SMT PNP is only hard because you have to do a lot of easy things right. - Page 1
Forum section: electronics / general

author: mrpackethead
author_rank: Super Contributor
timestamp: October 22, 2018, 01:58:43 am
content: My Thesis is "SMT PNP is only hard because you have to do a lot of easy things right."What do you think?

author: Reckless
author_rank: Frequent Contributor
timestamp: October 22, 2018, 04:43:45 am
content: That's been my experience. Although the programming aspect seems painful on older machines.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 22, 2018, 05:49:53 am
content: From the outside, it seems so easy. From the inside it is a hurricane of details that all have to be perfectly dealt with.The lack of forgiveness at any stage of the process is mind numbing. No particular detail seems to be overwhelming but the sheer volume of little challenges continues to be surprising.Short and misplld from my mobile......

author: SMTech
author_rank: Frequent Contributor
timestamp: October 22, 2018, 09:45:40 am
content: If it was that hard, none of these people building boards using plastic stencils and toaster ovens would have any success whatsoever.In our company we started doing surface mount in the late 90's, initially using a manual pick and place with feeders to build one clients boards and the odd SM corner of ours where that was starting to be needed. Its before my time but I think we got lucky with both the manual pick and place and a hot air rework station, however we had a small converyored reflow oven from the very start, there was no attempt to knock up some DIY solution for that. It wasn't long before we moved on to an automatic pick and place machine, a Versatronics RV4s, as our first hands on with anything like that we were quite pleased with it initially but I f'ing hated that thing by the time it was becoming increasingly clear it was rapidly becoming a bottleneck and a liability. The number of niggly little points and quirks on that machine are quite numerous and having looked at some of the Chinese machines promoted today, they have many similar niggles and some worse ones. Sure they might do the job, but I think they might drive the person forced to use them round the bend.However the process itself is very forgiving, I don't think you could say we experienced any particularly hard to resolve issues at any stage along the way. Use proper footprints (basically sticking to the rules) and use a decent stencil/squeegee and you get get away with all sorts when it comes to placement accuracy and reflow.Old machines do seem "fun" to program, both the Versatronics and Essemtec tho' are pretty straightforwards, give it part number xy + rot and they handle the rest, no manually programming tool changes or sequences. I think the key to programming a modern machine is a screen like this one attached - a graphical representation of the board as you want it built and the ability to use the overhead camera to overlay an outline of the parts on each location on a blank board if needs be; some people built the first run of a board onto sticky tape to verify - I don't need to.On a slight detour (but related) on a few other threads I've seen the idea that contracting out SMT is somehow complicated "because there's so much information you have to share". I really don't think this is true, as a contractor I want exactly the same information your own production line would want - fiducials in your design, a centroid file,a paste layer, a BOM (with alternatives/specs if we're purchasing) and a decent assembly layer or a sample. There is literally no excuse for not having that information prepared if you are in the business of making things, nor is it a very big list.

author: Kjelt
author_rank: Super Contributor
timestamp: October 22, 2018, 11:18:19 am
content: IMO SMT PNP is not that hard or there would be a need for specialists.Many amateurs do it every day by hand upto 0402.Setting up the entire automated PNP process from bareboard design with all the extra needed features and rules to obey and running an automated PNP line, now that is more complicated, esp with the smallest packages.Once setup correctly and having support from the machine vendors or spare parts to exchange to keep things running it is not that hard anymore.

author: SMTech
author_rank: Frequent Contributor
timestamp: October 22, 2018, 11:32:22 am
content: Not so much getting the little things right as, consistently getting them right when you scale up. When the numbers increase, "good enough" will no longer be up to scratch, you'll be chasing that 6 sigma target.

author: coppercone2
author_rank: Super Contributor
timestamp: October 22, 2018, 07:09:50 pm
content: A smart company that does PCB will have a dedicated guy for this. I don't think you would want the engineering department to handle the PNP/Reflow stuff.In a corporate setting you also have a crap load of documentation to deal with relating to manufacturing, which makes it all the more time consuming.Also its better for someone to deal with those minor manufacturing details so the people can focus on good circuit design, reliability and R&D.

