Automated Surface Mount PCB

Compared with through-hole mounting, surface mount assembly has the advantage of being much more efficient. The automation of the entire PCB mounting process, from solder paste printing to pick and place and reflow soldering, eliminates human error, dramatically cutting assembly time. However, it is important to understand that this method of assembly also has its drawbacks. For example, the components are usually smaller with shorter pins than their through-hole counterparts, making them harder to repair or replace. Moreover, the tiny printed circuit boards are more susceptible to heat damage.

A PCB assembly line consists of several machines, including a board loader that stores the bare PCB that is about to enter the production line. A conveyor system then transports the PCB to a stencil, where solder paste is applied evenly across the designated areas. Then the SMT line moves to the pick and place machine, where a robotic device places surface mount devices, or SMDs, on the PCB. A nozzle on the pick and place robot’s arm grabs SMDs from a feeder belt, and then they are precisely adhered to the pads of the PCB by suction.

Once the placement of the surface mount pcb is finished, the board is conveyed to the reflow soldering machine, where the SMDs and PCB are heated to a high temperature in order to form crucial electrical solder joints. During this step, the robot’s nozzles are used to inspect the SMDs for proper alignment with the printed circuit board and for other defects. Besides, the AOI (Automated Optical Inspection) machine uses infrared cameras to scan each SMD for a specific characteristic, such as its lead and package size, its orientation, and more.

Automated Surface Mount PCB – The Typical Process

If the SMDs are faulty, they will be rejected by the machine and removed from the conveyor. Afterward, the board will go back to the beginning of the SMT line for the mounting of the other side. In the end, the good PCBs will be sent to a packaging room. Not-good PCBs will be separated from the bad ones, and the not-good PCBAs will be reworked or repaired as needed.

The rework process involves soldering the defective SMDs with a special soldering iron or with a non-contact rework system. It is essential to use the right type of rework system, as certain types of SMDs are not compatible with the reflow soldering process. They might be sensitive to thermal stress or require a robust solder joint. For instance, a component with a crimp or folded connector leads must be removed after panelization separation, as it is not robust enough to survive the reflow soldering process.

A rework technician will then use the appropriate tools to remove the defective parts and place new ones in their correct positions. The rework process can take anywhere from 20 minutes to 1 hour, depending on the severity of the defect and the number of defective SMDs. Then, the rework technician will retest the board to ensure it is fully functional.

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