The Most Essential Facts about Surface Mount and pcba assemblyTechnology

Current Overview of SMT

Up to now, SMT is the most popular technology and technique in the industry of Printed Circuit Board Assembly (PCBA). Since its advent into market at the beginning of 1970s, SMT has become the main trend of modern electronic assembly industry, replacing wave soldering assembly that has to depend on manual insertion. This process has been regarded as the second revolution of electronic assembly technology. Put it in another way, SMT has been a global trend in international PCBA, leading to a large transformation of the whole electronic industry.

Moreover, SMT has pushed electronic components towards chip type, miniature, thinness, light weight, high reliability and multiple functions and it has been a symbol indicating a nation's scientific progress degree.

Technique and Attributes of SMT

SMT refers to a type of PCB assembly technology through which SMDs (Surface Mount Devices) are mounted on the surface of PCBs through some technique, equipment and materials coupled with soldering, cleaning and testing to complete assembly.

• SMT technique
SMT technique can be classified into different types according to soldering method and assembly method.
1). Based on soldering method, SMT technique can be classified into two categories: reflow soldering and wave soldering.
2). Based on assembly method, SMT technique can be classified into full-surface assembly, single-sided mix assembly and double-sided mix assembly.

Elements influencing soldering quality mainly include: PCB design, quality of solder (Sn63/Pb37), flux quality, degree of oxidation on soldered metal surface (component soldering termination, PCB soldering termination), techniques such as printing, mounting and soldering (suitable temperature curves), equipment and administrating.

Reflow soldering quality is influenced by the following elements: soldering paste quality, technological requirement for SMDs and technological requirement for setting reflow soldering temperature curve.

• Attributes of SMT
As a traditional PCBA method, Through Hole Package Technology (THT) is a type of assembly technology through which pins of components are inserted into through-hole vias on PCBs and then the pins on the other side of PCBs are soldered. THT has the following attributes:
1). Soldering points are fixed and technology is relatively simple, allowing manual operation.
2). Large volume and high weight, difficult to implement double-sided assembly.

Nonetheless, compared with Through Hole technology, Surface Mount technology contains more advantages:
a. High assembly density, leading electronic products to small volume and light weight;
b. High reliability and strong vibration resistance;
c. Low defect rate of soldering points;
d. High frequency, leading to electromagnetic and RF interference reduction;
e. Accessible to automation and improvement of volume production;
f. Cost saving by 30% to 50%.

Developing Trend of SMT

FPT refers to a type of PCBA assembly technology through which SMDs whose pin distance is within the range from 0.3 to 0.635mm and SMCs (Surface Mount Components) whose length times width is no more than 1.6mm*0.8mm are assembled on PCB. Fast progress of electronic technology on computer, communication and aerospace leads semiconductor ICs to increasingly higher density, SMC to smaller size and pin distance of SMD to increasingly narrower. Up to now, QFP whose pin distance is 0.635mm and 0.5mm has become a communication component that has been widely applied in industry and military electronic devices.

• Miniature, multiple pins and high density
SMCs will be developing towards miniature and large volume and they have developed to the specification of 01005. SMDs will be developing towards small volume, multiple pins and high density. For example, BGA that is being widely applied will be transformed into CSP. Application of FC will become increasingly more.

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