author: jmelson
author_rank: Super Contributor
timestamp: October 22, 2018, 08:27:55 pm
content: Quote from: Reckless on October 22, 2018, 04:43:45 amWell, my CSM84 is an "older machine", and it does have a teach mode, but that seemed totally insane, so I have NEVER used it.I got the pick and place file out of my CAD/CAM system, and hand-edited the first placement file, got it to work, and then wrote a C program to convert the P&P output to the file format the machine required. This is all pretty much automatic. I do have to create a component to feeder list for that program. The issue there is assigning feeder locations optimally, and remembering that feeders larger than 8mm use up two feeder slots. So, it is best to group all larger feeders together rather than alternating 8mm 12mm 8mm 16mm etc. which wastes more feeder positions. The most-often-used components are placed next to the board, so that XY travel is minimized.One other area is the solder stencil! Getting the right shrink of the apertures is a tricky business, and it took me a couple years to get it figured out MOSTLY right.But, yes, there are MANY steps, and fouling any one up could make a big mess. Loading the wrong part into a feeder slot will get you a bunch of rework. Hope it isn't a many-leaded chip.And, there are some parts that just are NOT made to do P&P on just any machine. I'm thinking of MELF and round-top LEDs. So, avoid those types if they will cause a problem on the machine you have.All machines have some height limit, so you have to be careful to not exceed that, or parts will go flying. Some machines have programmable trajectories, mine doesn't. You can, MAYBE, trick your way around this a bit by placing parts from back to front on the board, assuming the feeders are on the front. But, the machine still has to get the parts out of the tapes, so you really can't handle much taller parts, anyway.Jon

author: SMTech
author_rank: Frequent Contributor
timestamp: October 23, 2018, 06:10:22 pm
content: Quote from: jmelson on October 22, 2018, 08:27:55 pmOlder systems were restricted somewhat by the computing platforms they were based on, on top of that the focus was seemingly entirely based on production with the concept that an engineer setup each and every product before letting operatives loose on building them. There was little to no attempt at ease of use, integrated setup tools, speed of changeover or integrated intelligence, that just isn't how modern systems work, some of those features might be optional extras which would be unfortunate if you picked one up 2nd hand without them but on the whole anything from the last 10 years at least shouldn't be making you jump through hoops to carry out trivial tasks. However that is the ins and outs of operating a PNP machine. I maintain the process itself remains basically simple until you start attempting the funkier components such as the tall, the high powerQuoteFor the vast majority of parts you should be able to get away with 1:1, where you avoid this is on things like large pads (that you would probably crosshatch anyway) or on pads that you know extend further under the device than normal. Reasonable summary herehttp://www.surfacemountprocess.com/a-guide-to-effective-stencil-design.htmlyou can also probably get bags of advice or indeed a folder full from your stencil supplier (there are advantages to not using China for everything). If your footprints often cause you trouble you need to be looking at them or your pasting process. Of course some issues you cannot see with the naked eye, like voiding and that can require extensive work with both profile, stencil design and even reflow process if it is critical (vacuum helps $$$).QuoteThis is one of the many key arguments for intelligent feeders, you can still load the wrong part into the feeder of course if you aren't barcoding them on, but feeders that know where they are loaded and what is loaded on them and machines that alter the pick routine based on where they get slotted in... godsend, would never go back.QuoteInteresting, I wouldn't have had these down as machine issues, thats a nozzle issue, MELF has been around since forever, I spotted some in an retro computing article about an early Apple, I can place them wihth the same nozzle I'd use for their flat counterparts although you could opt for a nozzle with a notch cut out of it. Equally domed LEDs, I place 1000s with a standard kitted nozzle that is bevelled on its inner edge, the pick/placement parameters have some overtravel to compensate for the fact some of the device is in the tool. Those LEDs with a weird sticky gel lens however cause lots of people problems and often need a special tool.QuoteTall parts are new, old machines were often more akin to chipshooters than flex placers (even when they weren't quick) so they can't handle them, sadly the prime cretin here is the electrolytic which may get rather more prevalent once conflict mineral rules kick Tantalum in the ass in 2021. Depending on the machine you may or may not be able to trick it, on Essemtec it knows the maximum height for each feeder type, it won't let you tell it a tall component the machine or feeder cannot handle is located in one. These days its fairy reasonable to expect a machine to either include collision avoidance routines or offer you a way of defining rules, that way if tiny part A is right next to giant part B, the machine will avoid putting down B if A is not fitted. Equally 2 giant parts next to each might mean it has to alter its routine to not start z travel until it has reached destination. Invisible tasks on modern platforms, possibly not so on old ones.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 23, 2018, 06:44:01 pm
content: Quote from: coppercone2 on October 22, 2018, 07:09:50 pmIn small companys that may not be an option. You often have to do a lot of different things. Theres plenty of small smart companys about.QuoteOh really? Would it not be better for those 'minor' details to be resolved at design time. Having the people who are designing things, knowing how it can be manufactured is critical.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: October 24, 2018, 05:30:41 am
content: Exactly. I see my manufacturing experience as a HUGE advantage when it comes to design for manufacture. My boards are all manufacturable from the very first prototype.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 24, 2018, 05:43:31 am
content: Quote from: D3f1ant on October 24, 2018, 05:30:41 amMine are not bad, they tend to get improved for production.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 24, 2018, 08:36:47 am
content: QuoteIt's silly thet most of the Chinese.machines have software that's significantly less well designed than the 20+.year old Versatronics.I think Versatronics were a.bit ahead of their time in offering a low-end machine in the fairly.early days of smt, and folded before the market caught up.Their software was about 90% of the way to being ideal for a machine of that size when they died, with only a few minor bugs and design quirks, none of which get in the way too much of it still being a very useable, small and (now) very cheap system after all these years.

