Acceptable Yeilds from PNP line - Page 1
Forum section: electronics / general

author: mrpackethead
author_rank: Super Contributor
timestamp: October 03, 2018, 10:54:11 pm
content: I'm curious, to know what others consider to be acceptable yields from PNP lines.In an ideal world, when the board comes out of the oven, everything shoudl be perfect. the Reality seems to be a little different from that. What rate of faults is acceptable.

author: DerekG
author_rank: Frequent Contributor
timestamp: October 03, 2018, 11:13:46 pm
content: Quote from: mrpackethead on October 03, 2018, 10:54:11 pmFailure of 1 board in 1000. If you are getting more than this, redesign your board, modify your solder paste stencil or refine your component placements & your oven settings.

author: coppice
author_rank: Super Contributor
timestamp: October 03, 2018, 11:16:44 pm
content: That depends enormously on the size/complexity of the board, whether it has awkward shaped parts on it (i.e. ones with a significant placement error rate), and on the defect rate of the components being used. Medium sized boards loaded with 6 sigma components should have >99% first pass success rate. Small boards >99.9%.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 04, 2018, 03:23:49 am
content: Is there some kind of standard on this? Too reasons;Clearly getting it perfect is just not going to be possible, over a big enough sample. Somethign will go wrong, sometime.There likely is a economically 'sweet' spot. where the cost of process improvement will exceed the cost of faults. At that point it makes no sense to spend more money to make it better. This sweet spot is likely to differ for different people.I would love a finished board rate of 99.9% rate, but to be honest, I'm not achieving that. I'm an order of magnitude lower than that, and probably have around 2% of boards that have a flaw. tombstoned passives being the primary concern. Unfortuanly some issues wont' show themselves up in testing. for example a bypass cap, may not stop testing from working.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 04, 2018, 03:44:21 am
content: http://www.rayprasad.com/three-steps-to-improve-smt-yieldThis is an interesting article, and it suggests that less than 10% of companys have a FPY ( First Pass yeild ) rate of greater than 90%. In this picture my ~98% FPY is not too bad. @cOPPICE, what did you base your 99.9% on.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 04, 2018, 05:49:15 am
content: And another article. This one suggests a DPMO ( Defects per Million Opportunitys ) of 500 for SMT. I was doing a reletively low tech board that had 1388 DO's. ( joints )588 joints x 500Dpmo = 0.694% chance i'll have a failure on a board.. Guess if you are up in the 2-10DMPO range you migth get your 99.9%The flip side of this is if you were buidlnig cellphones or TV's, or motherboards, where you are building Millions of units, then the engineering time required to dial in your process, is probably worth it. For short runs, it may cost more to do that, than the cost of some rework.My head hurts.Quote

author: coppice
author_rank: Super Contributor
timestamp: October 04, 2018, 08:34:26 am
content: Quote from: mrpackethead on October 04, 2018, 03:44:21 amPeople who are best in class at first pass success rates aren't a little better than the average. They are a LOT better. A lot of it comes down to attitude. Some people shrug their shoulders and think they are probably doing the best they can. Others get competitive, and are determined to polish out every little source of failure they can. Several rounds of little bits of polishing really adds up.Small things can substantially impact defect rates. E.G. how QFPs are handled really matters. Many people like to pre-programme MCUs before they go to the assembly shop, and blow the fuse. This might make people feel better about industrial security, but it can really hurt the first pass success rate. Some amount of legs get bent at eachmechanical handling step. More mechanical handling steps means more failures. If the repacking of programmed chips is not handled well it often ends up as the dominant source of first pass failures. This is an area where QFNs (and most other legless packages) are a boon.A typical MCU based product, with an MCU, a few anciliary chips, and some passives, nicely panellised so the boards can be minimally handled and broken apart with low stress, should achieve 99.9% first pass success at the board level (perhaps less at the panel level, if the panel is large). People who take first pass seriously get 99.9% success on much more complex boards. If you can't get 99.9% on simple boards, how would you ever get a large complex board, like a computer server motherboard, to work at all?

