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Introduction to Printed Circuit Board Assembly

MOKO Technology Ltd | Updated: Oct 08, 2016

Some of you might have heard of the term PCB Assembly and thought, “What’s that”?

This article is meant to shed some light on the subject.

The whole process of manufacturing electronic devices is a long and complicated one.
The starting point for all electronics is in the material – Silicon or any other semiconductor.
Through a number of long and expensive clean room processes, these “wafers” are transformed into “smart” electronic microprocessors and chips.

These chips can’t do anything by themselves, and need to be integrated onto a printed circuit board (PCB) in order to be able to do something in the end (like operate your computer or telephone).

Now, there are a large number of companies that design these chips and sell end-products. However, these companies can’t afford to purchase all the equipment required to assemble their chips onto PCBs in order to devise their end-product.

This is what PCB Assembly companies are for. These (EMS) companies have a number of Surface Mount Assembly lines, and offer PCB Assembly services to other companies who are not interested in doing this themselves.

The PCB Assembly process consists of a number of different processes:

1) Solder Paste Printing – During this process the initial solder paste is printed onto the PCB using a stencil. This is basically the binding material of the devices to the PCB.

2) SMT Pick & Place Assembly – This is the heart of each PCB Assembly line. This process takes all the individual chips and accurately places them on their designated place on the PCB.

3) Reflow/Through-hole curing – After placing the chips onto the solder paste, the boards go through a conveyor oven to melt the solder and bind the chips to the PCB.

4) Conformal Coating – Some boards require a protective lacquer coating. Conformal “Selective Coating” machines quickly and accurately provide a layer of protective coating on the PCBs.

5) AOI and AXI – Automatic Optical Inspection and Automated X-ray Inspection. These processes are key to confirming that no mistakes have been made during the assembly process

6) Reworking if needed – If any mistakes or defects are found, some devices can be reworked. Reworking consists of heating the board or device, and removing it from the PCB so that a replacement can be placed in its stead.

Each of these processes is a world in its own right and is considered a technology field in its own. There are several specialist manufacturers for each of the these PCB Assembly fields. is a Semiconductor, PCB Assembly, and Microscopy discussion forum to help engineers discuss different technological subjects.

MOKO Technology Ltd