Solder paste provides a reliable connection between the PCB and the surface-mounted devices (SMDs). During reflow soldering, the melting solder, PCB copper pad, and the SMD undergo a phase change to form a solder joint. The solder paste printing and quality are critical for whether PCB assembly succeeds or not.
PCBONLINE provides PCB assembly services from prototypes to mass production for mid and high-end applications. We have rigorous management of the SMT solder paste. On the four SMT assembly lines of our turnkey PCB assembly factory, solder paste printing and inspection are automated with precision.
Lead-Free SMT Solder Paste Types
To meet RoHS compliance, PCBONLINE's PCB assembly factory only uses lead-free solder pastes. The common solder paste types we use are below.
- SAC305 (Sn96.5Ag3.0Cu0.5): melting point 217–220°C, best for high-reliability applications, such as automotive, industrial, and medical. It features strong joints and good wetting.
- SAC387 (Sn95.5Ag3.8Cu0.7): It has a higher silver content and provides better thermal fatigue resistance.
- Sn-Cu-Ni (e.g., Sn99Cu0.7Ni0.05): Melting point of about 227°C. It can be used for SMT assembly for consumer electronics.
- Low-temperature solder paste like Sn42Bi58: Melting point 138°C. It is used for heat-sensitive SMT soldering, such as LEDs and flexible PCBs, especially transparent circuit boards.
PCBONLINE's Smart Solder Paste Management
At PCBONLINE, the SMT solder paste is stored and managed in a smart solder paste cabinet. Our solder paste management maintains the high quality of the solder paste for PCB assembly. It features:
- Automated tracking with barcode labels
- Expiration alerts to ensure freshness
- Optimal storage conditions (20–25°C, <60% humidity)
Compared with traditional fridge storage, our smart solder paste management provides automated tracking, scan verification, and data-driven inventory control. With the reliable solder paste, PCBONLINE can pave the way for high-quality SMT PCB assembly.
Precision Solder Paste Printing Process
On the SMT line, the bare PCBs are first loaded onto an automatic loader. Then, solder paste is applied onto the PCB using an SMT stencil in an automated solder paste printing machine. The solder paste is squeezed by the machine scraper to pass through the stencil apertures and fall onto the PCB pads.
Our fully automated solder paste printing ensures perfect deposition and supports:
- 01005 SMD components
- 0.3mm pitch BGAs
- Thick-paste printing for power electronics
SPI Solder Paste Inspection
After printing, the PCB passes our 3D solder paste inspection (SPI) machine. Our 3D SPI inspection checks:
- Solder paste thickness (10–150µm, ±1µm)
- Solder paste coverage and shape
- Bridging or insufficient solder risks
With the perfect solder paste application and inspection, the SMT assembly process smoothly goes on to the next steps, including SMD pick-and-place, pre-reflow AOI, reflow soldering, and post-reflow AOI.
Why Choose PCBONLINE for PCB Assembly Services?
Founded in 1999, PCBONLINE is a trusted one-stop SMT assembly service provider for PCB manufacturing, PCB assembly, value-added, and box-build assembly.
PCBONLINE has two large advanced PCB manufacturing bases, one turnkey PCB box build assembly factory, stable material supply chains, and a dedicated R&D and engineering team. We also maintain long-term partnerships with top fixture and enclosure manufacturers in China.
Provides one-on-one free and professional DFM for PCB, PCBA, and box builds before and during prototyping/sampling, to ensure the manufacturability and project success.
The professionals at PCBONLINE design the PCBA fixtures and manufacturing molds that accurately fit the PCBA manufacturing and test processes.
Complete equipment and capabilities for PCB assembly services, including PCB manufacturing, PCB assembly, and post-assembly, such as functional test, IC programming, burn-in test, and application test.
PCBONLINE manufactures, assembles, and tests from PCBs and PCBAs to box builds as a source factory manufacturer under one roof, from prototypes to bulky production, saving costs and time for you.
High-quality PCBA manufacturing certified with ISO 9001:2015, ISO 14001:2015, IATF 16949:2016, RoHS, REACH, UL, and IPC-A-610 Class 2/3.
PCBONLINE can design the test points for your PCB and offer improvement suggestions for your design if there needs any optimization.
PCBONLINE provides comprehensive PCBA value-added services such as PCBA functional testing, conformal coating, IC programming, burn-in, enclosures, box-build assembly, application test, labelling, packaging, and shipping.
Whether you need prototype assembly, low-volume runs, or high-volume box build production, we have the equipment, experience, and capabilities to deliver superior results. To get a quote for PCB assembly services, email us at info@pcbonline.com.
Conclusion
Solder paste quality directly impacts PCB reliability. PCBONLINE's automated SMT line ensures accurate solder paste printing, SPI defect prevention before reflow, and smart solder paste management. To ensure the success of your PCB box-build assembly projects, partner with the turnkey PCBA manufacturer PCBONLINE.
PCB assembly at PCBONLINE.pdf
