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Sunday, 25 June 2017

What is SMD Components - English

What is SMD Components - English  

Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board.

Both technologies can be used on the same board for components not suited to surface mounting such as large transformers and heat-sinked power semiconductors.

An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component.

Semiconductor SMD packages

There is a wide variety of SMT packages used for semiconductors including diodes, transistors and integrated circuits. The reason for the wide variety of SMT packages for integrated circuits results from the large variation in the level of interconnectivity required. Some of the main packages are given below

Transistor & diode packages

SMD transistors and diodes often share the same types of package. While diodes only have two electrodes a package having three enables the orientation to be correctly selected.

SMD diodes on a printed circuit

Although a variety of SMT transistor and diode packages are available, some of the most popular are given in the list below.
  • SOT-23 - Small Outline Transistor:   This is SMT package has three terminals for a diode of transistor, but it can have more pins when it may be used for small integrated circuits such as an operational amplifier, etc. It measures 3 mm x 1.75 mm x 1.3 mm.
  • SOT-223 - Small Outline Transistor:   This package is used for higher power devices. It measures 6.7 mm x 3.7 mm x 1.8 mm. There are generally four terminals, one of which is a large heat-transfer pad.

Integrated circuit SMD packages

There are many forms of package that are used for SMD ICs. Although there is a large variety, each one has the areas where its use is particularly applicable.
  • SOIC - Small Outline Integrated Circuit :   This SMD IC package has a dual in line configuration and gull wing leads with a pin spacing of 1.27 mm
  • SOP - Small Outline Package:   There are several versions of this SMD package:
    • TSOP - Thin Small Outline Package:   This SMD package is thinner than the SOIC and has a smaller pin spacing of 0.5 mm
    • SSOP - Shrink Small Outline Package:   This package has a pin spacing of 0.635 mm
    • TSSOP - Thin Shrink Small Outline Package:  
    • QSOP - Quarter-size Small Outline Package:   It has a pin spacing of 0.635 mm
    • VSOP - Very Small Outline Package:   This is smaller than the QSOP and has pin spacing of 0.4, 0.5, or 0.65 mm.

QFP- Quad flat pack:   The QFP is the generic type of flat package for ICs. There are several variants as detailed below. 
  • LQFP - Low profile Quad Flat Pack:   This package has pins on all four sides. Pin spacing varies according to the IC, but the height is 1.4 mm.
  • PQFP - Plastic Quad Flat Pack:   A square plastic package with equal number of gull wing style pins on each side. Typically narrow spacing and often 44 or more pins. Normally used for VLSI circuits.
  • CQFP - Ceramic Quad Flat Pack:   A ceramic version of the PQFP.
  • TQFP - Thin Quad Flat Pack:   A thin version of the PQFP.

BGA - Ball Grid Array:   A package that uses pads underneath the package to make contact with the printed circuit board. Before soldering the pads appear as solder balls, giving rise to the name.

  • By placing the pads underneath the package there is more room for them, thereby overcoming some of the problems of the very thin leads required for the quad flat packs. The ball spacing on BGAs is typically 1.27 mm. Read more about the Ball Grid Array
  • PLCC - Plastic Leaded Chip Carrier:   This type of package is square and uses J-lead pins with a spacing of 1.27 mm. Read more about the PLCC Plastic Leaded Chip Carrier

SMD package applications

SMT surface mount technology packages are used for most printed circuit designs that are going to be manufactured in any quantity. Although it may appear there is a relatively wide number of different packages, the level of standardisation is still sufficiently good. In any case it arises mainly out of the enormous variety in the function of the components.

Watch Video | How to Soldering & D-Soldering SMD Component 

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