[ Date Time : 2013-3-27 ] [ Comments : 0
Selection and design of surface mount components is a key part of the overall design of the product, the designer in system architecture and detailed design stage determine the electrical properties of components and features, SMT Assembly design stage should be based on overall design of equipment and technology and asked to identify surface mount components of packaging forms and structures. Surface mount solder joint is both a mechanical connection and electrical connection point, reasonable choice to improve density, PCB design, testability and reliability of production has had a decisive impact.
there is no difference in Surface-mounted components and cartridge components functionality,the difference is the components of the package. When installing encapsulated in the welding surface subjected to high temperature of the milk components and substrate must have a matching of thermal expansion coefficient. These factors must be fully considered in product design.
Select the appropriate package, its mainly advantages are: 1).Toeffective saving PCB area; 2). provide better electrical performance; 3). components of the internal protection against environmental impacts such as wet; 4). providing good communication; 5). helps heat dissipation and facilitate the transmission and testing.
二： The surface-mount components selection
Surface mount components are divided into two types: active and passive. According to the pin shape is divided into the gull wing type and "J" type.The selection of components are classified as follow:
Passive components are mainly consiste of monolithic ceramic capacitors, tantalum capacitors and thick film resistors, it forms a rectangular or cylindrical shape. Cylindrical-shaped passive device called "MELF", using reflow soldering prone to rolling and also need to use the special design of the pad, and should generally be avoided.
Rectangular passive components referred to as "CHIP" chip components, its small size, light weight, high impact and shock resistance of the antibiotic, parasitic loss is small, are widely used in various types of electronic customer products pcba. In order to get a good solderability, you must select the nickel plating of the barrier at the end of it.
The surface mounted resistor capacitor encapsulation has a variety of shape size. When selecting we should avoid to choose too small size: < 0.08 inches X0.05 inches to reduce post put the difficulty, also should avoid to choose too large size: > 0 inches X0.12 inches to avoid using epoxy glass FR - 4 produce thermal expansion coefficient (CTE) mismatch electronic component requirements can withstand under 260 ℃ temperature 5-10 s of welding time.