SMT basic knowledge
1. Surface Mount Technology-SMT (Surface Mount Technology)
What is SMT:
Generally refers to the use of automatic assembly equipment to directly attach and solder chip-type and miniaturized leadless or short-lead surface assembly components/devices (referred to as SMC/SMD, often called chip components) to the surface of the printed circuit board (PCB) Or other electronic assembly technology on the specified position on the surface of the substrate, also known as surface mount technology or surface mount technology, referred to as SMT (Surface Mount Technology).
SMT (Surface Mount Technology) is an emerging industrial technology in the electronics industry. Its rise and rapid development are a revolution in the electronics assembly industry. It is known as the "Rising Star" of the electronics industry. It makes electronic assembly more and more The faster and simpler it is, the faster and faster the replacement of various electronic products, the higher the integration level, and the cheaper the price, have made a huge contribution to the rapid development of the IT (Information Technology) industry.
Surface mount technology is developed from the manufacturing technology of component circuits. From 1957 to the present, the development of SMT has gone through three stages:
The first stage (1970-1975): The main technical goal is to apply miniaturized chip components in the production and manufacture of hybrid electric (called thick film circuits in China). From this perspective, SMT is very important for integration The manufacturing process and technological development of circuits have made significant contributions; at the same time, SMT has begun to be widely used in civilian products such as quartz electronic watches and electronic calculators.
The second stage (1976-1985): to promote the rapid miniaturization and multi-functionalization of electronic products, and began to be widely used in products such as video cameras, headset radios and electronic cameras; at the same time, a large number of automated equipment for surface assembly was developed After the development, the installation technology and support materials of the chip components have also been mature, laying the foundation for the great development of SMT.
The third stage (1986-now): The main goal is to reduce costs and further improve the performance-price ratio of electronic products. With the maturity of SMT technology and the improvement of process reliability, electronic products used in the military and investment (automobile computer communication equipment industrial equipment) fields have developed rapidly. At the same time, a large number of automated assembly equipment and process methods have emerged to make chip components The rapid growth in the use of PCBs has accelerated the decline in the total cost of electronic products.
2. Features of SMT:
①High assembly density, small size and light weight of electronic products. The volume and weight of SMD components are only about 1/10 of traditional plug-in components. Generally, after SMT is adopted, the volume of electronic products is reduced by 40%~60% and the weight is reduced by 60%. ~80%.
②High reliability, strong anti-vibration ability, and low solder joint defect rate.
③Good high frequency characteristics, reducing electromagnetic and radio frequency interference.
④ It is easy to realize automation and improve production efficiency.
⑤Save materials, energy, equipment, manpower, time, etc.
3. Classification of surface mount methods: According to the different processes of SMT, SMT is divided into dispensing process (wave soldering) and solder paste process (reflow soldering).
Their main differences are:
①The process before patching is different. The former uses patch glue and the latter uses solder paste.
②The process after patching is different. The former passes through the reflow oven to cure the glue and paste the components to the PCB board. Wave soldering is required; the latter passes through the reflow oven for soldering.
4. According to the process of SMT, it can be divided into the following types: single-sided mounting process, double-sided mounting process, double-sided mixed packaging process
①Assemble using only surface mount components
A. Single-sided assembly with only surface mounting (single-sided mounting process) Process: screen printing solder paste → mounting components → reflow soldering
B. Double-sided assembly with only surface mounting (double-sided mounting process) Process: screen printing solder paste → mounting components → reflow soldering → reverse side → screen printing solder paste → mounting components → reflow soldering
②Assemble with surface mount components on one side and a mixture of surface mount components and perforated components on the other side (double-sided mixed assembly process)
Process 1: Screen printing solder paste (top side) → mounting components → reflow soldering → reverse side → dispensing (bottom side) → mounting components → high temperature curing → reverse side → hand-inserted components → wave soldering
Process 2: Screen printing solder paste (top side) → mounting components → reflow soldering → machine plug-in (top side) → reverse side → dispensing (bottom side) → patch → high temperature curing → wave soldering
③The top surface uses perforated components and the bottom surface uses surface mount components (double-sided mixed assembly process)
Process 1: Dispensing → mounting components → high temperature curing → reverse side → hand inserting components → wave soldering
Process 2: Machine plug-in → reverse side → dispensing → patch → high temperature curing → wave soldering
Specific process
1. Single-sided surface assembly process flow Apply solder paste to mount components and reflow soldering
2. Double-sided surface assembly process flow A side applies solder paste to mount components and reflow soldering flap B side applies solder paste to mount components and reflow soldering
3. Single-sided mixed assembly (SMD and THC are on the same side) A side applies solder paste to mount SMD reflow soldering A side interposing THC B side wave soldering
4. Single-sided mixed assembly (SMD and THC are on both sides of the PCB) Apply SMD adhesive on the B side to mount the SMD adhesive curing flap A side insert THC B side wave solder
5. Double-sided mixed mounting (THC is on side A, both sides A and B have SMD) Apply solder paste to side A to mount SMD and then flow solder flip board B side apply SMD glue to mount SMD glue curing flip board A side to insert THC B Surface wave soldering
6. Double-sided mixed assembly (SMD and THC on both sides of A and B) A side apply solder paste to mount SMD reflow soldering flap B side apply SMD glue mounting SMD glue curing flap A side insert THC B side wave soldering B-side manual welding
Fives. SMT component knowledge
Commonly used SMT component types:
1. Surface mount resistors and potentiometers: rectangular chip resistors, cylindrical fixed resistors, small fixed resistor networks, chip potentiometers.
2. Surface mount capacitors: multilayer chip ceramic capacitors, tantalum electrolytic capacitors, aluminum electrolytic capacitors, mica capacitors
3. Surface mount inductors: wire-wound chip inductors, multilayer chip inductors
4. Magnetic beads: Chip Bead, Multilayer Chip Bead
5. Other chip components: chip multilayer varistor, chip thermistor, chip surface wave filter, chip multilayer LC filter, chip multilayer delay line
6. Surface mount semiconductor devices: diodes, small outline packaged transistors, small outline packaged integrated circuits SOP, leaded plastic package integrated circuits PLCC, quad flat package QFP, ceramic chip carrier, gate array spherical package BGA, CSP (Chip Scale Package)
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Post time: Jul-23-2020