Detailed Process Of SMT Processing

- Jan 18, 2019-

Detailed Process of SMT  Processing 

1. Material Purchase Processing and Inspection The material purchaser carries out the original purchase of materials according to the BOM list provided by the customer to ensure that the production is basically correct. After the purchase is completed, the material inspection and processing, such as pin headers, resistor pins, etc., are performed. Inspection is to better ensure the quality of production. Connaught's electronic materials procurement is supplied by specialized suppliers, and the upstream and downstream procurement lines are fully mature. 

2, silk screen Silk screen, that is, screen printing, is the first process of SMT processing. Silk screen printing refers to the printing of solder paste or patch glue onto the PCB pad to prepare for component soldering. The solder paste is infiltrated through a stainless steel or nickel steel mesh to the pad by means of a solder paste printer. If the steel mesh used for silk screen printing is not provided by the customer, the processor needs to make it according to the steel mesh file. At the same time, since the solder paste used must be stored frozen, the solder paste needs to be thawed to a suitable temperature in advance. The thickness of solder paste printing is also related to the blade. The thickness of the solder paste should be adjusted according to the processing requirements of the PCB. 

3. Dispensing Generally, in SMT processing, the glue used for dispensing is red plastic, and the red glue is dropped on the PCB position to fix the components to be welded to prevent the electronic components from being self-weight or not during the reflow process. Drop or solder joint for reasons such as fixing. Dispensing can be divided into manual dispensing or automatic dispensing, which can be confirmed according to the process requirements. 

4. Mounting The placement machine realizes the quick and accurate mounting of SMC/SMD components to the PCB board by means of suction-displacement-positioning-placement and other functions without damaging components and printed circuit boards. The pad position. Mounting is generally preceded by reflow soldering. 

5, curing Curing is the melting of the patch glue, the surface mount components are fixed on the PCB pad, generally using thermal curing.

6.  Reflow soldering is a mechanical and electrical connection between the soldered end of a surface-mount component or a pin and a printed circuit board pad by re-melting the solder solder pre-dispensed onto the pad of the printed board. Soldering. It mainly relies on the action of hot gas flow on the solder joint, and the gel-like flux reacts physically under a certain high temperature airflow to achieve SMD welding. 

7. Cleaning After the soldering process is completed, the board surface needs to be cleaned to remove the rosin flux and prevent them from causing short circuits between components. Cleaning is to place the soldered PCB board in the cleaning machine to remove the flux residue that is harmful to the human body on the surface of the PCB assembly board or the flux residue after reflow and manual soldering, as well as the contaminants caused during the assembly process.

8. The inspection is to perform welding quality inspection and assembly quality inspection on the PCB assembly board after assembly. The AOI optical inspection, flying probe tester and ICT and FCT functional tests are required. QC team conducts PCB quality inspection, inspection of substrate, flux residue, assembly failure, etc.

9. Rework SMT is usually to remove components that have lost function, pin damage or misalignment, and replace new components. Maintenance personnel are required to be familiar with the repair process and technical mastery. The PCB board needs to be visually inspected to see if components are missing, wrong direction, soldered, shorted, etc. If necessary, the board in question needs to be sent to a professional rework station for repair.