author: mrpackethead
author_rank: Super Contributor
timestamp: October 04, 2018, 08:52:16 am
content: if the claim that only 10% are getting better than 90% FPY is correctly, then getting 99.9% is amazing. its 100x better. I know that I'm getting better rates than my old contract manufactuers did. Maybe becuase i actually care about my work, maybe because i am doing a better job of optimizing my designs for our line.Maybe because for the main, i can get solder paste on the boards relaibly!I'd like to get higher than 98%. But Polishing costs money. I'm often doing projects in teh order of 100-500 units. Two approaches.. If i was making 500,id expect 10 to have an issue. I could just overmake units.. and not bother to fix the broken ones. This sounds wasteful, but it might be the best way. ( an increase of 2% costs of materials ). Or i could take the hit and fix thm. Either way, its possiby cheaper than spending a week or more time to make the required changes, to optimize things better. On a job when your going to make 10,000,000 then it certainly makes sense.There are things i've done that have made great improvements.- I moved to using GC10 paste. For small runs its so easy to use, its a big time saver- I upgraded stencil printer. That made a big improvement.- I dont' let the Stencil manufacturer do stencil reductions... Its all calcualted.I agree with you, the use of QFN's over QFPs' are a great thing.I'm not in this game to get 99.9% rates. I'm in it to optimize profits. I'm trying to figure out where teh right target should be.

author: coppice
author_rank: Super Contributor
timestamp: October 04, 2018, 09:09:46 am
content: Quote from: mrpackethead on October 04, 2018, 08:52:16 amA well polished line getting 100x less defects than a less well polished line is not strange at all. That's how statistical processes work.Quote from: mrpackethead on October 04, 2018, 08:52:16 amMuch of the polish needed for high yields has little to do with your run size. Its a matter of polishing your processes, so runs of every design you produce can benefit. There will always be some design specific factors, but if you get your underlying processes right you can see big improvements across all designs. If you've never tried them, you might be surprised how far simple things like check lists can take you. Every time you have a production problem, add the cause of the problem to a check list, so its one of the things you specifically look for in future designs, before you sign them off and make a batch. Remember the circuitry changes a lot for each new board, but only a small number of production related things, like a weird new connector, change. Keep what is common as common as possible, and polish it.

author: Araho
author_rank: Regular Contributor
timestamp: October 04, 2018, 09:18:01 am
content: Quote from: mrpackethead on October 04, 2018, 08:52:16 amYou will generally always have a larger number of passives available anyway, and you'd probably buy some stock of others for rework/repair etc. If so, making a few boards more than the customer ordered while running the process anyway makes sense. Not necessarily completing the product with enclosures etc for all of them, just minimizing the time-to-customer in case of production defects and for RMA's.If you are producing to stock and not to order (which sounds more likely with ~500 boards), this is not as big of a deal in my opinion.Although to me who's fresh in the game, 98% first-pass with no rework sounds damn good!

author: coppice
author_rank: Super Contributor
timestamp: October 04, 2018, 09:29:41 am
content: Quote from: Araho on October 04, 2018, 09:18:01 amSuperficially it seems like if you get 98% first pass success you can simply throw away the 2% that fail, and your costs are not horrible. The snag is that if you only get 98% to pass first time, you probably have some percentage of marginal passes that will fail in the field. When you get 99.9% first pass success your processes are usually tight enough to massively reduce the marginal passes as well as the hard failures, and reliability is much better.

author: Araho
author_rank: Regular Contributor
timestamp: October 04, 2018, 10:29:51 am
content: Excellent point about reliability! (Just to be clear, I meant first-pass as in first built revision of design - which still seems a bit daunting. Although that probably counts as design issues, not production fault I guess)

author: DerekG
author_rank: Frequent Contributor
timestamp: October 04, 2018, 11:21:08 am
content: Quote from: mrpackethead on October 04, 2018, 08:52:16 amIt is always best to examine at least some of the failed boards as you often find that the failures are due to the same assembly fault. It might simply be a solder bridge or open circuit at the same spot on the board (which is quick to fix once it has been located the first time).

