Why Ali's PNP machines can't do 0201 - Page 1
Forum section: electronics / general

author: Dave_PT
author_rank: Frequent Contributor
timestamp: December 16, 2021, 11:38:51 am
content: Hi.I hope I don't repeat the doubts, but I haven't found the answer to the question I'm looking for.What is the main reason whyaliexpress PNPs(low cost) cannot put 0201?Will it be the belt system and not the linear spindle?Will it be a problem with the nozzle? I don't believe in this hypothesis, because that way it was enough to change the nozzle to one with the capacity to make 0201 components...Does anyone have feedback on this type of PNP?I will need to put "a lot" 0402 and some 0201...Thanks!

author: SMTech
author_rank: Frequent Contributor
timestamp: December 16, 2021, 12:43:39 pm
content: Lets start with what you are linking too, the cheapest lowest end of the Chinese desktop machine market, 0201 is really quite small, with a pocket every 2mm in a tape, the feed method just isn't good enough present small parts or even for those small parts to not leap right out of the tape.Most of cheap machines have no linear encoders, so the head position is entirely determined by end stops and stepper control. Smaller less accurate belt driven systems do exist at the bottom end of the market (which is the end you are pointing at with your link) which amplify those issues. There's nothing inherently wrong with belt drive (My Essemtec is belt driven but the belts are huge and it has hi-res encoders on the axes), but those very little machines are not well specified or put together. From what I have seen (its not always clear) most of the slightly larger "Ali" machines do in fact use ballscrew drives just as many production level machines do.Other factors will include, machine rigidity, & stablity, image algorithms, movement algorithms, the quality of the z-axis movement, the quality of the copied nozzle, the accuracy of the feeder to accurately present an 0201 to the nozzle in a consistent location. These things all add up, there are people who say they play 0201 with some of these machines but with the "with lots of careful tweaking/setup" caveat. All those little things that aren't quite perfect just add up to an unsatisfactory experience.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 16, 2021, 01:52:10 pm
content: Don't expect it to do even 0402 reliably. The real limit for <10kUSD Chinese no-name machines tends to be 0603.The biggest problem is always in feeders. Picking up tiny parts that weigh not much more than dust particles, is just too challenging. Even if the XY table itself is rigid and accurate, and even if the computer vision part works, then the nozzle hits the carrier tape the wrong way, tape bounces, parts fall off, and so on.0603 parts are heavy enough so that pickup is rarely a problem.

author: Dave_PT
author_rank: Frequent Contributor
timestamp: December 16, 2021, 02:19:08 pm
content: Thank you both for the feedback!I've worked with an old Samsung CP40, and the placement capability is 0402 too. With some magic we hacked the machine to place some 0201... but nothing very reliable.Right now, in another company, we are trying to assemble a very small assembly line to do some engineering samples. PCB's that now are assembled by hand (with some patience), but we re looking for some way to speed up things...An alternative is to use the chinese PNP to place big components and, slowly, until 0402 and then assemble by hand the 0201 maybe...

author: voltsandjolts
author_rank: Unknown
timestamp: December 16, 2021, 02:50:16 pm
content: Quote from: Dave_PT on December 16, 2021, 02:19:08 pmSave your self some time and money: low volume prototype run sounds like a perfect use-case for outsourcing.e.g.eurocircuits assembly

author: SMTech
author_rank: Frequent Contributor
timestamp: December 16, 2021, 03:49:50 pm
content: Quote from: voltsandjolts on December 16, 2021, 02:50:16 pmThat's the trick tho' right, seeing past the cost to outsource realize your own time is worth more. And that's assuming it is, if you're a micro hobby business maybe it isn't.However personally I don't think manually handling 0402 is much fun so 0201 definitely isn't. And as always if your working down to 0201 make sure you're doing it for a reason. We are both an OEM and CEM and we have to date never been asked to place something 0201, you also then need to know what your doing with stencils, if you have a mix down to that scale it infers things about the dimensions of other pads and parts that probably means you should be using stepped stencils and have a good pasting setup.

author: voltsandjolts
author_rank: Unknown
timestamp: December 16, 2021, 04:15:18 pm
content: Yup, those smaller parts are no fun for hand assembly.Another hidden cost people don't foresee with hand assembled boards is time spent debugging them - it's so easy to 'zone-out' when your on your 30th board and misplace components.With auto assembly you don't get that, they all work, or they all don't, mostly, when using a reliable line.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 16, 2021, 04:18:28 pm
content: Handling tiny SMDs is not unlike quantum physics - the surface-area to mass ratio is so high that things like stiction, static and many other factors become far more significant than mass, though the low mass also means that the tiniest shock or vibration will catapult parts right across the room.Feeders have always been the hardest thing to make work reliably, and this gets harder as parts get smaller.Paste printing also needs to be much more accurate, and you need to use finer paste.

author: NorthGuy
author_rank: Super Contributor
timestamp: December 16, 2021, 09:37:34 pm
content: Quote from: Dave_PT on December 16, 2021, 11:38:51 amThere are two kinds of problems.One is that the belt is not absolutely precise - the distance between teeth is uneven, so when the machine positions the head, depending on where you PCB is, the head me be some distance (say 0.1-0.2mm) away from where the machine thinks it is. Therefore, the placement will be slightly off.The second problem is backlash - when the motor position is fixed, the head can still move - slack in transmission, belt stretching, parts bending, so depending on how you arrived into the specified location, the head position will vary, may be another 0.1-0.2 mm.Some of these you can try to correct in the software (if you write your own software that is), but there will be some error anyway.So, the positioning isn't precise enough for 0201 - it'll either pick in a wrong place or place to the wrong place. You need more precision, and to achieve more precision you need more rigidity (e.g. better frame, better rails, better head construction), better transmission (e.g. a ball screw), also better positioning software.

author: Dave_PT
author_rank: Frequent Contributor
timestamp: December 20, 2021, 09:16:25 am
content: Thank you all!I have all the information and feedback I need.Maybe in the future I'll come back with some questions, but now all this information fits what I'm looking for.