SPI and AOI Machine Feaures. - Page 1
Forum section: electronics / general

author: Kiwi
author_rank: Newbie
timestamp: February 11, 2021, 09:05:42 am
content: Hello.I am sourcing machines for an SMT line (for the first time) and would like to understand features of current and earlier model SPI and AOI machines.In the intended application, a high volume of PCAs aren't required to be processed but there are often hundreds of components per PCB and several PCBs per product, so a product containing more than 1,000 components is typical. Inspection machines are being considered in an attempt to ensure a low level of field failures. In addition to SMT, there will be hand soldered components. Some PCBs are wave soldered.It appears 3D SPI is required to ensure paste is appropriately deposited. To cover all placement fault mechanisms, it seems 3D AOI is required. Buying two machines is expensive, so a machine that performs both tasks would theoretically reduce costs.Secondhand equipment is less expensive than new. However, secondhand machines have different features than newer machines. I have read, due to change in automated inspection methods, there has been a significant improvement in inspection capability over time.The questions I have are:1. Are there inspection machines that can perform both SPI and AOI tasks and if so, which manufacturers and models?2. Can SPI be performed effectively by a screen printer or dispenser and if so, which manufacturers and models?3. What is the difference in inspection methods for machines prior to and after inspection method improvements?4. Did setup times significantly reduce when the new inspection methods were introduced and if so, what are typical times?5. When did the significant inspection method improvements(s) occur and what are the manufacturers and models of inspection machines that have the improvements?6. What should the electrical test first pass rate be following inspection?7. What level of inspection false positive results are expected?8. Are important points being missed above?Sorry for all the questions! They all relate, hence the single post.The question numbers are intended to make it easier for people to understand which question a response is related to.Thank you.

author: SMTech
author_rank: Frequent Contributor
timestamp: February 11, 2021, 10:03:47 am
content: You can add all sorts of things to your line to try and catch all sorts of things, I wouldn't say any of the things you lists are "required" although I'm sure people will sell them to you quite happily. A modern printer will have a 2D/2.5D/2D+ paste inspection option, possibly with some form of it as standard, it will perform some basic but effective coverage checks and will also check the stencil for residual paste in apertures. I wouldn't go adding dedicated SPI unless I knew I was running processes & volume for a relevant market that meant it would be catching things that cost value or reputation. Lower volumes, specially in a setup where they are low enough you are considering a dual purpose machine (so no conveyor presumably) do not suggest a need for all this expense. Because these belong at opposite ends of a line you'd be looking at a desktop machine like the MEK IMHO. However if you have the volume, value or potential liability then Industry 4.0 has your back, all the machines can then talk to each other in a continuous feedback system, best achieved by picking a single vendor line just get your $1M readyI've not had the opportunity to compare old and new AOI but I think its very safe to assume algorithms and software got better over time along with speed and camera quality. Some of that of course just helped the bottom end catch up with the the top. A proper 3D inline AOI is well over 100k, 2.5D using top down cameras, angled light and maybe a laser for checking coplanarity can be half that. 2nd user models may have extra expenses like high support/license costs and I've seen several reports of really buggy software on some quite big names. I've seen pretty impressive results from an ALeader in a demo which is a quite affordable entry point. Its a very crowded market different, players moving at different speeds. I don't think you will find a key then and now point with a sudden switch over, and most of it will be code. The signifcant tech I am aware of is the polarised light used in expensive 3d machines form Omron or KohYoung.I would not attempt to short circuit the process, read the brochures etc, talk to the sales&technical teams understand what you are buying and your potential need and work form there.AOI should NEVER pass a board that should have failed, its algortihms and anything you set in your thresholds should be conservative, otherwise what would be the point.

author: Kiwi
author_rank: Newbie
timestamp: February 11, 2021, 10:35:33 am
content: Thanks for that SMTech.As the number of PCAs being assembled is expected to be low, I thought it might be possible to paste, perform SPI in SPI / AOI machine, pick-and-place, reverse the direction to perform AOI in SPI / AOI machine, then pass through the pick-and-place machine.Due to the lack of throughput, a Dispenser should be fast enough. Are there limitations or advantages when performing SPI / AOI with Dispenser versus Stencil Printer?Thanks!

