SMT, which stands for Surface Mount Technology, is a method of directly mounting electronic components onto the surface of a PCB. This method is commonly used for installing Surface Mount Devices (SMDs), which have smaller pins or are pinless in structure. Compared to traditional through-hole technology, SMT provides higher levels of automated manufacturing capabilities, reduces costs, and improves quality. Additionally, SMT allows for the installation of more components on a limited PCB board area. Through-hole technology is typically used for components such as large transformers and high-power heat-dissipating semiconductors that are not suitable for surface mounting. SMT components have smaller leads or no leads at all, and common structures include short pins or leads, flat contacts, and Ball Grid Arrays (BGAs).
PCBWay SMT Assembly Capability Overview
We have the capabilities to assemble SMT prototype PCBs in small production runs with manual and/or automated SMT production processes, including single- or double-sided component insertions. Our production facilities can assemble the following SMT types:
Let's now take a video tour to get an overview of the entire SMT line at PCBWay!
PCB, SMC, Stencil Preparation and Examination
Prepare the PCB, surface-mount components, and stencil, and inspect them for any defects.
Solder Paste Printing
The solder paste screen printing machine used for SMT is required to print solder paste onto the PCB before surface-mount components undergo reflow soldering.
3D Solder Paste Inspection
The solder paste printing process is one of the most critical stages in SMT assembly. The earlier the defects are identified, the lower the cost of correcting them. To ensure defect-free solder paste deposition in the required quantity, it is recommended to perform a comprehensive inspection of each printed PCB before commencing component placement.
3D solder paste inspection not only checks the coverage area and short circuits of the solder paste but also accurately measures the shape and volume of the solder deposits. On the other hand, 2D solder paste inspection cannot assess the volume or shape of the solder deposition.
Pick & Place
The SMT pick and place machine is one of the most crucial equipments in surface mount technology. It is also referred to as the pick-and-place robot. Prior to soldering, it picks up SMDs and places them onto the PCB.
Reflow Soldering
Reflow Oven: After the surface mount components are placed, the PCB is sent into the reflow oven.
Preheat Zone: The first zone in the reflow oven is the preheat zone, where the temperature of the PCB and all components gradually increases simultaneously. The heating rate in this stage is 1.0°C-2.0°C per second until it reaches 140°C-160°C.
Soaking Zone: The PCB remains at a temperature of 140°C-160°C for a soaking period of 60-90 seconds.
Reflow Zone: The circuit board then enters a peak temperature zone where the temperature rises at a rate of 1.0°C-2.0°C per second until it reaches a peak of 210°C-230°C. This melts the solder in the solder paste, bonding the component leads to the solder pads on the PCB. The surface tension of the molten solder helps to hold the components in place.
Cooling Zone: In the cooling zone, the heated PCB and components gradually cool down, allowing the solder joints to solidify and stabilize. The cooling process is critical for the formation of solder joints and securing the components. It helps ensure the reliability and mechanical strength of the solder joints.
If the circuit board is double-sided, the printing, placement, and reflow process can be repeated using solder paste or adhesive to secure the components in place.
AOI Machine Inspection
After the soldering process, professional quality inspectors will perform AOI on the circuit boards to check for any defects before the products are stored in the warehouse.
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