Ask the Experts
August 24, 2011 - Updated
August 22, 2011 - Originally Posted

3D Solder Paste Inspection

Some folks at our facility are pushing us to purchase a 3D solder paste inspection machine/system. Are these systems common? Under what conditions should we consider buying one of these machines/systems?

P. P.

Expert Panel Responses

Automated solder pasteinspection (SPI)systems are very common in the U.S. and abroad. There are many companies who make SPI equipment. I recommend you look atKoh Young, MVP, CyberOptics, Saki, V.I. Technology, Omron, Mirtec, and Marantz (in no particular order) for starters. But before you randomly startsalivating at machines, you need to do your homework. Here aresome questions you need to ask yourself:
  • What is your goal, and how do you see SPI helping you?
  • What is your most glaring need in terms of understanding your current solder paste print process?
  • Are you a high-volume/low-mix business, or amid-volume/average mix, or a prototype/development house?
  • Which type of SPI machine best fits your needs?
  • Do you have any current specific, well-understoodprocess controlneeds for your product, and have you considered what your future business will be?
For example, if you are a high-volume medical manufacturer using 00105, 0201, and 0402 components along with flip-chips being attached with solder paste, or micro BGAs, you may need a good, high-speed 3D inline system with at least a 6 megapixel camer ato handle both the volume requirements along with the more advanced camera and lighting scheme capabilities to ensure you can achieve Six Sigma DPMO print levels (some companies require Seven Sigma!). If, on the other hand, you build small volumes andseldom print anything smaller than an 0402, then perhaps a good 2D machine with a 4 or 5 megapixel camera will be more than adequate. Do you also need a printer? Many new printers have built-in SPI capability, ranging from basic 2D systems to very advanced 3D systems. New printers that utilize jet-print capability may make SPI systems obsolete in the near future, but I know they are not quite there yet. Perhaps your best strategy may be to get a system thatwill provide the most bang for the buck for today, with a plan to investigate a jet-printing system later. But where is your budget? Oftentimes many companies find that they can get by with a benchtop SPI that has the same inspection capabilities as an inline, but at a much lower cost. However, keep in mind that a good, well-matched SPI system can save you literally hundreds of thousands of dollars every year because of their capability to perform 100% more comprehensive inspection at speeds several times faster than even several inspectors can, with much less variation. Along with this is the ability to stop your line quickly if a bad printer set-up is detected, as well as bad lots of paste, and print processes thatdrift out of control due to improper set-up, PWB lot variation,orenvironmental factors such as room temperature and humidity or expiration of shelf life. Most good SPI systems havereal-time CpK monitoring alarms or email notification systems that will automatically indicate trends or processes that are outside of acceptable pre-set limits. In addition, the use of a good SPI system can free up one operator with the result being that he/she can more easily run an entire SMT workcell consisting of the load, paste print, pick/place, and reflow entry processes. So you need to look at it from the perspective of reduction of inspection time, reduction of defects going undetected until after reflow, and reduction of production labor, rework and board wash/re-printsas a result. All of these can add up quickly to a significant savings, making the decision of whether or not to buy the SPI a real "Well, Doh!". However, keep in mind that there is also a cost factor that MUST be acknowledged and planned for (besides the machine's price); the simple fact that the machine is going to require some programming and support. This may be heavy initially, but should subside as the print(brick)libraries and familiarity increase. Most good inspection stations will automatically map print defects, aiding in rework time reduction. Their software options automatically track statistical process control data (SPC charts) so you can effectively track which CCA stencils or set-ups cause more issues than others, and why. Nothing is so inefficient as having operators attempt to tediously inspect solder paste prints and manually input defect data into a system that some other engineer or tech subsequently spends hours crunching the numbers, only to find two weeks or a month later that the paste, stencil, or set-up for a given assembly had an issue. Too late. Far too late. Who cares now? What good does it do? Maybe next time? As we say here in Minnesota, "Uh, huh, sure. Ya betcha." You need to take full stock of your present printprocess and at least have some understanding what type of defects you are seeing in order to determine which machine is best for your needs, or whether you can justify it at all, for that matter. Ninety percentof the time, it is easily justified. You just may not know it. A smaller 2D benchtop or inline system may work quite well for you. It will monitor solder paste brick and pad coverage, and automatically detect missing paste indicating a rheology (viscosity) issue or clogged stencil issue (cleaning frequency/worn apertures). Misprinted (shifted or misregistered) paste and smearscan also be detected by most 2D systems. To be able to detect variations in paste volume (squeegee pressure/snapoff height adjustment), print footprint (slumping issues), and very small prints such as .005" by.005" flip-chip or 0201 deposits, you will need a more advanced 3D camera system. Even a 5 megapixel resolution cameramay not be sufficient for these more demanding assemblies. 3D is simply a more robust or capable system than 2D. Cycle time isusually important, but may not be important at all. As mentioned earlier, a manufacturer of high volume and complex electronic medical products is going to place a lot more weight on cycle time than a manufacturer of advanced avionics assemblies, but both require a high level of detection capability (3D) in their system. Most of the time, SPI reduces or eliminates a major constraint. A typical CCA about 8" by 8" with perhaps 2000 print bricks can be inspected completely in less than 15 seconds by most SPI machines. So, if paste printinspection is no longer the constraint, the speed of inspection may turn out to be a non-factor; you can only cue up so many CCAs while waiting for them to enter a longer pick/place or reflow process, right? Whatever systems you decide to evaluate, you should perform testing using one or two samples to evaluate the capability of that SPI candidate. Test samples can be made up using solder test coupons provided by your PWB supplier. You can print paste using a production stencil on this sample, then pop it into an oven set at 150 Deg. C for about 15-30 minutes. This will bake the print deposit well enough to eliminate any rheology changes (lock in the print shape), and you can then create some paste print defects such as remove all paste from a given pad(s), reduce some paste from individual brick(s), add a smear or two or three, etc. Along with this, you need at least one "golden" PWB with a perfect print, also baked, for programming use. Then you are ready to test some systems. Service and support after the sale, and availability of training for operation, programming, and maintenance are extremely important. Be sure you do your homework; ask the machine vendor for a list of installations in your area. Contact those companies, ask questions as to how the machine has helped them, as well as as how they rate their experience with the vendor, speed of response and availability of local tech support, etc. The contacts you make doing this usually will pay off later if you buy the same or similar machine, networks and friendships form that benefit both companies. Be sure the vendor you choose has a good, well established installation base inyourarea, as the availability of good support technicians willing to travelis extremely limited these days, and this alone has caused more than one SPI vendor to decide to get out of the business. This can leave you with a machine for which you have little or no support. Yes, I have seen this happen, and more than once. Ease of programming is another important factor. The average OPERATOR, not technician, should be able to load programs and make minor changes if needed. Beware of SPI machines that require a skilled technician or engineer to operate them, even on a part-time basis. So think carefully about this, what you don't know may already be hurting you. Good luck, whether you choose to buy one or not. Feel free to contact me.

Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

Three D inspection systems are very common in high volume operations. This is the perfect place for automation to be set up as the product exits from the paste deposition process, it can be verified relatively quickly as to whether there is enough paste on the pads. When inspecting for paste application, one must also consider the height of the brick of paste, not just the size, (length and width), and this equipment can do this automatically, which would eliminate the manual observation which is not 100 percent effective. So to answer the question, yes these systems are used in many places.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

I have 5 years of experience in using 3D SPI, there are two Possible methods of 3D SPI Installation

1. 3D- Inline: if you use in inline definitely you will become a master in Solder Paste Printing problems, initially your internal defect at Solder paste printing will increase and internal defect cost will decrease since you are detecting the majority of the soldering issues because of solder paste printing at its stage only, nevertheless in a long run it will be compromised and your product reliability will also be good too.

2. 3D - Offline: its only to cross check the solder paste printing process but it won't work as it in inline, since solder paste printing is a setup dominant process no one can predict by sampling, if you need to study the solderpaste printing then you should go into statistical methods with Inline

My suggestion: To become an expert in solder paste printing then we should know its behavior, Inline 3D SPI is one of the good feedback system to arrest the root causes at Solder Paste Printing. we should use this machine as Optimization tool for Solder paste Printing rather than a test gate.

Keshava Murthy
Process Engineer
Bosch Automotive Electronics India Ltd.
Keshava Murthy is a Process Engineer in the PCB assembly industry working in Bangalore, India.
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