SMD Packages are available in wider range of shapes and sizes and are generally designed to be placed on PCB boards by machines rather than by hand. SMT components or SMDs have a number of standardized packages including 1206, 0805, 0603, 0403, 0201, SOT, SOIC, QFP, BGA, etc. Surface-mount components are usually smaller than their counterparts with leads, and are designed to be handled by machines rather than by humans. The electronics industry has standardized package shapes and sizes (the leading standardization body is JEDEC).
Passive Two-terminal Components
These passive components are generally resistors and capacitors and make up the majority of the components placed. There are several different sizes available -physical sizes can be seen below:
|
Physical size |
Imperial Name |
Metric Name |
| 6.3mm x 3.2mm (0.25” x 0.12”) |
2512 |
6332 |
| 5.0mm x 2.5mm (0.20” x 0.10”) |
2010 |
5025 |
| 4.5mm x 3.2mm (0.18” x 0.12”) |
1812 |
4532 |
| 3.2mm x 2.5mm (0.125” x 0.10”) |
1210 |
3225 |
| 3.2mm x 1.6mm (0.125” x 0.06”) |
1206 |
3216 |
| 2.0mm x 1.2mm (0.08” x 0.05”) |
0805 |
2012 |
| 1.6mm x 0.8mm (0.06” x 0.03”) |
0603 |
1608 |
| 1.0mm x 0.5mm (0.04” x 0.02”) |
0402 |
1005 |
| 0.6mm x 0.3mm (0.024” x 0.012”) |
0201 |
0603 |
| 0.4mm x 0.2mm (0.016” x 0.008”) |
01005 |
0402 |
| 0.3mm x 0.15mm (0.012” x 0.006”) |
– |
03015 |
| 0.2mm x 0.1mm (0.008” x 0.004”) |
008004 |
0201 |
Some passive two-terminal components have a polarity and so it is important for these parts to be fitted in the correct orientation.
SMD Packages: Components with Leads
There are different lead styles available but the most common two styles are Gull-wing and J-Lead.
- Gull-wing leads are small and fragile. They can easily be damaged.
- J-Leads are sturdier than gull-wing leads; however, they take up more space and so there will be fewer leads available on the same size device.
SMD Packages: Components without Leads
This type of components is usually referred to as QFN devices and are becoming increasing popular due to their small form factor, reducing cost and good thermal and electrical performance.
One common problem that can occur when soldering this type of device is voiding. Voiding is simply trapped gas resulting from the reflow soldering process but can cause a reduction in the ability to dissipate heat and may also lift the device leading to open-circuits on the periphery.
A possible solution to reduce the amount of voiding is to change the stencil design for the central ground pad aperture by splitting the aperture to allow space between each solder deposit for the flux outgassing to escape.
SMD Packages: Components with Ball Grid Array (BGA)
A BGA is a type of surface mount device that has been developed to keep up with the demand for the number of electrical connections required for many modern applications. Being sure that these devices are soldered correctly can be a challenge and so process verification is very important. The BGA SMD package has all its contact pads underneath the device package. Before soldering the pads appear as solder balls, giving rise to the name.
Placing the contacts underneath the device reduces the area required whilst maintaining the number of connections available. This format also overcomes some of the problems of the very thin leads required for the quad flat packs and makes the package physically more robust.