SMD definition and classification:
SMD: short for Surface Mounted Devices, meaning Surface Mount Devices, it is one of the components of SMT(Surface Mount Technology). In the initial stage of PCB production, the through-hole assembly is completely completed by hand. After the first automated machines were introduced, they could place simple pin elements, but complex elements still needed to be placed manually to reflow. Surface Mounted components mainly include rectangular component, cylindrical component, composite component and special-shaped component.
1). Connection (Interconnect) : provide mechanical and electrical connection/disconnect, which consists of connecting plug and socket, connecting cable, bracket, chassis or other PCB to PCB; However, the actual connection to the plate must be through surface mount contact.
2). A Active electronic component (Active) : in analog or digital circuits, you can control the voltage and current by yourself to produce a gain or switching effect, that is, you can change your basic characteristics in response to the applied signal. (the simplest and most direct understanding is that it always has an external power source, hence the name active);
B passive electronics (Inactive) : provides a simple, repeatable response without changing its characteristics when an electrical signal is applied. (the simplest and most direct understanding is that it does not need and does not have additional power to work, so the name passive);

3).Odd-form: the geometry factor is Odd, but not necessarily unique. Therefore, it must be manually mounted, and the shell (in contrast to its basic function) has a non-standard shape such as many transformers, mixed circuit structures, fans, mechanical switch blocks, etc.

SMT definitions and characteristics:
SMT patch refers to the abbreviation of a series of processes processed on the basis of PCB. PCB (Printed Circuit Board) is a Printed Circuit Board. SMT is Surface Mounted Technology (short for Surface Mounted Technology), one of the most popular technologies and processes in the electronic assembly industry.
1). Silk screen printing: its function is to leak the solder paste or smudge adhesive onto the PCB solder pad to prepare for the welding of components. The equipment used is silk screen printing machine (screen printing machine), located at the forefront of SMT production line.
2). Glue dispensing: it drips glue to the fixed position of PCB board, and its main function is to fix components to PCB board. The equipment used is the dispensing machine, located at the front of SMT production line or behind the testing equipment.
3). Mounting: its function is to accurately install the surface assembly components to the fixed position of PCB. The equipment used is the mounter, which is located behind the screen printer in SMT production line.
4). Melting: its function is to melt the SMT adhesive, so that the surface assembly components and PCB board firmly stick together. The equipment used is curing furnace, located in the SMT production line behind the mounter.
5). Reflow welding: its function is to melt the solder paste and make the surface assembly components firmly adhere to the PCB board. The equipment used is the reflow welding furnace, located behind the SMT production line SMT mounter.
6). Cleaning: its function is to remove harmful welding residues such as flux from the assembled PCB board. The equipment used for cleaning machine, the position can not be fixed, can be online, but not online.
7). Inspection: its function is to inspect the welding quality and assembly quality of the assembled PCB. The equipment used are magnifying glass, microscope, online tester (ICT), flying needle tester, automatic optical detection (AOI), X-ray detection system, functional tester, etc. The location can be arranged in the appropriate place of the production line according to the need of inspection.
8). Repair: its function is to rework the PCB board with faults. Tools used for soldering iron, repair workstation, etc. Configuration at any location in the production line.

SMD is different from SMT:
1).SMD is a component, SMT is a technology and process, one is an object, one is a non-object.
2). Different functions. After the first automated machines are introduced, SMD can place some simple pin elements, while SMT is a circuit assembly technology that installs non-pin or short-lead surface assembly components on the surface of printed circuit board.
SMD. It stands for Surface Mounted Devices, meaning Surface Mount Devices, and is one of the components of SMT(Surface Mount Technology). In the initial stage of PCB production, the through-hole assembly is completely completed by hand.
SMT: it is a Circuit assembly technology in which components (SMC/SMD, short lead) are assembled on the surface of a Printed Circuit Board (PCB) or other substrate by reflow or dip welding.

SMD packaging has the following characteristics:
1). The package size is the same as the size of bare film;
2). The smallest I/O pin;
3). No bottom filling material is needed;
4). Wire spacing is 0.5mm;
5). No interposer is needed between the chip and PCB.
The main advantages of SMT packaging are:
1). Effectively save PCB area;
2). Provide better electrical performance;
3). Protect the internal parts of components from environmental influences such as dampness;
4). Provide good communications;
5). Help to dissipate heat and provide convenience for transmission and testing.

SMD and SMT applications:
SMT is focused on the process technology, SMD is in the side of the machine equipment;
SMT mainly refers to a professional technical field, while SMD mainly refers to some equipment or parts to be used in SMT industry, which is the difference between technology and actual objects.
SMT refers to the whole technical industry of mounting, which is relatively professional, while SMD is more used for the division of factories in departments.
SMD SMT fuse is widely used in portable electronic products, power converters, vehicle-mounted entertainment facilities, communications peripherals, household audio-visual equipment and other aspects especially prominent. Among them, portable electronic products cover a wide range, including mobile phones, digital cameras, PDA, laptop computers, game consoles, PMP, MP3, learning machine and so on.
1). In terms of power converter application, lithium battery protection board and inverter protection of mobile phones and other products are the most important application fields at present, and this kind of application amount is large and wide, accounting for a considerable share of SMD fuse applications;
2). In terms of on-board entertainment facilities, it includes GPS navigation system, on-board TV/radio /DVD, etc. With the rapid development of automotive electronics industry, the potential of such applications is also valued by the industry;
3). Applications on communication peripheral devices, including chargers, network access distribution lines, routers, modems, network CARDS, etc.;
4). Home use is mainly focused on LCD monitors/TVS, set-top boxes and other products.

SMT is mainly used in: large screen color TV and small communication machines, disk drives, program-controlled switches, fax machines, cellular mobile phones, notebook computers, video cameras, digital cameras and military electronic equipment.