SMT chip processing refers to the process of attaching electronic components and other materials on the PCB bare board. It is a popular processing technology in electronic assembly industry at present. The SMT patch processing process is composed of multiple processes, and the process control in the process determines the quality of the finished products. Next, we will introduce you in detail the processing flow of SMT patch processing.
Preparation before SMT patch processing.
1. Circuit board data (Gerber).
Standard circuit map electronic files should include at least 4 layers: PAD file, through-hole file, text file, anti-welding layer file;
Preferably the connecting plate Gerber; provided by PCB board factory.
Standard plate edge specification: 10mm board edge is left at the top and bottom;
Standard positioning hole specification: there is one positioning hole on the left and right side of the same plate edge, and the center of the circle is 5mm diameter and 4mm round hole on both sides of the plate edge.
Standard visual mark point specification: 1mm solid tin spray dot with opposite edge diagonally asymmetrical, outer ring 3mm diameter transparent ring;
2. Material list (BOM).
The location coordinates of the electronic file (the CAD, extension is “. The text file of “TXT”);
Mixing list of SMT positive and negative materials and DIP materials (please provide part coding principles and ways to distinguish between positive and negative parts);
Separate list of materials used for SMT and DIP (please provide the way to distinguish between positive and negative parts);
Separate list of SMT front / SMT back / DIP materials.
3. Auxiliary data.
Measuring furnace temperature plate (scrap board with important parts);
For empty PCB board, the electrons of Nuo are usually Class A PCB board.
Printing steel plate;
Second, the detailed process of SMT patch processing.
1. Material procurement, processing and inspection.
The material buyer makes the original material purchase according to the BOM list provided by the customer to ensure that the production is basically correct. After the completion of the purchase, carry out material inspection and processing, such as row needle shearing, resistance pin forming and so on. The purpose of inspection is to better ensure the quality of production. Nuodi electronic material procurement is supplied by special suppliers, and the upstream and downstream purchasing lines are complete and mature.
2. Screen printing.
Screen printing, that is, screen printing, is the first step in the SMT processing process. Screen printing refers to the leakage of solder paste or patch glue to the PCB pad to prepare for the welding of components. With the help of the solder paste printer, the solder paste is attached to the pad through the stainless steel or nickel steel mesh. If the steel screen used for screen printing is not provided by the customer, the processor needs to make it according to the steel screen document. At the same time, because the tin paste used must be frozen, the tin paste needs to be thawed to the right temperature in advance. The printing thickness of solder paste is also related to the scraper, so the printing thickness of solder paste should be adjusted according to the processing requirements of PCB board.
In general, in SMT processing, the glue used for dispensing is red glue, which is dripped on the PCB position to fix the components to be welded and prevent electronic components from falling or virtual soldering due to self-weight or unfixed in the process of reflow soldering. Dispensing can be divided into manual dispensing or automatic dispensing, which can be confirmed according to the needs of the process.
Through the functions of suction-displacement-positioning-placement, the placement machine can quickly and accurately mount SMC/SMD components to the position of the pad specified by the PCB board without damaging the components and the printed circuit board. The mounting is generally located before reflow soldering.
Curing is to melt the patch glue, is the surface mount components fixed on the PCB pad, generally using thermal curing;
6. Reflow soldering.
Reflow soldering is to realize the mechanical and electrical connection between the solder ends of surface assembly components or pins and PCB pads by remelting the paste solder pre-assigned to the PCB pad. It mainly depends on the effect of hot air flow on solder joint, and the gelatinous flux carries out physical reaction in a certain high temperature air flow to achieve SMD welding.
After the welding process is completed, the plate surface needs to be cleaned to remove rosin flux and some tin balls to prevent them from causing a short circuit between the components. Cleaning is to put the welded PCB board in the cleaning machine to remove the harmful flux residue on the PCB assembly board surface or the flux residue after reflow welding and manual welding as well as the contaminants caused in the assembly process.
Inspection is the welding quality inspection and assembly quality inspection of the assembled PCB assembly plate. Need to use AOI optical testing, flying needle tester and ICT and FCT functional testing. QC team conducts sampling inspection of PCB board quality, testing substrate, flux residue, assembly failure, etc.
9. Return to repair.
The repair of SMT is usually to remove components that are out of function, damaged pins or misarranged, and replace new components. Maintenance personnel are required to be familiar with the repair process and technology. The PCB board needs to go through visual inspection to see if the components are missing, wrong direction, false welding, short circuit, etc. If necessary, the defective board needs to be sent to a professional repair table for repair, such as ICT testing or FCT functional testing, until the PCB board is working properly.
The above is the detailed process of SMT patch processing, although there are more process details, which require the rich experience of the operator to control. At this point, I believe you also have a more in-depth understanding of the SMT patch processing process, need to further understand the level of understanding, welcome to the electrons.