author: SMTech
author_rank: Frequent Contributor
timestamp: February 11, 2021, 11:09:11 am
content: To my knowledge, there is no such thing as a placement machine that would shuttle a board in, out and back in again to fit this workflow.Dispensed paste obviously looks very different to a printed board, before and after reflow it will require its own unique set of rules to pass consistently even if the coverage and volume is good. Clearly your train of thought is pointing you at Essemtec, good though Essemtec is, I personally don't follow their theory you can start with an all in one Fox2 placement/dispensing solution and grow that line from there. They just aren't fast enough or capable enough to fulfill that promise, the dispense head on the Fox2 costs enough to buy you a printer, stencils are not expensive enough to sway the equation. As a solution I think it belongs in well funded specialist labs not factories, Mycronics dispensing is more advanced and more capable and they don't try and wedge it into their placement machine. SMT volumes grow quicker than you might think, buy more throughput than you think you need to make your life easier in future. I chose our Essemtec for a reason, closely matched to where we were at the time. Today I would not, they have got more expensive, they haven't made strides in the areas I think they should and some of the consumables are expensive with no 3rd party alternatives and I want different things.

author: Mnyut
author_rank: Newbie
timestamp: February 12, 2021, 09:39:58 am
content: @Kiwi, visual inspection is not an alternative to AOI, the performance is too poor for that. However, wave soldered THT solder joints are not as good at AOI inspection. Wave soldered or hand soldered SMD components will also produce more pseudo defects.SPI can of course be an advantage, on small production lines it is often not important to have the highest possible speed and efficiency, there you can also visually inspect non-visible solder joints like on BGA or QFN before assembly. All other print defects then require more repairs. There are only a few customers who forbid repairs. However, it can happen that not all defects are repaired when there are many repairs. This process must then be safely worked out or is a retest necessary.The mentioned modern printer with paste inspection option can be quite sufficient for this.Many used machines allow the use of current software, especially if the hardware platform has not changed. Sometimes the computers have to be renewed or upgraded.Additionally, how high the initial pass rate of the electrical test is also depends on how well the process is organized. Often AOI are sold with the argument that different users or programmers have no influence on the test result.False-positive inspection results often occur when the specifications for inspection plan generation are not good. Poor component quality also has a big influence (especially material provided by the customer). The limitations of the machines come much later.Quote from: SMTech on February 11, 2021, 10:03:47 amFaulty software is a big problem, unfortunately all manufacturers I have seen have this problem. You have to imagine that, suppliers of quality assurance equipment do not have their own quality under control. I also see the large number of suppliers as a big problem. As a result, the pressure to innovate is so great that new functions become more important than quality.Just a few years ago, German manufacturers said 3D AOI has no relevance, it's hype. I met many users of 3D AOI systems because the requirement was angled cameras, but after the demo of 3D AOI with only one camera from above, these were no longer necessary. We felt the same way.

author: Kiwi
author_rank: Newbie
timestamp: February 12, 2021, 09:56:50 am
content: My basic interpretation of the changes that have occurred to SPI and AOI over time are that formerly comparisons were made between two images, i.e. a reference or 'good' PCB / PCA image and the current image and more recently involve characteristic comparisons, such as the shape of solder fillets and paste or component volume calculations. In the former method, failure identification was due to differences between the reference and current images. In the later method, failure identification was due to differences between measured values and those predicted from screen dimensions. Due to the lack of requirement for a reference or 'good' PCB / PCA, setup times could be reduced significantly with the newer method. Perhaps the first method is that associated with 2D inspection and the second 3D inspection. However, there are terms used by the various manufacturers, such as 'True 3D'. I don't know how machines that aren't of such types compare. Is it just a gradual increase in the number of features by, for example, more cameras, higher definition, different image processing techniques, or a step change that enabled significantly more failure modes to be detected? Several of the manufacturers claim to hold patents and claim to be world or class leading. Current model capabilities can be determined from manufacturer's websites but capabilities of older machines are harder to find. Harder to describe differences, such as changes to software, are less easily advertised but may have a significant influence on operation. These types of differences can presumably be described by experienced users who have seen the differences first hand. I hope to receive feedback from such users.

author: Kiwi
author_rank: Newbie
timestamp: February 12, 2021, 10:01:31 am
content: Thanks again SMTech.Yes I have been considering Essemtec. I see Essemtec also have sold Stencil and Dispense machines and continue to sell Dispense machines. Use of such machines, instead of integration into the Pick-and-Place machine, wouldn't slow the Pick-and-Place operation down. I read somewhere, and I thought it was describing an Essemtec machine, although it may have been a Stencil or Dispense machine, that the direction of the PCB could be in and out on the same side, it could go in either direction or in and out the same side; if those are possibilities, I thought the only remaining question is can the direction be changed, perhaps via the SMEMA or Hermes interfaces but my reading so far has not revealed either of these standards accommodate this feature.Are you aware of the price of the machines you describe below, i.e. MEK IMHO and ALeader. I see another Korean company, Test Research Inc Innovation, offers 2D and 3D inspection machines. Do you know if these are one of the expensive brands?

