I have lately been trying to familiarize myself with SMT/SMD packages of electronics components and I thought I’ll share my findings with all of you so that it might be of some use to others
An overview of the most common surface mount package sizes and formats, such as QFP, TSOP, 0602, 0805,etc. will be discussed here.
Surface mount technology, SMT components come in a variety of packages.
As surface mount 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.
Integrated circuits (ICs) and electronic components come in a bewildering variety of shapes and sizes (often called ‘packages’), and it can be difficult for any beginner to keep track of what the main characteristics are of each package type. ICs are often referred to by abbreviations such as LQFP, TQFP, TSOP, SSOP, etc., and discrete components (resistors, capacitors, etc.) are typically given names that correspond to their physical dimensions, such as 0402, 0603, 0805, and 1206. To make things even worse, the names of discrete components are sometimes different depending on whether you are using metric or imperial measurements (cms versus inches), although imperial names (0603, 0805, etc.) are common even in European and other metric regions.
This guide will hopefully serve two purposes: To give you an overview of the most common IC and component packages and sizes, and to help you decide which package type you should be buying or using in different situations.
Discrete Components
A “discrete component” is a fancy label for the single circuit electronic components that make up most of your board, and they are generally divided into two categories: passive components (Resistors, Capacitors, Diodes, etc.) and active components (Transistors, LEDs, etc.). Most of these discrete components come in common shapes and sizes, and are relatively easy to identify.
Resistors
Resistors, along with many other discrete components, most commonly come in rectangular packages named after their physical dimensions. The most common of these standard packages sizes are 0402, 0603, 0805 and 1206. The numbers represent ‘1/100th of an inch’, meaning an 0603 package is theoretically 0,06″ x 0,04″ (1,524mm x 1,016mm). I say ‘theoretically’ because there is always some variation between manufactuers and different component types.
It’s worth noting that resistors are only able to handle a certain amount of electrical current before burning out (a 1/4 watt resistor, for example, can handle twice as much power — or about 41% more current — as a 1/8 watt resistor). Since there is a relationship between the physical size of a component and the amount of current that it can safely handle, manufacturers need to increase the size of the resistors as the rating goes up. For example, 1/8 watt resistors are widely available in 0805 packages, but you will need to move up to 1206 or larger if you need a 1/2 watt or higher resistor.
Capacitors
Capacitors act as ‘mini-batteries’ of sorts, helping ensure that you have a smooth, steady power supply available to all your on-board components and peripherals. They come in a wide variety of packages, depending on the type of capacitor used and their technical specifications. There are three main types of capacitors you are likely to encounter in electronics:Ceramic, Tantalum and Electrolytic, with each type generally having it’s own set of standard package sizes.
Ceramic capacitors typically come in the common 0603, 0805 or 1206 packages. Tantalum capacitors have their own standard rectangular package sizes, referred to by letters A, B, C, D, E, etc. Electrolytic capacitors are usually round and ‘stick up’ from the board, but there aren’t really any strictly followed standard sizes used by all manufacturers. As such, you may need to pay a bit more attention when adding electrolytic capacitors to your board. For all capacitors, the larger their ‘capacity’, the larger the physical package will necessarily be.
LEDs
Surface-mount LEDs (or Light Emitting Diodes) most commonly come in 0603, 0805 and 1206 packages, and are polarised meaning that they need to be placed in the right direction on your board. The electrical current on your LEDs should flow from the Anode (A) to the Cathode (K) side of your LED, with a current-limiting resistor to keep the LED from drawing too much current and burning out (see our entry on “Ohm’s Law” for information on this and a calculator to help you determine which resistor to use with your LED). Before placing any LEDs on your board, be sure to read the datasheet to determine which side is A and which is K.
Diodes, Transistors, and other discrete components
While Diodes are available in SOT223 and SOT23 packages (see below), they also have their own standard package sizes, with one of the more common sets being SMA, SMB and SMC (an SMA diode can be seen in the second photo below). SMA is probably the most common in small microcontroller projects.
