How printed circuit board assembly is done

When you talk about manufacturing circuit boards, note that this is not a simple thing; rather it is a long and complicated process. The entire process consumes time, requires expert brains, technology and electricity, and much more. All these are used to make way for manufacturing the end product, i.e. your mobile phone, or computer system or any other electronic equipment you see around you.

The PCB (Printed Circuit Board) integrates all chips and microprocessors to form the operational part of every electronic device. So, needless to say, PCB assembly is the most important factor in the manufacturing of all electronic devices. Here we will discuss about how printed circuit board assembly is done. So, let’s get started.

Beforehand, it’s good to know that we are not going to cover PCB design and manufacturing. So what we will discuss is what's done to the PCB after it is manufactured, means PCB assembly or integration to all microprocessors and equipments.

PCB assembly is done using 2 types of construction methods.

1. Through-hole construction: Here the leads of the components are inserted into holes.

2. Surface-mount construction: In this case the components leads are placed on the outer surface of the PCBs using some lands or pads.

Both these construction methods include the fixing of component leads to the PCB with molten metal solder electronically or mechanically. When the production volume of the circuit boards is more, then soldering components to the printed circuit board is best done by machines. And, if the production demand is less, hand-made soldering is fine (Ball grid arrays cannot be soldered by hand however).

When the circuit board has the possibility of going through any physical stress, Through-hole construction method practically has the edge on Surface-mount method as it gives more strength and grip to the components. Otherwise, Surface-mount technique works good as it takes up less space on the PCB.

In Circuit board assembly process next comes the testing phase. After the board and components have been fully constructed they are tested to ensure that there is no fault in the operation and the performance of the device is fine. The testing process includes:

1. A thorough visual check to inspect whether all the components are soldered and assembled properly to the circuit board or not (this is accomplished when power is off).

2. When power is OFF, Analog Signature Analysis is also performed. Here a current-limited AC sinewave is applied across two points of the components and the circuit.

3. Switching the power ON, an In-Circuit test is performed to check all the physical measurements like voltage, frequency etc.

4. When power in ON the final Functional Test is also performed to verify whether the circuit board is functioning properly or not. This confirms the product delivery time.

During the testing phase if any part is found improper, then it is removed from the board and allowed to process again which is called Reworking. This concludes the entire PCB assembly process.

PCB assembly process and its importance

Have you ever seen what is there inside your cellphone or computer that operates the system software? It’s not only your computer or mobile but every electronic device works because of an electronic circuitry present inside the device. This circuitry is the main functional unit which is a combination of many small components assembled with a printed circuit board (PCB).

The PCB assembly process:

The entire PCB assembly is a complicated process that involves the following processes.

• Solder paste printing: In this process an initial solder paste is applied on the PCB using a stencil. This concludes the initial binding process of the various components to the PCB.

• SMT Pick and Place assembly: This is considered as the heart of the entire assembly line. Here all individual chips are taken and placed accurately on their designated spots on the PCB.

• Through-hole curing: This is otherwise known as the Reflow mechanism. In this mechanism the board, after fixing the chips onto the solder paste, goes through a conveyor oven to melt the solder and bind the chips the PCB.

• Conformal coating: There are some boards which require lacquer coating for protection. Conformal coating process involves some special machinery work to apply a protective coating quickly and accurately.

• AOI & AXI: Automatic Optical Inspection (AOI) and Automated X-ray Inspection (AXI) are two processes done to make sure the total assembly process is free from errors and mistakes.

• Reworking: Well, this is done once any component or device is found defective or the whole assembly does not function properly. After testing reworking is done by heating the board and replacing the defective part of the PCB with a good one.

Each of these processes is again a complex process altogether which needs heavy technology involvement, specialist man-power and material consumption.

Importance of PCB manufacturing and assembling:

• Microprocessors and chips cannot do on their own. The process of building microprocessors and chips is itself a long and complicated process. But these chips, after they are manufactured, cannot perform their operations if they are not integrated onto the printed circuit board (PCB). So a PCB is an essential part of every electronic device.

• PCB manufacturers are specialists. All companies designing chips and microprocessors can also invest in making PCB integration; but it requires technology and specialists to make components and equipments needed for the integration and assembling of chips onto PCB.

• PCB assembly companies help devise the end-product. To facilitate the assembly work and provide assembly services the PCB integration companies have a no. of Surface Mount Assembly lines making sure the end-product is manufactured successfully.