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The Differences between Inline SPI and Desktop SPI
作者:stk 来源： 时间：2015-11-27 15:52:46
From the Solder Paste Thickness Inspection System to the current Automatic 3D Solder Paste Inspection System, the Solder Paste
Inspection System has developed for more than a decade, now more and more SMT users begin to focus on the application of it.
How to treat the application of Solder Paste Inspection System (SPI) , I will share my opinions as follows:
* Component miniaturization
* Pitch intensification
* Wide use of lead-free solder paste
* Growth of labor costs
* One-time passing rate control
The sooner the problems can be found,the sooner the problems can be solved.The SMT managers are bothered constantly by the
problems of component costs, processing costs, repair costs, onetime passing rate, customer satisfaction etc. There are too many
reasons that the SMT users decide to add more inspection systems to the production line from the back of the line to the front, from
the ICT to the AOI in the back of the Reflower, then to the AOI in front of the Reflower,and then move to the SPI in front of the
SPI has two basic functions:
1) Timely detection of defects in printing quality
SPI can visually distinguish the good and bad printings for the users and provide the information of the detect types.
2) we can found the quality trends through a series of solder joints inspection.
The change trends are caused by one or more than one potential factors. We can not see the potential factors, but we can see the
trend changes so as to analyze the potential factors through trend changes.
SPI can find the quality trends through a series of solder paste inspection, and find the potential factors that lead to this kind of
trends before the quality is out of range, such as the regulation parameters of the printers, human factors, solder paste changes, etc.
And the timely adjustments is very important to prevent the trend continues to spread, which can realize the process control.
The Differences between Inline 3D SPI and Desktop SPI
Automatic Inline 3D Solder Paste Inspection System;
It can conduct Inline automatic and full inspection for all the solder paste in the board, including the volume, area, height, XY offset,
shape, bridging, etc. and with the powerful SPC process control software to monitor the realtime printing quality. Such equipment
put the PMP white light as the mainstream, and the accuracy and speed have greatly improved than the previous laser detection
Semiautomatic desktop 3D Solder Paste Inspection System; it uses the step motor to drive the Xaxis and Yaxis, and conducts
sampling inspection to some solder joints on the printed circuit board, generally the samples
will be 5-10 or less,and it mainly detects the height of the solder paste,and combined with simple SPC functions.
Such devices put laser detection as the principle, the program is more complex and can not truly reflect of the printing quality of
solder paste, now they are gradually being replaced by full and automatic inspection equipment.
The limitations of the traditional Solder Paste Thickness Inspection System is increasingly obvious in the present solder paste
inspection. The traditional Solder Paste Thickness Inspection System mainly measures the height of a certain point. The detecting
light source is laser,and according to the distortion of the laser beam that are generated at different heights plane, we can manually
click the measured height using the mouse.
However,The detection of the height of solder paste is completely inadequate.The volume control of solder paste is critical to the
printing process. There will be different volume in the same area,and there will be different area in the same volume, etc. The
traditional Solder Paste Thickness Inspection System can only detect a single or a few solder joints,but do these solder joints can
really represent the entire board? The answer is absolutely no. Because a certain kind of solder joints even a single solder joint are
unique,any solder joint defects can cause NOT GOOD of the entire board.
Desktop equipment can monitor the print quality by regular sampling, but it is not able to conduct realtime inspection for the process
consistency in actual production, which often requires the technical personnel to make a judgment based on past experience;
At present, the production staff mobility is great, so it is unrealistic to rely on staff experience, and the standardized plant currently
are relying on automation to realize the realtime monitoring. InLine SPI meets the speed requirements in the SMT production line,
it can conduct full inspection for every single point of every piece of circuit board in the SMT production line, and the SPC data
obtained also show if the actual printing process is good or not, what’s more, it can control the process trends according to SPC data,
which can completely solve the uncertainties of human experience.
Generally speaking, occasionally sampling a plate of the offline SPI is just like fishing, which is a problem of probability; and the
detection of several points is like casting a net to catch fish, and the slip is inevitable; while the Inline SPI can conduct full inspection
for every single point of every piece of circuit board, it is like pouring the water and catch the fish in a pond, any problems can not be
The advantages of Inline SPI
1. The Sampling Mode is FOV Formula
Because the accuracy of solder paste inspection shall reach micron or even smaller level when detecting the height, FOV will take
pictures when it is still and sample multiple times, avoiding interference of the mechanical components and external vibration, and the
GGR can reach 6 Sigma within 1 micron. If we adopt scanning and single sampling, it can not avoid the interference of the mechanical
transmission and external vibration, so the repeatability accuracy of the device itself will be very poor.
2.Choice of Reference Plane
Inline SPI solder paste inspection system, with excellent performance, is to automatically defined a relative reference plane for each
test point, and simple to operate and with high accuracy. Offline SPI is to manually select more than three points to define an absolute
reference plane,which is complex and with low accuracy and efficiency.
The inspection rate of inline SPI is four times faster than the offline SPI. Its high efficiency can keep up with the speed of the SMT
production line; while the offline SPI is designed for sampling, it doesn't have too many requirements.
4.Automatic Full Board Inspection
The inline SPI can detect all the solder paste on the entire circuit board; During the printing process, part of the solder joints on several
sampled circuit board have no representativeness. Good is good, bad is bad. We can not judge the other hundreds of points from a single
point. With the improvement of lean manufacturing requirements Solder paste inspection needs to detect all the solder joints in the board,
so as to find problems in the production process in advance and reduce repair costs.
5.The inline SPI is equipped with powerful SPC process control software
SPI, as a hardware device,can find the printing defects timely. If you want to know the trend changes,then a powerful SPC(software of process control ) is needed to assist. SPC is able to provide statistical analysis, comparison and trends in graphs through a
series of solder paste inspection results.
The general XBarS, XBarR, Histogram, Single View, Multi View, CP, CPK, G&GR and other reports are indispensable tools.