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What does Surface-Mount Device (SMD) mean?

A surface-mount device (SMD) is an electronic device whose components are placed or mounted onto the surface of the printed circuit board (PCB). This method of manufacturing electronic circuit boards is based on the surface-mount technology (SMT), which has largely replaced the through-hole technology (THT) especially in devices that need to be small or flat. Compared to the latter, SMT allows both sides of a PCB to be used when required.

Here's a view on common SMDs (Surface Mount Devices).



SMD resistors
SMD resistors come into several possible case sizes. Each size is described as a 4 digits number. The first 2 digits indicate the length; the last 2 indicate the width (in 0.01", or 10 mils units).

For example, the three most popular sizes are:
  • 0603: means 0.06"x0.03", or 60x30 mils, or 1.6x0.8mm
  • 0805: means 0.08"x0.05", or 80x50 mils, or 2.0x1.25mm
  • 1206: means 0.12"x0.06", or 120x60 mils, or 3.2x1.6mm
SMD capacitors
Capacitors from 1pF to 1uF are available in the same sizes, 0603 to 1206.
The most popular technology is ceramic.
SMD Tantalum capacitors
Tantalum is the technology of choice for capacitors 1uF and higher.
Case sizes are indicated by a letter from "A" to "E".

Case L x W x H (mm)
A 3.2x1.6x1.6
B 3.5x2.8x1.9
C 6.0x3.2x2.5
D 7.3x4.3x2.8
E 7.3x6.0x3.6

Tantalum capacitors are polarized; a bar on the case indicates the positive side.
SMD transistors
The most popular size for small-signal transistor is called "SOT-23".
The second most popular is "SOT-223".
SMD Integrated Circuits ("ICs")
The two most popular sizes are "SO-8" and "SO-14" (also named "SOIC-8" and "SOIC-16").
SMD FPGAs
Nowadays, there are three popular packages:
  • TQFP (Thin Quad Flat Pack), 100 or 144 pins.
  • PQFP (Plastic Quad Flat Pack), 208 or 240 pins.
  • BGA (Ball-Grid Array), 256 to 1000+ pins.
SMD QFPs


TQFPs 100 pins and 144 pins are reasonably easy to solder manually, because the pins are sturdy.
PQFPs 208 pins and 240 pins are not as easy because the pins bend very easily.

Pins are separated by 0.5mm.
See below for tutorials and links about soldering these components.
SMD BGAs


The bottom of a BGA component is actually a circuit board, with pads covered by solder balls (that's what you can see on the above picture).
The BGA balls are not made of solid metal but of solder. During board assembly, the BGA goes through an oven, melting the balls between the BGA circuit board and the application circuit board.

Balls are commonly separated by 1mm or 1.27mm, less often by 0.8mm.
How to solder SMDs
You need the following equipment:
  1. A temperature-regulated ("thermo-regulated") solder iron with a small tip.
  2. A flux dispenser, in bottle or pen form.
  3. Tweezers, to hold the components while soldering them.
  4. Solderwick, to clean up excess solder.
Explanations:
  1. A temperature-regulated solder iron stays at a constant temperature, no matter if used to solder light or heavy loads. That's different than a simpler (and cheaper) power-regulated iron. A power-regulated iron might get too hot when not in used, and too cold when in heavy use.
  2. Flux is essential to solder SMDs. Most solder contain a flux core already, which may have been adequate for yesterday's soldering jobs, but SMD soldering requires additional source of flux to get good soldering quality. The flux is used to reduce the oxidation of the solder (happens very quickly at soldering temperatures). It allows the solder to flow easily and make good solder joins.

What is SMD or Surface Mount Device or Surface Mount Electronic Component?

Surface mount devices of SMD are electronic components that are easily soldered or mountable on the surface on the PCB. Most of these PCBs are multilayered PCB which means these PCB have more than one layer. The technique of soldering or utilizing SMD components is called SMT (Surface Mount Technology).

What are Advantages of SMD?

SMD type electronic components offer many advantages. The main advantage is that they are space saving. The size of mobile phones has been significantly reduced because of the use of SMD components. SMD components use less electricity and voltage loss is also very less.

Uses of SMD Electronic Components?

Presently SMD of Surface Mount Devices are used in ultra modern electronic equipments like mobile phones, smartphone, computers, laptops tablets etc. all the components used in Surface Mount Technology are mostly in the form of chips or IC (Integrated Circuit). These chips or ICs are classified into different categories depending of the type of legs or leads they have and their function. These components are mounted directly at the specified location on the copper track of the Printed Circuit Board using Surface Mount Soldering Technology.


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