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SMT Soldering Procedures in PCB Assembly Factory

PCBs are found in practically every electronic device, and their production rate is increasing day by day as the need for electronic gadgets grows around the world. There are numerous small and large PCB manufacturers throughout the world, all of whom are attempting to differentiate themselves from the competition by providing high-quality services and client satisfaction. Though their services may range in terms of quality and quantity, they all use a similar PCB assembly technique to construct the PCB. As a result, we'll go over the PCB assembly process in depth today.

In general, a quality PCB manufacturer offers a variety of services, such as SMT assembly, BGA assembly, through-hole assembly, mixed assembly, rigid-flex PCB assembly services, and so on, and they follow a variety of industry standards, such as IPC 610 Class 2 and Class 3.

Soldering with SMT (Surface-mount Technology)

We've broken down the entire SMT soldering process into 9 steps:
1. Printing
2. Component Placement
3. Pre-Reflow Automated Optical Inspection (AOI)
4. Reflow Soldering
5. Post-Reflow Automated Optical Inspection (AOI)
6. Conformal Coating
7. Final Inspection and Functional Test
8. Washing & Drying
9. Packaging & Shipping

Now we'll go through each step in great detail.

Step 1: Printing


The first step in the PCB assembly process is to print solder paste on the solder pad of the PCB. It is carried out by a solder paste printing machine at the end of the production line, which prints solder paste or patch adhesive onto the PCB's solder pad in order to prepare components for welding.


Automatic solder paste printing machine in YINGSTAR PCBA factory

 

Step 2: Component Placement
 

After the printed PCB has been validated to have the proper amount of solder paste deposited, it moves on to the component installation stage of the manufacturing process. Each component is removed from its packing using a vacuum or gripper nozzle, inspected by the vision system, and inserted at fast speed in the programed spot. There are many different machines available for this procedure, and the sort of equipment chosen is very dependent on the business. For instance, if the firm is focused on huge build numbers, the placement rate will be critical; but, if the focus is on small batches/high mix, flexibility will be more critical.


This picture shows the Component Placement Machine(SMT) in YINGSTAR Assembly factory.
 

Step 3: Automated Optical Inspection (AOI) Prior to Reflow

 
It is critical to examine after completing component placement since whether components are connected correctly or not can affect the PCB's overall function. Using an AOI machine to check for component presence, type/value, and polarity is the ideal method to do this.
 

Step 4: Reflow Soldering

 
Reflow soldering is a technique in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily link one or more electrical components to their contact pads, and then the entire assembly is heated to melt the solder and permanently connect the junction. Passing the assembly via a reflow oven or under an infrared lamp, or soldering individual joints with a hot air pencil, are all options for heating.The most typical technique of attaching surface mount components to a circuit board is reflow soldering, however through-hole components can also be attached to a circuit board by filling the holes with solder paste and inserting the component leads through the paste. Reflow is rarely utilized on pure through-hole boards since wave soldering is easier and less expensive. Through-hole reflow eliminates the wave soldering step from the assembly process when utilized on boards with a mix of SMT and THT components, potentially lowering assembly costs.



 

Step 5: Automated Optical Inspection (AOI) After Reflow

The final step in the surface mount assembly process is to double-check for errors by using an AOI machine to inspect solder junction quality. The movement during the reflow process might sometimes result in poor connection quality or no connection at all. In other words, because misplaced components can sometimes join areas of the circuit that should not connect, shorts are a common side effect of this movement. As a result, inspection after reflow soldering is critical, and checking for these faults and misalignments can be accomplished using a variety of inspection methods.The following are some of the most prevalent examination methods:
1.Manual Inspections
2.Optical Inspection (Automatic) (AOI)
3.X-ray examination by computer (AXI)

 



YINGSTAR PCB Assembly factory AOI machine

Step 6: Conformal Coating

Conformal coating is a thin polymeric film that adheres to the contours of a Printed Circuit Board to protect the components on the board. It is typically sprayed on electronic circuitry at a thickness of 25-250 m (micrometers) to protect it against moisture, dust, chemicals, and temperature extremes. If the electronics are not coated (protected), they may be damaged or fail to work. Conformal coatings or potting compounds provide protection for devices that must tolerate hostile conditions or impact.Most circuit board assembly shops employ a transparent conformal coating instead of potting because it is lighter and easier to check.
 


Conformal coating in the YINGSTAR assembly factory

Step 7: Final Inspection and Functional Test

After the soldering and conformal coating processes of the PCB assembly process are completed, the Quality Assurance team will do a final inspection to ensure the PCB's functionality. A "functional test" is the term for this type of inspection. The customer normally provides the test software and tools, but the PCBA factory can also create fixtures to meet the customer's needs. The test puts the PCB through its paces by imitating the PCB's usual operating conditions. In this test, testers examine the electrical characteristics of the PCB as power and simulated signals are sent across it.
 


Step 8: Cleaning and Drying

 Because oil and grime are present throughout the manufacturing process, the PCB is cleaned and dried before being shipped. Soldering paste, for example, leaves some flux behind, and human handling can transfer oils and grime from fingers and clothing to the board's surface.


Step 9: Packaging and Shipping

All assembled boards are packaged (anti-static packaging is available upon request) and dispatched via various courier services like as DHL, FedEx, UPS, EMS, and others. Unused components are returned to the buyer according to their instructions. Customers are also notified through email when their products are shipped. The following are some examples:
 

The pictures show YINGSTAR packaging standard