SMD: It is an abbreviation of Surface Mounted Devices, meaning: surface mount device, which is one of the SMT (Surface Mount Technology) components. In the initial stages of electronic circuit board production, via assembly is done entirely by hand.
SMD means surface mounted diode. This is a better technology than the first generation DIP LEDs. The SMD type LEDs are mounted on an aluminum substrate and enveloped in an epoxy resin.
When the first automated machines were introduced, they could be placed with simple lead components, but complex components still required manual placement for reflow soldering. Surface Mounted components mainly include rectangular chip components, cylindrical chip components, composite chip components, and profiled chip components.
Development of SMD:
Surface mount components were introduced about twenty years ago and have opened up a new era. From passive components to active components and integrated circuits, they eventually become surface mount devices (SMDs) and can be assembled by pick and place equipment. For a long time it has been thought that all pin components will eventually be available in SMD packages.
Classification of SMD:
There are mainly chip transistors and integrated circuits
Integrated circuits include SOP, SOJ, PLCC, LCCC, QFP, BGA, CSP, FC, MCM, etc.
Examples are as follows:
1. Interconnect: Provides mechanical and electrical connection/disconnection, consisting of connecting plugs and sockets, connecting cables, brackets, chassis or other PCBs to the PCB; however, the actual connection to the board must be through surface mounting Type contact.
2, a.active electronic components (Active): In analog or digital circuits, you can control the voltage and current to generate gain or switching, that is, respond to the application of signals, you can change your basic characteristics. (The simplest and straightforward understanding is that it always has an external power supply, so the name is active)
b. Passive electronic components (Inactive): Provides a simple, repeatable response when the electrical signal is applied without changing its characteristics. (The simplest and straightforward understanding is that it does not need to work without an external power supply, hence the name passive)
3. Odd-form: The geometry factor is peculiar, but it does not have to be unique. Therefore, it must be manually mounted, and its outer casing (compared to its basic function) is not standard in shape, for example: many transformers, hybrid circuit structures, fans, mechanical switch blocks, and the like.
Characteristics of SMD:
The assembly density is high, the size of the electronic product is small, and the weight is light. The volume and weight of the chip components are only about 1/10 of that of the conventional plug-in components. After the SMT is generally used, the volume of the electronic product is reduced by 40% to 60%, and the weight is reduced by 60%. 80%.
High reliability and strong anti-vibration ability. The solder joint defect rate is low.
High frequency characteristics are good. Reduced electromagnetic and radio frequency interference.
Easy to automate and increase productivity. Reduce costs by 30% to 50%. Save materials, energy, equipment, manpower, time, etc.
Package of SMD:
Micro SMD Wafer Level CSP Package:
Micro SMD is a standard thin product. There is a solder bump on one side of the SMD chip. Micro SMD production process steps include standard wafer fabrication, wafer repassivation, deposition of eutectic solder bumps on I/O pads, backgrinding (for thin products only), protective package coating, wafers The platform was selected for testing, laser marking, and packaging in tape and roll form, and finally assembled on the PCB using standard surface mount technology (SMT).
The Micro SMD is a Wafer Level Chip Size Package (WLCSP) with the following features:
1. The package size is the same as the die size;
2. The smallest I/O pin;
3. No underfill material is required;
4. The connection spacing is 0.5mm;
5. There is no need for an interposer between the chip and the PCB.
Precautions of SMD:
Surface Mount Precautions:
a. Micro SMD surface mount operations include:
1. Printing flux on the PCB;
2. Component placement using standard pick and place tools;
3. Reflow soldering and cleaning of solder bumps (depending on the type of solder).
b. Surface mount advantages of micro SMDs include:
1. Shipped in standard tape and roll package for easy operation (according to EIA-481-1);
2. Standard SMT pick and place tools can be used;
3. Standard reflow process.
Package size of SMD chip components:
Inch system: 1206–0805–0603–0402–0201–01005
0603 has metric, English distinction
The metric system 0603 is imperial 0201
The metric system of the English system 0603 is metric 1608
Also pay attention to the distinction between 1005 and 01005
1005 also has a metric system, the distinction between English and English
The metric system of the British system 1005 is metric 2512
The metric system 1005 is the British system 0402
As in ProtelDXP (Protel2004) and later versions, there are already package libraries for SMD chip components, such as
CC1005-0402: For chip capacitors, metric 1005, inch 0402 package
CC1310-0504: For chip capacitors, metric 1310, inch 0504 package
CC1608-0603: For chip capacitors, metric 1608, inch 0603 package
CR1608-0603: For chip resistors, metric 1608, inch 0603 package, the same size as CC16-8-0603, just for easy identification.
Surface mount packages are available in both non-welded shield definition (NSMD) and solder joint shield definition (SMD). Compared with the SMD method, the NSMD method can strictly control the copper etching process and reduce the stress concentration point on the PCB, so this method should be preferred.
In order to achieve a higher ground clearance, it is recommended to use a copper layer with a thickness of less than 30 microns. A copper layer having a thickness of 30 microns or more reduces the effective ground clearance, thereby affecting the reliability of the soldering. In addition, the width of the line between the NSMD pad and the ground pad should not exceed two-thirds of the pad diameter. It is recommended to use the pad sizes listed in Table 1:
PCB layouts using via-via via structures (micro vias) should be defined in accordance with the NSMD pad to ensure adequate solder pads on the copper pads to enhance soldering.
Considering the internal structural properties, an organic solderability protection (OSP) coated circuit board treatment can be used, which can be copper OSP and nickel-gold plating:
1. If nickel-gold plating method (electroplated nickel, deposited gold) is used, the thickness should not exceed 0.5 micron to avoid brittleness of the solder joint;
2. Since the flux has surface tension, in order to prevent the component from rotating, the printed wiring should be symmetrical in the X and Y directions;
3. It is recommended not to use the hot air solder coating (HASL) board processing method.