Other discrete components: While many discrete components come in standard package sizes (0805, 1206, etc.), there are certain components that require three or more pins to function and they often come in a set of standard package sizes with the SOT prefix such as SOT223 or SOT23. A very common example is the LM1117 adjustable voltage regulator seen in the first photo below, which is in a four pin SOT223 package. Depending on the number of pins, the package names vary slightly. For example, while a SOT223 device has four pins (three on the bottom and one on top), a SOT223-4 device has 5 pins (four on the bottom), and a SOT223-5 device has 6 pins (five on the bottom). The same is true for SOT23 packages: while a normal SOT23 has 3 pins (one on top, and two on the bottom) a SOT23-5 has 5 pins (two on top, and three on the bottom). A third SOT package you may encounter is the three pin SOT323, which has one pin on top and two pins on the bottom. (If you’re having a hard time to understand the differences between these admittedly similar package sizes, we’ve added some footprint outlines in the images below.)
Large Integrated Circuits
QFP, SOIC, TSOP, and other “leaded” packages
These types of IC packages are easy to identify because they have external ‘leads’ (or ‘pins’) that are soldered directly to the PCB. They are probably the most common type of IC package that you are likely to encounter, though “leadless” packages like QFN (see below) are becoming more and more common.
While a wide variety of leaded packages exist, three of the most common families are QFP (Quad-Flat Package), TSOP (Thin Small-Outline Package) and SOIC (Small-Outline Integrated Circuit). Variations exist in each of these ‘families’, such as LQFP, TQFP, etc., but the differences are minimal and often refer to the physical height of the package.
In general, leaded packages will probably be the easiest to work with for prototyping and small scale production and should be given preference if you have the choice since they can be easily hand-soldered and removed from PCBs, and arevery easy to inspect. (QFN packages, which have their leads hidden underneath the edge of the chip can still be hand-soldered, but inspection is harder and some care is required when working with them. BGA packages can’t be hand-soldered at all, and generally require expensive equipment for both placement and inspection.)
QFN (Quad Flat No leads)
QFN packages have their leads hidden underneath the chip, and are visible when you look at the chip from the side. They are becoming more and more common due to the fact that they are less fragile than QFP or other “leaded’ parts (where the external leads can be bent or damaged) and because they take up less physical space than parts with external leads.
QFN packages can be hand-soldered, but it takes a bit more effort, and you will likely find them easier to solder with solder paste than a with traditional soldering iron.
BGA (Ball-Grid Array) and CSP (Chipscale)
Ball-Grid Array and Chipscale are miniaturised packages that are designed to add the maximum number of pins in the smallest physical package size possible. Rather than having one row of pins along the edge of the chips — as is the case with both QFP/SOIC/TSOP and QFN/DFN — BGA and Chipscale packages have several rows of ‘balls’ underneath, allowing manufacturers to add a much higher pincount to their chips than would be possible with any other package type. This is essential in situations where space is at a premium, such as in mobile phones or small hand-held devices, but as microcontrollers become more and more complex and add more features the need for more physical pins also necessitates the use of BGA in most modern MCUs. It’s difficult to find ARM9 processors in anything other than BGA, for example.
Unfortunately, BGA packages are much more difficult and expensive to work with since they require specialised equipment for inspection and are very difficult to place by hand. They’re designed for large production volumes and automated machinery, and you should probably choose a QFP (etc.) or QFN variety if one is available for your IC or MCU. (Unfortunately, this isn’t always the case). An exception to this is Chipscale (CS/CSP) packages, which often have only a few pins (6 or 8 isn’t uncommon). While somewhat challenging to work with due to their size, you can hand-place and inspect small chipscale packages under a microscope, so long as there is only one row of balls on each side (i.e., there isn’t a second layer of balls in the middle that you wouldn’t be able to see by turning the chip 90° on it’s side and looking at it under a microscope).
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.
- PLCC – Plastic Leaded Chip Carrier: This type of package is square and uses J-lead pins with a spacing of 1.27 mm.
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.
SHRIRAM SPARK 
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