Surface Mount (SMT) PCB Assembly Services - QFPCB
QFPCB is an experienced SMT assembly house, providing solutions for all types PCB assembly, including rigid PCB, metal core PCB, flex and rigid-flex PCB, to many across a multiple of industries. We have been assembling SMT designs for over 15 years now, and we take pride in the prototype, low– to high-volume PCB assembly we perform through our highly trained professional assembly engineer, technicians and advanced assembly lines. We always work with your design in mind, and keep you updating of your PCB assembly project that work with us.
Whether your project requires small batches or high-volume SMT assembly, we are dedicated to delivering the highest quality product. We achieve this through our vast experience, commitment to continuous improvement, and utilization of surface mount devices (SMDs) which optimize both performance and cost-effectiveness.
What is SMT Assembly?
SMT (Surface Mount Technology) evolved from Through Hole Technology (THT). From a technical perspective, SMT is a complex system engineering that integrates components, printed circuit boards (PCBs), SMT design, assembly processes, equipment, materials, and testing technologies.
Surface Mount Components (SMC) and Surface Mount Devices (SMD) form the foundation of SMT. PCBs serve as the structural components for component interconnection and play a crucial role in ensuring the electrical performance and reliability of electronic assemblies. Assembly processes and equipment are the tools and means for achieving SMT products, directly affecting production efficiency and quality outcomes. Testing technology is a key guarantee of surface-mount product quality.
Single-sided SMT assembly
The single-sided SMT assembly uses a single-sided PCB , the design process is simple, and the functions implemented are relatively simple, generally suitable for some relatively simple functional circuits.
Double sided SMT assembly
The double-sided SMT assembly uses a double-sided PCB. One side has a large IC period, and the other side is mainly composed of chip components. The design process is relatively complex, and the functions to be realized are also relatively complex.
SMT Assembly vs. THT Assembly
An electrical component mounted with SMT assembly manner is referred to as a surface mounting device (SMD). In PCB assembly industry, SMT assembly approach has largely replaced the through-hole technology (THT) construction method of populating components, in large part because SMT allows for increased manufacturing automation which reduces cost and improves quality -it allows for more components for fitted to a given area, especially when electronic devices are in pursuit of size miniature. Both technologies can be used on the same board at the same time, with the thru-hole technology (THT) often used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.
As SMT component is usually smaller than its thru-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component.
Printing solder paste during SMT assembly
Printing solder paste is one of the most important processes in the SMT assembly process. QFPCB uses an automatic printing machine, adopts the method of stencil printing, and prints the solder paste to the position corresponding to the PCB pad through the movement of the squeegee.
There is a place that is easy to be overlooked here: it is the solder paste. The quality of the solder paste also affects the quality of the SMT assembly. In order to ensure the performance of the solder paste, QFPCB has always been refrigerated and stored, and opened and used after returning to temperature.
SMT during SMT assembly
SMT patching is mainly done by automatic placement machines.The automatic placement machine has set the program in advance to set the XY position of each component on the circuit board, which can ensure that the machine can accurately take out the components from the specified position and accurately install them in the correct position.
QFPCB’s placement machine is the most technical and most expensive machine in the production line. It can place hundreds of materials at the same time, and can automatically identify material code information to reduce material misalignment. The placement is precise and meticulous. The minimum placement component is : 01005.
Reflow soldering during SMT assembly
Reflow soldering is the most important process in the SMT assembly process. In this process, the most important thing is the setting of the temperature curve of the reflow soldering machine. For the setting of the temperature curve, QFPCB is completed by professional engineers. The engineer sets the temperature curve according to the physical and chemical changes of the solder paste during the reflow soldering process. Welding defects can be reduced, thereby improving production quality and efficiency.
Inspection during SMT assembly
The inspection of QFPCB is mainly AOI inspection, X-ray inspection and visual inspection. 100% inspection can greatly improve the quality of products. AOI inspection is mainly to detect different placement errors and welding errors, X-ray inspection is mainly to detect internal problem areas without damaging the object to be tested, and visual inspection is mainly to detect product appearance errors.
Materials Utilized in SMT Assembly
The SMT assembly process relies on several key materials to ensure the proper placement and soldering of components onto printed circuit boards. These materials include solder paste, flux, adhesive, cleaning agents, and heat transfer mediums. Each plays a critical role in achieving reliable and functional electronic assemblies.
Solder Paste
This material serves the dual purpose of both soldering and temporarily adhering surface-mount components (SMCs/SMDs) to the PCB. Common solder paste compositions include Sn63/Pb37 and Sn62/Pb36/Ag2, which offer well-rounded performance characteristics. For applications requiring lower melting temperatures, Sn43/Pb43/Bi14 is often utilized. Additionally, Sn-Pb intermetallic compounds (IMCs) are favored for their strength and ability to readily wet surfaces, making them ideal for specific soldering needs.
Flux
This material facilitates the soldering process by promoting smooth and effective solder flow. Flux comes in two primary types: acid and resin. Both types work to remove oxides and contaminants from metal surfaces, thereby enhancing the solder’s ability to wet and bond with the components.
Adhesive
As its name suggests, adhesive plays a crucial role in securing SMDs in place during the SMT assembly process. This prevents components from shifting or falling off the board before and during soldering.
Cleaning Agents
After the soldering process, cleaning agents are used to remove any residues left behind by the solder paste and flux. These agents must be chemically stable and exhibit thermal resistance to avoid decomposition during storage or application. Additionally, they should not react with other chemicals or corrode the components on the board. Ideally, cleaning agents should also be non-flammable and have low toxicity for safe handling. The cleaning process itself should be efficient and cause minimal loss while effectively removing residues within specified time and temperature parameters.