How to choose SMT mounting processing components reasonably

Today, FASTPCBA Electronics's share how to reasonably choose SMT  processing components. The selection and design of SMT surface mount components is a key part of the overall design of the product. The designer determines the electrical performance and function of the components in the system structure and detailed circuit design stage. In the SMT design phase, it should be based on the specific conditions of the equipment and process. The overall design requirements determine the package form and structure of the surface mount components. Surface mount solder joints are both mechanical joints and electrical joints. Reasonable choices have a decisive influence on improving PCB design density, manufacturability, testability and reliability.

First, choose the right package, mainly has the following advantages:

1. Effectively save PCB area and provide better electrical performance.

2. Provide good communication links to help dissipate heat and facilitate transmission and testing.

3. Protect the internal parts of the components from the environment such as moisture.

Second, SMT surface mount components selection method:

SMT surface mount components are divided into active and passive categories, which can be divided into gull wing type and "J" type according to the pin shape.

1.Passive components

Passive devices mainly include monolithic ceramic capacitors, tantalum capacitors and thick film resistors, which are rectangular or cylindrical in shape. The cylindrical passive device is called “MELF”. It is easy to roll when reflow soldering. It needs special pad design and should be avoided. Rectangular passive components are called "CHIP" chip components. They are small in volume, light in weight, good in anti-impact and shock-resistant, and have low parasitic losses. They are widely used in various electronic products. In order to obtain good solderability, it is necessary to select a plating of a nickel bottom barrier layer.

2.Active devices

There are two main types of surface mount chip carriers: ceramics and plastics.

The advantages of ceramic chip package are:

A. Good air tightness and good protection for internal structure

B. Short signal path, significantly improved parasitic parameters, noise and delay characteristics C.Reduced power consumption.

The disadvantage is that no pins absorb the stress caused by solder paste melting, and the mismatch of CTE between the package and substrate can lead to solder joint cracking during welding. The most commonly used ceramic chip carrier is the leadless ceramic wafer carrier LCCC.

Plastic packaging is widely used in military and civilian production, with good cost performance. The package form is divided into: small outline transistor SOT; small outline integrated circuit SOIC; plastic packaged lead chip carrier PLCC; small outline J package; plastic flat package PQFP.