Solder paste print quality is becoming more and more important as electronic systems get increasingly sophisticated with the components getting smaller and smaller. Solder paste inspection (SPI) is the key testing method to control the quality of solder paste printing in SMT. Hence, the cost of a wrong buying decision can be high.
Solder paste inspection (SPI) equipment is used to monitor and control one of the most critical steps affecting the quality of printed circuit board (PCB) assemblies. Solder paste deposition is a key process in PCB assembly operations, and modern manufacturing systems try to prevent repairs by improving process control. Recent studies have found that more than 60 per cent of end-of-line defects can be traced back to printing errors. Preventing these defects enhances ‘first time right’ production and product reliability. It can reduce rework costs and accelerate production as well as the return on investment.
Why use a SPI system?
In the early era of electronics manufacturing, big components were used (i.e., above 1608 and more than 0.5 pitch ICs). Hence, there were no inspection options for paste printers. When small components were first used for SMT manufacturing, the 2D inspection function was added to the screen printer. When BGA, micro BGA and fine pitch components were introduced, 2D inspection was not enough as it checked only the presence of the solder paste. That is when SPI machines were introduced. These also checked the volume of the solder paste, and reduced the incidence of solder-related defects to statistically insignificant levels.
Visual inspection is not at all a viable option when checking the condition of solder paste printing, as manual checks are not an inline process. With the need to bring high volume, high quality products to market quickly, very reliable and fast testing methods are needed to ensure that product quality remains high. SPI equipment ensures costs are kept as low as possible by detecting faults early at the solder printing stage of the production line.
|How to make the right buying call
With a solder paste inspection system, you can measure the height, volume and area of paste deposits. You can also compute stencil offsets and detect defects such as bridges, as well as 2D and 3D patterns on the PCBs. And you can use statistical analysis to make a selection.The main challenge for an SPI lies in its ability to reference correctly in the Z-axis and adapt to the PCBs’ specific characteristics. The SPI system’s ability to measure small pads accurately depends on striking the right balance between the following:
Therefore, an ideal SPI system is quite different from a system designed to measure the height of a perfectly cylindrical target placed on a smooth surface. This is a better way to quantify the printing process, rather than measuring the volume of a single solder deposit under comparable conditions or repeatability conditions.
In order to get the right equipment and help you decide before investing in the production line system, it is recommended that you rent or borrow one, to check it through a series of demonstrations.
Note: This information has been taken from a white paper written by the team at Vi Technology.
Where to use SPI
SPI systems are placed in the production line just after the solder printing process (screen printer). In this way, problems are caught early in the production process, and this information is used as feedback to quickly address the issue. A rapid response ensures that problems are recognised quickly and rectified before too many boards are built with the same issue.
SPI inspects the solder paste printed PCB for defects like less or excess solder, missing solder, solder shift, solder short and solder volume. SPI uses two types of techniques to analyse whether a board is satisfactory or has any defects.
Laser measurement system: Two laser beams are projected from opposite directions to eliminate the risk of shadowing. The beams are then scanned onto the PCB and reflected back to a high-resolution camera (CMOS) to calculate height with X-Y spatial resolution. The result is a highly accurate 3D model construction.
Camera measurement system: Angled cameras are used to take 3D images, which help to measure the alignment and volume of the solder paste. SPI systems compare the image with the program.
Real-time data communication with the screen printer (the previous step in the process) helps to solve fundamental problems and optimise the process by exchanging information such as the location of the pad and solder paste. However, using SPI systems is not compulsory in SMT manufacturing. These need to be used only if the product contains BGA and fine pitch components.
In the following section. We take a look at some of the SPI systems launched in the last one year. However, not all the latest models are currently available in India through distributors. In order to procure such equipment, you need to directly get in touch with the manufacturer and ship the product to India.
Recently launched SPI models
|Model: KY8030-3; Manufacturer: Koh Young|
|The latest SPI system from Koh Young Technologies Inc. offers accurate and fast 3D measurement capabilities that address the shortcomings and vulnerabilities of conventional paste inspection systems and 2D SPI/AOI systems.
|Model: SE3000; Manufacturer: CyberOptics Corporation|
|The new SE3000 SPI system has incorporated the industry-leading MRS sensor technology with a finer resolution for accuracy, repeatability and reproducibility —even on the smallest paste deposits. Combined with easy-to-use SPI software, the SE3000 has the capability to work on large boards.
Contact details: www.cyberoptics.com
|Model: VP6000-V; Manufacturer: Omron|
|The VP 6000-V has a unique 3D process for measuring the volume of solder used in screen printing. It guarantees reliability and repeatability of high quality. The choice of resolution for the purpose, as well as the setting of standards, is done by software, and thus gives more accurate measurement. The GUI and very sharp statistical analysis allow a rapid and targeted improvement process. The new VP6000-V can complete the 3D inspection and correct the excesses of your screen printing process.
|Model: TROI 7700 series; Manufacturer: Pemtron|
|Using Moire’s pattern, Pemtron’s three-dimensional lead application dosage tester combines 2D colour images with 3D measurement data to provide more detailed, near-real PCB images, unlike traditional colour maps.
Contact details: www.pemtron.com