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SMT Knowledge
Essential basis for SMT Engineer

SMT Basic Course
1, the traditional process Introduction
Traditional perforated electronic assembly process Naishi component of the guide pin insertion hole PCB fixed, the use of wave soldering (Wave Soldering) of the manufacturing process, as shown in Figure 1, after a flux coating, preheating, solder coating , detection and cleaning steps that complete the whole welding process.
 
Figure 1. Wave soldering process of the process2, Surface Mount Technology Overview
As electronic products industry, and trends over time, constantly short of its product design into a lightweight, relatively to promote a variety of components, becoming smaller and smaller size and weight, its functional density is also enhanced to meet the trend of the times and customer needs in this changing under the influence of surface-mount components will become the main component on the PCB, its main feature is greatly save space in order to replace the traditional dip soldering-type components (Dual In Line Package; DIP).
Surface-mount assembly process includes the following main steps: solder paste printing, component placement, reflow soldering.
Each of its steps are outlined below:
Solder Paste Printing (Stencil Printing): solder paste for surface mount components and PCB to connect with each other and then turn the material, first by etching or laser cut steel plate, by the printing press of the blade (squeegee) to paste through the plate printed on the openings of the solder pad to the PCB in order to enter the next step.
Component placement (Component Placement): Component Placement SMT manufacturing process of the whole technology and the key focus of the work, their process uses high-precision automated placement equipment and computer programming through the surface mount components will be accurately placed in the PCB solder paste has been printed welding mat. As the surface-mount component design increasingly sophisticated, the pin spacing also will be smaller, so the technical level of the placement operation is increasingly becoming difficult.
Reflow soldering (Reflow Soldering): reflow soldering is the placement of surface mount components have been PCB, through the reflow furnace preheated prior to activation of flux, and then raise the temperature to 183 to melt solder paste, component pin and the PCB's pad-linked, and then, after refrigeration cooling, so that solder solidification, namely, the completion of surface-mount components and PCB for bonding.
3. SMT Equipment Introduction
1. Stencil Printing: MPM3000 / MPM2000 / PV
2. Component Placement: FUJI (CP643E / CP742ME & QP242E / QP341E)
3. Reflow Soldering: FURUKAWA (XN-425PHG / XN-445PZ / XN -651PZ) ETC410, ETC411.

4. SMT Common Name Resolution
SMT: surface mounted technology (SMT): directly to the surface-mount component placement, soldering to the printed circuit board surface, the provisions of the assembly position.
SMD: surface mounted devices (surface mount components): a rectangular sheet shape, cylindrical-shaped or shaped line, its solder-side or pin-making in the same plane, and applies to surface mount electronic components.
Reflow soldering (reflow soldering): By re-melting of pre-assigned to the printed circuit board solder pads of the paste solder paste to achieve surface-mount component terminals or pins with the printed circuit board pad between the mechanical and electrical connections.
Chip: rectangular chip component (rectangular chip component): No leads at both ends, with solder side of a rectangular shape for the thin surface-mount components.
SOP: small outline package (small-outline package): a small molded plastic package, both sides of the wing or J-shaped with a short-pin surface mount components.
QFP: quad flat pack (Quad Flat Package): four sides with a wing a short pin, pin pitch: 1.00,0.80,0.65,0.50,0.40,0.30 mm thin plastic packages such as surface mount integrated circuit.
BGA: Ball grid array (ball grid array): IC packaging, its input and output point is at the component surface by the end of the solder ball grid array pattern.


5. Component packaging.
Article feed (magazine / stick) (shipping tube) - the main components of the container: transparent or translucent material made from polyethylene (PVC) material composition, extruded into a meet current industry standards can be applied to a standard form. Article expected size of industry-standard automatic assembly equipment components to provide appropriate positioning and direction. Material of a single material the number of combinations of packaging and transportation.
Tray (tray) - the main components of the container: tray from the toner or fiber materials, these materials based on the maximum temperature-specific rate of tray selection. Is designed to require exposure to high temperatures of the components (moisture-sensitive components) of the tray with a typically 150 C or higher temperature. Cast molded into a rectangular tray standard form, with a unified white pockets matrix. Pockets boosting components, the provision of transport and the protection of components during processing. Intervals in the circuit board assembly process for the placement of the standard industrial automation assembly equipment to provide accurate location of the components. Tray packaging and transport is based on a combination of the form of a single tray, and then stacked and tied together, have a certain rigidity. An empty tray on the lid has been installed components and stacked together on pallets.
Tape & Reel (tape-and-reel) - the main components of the container: a typical coil structures are designed to meet modern industry standards. There are two generally accepted structure of the coverage Reel standards. EIA-481 embossed structure used (embossed), while the EIA-468 applies to the radial-lead (radial leaded) components. So far, for the active (active) IC of the most popular structure is embossed tape (embossed tape).

6. Whv the application of the surface mount technology no-clean processes?
1. The production process of waste water discharged after the cleaning products and bring water, and earth, as well as plant and animal contamination.
2. In addition to water washing, the use of organic solvents containing chlorofluorocarbons (CFC & HCFC) for cleansing, but also on the air, the atmosphere of pollution, destruction.
3. Cleaning agent left in the machine to bring the board corrosion, seriously affecting product quality.
4. To reduce the cleaning process operation and equipment maintenance costs.
5. No-clean can reduce the group board (PCBA) in the mobile and the cleaning process damage caused. There are still some components not stand cleaning.
6. Flux residues have been brought under control, can meet the product requires the use of appearance to avoid visual inspection of cleanliness status of the problem.
7. Residual flux has been reforming its electrical properties, produce finished products in order to avoid leakage, resulting in any harm.
8. Disposable process has passed a number of international safety tests to demonstrate that flux of the chemical substance is stable, non-corrosive

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