author: ar__systems
author_rank: Frequent Contributor
timestamp: October 04, 2018, 01:25:01 pm
content: Quote from: Araho on October 04, 2018, 09:18:01 amThat's how proper manufacturers operate.If I order 1000 of something, the quote will stipulate they are allowed to overship, up to 1020 or so.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 04, 2018, 05:24:11 pm
content: Quote from: mrpackethead on October 04, 2018, 08:52:16 amThis isn't a question of PNP performance and oven profiles.Not yet.This is a question for your spreadsheets. What is the cost breakdown for hand rework? How does the added build time affect your customers (are they willing to pay more for faster guaranteed builds, or are you stuck with competitive pricing)?Then you can ask about how much effort it will take to improve your process. This includes footprints (which probably come from the customer, in which case you'll need a DFM process to verify their designs are likely to have good results with your house process), solder paste (which may or may not come from the customer -- I've never been asked to make paste changes myself, and assume the assembly house takes care of it), and programming and fine tuning of the various machines involved (are your PNP machines calibrated correctly? is your oven set to the right profile for the size and kind of board, number of components, type of paste, etc.?).(Or maybe you've already done the first analysis, and that's why you're asking the step ahead.)Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: October 04, 2018, 07:27:51 pm
content: This isn't a question of PNP performance and oven profiles.No, its about questions of everything we do.This is a question for your spreadsheets. What is the cost breakdown for hand rework? How does the added build time affect your customers (are they willing to pay more for faster guaranteed builds, or are you stuck with competitive pricing)?For me, we are *only* doing PNP for products we design and are selling as completed items. We are not contract manufacturing. Added build time in most is'nt the end of the world, however, it does cost. Rework costs $65/hour, in real costs. ( staff costs + plant + overhead ). Its something to avoid as far as we can. That being said we are not making commodity electronics. ( yet ).Really the question, ( just to clarify it ) was about finding a yard stick to compare ourselves against. Coppice suggested that 99.9% would be a rate. that would be an improvement of about 20x over what we are currently achieving. ( I will add right now that we are doing a better job than our old CM did, and each job we do, we seem to get better ). The differnece being that in a small company we dont' have dedicated people doing every task.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 04, 2018, 07:50:24 pm
content: One product I'm really glad I don't have to make is the LED tiles for video walls - the higher density ones have 4096 LEDs with almost no space between them, which must be near-impossible to rework, so off-the-machine yield has to be very high for them to be under $50 1-off shipped :e.g.This oneThough I suppose the high volume and specialisation mean they may have custom jigs for reworking them.Back on-topic there's always going to be a tradeoff between time spent optimising the process and rework or scrap costs. For lower volumes, it may well be cheaper to only look at the low-hanging fruit when optimising.

author: jmelson
author_rank: Super Contributor
timestamp: October 04, 2018, 08:14:56 pm
content: Quote from: mrpackethead on October 04, 2018, 03:23:49 amInteresting! I have such a rare occurrence of true tombstone parts it is surprising. I do occasionally see a resistor that is only soldered on one end. But, in thousands of boards, I have only seen, maybe 5 tombstones with the part flipped vertical. This may have something to do with the thermal control of the oven. I use a GE toaster oven with 4 rod-type IR elements, and a thermocouple ramp-and-soak controller with a thermocouple poked into a PTH on one of the boards.I DO have problems with high-density QFPs, though. Some of my stencils have too big apertures, and I get solder bridges. To fight that, I shrunk the stencil apertures, and then I have leads that did NOT solder. I haven't really found a sweet spot, yet. I just changed over to Loctite GC10, but haven't done enough boards with it to know how much it helps. I'm using a lot of Xilinx parts in the 144-pin 0.5mm pitch QFP package, and those are the ones giving me fits. 0805, 0603 and SOIC parts are pretty close to 100% perfect.Jon

author: mrpackethead
author_rank: Super Contributor
timestamp: October 04, 2018, 08:19:27 pm
content: Quote from: mikeselectricstuff on October 04, 2018, 07:50:24 pmYes. exactly.

author: DerekG
author_rank: Frequent Contributor
timestamp: October 05, 2018, 01:04:44 am
content: Quote from: jmelson on October 04, 2018, 08:14:56 pmAnother possibility is to reduce the thickness of the solder paste stencil instead of the aperture.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 05, 2018, 02:22:09 am
content: Quote from: DerekG on October 05, 2018, 01:04:44 amor if possible use QFN's. Thats been a big bonus for me.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 05, 2018, 09:48:38 am
content: An issue with low volume production is you may not get enough failures to identify specific causes above the noise of random occurrences, or measure the effect of changes to the process to a statistically significant level.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 05, 2018, 02:49:31 pm
content: A lot of people wince at QFNs and other no-leads and exposed-pads, but the truth is this: even if you don't have hot air, they're... not impossible (though to do by iron, you really need to make a big hole to access the exposed pad and glob onto that), but a passable hot air machine is cheap and gives SO, SO MUCH BETTER results, easier than using an iron.Tim

author: coppice
author_rank: Super Contributor
timestamp: October 05, 2018, 02:52:14 pm
content: Quote from: T3sl4co1l on October 05, 2018, 02:49:31 pmMaking a prototype with QFNs is no problem at all. Making a production quality board, with low thermal stresses, is not so trivial. Even heating takes real effort.

