The specifics of the SM placement process play a crucial role in determining the quality of PCB production. In simple terms, the process can be summarized as follows: customer order → customer information → raw material procurement → incoming inspection → on-line production → post-sale packaging. Below is a detailed overview of the SMT patch processing.

1. Material procurement, processing, and inspection

The material purchaser initiates the procurement of materials based on the BOM list provided by the customer to ensure production accuracy. Once procurement is complete, materials undergo inspection and processing, including tasks such as pin header cutting and resistor pin forming. This inspection is vital for maintaining production quality. Nuo’s electronic material procurement is handled by specialized suppliers, ensuring that both upstream and downstream procurement processes are comprehensive and well-established.

2. Silk screen

1. **Silk Screen Printing**

Silk screen printing, also known as screen printing, is the initial step in the SMT process. This method involves applying solder paste or adhesive onto the PCB pads to prepare for component soldering. Using a solder paste printer, the solder paste is forced through stainless steel or nickel mesh to adhere to the pads. If the stencil for silk screen printing is not provided by the customer, the processor must create it based on the stencil file. Additionally, since the solder paste needs to be stored frozen, it must be thawed to the appropriate temperature beforehand. The thickness of the solder paste application is influenced by the squeegee, and adjustments should be made according to the PCB processing requirements.

2. **Dispensing**

In SMT processing, the adhesive typically used for dispensing is red glue, which is applied to specific positions on the PCB to secure components for soldering. This prevents electronic components from falling due to their weight or becoming dislodged during the reflow soldering process, which can lead to poor connections. Dispensing can be either manual or automated, depending on the process requirements.

3. **Mounting**

The placement machine efficiently and accurately positions SMC/SMD components onto designated pads on the PCB without causing damage to either the components or the printed circuit board, utilizing suction, displacement, positioning, and placement functions. Mounting generally occurs prior to reflow soldering.

4. **Curing**

Curing involves melting the adhesive to secure the surface mount components onto the PCB pads. Typically, heat curing is employed for this process.

5. **Reflow Soldering**

Reflow soldering remelts the solder paste pre-applied to the printed board pads, establishing mechanical and electrical connections between the solder joints or pins of the surface mount components and the PCB pads. This process primarily relies on hot air flow to facilitate solder joint formation. The flux undergoes a physical transformation when exposed to high-temperature air flow, enabling SMD soldering.

6. **Cleaning**

Once soldering is completed, the board surface must be cleaned to eliminate rosin flux and solder balls, which can cause short circuits between components. Cleaning involves placing the soldered PCB in a cleaning machine to remove harmful flux residues from the surface of the PCB assembly, as well as any contaminants that may have accumulated during the assembly process.

7. **Detection**

Inspection is crucial for assessing the welding and assembly quality of the finished PCB assembly. Techniques such as AOI optical inspection, flying probe testing, and both ICT and FCT function testing are employed. The QC team performs random inspections to evaluate PCB quality, checking for substrate issues, flux residue, and assembly defects.

8. **Repair**

SMT repair typically involves removing non-functional components, damaged pins, or incorrectly positioned parts and replacing them with new components. Personnel must be well-versed in repair processes and techniques. The PCB must undergo visual inspection to identify missing components, incorrect orientations, cold solder joints, or short circuits. If necessary, boards requiring attention may be sent to a specialized rework station for repair, especially after ICT or FCT testing, until the PCB functions normally.

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