PCB Assembly Basics

At pcbnet.com, PCB assembly is made fast and easy. This guide will give you an overview of the board assembly process and why we are your most reliable source for high-quality PCBs.

pcb-assemblyThe assembly of printed circuit boards (PCBs) is a process that includes multiple stages such as through-hole technology and surface mount technology (SMT). In the through-hole stage, the component leads are soldered onto the PCB through a wave soldering method. The SMT stage, on the other hand, begins by depositing solder paste on the connection pads of the board, followed by many other steps which are explained below.

Materials Needed for PCB Assembly

1.Printed Circuit Board (PCB)
2.Electronic components
3.Soldering flux
4.Soldering materials such as solder bar, solder paste, solder wire, solder preforms
5.Soldering equipment such as SMT equipment, wave-soldering machine, soldering station, and testing and inspection equipment

The PCB Assembly Process

Here are some of the steps involved in PCB assembly:

Solder Paste Printing

The solder paste is applied onto the PCB, usually through a stencil printer with a pin-registration system or an optical alignment. The quality of the print must be verified first before moving on to the next stage.

Instead of using stencils, we use a unique tool to jet the solder paste. This technique reduces time and cost in manufacturing and has become the standard in the PCB industry.

Component Placement

After the solder paste is applied to the board, small SMT components are placed using a pick and place machine. Placing the components by hand can be dangerous and so it is not recommended for surface mount technology or SMT. If making a double-sided surface mount assembly, it is necessary to dispense glue to hold the components in place on both sides.


After placing the components, the completed board is typically placed on an oven conveyor belt for the re-flow process. In this stage, the solder that was applied is melted and the component joints are connected permanently by means of controlled heat.

Manual Insertion

Before the manual insertion process takes place, the leads of the component are cropped as leads should have proper length. Leads that are too short may not extend into the thru-holes, while leads that are too long may impede the components from sitting on the correct position on the board.

After cropping to appropriate length, the leads are then curved to a particular shape to relieve tension, and the components are manually inserted into the PCB.

Wave Solder

In this process, the board is passed over a wave solder and a connection between the leads of the electronic components is established.


In the cleaning stage, residues of solder flux round the solder joints are removed using de-ionized water and/or solvents. Typically though, a non-messy solder paste is used for printing with solder paste. In this case, it is unnecessary to remove flux residues after the soldering stage.


Using inspection machines, the quality of PCB assembly is verified in the final inspection stage. There should be no bridges between the solder balls, no shorts, and no loose balls surrounding the components or the leads.

PCB Quality Class Standards

Currently, there are three quality class standards in the PCB industry. Among these three, 1 and 2 are most popularly followed.

C lass 1

This is for general electronic products. This is also used to test and verify designs.

Class 2

This is for dedicated service electronic products including high-level business machines, communication equipment, and instruments that require extended life and high performance, and for which service must not be interrupted.

Class 3

Products under this class are usually used in some types of military, aeronautics, and medical applications, which require uninterrupted and highly-reliable service.

To ensure that our prototypes meet your specifications in production, we always give Class 2 to our customers.


We are first to have the Full TurnKey quote innovation that lets you obtain a PCB quote in no time. You can get one by either filling out the online quote form or by sending us the following info:

•Bill of Materials (BOM)
•Gerber Files
•Pick and Place Data
•Lead Time and Quantity Desired


After sending the above information to us, we will contact you shortly and send you a TurnKey quote within the same day (if received before 11 a.m. CST). As we use caliber equipment in the assembly of your PCB, you can guarantee that the result is of the highest standards.