author: SMTech
author_rank: Frequent Contributor
timestamp: October 24, 2018, 09:53:36 am
content: Yep, [however it does have a spiritual successor in the iMP from Intelligent Drives, which in real terms is actually cheaper (assuming it still exists, website down right now)]on the RV4:The Good:SmallCheap - it was <£25k new, you shouldn't pay more than £3k now.Needs no air supplyFairly quietSingle phaseUsable software that was surprisingly stable considering the W9x platform it ran on. Also this is before the days of rapidly issuing updates online and using your users as guinea pigs so it was stable based on presumably quite limited testingMany of the control boards turned out to be fairly easy to clone so there are spares possible.The Irritating:The feeders are fiddly to load and even fiddlier to service, made fiddlier by the choice to mount the reels above rather than hanging blow like TWS or EssemtecFeeders in banks compromises an already low max feeder countNo component DatabaseDumb(not intelligent) feedersPretty weak vision routines, but all you could really expect for the era and budget, rivals would have been laser if you were lucky and mechanical alignment if notSeparation of different jobs into different programsNo understanding of complex panelsOnly 80 feeder lanes, and the Chinese machines are WORSE.No collision avoidance, you could try and trick it into placing the taller part 2nd but a feeder error or say both parts coming on the same size tape would frustrate those efforts.Some odd undocumented quirks/features in the software, or located other than where you might expect.The documentation basically boiled down to the training manual you worked though when it was delivered.Really picky about gerber format parameters, which was one of the ways you could program it.Component rotation is defined against its orientation in the tape, which is really really stupidIts positional accuracy was most certainly challenged by larger&/or fine pitch partsThe cable management in the arm frankly leaves room for improvement.It is slow, 1300cph is probably about the top speed it can manageThe bad:The robotic arm giving a silly pick/placement area (had the next incarnation of the company survived the QPlacer fixed this one).The lack of positional feedback.The build quality on some of the original boards was apparently, not great.The feeders were pretty poor in general, plastic tapes being the worst.The fact that the above meant the machine was capable of breaking itself if it got confused.Baffling CAD import menus that possibly didn't even work and an entire program that apparently did nothing.The vision system is easily upset by changing light conditions.

author: Kjelt
author_rank: Super Contributor
timestamp: October 24, 2018, 10:10:49 am
content: Quote from: mikeselectricstuff on October 24, 2018, 08:36:47 amThis will change over time, the chinese manufacturers will realize that software is a major part of the machines sellingpoint.They should have hired some Indian SW engineers or firm to create the software or port to OpenPNP.

