SMT PACKAGES

Surface mount technology (SMT) components come in a variety of packages. As technology has improved many packages have decreased in size. Additionally there is a variety of different SMT packages for integrated circuits dependent upon the interconnectivity required, the technology being used and a variety of other factors.

To provide some degree of uniformity, sizes of most SMT components conform to industry standards, many of which are JEDEC specifications. Obviously different SMT packages are used for different types of components, but the fact that there are standards enables activities such as printed circuit board design to be simplified. Additionally the use of standard size packages simplifies the manufacture because pick and place machines can use standard feed for the SMT components, considerably simplifying the manufacturing process and saving costs.

The different SMT packages can be categorized by the type of component, and there are standard packages for each.

Passive rectangular components
These SMT components are mainly resistors and capacitors which form the bulk of the number of components used. There are several different sizes which have been reduced as technology has enabled smaller components to be manufactured and used

• 1812 - 4.6 mm × 3.0 mm (0.18" × 0.12")
• 1206 - 3.0 mm × 1.5 mm (0.12" × 0.06")
• 0805 - 2.0 mm × 1.3 mm (0.08" × 0.05")
• 0603 - 1.5 mm × 0.8 mm (0.06" × 0.03")
• 0402 - 1.0 mm × 0.5 mm (0.04" × 0.02")
• 0201 - 0.6 mm × 0.3 mm (0.02" × 0.01")

Of these sizes, the 1812, and 1206 sizes are now only used for specialized components or ones requiring larger levels of power to be dissipated The 0603 and 0402 SMT sizes are the most widely used.

Tantalum capacitors
As a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.

• Size A   3.2 mm × 1.6 mm × 1.6 mm (EIA 3216-18)
• Size B   3.5 mm × 2.8 mm × 1.9 mm (EIA 3528-21)
• Size C   6.0 mm × 3.2 mm × 2.2 mm (EIA 6032-28)
• Size D   7.3 mm × 4.3 mm × 2.4 mm (EIA 7343-31)
• Size E   7.3 mm × 4.3 mm × 4.1 mm (EIA 7343-43)

Semiconductors
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 packages

• 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 × 1.75 mm × 1.3 mm
• SOT-223 - Small Outline Transistor. This package is used for higher power devices. It measures 6.7 mm × 3.7 mm × 1.8 mm. There are generally four terminals, one of which is a large heat-transfer pad

Integrated circuit packages

• SOIC - Small Outline Integrated Circuit. This has a dual in line configuration and gull wing leads with a pin spacing of 1.27 mm
• TSOP - Thin Small Outline Package. This package is thinner than the SOIC and has a smaller pin spacing of 0.5 mm
• SSOP - Shrink Small Outline Package. This has a pin spacing of 0.635 mm
• TSSOP - Thin Shrink Small Outline Package.
• PLCC - Plastic Leaded Chip Carrier. This type of package is square and uses J-lead pins with a spacing of 1.27 mm
• 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.
• 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 wit 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.

Applications
SMT 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