author: Mnyut
author_rank: Newbie
timestamp: February 12, 2021, 11:27:04 am
content: There are, of course, AOI systems that base on Goldenboards like the AgnosPCB recently presented here. I have only tested it for a short time myself so far.Comparisons with goldenboards have the problem that these golden PCBs have to be found first. You can't manually change anything on them, because that looks different than from the production line. One possibility I already used and it works is GIMP ;-).And there are systems that use goldenboard technology only for some checks, but count black and white pixels or parts of colors for solder joints (very nice example how to think about it:https://www.eevblog.com/forum/projects/diy-aoi-rgb-inspection-light/).Most 2D AOI probably use some kind of pixel counting, even if you often just get a score value, because more or less complex algorithms are used here.A 3D system determines volumes, but not voxels, instead of pixels. Techniques from 2D can be added for a more accurate result.An old 2D system can benefit from new software if it continues to be supported by it. The same is true for 3D systems.

author: SMTech
author_rank: Frequent Contributor
timestamp: February 12, 2021, 01:00:58 pm
content: I think quite a few AOI system, from 10 years ago or so were golden board based comparison engines, even quite expensive ones. I got the impression from some demos that some training from golden samples is still used on modern systems but its more of a "this is a good joint" sample, not "here is a good board".It's not a step we've made as a small CEM, we keep getting close, looking at the odd system and then stepping back as the cost is high and workloads change, the smaller your batches are the more difficult it is for AOI to prove its worth. However as a CEM we are finding an in increase in work with no test rigs or data, we were previously quite reliant on functional test as well as luckily building mostly simple assemblies. That pushes it higher up the list again and the research start again.There are a few tiersLow end 10-30k- Similar capabilities to Agnos but bigger boards, standalone. These spot missing, reversed wonky and wrong if they have legible markings. Some make some attempts at reading paste (it's there it isn't) but they can't measure itLow end inline - mostly the same as the desktop systems.These might be something like thishttp://www.aoisystems.com/products.htmlor thishttp://optimumtechnical.co.uk/wp-content/uploads/2017/06/AOI-Bochure_Web.pdf,clearly useful tools but plenty can get past them and arguably a well configured line shouldn't really be having many of the issues it can catch. Some would say these are NOT AOI systems as we expect these days and arguably they are correct, indeed some of the machines in this bracket never claim to be.Entry Level AOI:Here we're talking your angled light roving camera setups here's a UK example,http://www.dcbautomation.com/products/we had on on site demo of one of these 10 years ago and there was a previous model that seemed quite popular. they seem to be defunct now buthttps://detech-europe.com/inspection-systems/prey-aoi-inspection/#these machines seem to take on the mantle and the previous models looked eerily similar to the DCB ones. Presumably if the UK has these home grown entry level examples there are others out there too. This is also the the point a brand like Aleader starts with a cheaper offering, Aleader is one of several Chinese AOI offerings that make a proper push in external markets with regional offices and picking largish partners for their distribution. You will find other random offerings from all those manufacturers of Chinese SMT machines but I have no idea what their abilities are -you can see them on Ali for like 25kMid Range (sub 100K)I'd stick your bigger brands in here as I said before super crowded market these will be bigger, faster more accurate versions but still (mostly) not true 3D. However most of these machines will claim to measure solder fillets, catch lifted leads, wonky QFNs/BGAs and pretty much any other fault you can without an X-RayHigh endYou true 3D with all the fancy light tricks and prices well past 100K. Machines like the Koh Young or Omron or maybe CyberOpticsYou need to work out what your product needs, your expectation from AOI and then your options. Its so crowded I would be tempted to suggest the right machine is the one sold by the company you trust the most or knows the product best. Or if shopping around a 2nd user the one you can get with support. I would expect the number of offerings to shrink rapidly as adoption accelerates, pick and place is now dominated by only a few brands when once there were many. The most common 2nd user machines in the UK seem to be the MEK desktop units, whether thats because they are good and common or they have recently stopped being useful as tech progresses is another question.