gaining popularity in the industry. However, lead-free solders have a challenge in that they have a higher tendency of forming tin whiskers. Engineers use conformal coatings to prevent the whiskers from forming and protect metals from humidity and corrosion.

What Is a Flux Core Solder?

Flux core solder is another type of solder used; it features a reducing agent in the core. It is sold as a single reel and the featured reducing agent removes whatever oxide film is on the metal contacts. This is to ensure there is high conductivity in the electrical contact. If you are soldering the PCB by hand, a major factor to consider is the type of material that exists in the core.

Types of Materials in Solder Pastes

Every solder paste contains one of the following types of materials: organic acid flux, rosin flux, and solid core solders. The materials are responsible for fluxing the metal contacts during the PCB soldering process. For instance, organic acid flux is an acid-based flux that ensures oxides are removed from metal contacts as they are soldered – aggressively. It is water soluble and leaves residues that must be cleaned after the soldering process to prevent corrosion.

Rosin Flux and Solid Core Solders

Rosin is resin solidified and is derived from conifers; residue from this type of flux does not cause corrosion. Thus, rosin flux is often used in situations where removing residue from organic acid flux may be more difficult. In some cases, solder wires have a solid core and no flux, in which case flux must be applied by hand. Solid core solders are very useful in hand soldering, provided there is flux available.

What Are the Various PCB Soldering Processes?

There are three processes used in soldering printed circuit boards, including wave soldering, reflow soldering, and selective soldering. Wave soldering is commonly used for through-hole components while reflow soldering is used for surface mount components (or SMT components). Meanwhile, the PCB selective soldering process is used when a through-hole component is likely to get damaged by high heat. It also comes in handy when a through-hole component is unsuitable or the first two processes (wave and reflow).

How to Solder PCB Components

First, apply solder paste or flux to the metal contacts on the circuit board; this reduces oxidation and evens out molten solder flow. The easy movement of molten solder is essential as it powers the eventual soldered joint on the board. If you’re giving a PCB designer, like Hillmancurtis, it will be assumed that you want to use lead-free solder paste.

Meanwhile, according to soldering experts who can work on any computer, you can mix these materials. However, remember that the final alloy may have mechanical properties lying in-between lead-based and lead-free alloys. You can watch the appropriate video or latest innovatory ones that explains or can illustrate how assemblies are done using the relevant technology.

With a photographic guide that offers a detailed study of how a soldering iron works, you can assemble variants together and achieve your desired industrial construction. You can also pay attention to places in the photographic guide where major topics consider safety for assembly variants.

How Can Hillman Curtis Help?

When you are done with your design, you can release the Gerber files to Hillman Curtis as a PCB manufacturer. Hillman Curtis is an expert PCB manufacturer and assembly with over ten years of experience in the industry. You can also contact us for any discussion relating to quality soldering assembly methods or any other discussion that will help you grasp


The manufacturing process and assemblies of printed circuit boards covers different light stages, one of which is component soldering off the device based on the methods you want to employ. For some, they may need to watch videos while others may not need to watch videos to understand major topics on use, cleaning, and soldering assembly. When it comes to PCB soldering, the idea for technicians or anyone who does the job of technicians is to choose the right blend of semiconductor materials to fit into the manufacturing process.