author: SMTech
author_rank: Frequent Contributor
timestamp: October 24, 2018, 10:26:28 am
content: I was curious enough to watch the tutorial video the US Neoden chap had put together.If that was anything to go by some of the software could be improved by some common sense, there were steps that seemed superfluous, copying numbers from one screen to another for example. Stupid ways of setting up feeders and defining pick heights, manually setting the tool for each part, all sorts of madness that the user shouldn't need to concern themselves with. Fiddly slider controls when up down arrows, keyboard shortcuts or a joystick would make more sense, really odd screens and names/labels.Some things might need hardware changes to do but measuring pick and PCB height for instance should be something the machine can do itself. Indeed most machines don't measure PCB height unless they are pasting/gluing as the top of the PCB is always in the same place as it is clamped up against the fixture not down to it.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 24, 2018, 12:59:03 pm
content: Quote from: SMTech on October 24, 2018, 09:53:36 amI don't understand how that is stupid, unless it's to do with how the gerber util used it, which I don't use.Surely all part rotations should be relative to tape, so they don't need adjusting for feeder.bank.QuoteNo argument there, probably a combination of both the vision system and mechanics being at their limit.QuoteYes but it was the cheapest machine you could buy at the time.QuoteThe odd area can be annoying but it was a clever way to keep the size and mechanical complexity down.I've never had the need for collisdion avoidance as the height above the board is prettyGood, way higher than most Chinese machines, though I have had to machine down some feeders to take deeper tape-stuff like JSTHCH cons. I Don't use smd electrolytics though.I think a lot of the issues were down to it.being a small company with limited resources, but even then they produced a machine that is still doing useful work today with zero support for the last decade or so.A lot of the fiddliness goed away once you write software to generate the files direct, though I wouldn't want to run one as a cobtract manufacturer, dealing with multiple customers' designs.If only we could get hold of the source code to fix a few annoyances.

author: SMTech
author_rank: Frequent Contributor
timestamp: October 24, 2018, 01:23:46 pm
content: Part rotation should be defined against a standard, ideally an IPC one, independent of how it may be packaged. For each component you then define its orientation on the tape and for the board. The key to this is for the machine to use something resembling a database for all your parts.And the advantage - one single part number can have multiple packaging types - a QFN might for example come in tube, tray or tape. On the RV if for some reason your parts came packaged differently, editing your component definition affected your placement file rotation.You didn't necessarily need an electrolytic to encounter collision issues, if you had a CaseA Tant with say a 0805 cap right next to it, if the RV placed the Tant first, placing the 1206 would knock it over. Some people really love to cram things onto a board and take datasheet "place as close as possible" suggestions a little too far... However I would agree that if you circumvent the limitation of the feeders and disable merge moves the RV is more capable than many machines of handling taller parts.Many new machines advertise massive max heights these days, 34mm on a Europlacer, 25mm on several fast machines from Juki/Yamaha, IME however I think if you can do 12mm components, and the feeders can handle a pocket depth to match, that covers most bases; bigger than that and you are probably handling weird stuff like giant studs.

author: Kjelt
author_rank: Super Contributor
timestamp: October 24, 2018, 02:07:05 pm
content: Quote from: SMTech on October 24, 2018, 01:23:46 pmInteresting, do you know if those heads are pneumatic type, since elektromechanical movement would cost too much time ?

author: SMTech
author_rank: Frequent Contributor
timestamp: October 24, 2018, 02:37:29 pm
content: Quote from: Kjelt on October 24, 2018, 02:07:05 pmWithout sticking my head in a few to confirm I'm pretty certain they are all electronic for the level of control you need, if you read the brochure for the Juki RS-1 for example you will notice that it alters its nozzle height based on whatever its is doing an alters its route accordingly, bigger parts parts place slower. On a Europlacer they have a Turret head, it can pick up 8/12 parts of 12mm or under, taller than that - just the one. On an ASM E series you have have single pipette for awkward parts on the same head the the turret (c12pp). Depending what you are doing it might be better to have one machine that can do everything instead of having a dedicated awkward parts placer on the end of your line doing sod all most of the time, but there are usually compromises, these however seem to be getting smaller.The Essemtec Paraquda handles 18mm as standard but then it isn't exactly lighting quick (it will give single Europlacer Turret head a run for its money tho' on certain PCBs).

author: Kjelt
author_rank: Super Contributor
timestamp: October 24, 2018, 03:11:08 pm
content: Would be interesting to see the elektro-mechanical solution, if you find any pictures or pdf's please share.