Surface-mount technology (SMT) revolutionised electronics assembly by placing components directly onto the surface of a printed circuit board (PCB), rather than through holes in the board.
The technology allows devices to be smaller as PCBs can achieve a higher component density. SMT is also ideally suited to high-speed automated production.
Smaller components and shorter signal paths within SMT assemblies improve performance, including higher operating frequencies and reduced signal noise.
SMT, however, is a process that calls for careful design, high precision, and a controlled production environment.
Design
Design for Manufacturing and Assembly (DFMA) is a critical consideration to reduce production time and cost. As well as configuring the overall PCB design to avoid overcrowding it helps to pay attention to component orientation. Consistency with polarity and pin directions speeds up assembly and makes it easier for inspection equipment to check for the correct orientation.
Design for testing is another important consideration so that there are convenient and clearly marked locations for signal measurement and troubleshooting.
Pick And Place
Pick and place systems have a huge influence on the potential throughput. The S20 Hybrid Modular Mounter we use in the Trizo production facility can achieve a throughput of up to 45,000 CPH. It also offers precise control over placement and the downward force applied to components, which can affect the performance and reliability of assemblies.
Integrated component testing technology measures the characteristics of passive components and the correct polarity of diodes. This eliminates human error and ensures that out-of-specification components are never installed.
Inspection
High precision and high throughput manufacturing places particular demands on inspection. Automated optical inspection is commonly used to quickly identify obvious defects such as misalignment, solder bridges, or missing components.
Not all defects are visible. And the smaller solder joints used in SMT compared to through-hole assembly make minor defects potentially more significant.
High resolution X-ray inspection (μAXI) identifies tiny hidden defects such as voids or cracks in the solder, making this technique valuable for high reliability markets such as healthcare and aerospace.
Trizo has invested in the latest offline AXI equipment as part of our drive towards zero-defect, risk free manufacturing.
Soldering
Solder paste has to be stored and handled with great care to prevent contamination. Precise control over the solder paste printing process is also essential as minor variances can lead to short circuits or poor reliability.
The environment is critical as any humidity or contamination in the air will compromise quality and performance. Using a high-purity nitrogen source is an effective way to maintain a clean and dry production process to avoid oxidation and dross formation.
Trizo installed a N2C-8NCALA Parker Nitrogen Generator that produces a purity level above 99.995% (50ppm) to ensure we can maintain a controlled and contaminant-free production environment.
Reflow Oven Temperature Control
For high-precision, high-reliability applications, controlling the heating and cooling profile of the reflow soldering process is critical. Temperature profile, conveyor speed, and atmosphere are important parameters that have to be controlled with precision to achieve optimal solder reflow conditions.
The flux in the solder paste includes the resin, active agent, viscosity enhancer and solvent. During the pre-heating phase the solvent evaporates. This must be done gradually to minimise the thermal stress on components and to avoid the solder paste collapsing to create a short circuit.
The next heating phase achieves a uniform temperature for the PCB board to minimise thermal stress and avoid defects such as components lifting due to differential heating of connections. Careful heating ensures effective wetting by the molten solder to produce a sound joint.
Controlling the soaking time and temperature ensures that the flux cleans the soldering surface thoroughly but is not completely consumed before it reaches the reflow.
Component Traceability And Supply Chain Management
Supply chains are critical as SMT production involves high volumes of components – any of which could compromise the performance of the entire assembly. Trusted suppliers are one of the most effective safeguards for ensuring consistent high quality output and performance.
An effective production regime must include robust material management systems that track components, solder paste, and PCBs throughout the assembly process. A rigorous process will help identify and rectify any quality issues that arise with minimal disruption to production.
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Data Analytics And Monitoring
With such high volumes, automated test data logging linked to component traceability technology is essential for complete visibility and enhanced analytical capabilities.
The production process must leverage data analytics, statistical process control and real-time monitoring systems to gain insights into production performance and identify potential areas for improvement.
KPIs include defect rates, cycle times, and equipment downtime. Dynamic monitoring allows manufacturers to make informed decisions to optimise processes and enhance overall efficiency.
The final key capability is to rapidly and accurately investigate defects to understand root causes and implement preventive measures with minimal disruption to production.
SMT isn’t just about shrinking circuits; it’s about speeding them to market. By embracing lean principles, process optimisation, and robust quality control, engineers can leverage SMT’s efficiency without compromising on quality, ensuring a winning combination for successful product launches.
