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Reduce Solder Defects Right Now or Catch Them Later? SPI Tells.

To strive for high reliability and high efficiency in SMT (Surface Mount Technology) assembly has been a target for electronics manufacturers expecting for consistency. That depends on the optimization of each detail of the whole process. As far as SMT assembly is concerned, it’s been concluded that 64% of defects derive from improper solder paste printing. And, defects lead products to be of low reliability, reducing their performance. Therefore, it’s of great necessity to carry out high-performance solder paste printing to minimize the possibility of low quality.


Inspections are must-have measures called for by SMT assembly. Commonly-used inspections currently include visual inspection relying on naked eyes, AOI (Automated Optical Inspection), X-ray inspection etc. To stop improper solder paste printing from reducing end products’ performance, Solder Paste Inspection (SPI) should be implemented after solder paste printing in the process of SMT assembly.


Based on 14 years’ electronics manufacturing experience, PCBCart has won excellent reputation from world electronics industries due to the deep focus on RELIABILITY of products. PCBCart’s smooth running of one-stop PCB solutions, that is, PCB Layout, PCB fabrication, Components Sourcing and PCB Assembly derives from rigorous process control in the workshop.


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Introduction of SPI

Prior to the introduction of SPI, it’s necessary to get fully aware of SMT assembly procedure. Briefly speaking, SMT assembly consists of four steps: solder paste printing, chip placement, reflow soldering and cleaning. Solder paste printing indicates the beginning and its quality determines that of SMT assembly.


Before the advent of SPI equipment, visual inspection is used to find out solder paste printing defects. And its main disadvantages include accuracy and slowness. Using optical principles, SPI machine is a type of in-line SMT inspection equipment capable of figuring out the height or thickness of solder paste printed on PCB pad through triangulation. With height of solder paste within each pixel known, accurate volume of solder paste on PCB pad can be figured out through a series of accumulation and calculation. As a result, the items SPI is capable of covering include solder paste volume, area, height, XY offset and shape. And, the leading defects SPI can find out contain missing, insufficient solder, excessive solder paste, bridging, displacement, improper shape and board residue.

SPI usually comes after solder paste printing in order to find out printing defects in time so that they can be corrected or eliminated before chip placement. Or, more defects or even disasters may be caused in later phases.


Advantages of SPI

• Defect Reduction


SPI is used firstly to reduce defects due to improper solder paste printing. Thus, the foremost advantage of SPI lies in its capability of defect reduction. Defects have been the main concern as far as SMT assembly is concerned. And their shrinking in count will be a solid foundation for products’ high reliability.


• High Efficiency


Think of the traditional rework mode of SMT assembly process. Defects won’t be exposed unless inspections are implemented, that is, usually after reflow soldering. Normally, AOI or X-ray inspections are used to find out defects, after which rework will be carried out. If SPI is used, defects can be known after solder paste printing, just at the beginning of SMT assembly process. As soon as improper solder paste printing is found, rework can be immediately done for high-quality solder paste printing. More time will be saved and manufacturing efficiency will rise.

• Low Cost


Low cost features two meanings when it comes to the application of SPI machine. On one hand, time cost will be lowered since defects can be found in the early phase of SMT assembly process and rework can be done in time. On the other hand, money will be decreased as well since defects can be stopped earlier to avoid early defects from being delayed to later manufacturing phases to cause threatening defects.


• High Reliability


As is discussed at the beginning of this article, a majority of defects in SMT assembled products derive from low-quality solder paste printing. Now that SPI is beneficial for defect reduction, it will help increasing products’ reliability through rigorous control on defect sources.


Comparison between 2D and 3D SPI

SPI has gone through a path from 2D to 3D.

2D SPI equipment is only capable of measuring the height of some point of solder paste deposit on pad while 3D the height of the whole pile of solder paste on pad. Therefore, 3D is capable of indicating the accurate thickness of solder paste printed on pad. Besides, 3D SPI can also measure the area and volume of solder paste deposit on pad.


2D SPI machine depends on manual focus that leads to more errors while 3D SPI machine depends on automatic focus with measurement data being more concise and correct.

3D SPI Ready for Your SMT Assembly Quality Control in PCBCart’s Workshop

Focusing on quality and performance of electronics manufacturing for more than a decade, PCBCart specializes in providing one-stop PCB solution covering PCB fabrication, components sourcing and PCB assembly. 3D SPI equipment is used in PCBCart’s workshop as a main process control measure. It measures solder paste volume and alignment through angle cameras to take rapid 3D pictures. Furthermore, professional engineers are available at 3D SPI to operate on it with high speed and sufficient experience. Therefore, we’re fully capable of providing HIGH-QUALITY, HIGH-EFFICIENCY and LOW-COST electronics manufacturing service.


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