Knowledge Base

SMT production line assembly system

We must first know about the SMT process to understand the SMT production line. The full name of the "SMT" is surface mount technology. Originally , the SMT process was designedin order to mount electronic components. Components such as resistors, capacitors, transistors , integrated circuits, etc... Can be easily mounted on top of the printed circuit board. Through the process, the components form electrical connections through the wave soldering process. The SMT line is a PCB assembly line composed of surface coating equipment. The equipment includes welding, cleaning, testing, and other machinery. In some cases, we'd call the SMT process simply an SMT assembly line .

pcb smt process

At present, not all the components can be surface mounted on top of the PCB. Thus, through-hole or in short THT components provides an alternative. The Through-hole components are bulky and need manual assembly. But through-hole components will work as well as SMT components, sometimes even better. Generally speaking, surface-mounted components come in two types: insert and mount.

In some cases, the inserts and mountings in the SMT production line need a hybrid assembly. This type of assembly includes both THT components and SMT combined. All AMT assembly lines that use SMC/SMD (SMD production line) become surface assembly. THT components need manual and wave soldering techniques.

Different assembled projects, processes, and methods need a variety of PCB assembly lines. An SMT production line is used for SMT while reflow soldering is kept for THT.

Another form of assembly would be the Single-line form. Single-line assembly occurs when we only need to assemble a single layer of the PCB.

If we assemble SMC or surface-mounted devices on both sides of the PCB, we need a two-line SMT production line. Sometimes the PCB components placement will exist in many places. In such a case, it could be necessary to add an extra interposing assembly line. The interposing assembly line is based on the original PCB SMT assembly line.

Scale SMT manufacturers have established equipment with feeding trolleys. The surface-mounted components are controlled and managed by the computer. This is an advanced organization form for automated assembly and SMT production lines.

pcb smt

SMT assembly equipment and SMT assembly line

Closer to home, what processes does the SMT production line include? We must first understand the SMT assembly line process so we could find a good manufacturer. The following is the general process of the SMT production line. soldering method and dispensing process are all different depending on the wiring method.

1. Printing: 

PCB Stencil printing

The solder paste or patch glue is printed on the smt stencil to prepare for the soldering of the components. All equipment is a solder paste printer located at the front of the SMT production line .

2. Dispensing:

Solder paste printing machine for SMT processing

The glue dispenser is used to drop glue onto the fixed position of the SMT stencil. Its main function is to fix surface-mounted components on the PCB when wave soldering is used. The glue dispenser is found in front of the SMT production line or behind the testing SMT assembly equipment.

3. Mounting: 

pcb smt mounting

A placement machine is often used to mount the surface-mounted components on a fixed position of the SMT stencil. It is located behind the solder paste printer in the SMT production line.

4. SMD glue curing: 

A curing oven is used to cure the SMD glue so that the surface assembly components and SMT stencil are firmly bonded together. It is located behind the placement machine in the SMT production line.

5. Reflow soldering: 

pcb smt reflow soldering

Melt the solder paste to firmly bond the surface-mounted components and SMT stencil. The equipment used is a reflow oven. Located behind the placement machine in the SMT production line.

6. Clear: 

Cleaning machine for PCBA

Remove the solder residues, such as flux, harmful to the human body or the product on the assembled PCB. The equipment used is a cleaning agent, and the unknown may not be fixed. It may be online or offline. When using no-clean welding technology, this process is not provided.

7. Inspection:

BGA welding under X-Ray inspection


We use a variety of tools to inspect the welding and assembly quality of the surface mount component. The equipment includes a magnifying glass, microscope, online tester, first article tester, and more... The specific equipment used will depend on the specific testing needs. These tools can be placed in a suitable location on the SMT production line.

8. Repair: 

Repair of faulty PCB board

Repair the SMA that is faulty. The tools used are electric soldering irons, rework workstations, etc. Configured anywhere in the  smt line .

9. pcb recheck

After we have repaired all the PCB's, we will recheck them once more. Until all the problems are repaired, the whole production process is completed.