What Is SMT Assembly?
Surface mounting is a method of producing electronic circuits by placing components directly onto the board's surface.
SMT assembly is an alternative to the through-hole method of PCB manufacturing, which was the dominant process in the 1970s and 1980s. As electronics manufacturing continued to grow, there was a need for a more efficient and better process. SMT assembly was developed to meet this need.SMT assembly for PCBs has a broad range of uses. However, there are also a few limitations that your design team should consider.
SMT PCB Assembly Basic Process Steps:
1. Solder Paste Printing

Means the use of a stencil to apply solder paste to the pads of a PCB. Solder paste usually consists of solder particles and flux and serves to hold the component in place and provide soldering material.

Precautions:

  • Ensure that the thickness of the stencil is appropriate and that the solder paste is applied evenly and without residue.
  • Temperature and humidity should be controlled when storing and using solder paste to avoid deterioration.

2. Component Placement

Use automated placement machines to accurately place electronic components (e.g., resistors, capacitors, ICs, etc.) into designated locations on the PCB.

Precautions:

  • Component polarity direction must be correct (e.g. electrolytic capacitors, diodes, etc.).
  • The accuracy of the mounter needs to be calibrated periodically to prevent offsetting or incorrect placement.

3. Reflow Soldering

A PCB with components attached is passed through a reflow oven where the solder paste is melted to form a reliable solder joint and cooled to complete the soldering. The reflow process usually consists of four stages: preheating, constant temperature, reflow and cooling.

Precautions:

  • The soldering temperature profile needs to be adjusted according to the component and solder paste characteristics to avoid too high or too low.
  • Prevent cold soldering, false soldering or continuous soldering phenomenon.

4. Inspection

Use automatic optical inspection (AOI) or X-ray equipment to check the quality of the soldering to ensure that there are no defects.

Precautions:

  • Detect and correct defects as early as possible to prevent them from flowing into the next process.

The Advantage of SMT PCB Assembly
1. Miniaturisation and High Density

  • SMT is capable of mounting components directly onto the surface of the printed circuit board, making circuit design more compact and increasing component density, thus enabling miniaturisation and lightweighting of products.
  • It is particularly suitable for modern electronic devices, such as mobile phones, tablet PCs, smart wearable devices, etc.

2. High Efficiency

  • The SMT process is highly automated, which can significantly improve production efficiency and reduce manual intervention, making it suitable for mass production.

3. Good Electrical Performance

  • SMT Soldered components have short pins, low parasitic inductance and capacitance and fast signal transmission speed, suitable for high frequency and high speed circuit design.

4. High reliability

  • SMT soldering has stable quality, high solder joint strength, excellent vibration and shock resistance, suitable for products with high reliability requirements.

5. Material and cost saving

  • Reduced of components and printed circuit boards, reducing the amount of solder used in the production process.

6. Process Flexibility

  • SMT is suitable for different types of components and complex circuit designs, and supports multi-layer PCB processing.

Process Considerations for SMT PCBA Soldering

1. Equipment Maintenance

Regularly clean stencils, bonder nozzles, and reflow ovens to ensure proper equipment operation.

2. Environment Control

The workshop environment should be controlled within a suitable temperature (22-28°C) and humidity (40-60% RH) range to prevent solder paste from getting wet or components from absorbing moisture.

3. Component and PCB Storage

Components and PCBs need to be stored properly to avoid moisture, oxidation or contamination.

4. Anti-static measures

Operators are required to wear anti-static clothing and anti-static bracelets to prevent static electricity from damaging sensitive components.

5. Quality Control

A comprehensive quality control system is set up to strictly monitor everything from raw materials to production processes.

By strictly implementing the above steps and paying attention to all details, the quality and efficiency of SMT PCBA soldering can be effectively improved.

SMT PCBA Soldering in Makerfabs

As a turnkey PCB assembly service vendor with extensive experience in electronics manufacturing, Makerfabs offers SMT assembly services for both small-batch PCBA prototyping and mass production. 

Our reflow temperature loggers facilitate segmented temperature monitoring, ensuring that each soldering stage is within the optimal temperature range. Precise temperature control mitigates soldering issues and enhances product quality. Enhance the stability and reliability of your boards with our precision monitoring solutions.

Our production facilities are equipped to assemble the following SMT types:

● 0201/ 0402/ 0603/ 0805/ 1206
● BGA (Ball Grid Array) > 0.3mm Pitch
● uBGA (Ultra-Fine Ball Grid Array)
● QFP (Quad Flat Package)
● QFN (Quad Flat Pack No-Lead)
● SOIC (Small Outline Integrated Circuit)
● PLCC (Plastic Leaded Chip Carrier)
● PoP (Package-On-Package )
● Small Chip Packages (pitch of 0.2 mm)

Above are some PCBA boards manufactured by Makerfabs , submit your PCBA project to us and we will deliver a quality product to you.