author: SMTech
author_rank: Frequent Contributor
timestamp: October 05, 2018, 06:14:51 pm
content: Volume definitely makes a difference.When building small batches you are far more likely to also have parts that come in small quantities, these have often been handled or repackaged by the poorly trained monkeys that inhabit Farnells warehouses and this radically increases the likelihood of a device being presented to the nozzle that can still sneak through the optical checks (if that applies to your machine) and end up on the board. So for low volumes under ~30, I might at a squint say 90% for the SMT process is OK (ish).However once you move onto jobs with components on nice reels or virgin trays 99+% should be the order of the day.Tombstoning should be very rare and usually points to a footprint or layout issue. The only consistently tombstoning device I have ever encountered was an 1812 resettable fuse where the designer had out quite a lot of pad under the device. This fuse can be purchased in two variants, the one with flat ends would tombstone, the version with a channel in the end of the pad, does not. The fault however is the footprint, the fact the channel variant mitigates that is just luck.

author: jmelson
author_rank: Super Contributor
timestamp: October 05, 2018, 07:48:15 pm
content: Quote from: DerekG on October 05, 2018, 01:04:44 amI'm already down to 0.003" (~ .076 mm) to keep the apertures from just disappearing. One thing I did find on the last run, and don't know how to fix, is that fixturing the board in a frame lead to variations in the alignment of the paste. So, if the PCB fabricator has a lot of variation in the routing of the board exterior, I might need to realign the stencil on each board! UGH, that would totally mess up my system, I sure hope I don't need to do THAT!Jon

author: jmelson
author_rank: Super Contributor
timestamp: October 05, 2018, 07:53:31 pm
content: Quote from: mrpackethead on October 05, 2018, 02:22:09 amWell, the problem with those is you can get solder bridges UNDER the part, and there is almost no way to see them, or fix them. I did do one board with chip-scale QFNs, and it was a NIGHTMARE. 65 chips on each board, parallel on the power rails. Which one has the short?So, I'm really afraid of ever using such parts again.Jon

author: mrpackethead
author_rank: Super Contributor
timestamp: October 05, 2018, 07:56:06 pm
content: Quote from: coppice on October 05, 2018, 02:52:14 pmIm using Vapour Phase, and it made it really easy ( compartively ). I'm not getting voiding or having to overheat it. Where possible, going to QFN's over QFP's has really helped.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 05, 2018, 07:59:46 pm
content: Quote from: jmelson on October 05, 2018, 07:53:31 pmShorts don't happen with correct paste application. You have to put down a LOT of excess to get that to happen, AFAIK.I have the luxury of most of my (commercial) designs being proto'd at a full service shop, where anything with a no-lead ends up with an "XRY" sticker on it...Tim

author: mrpackethead
author_rank: Super Contributor
timestamp: October 05, 2018, 08:05:31 pm
content: Quote from: SMTech on October 05, 2018, 06:14:51 pmWhile 99.9% would be great, if i can get to 99%, it woudl be a big improvement from my current 98%. I'm resonably happy with the precision of the PNP line itself. I am confident that most of my issues are related to solder paste application, and improving that part of my process will improve things. Starting to look for a new printer.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 05, 2018, 08:30:06 pm
content: Quote from: jmelson on October 05, 2018, 07:48:15 pmI never assume that my boards will be consistently routed out. Because routing tolerance is around +/- 0.15 mm or so.. ( they claim better but i'm being realistic ).. The automatic Stenciling machines have optical systems and move the boards to suit.. If your doing it manually, you have to be able to adjust each time. It should'nt be much, but it will be a little..

author: mrpackethead
author_rank: Super Contributor
timestamp: October 05, 2018, 08:31:34 pm
content: Quote from: T3sl4co1l on October 05, 2018, 07:59:46 pmIf your getting shorts, then somethign has gone wrong!

author: SMTech
author_rank: Frequent Contributor
timestamp: October 05, 2018, 09:27:50 pm
content: QuoteI actually don't think it takes all that much when you get down to 0.5mm pitch QFP and below and there are more than a couple of ways you can end up with too much paste. Apertures, stencil tension, stencil thickness,PCB/Stencil gasketing, footprint, paste age/liquidity will all play a partQuoteOne tip I would give is to ignore perhaps 90% of anything you might find on Youtube where people manually paste because it is on the whole done VERY badly. When the squeegee blade passes over the stencil the stencil should be CLEAN behind the blade, the blade should be at a fairly steep angle (30 degrees off perpendicular) so that the paste "rolls" into the apertures rather than being pushed through them by the flat of the blade, if your paste doesn't do this it is either too cold, not well mixed or f*cked.For fine pitch boards you will want to periodically clean the underside of the stencil to make sure paste isn't affecting the PCB/Stencil gasketing but also to make sure finer apertures are not getting blocked. Fully automated machines pretty much make this a standard feature these days. If running a semi-auto setup, depending how your system works you may need to look at checking the alignment for every PCB, some rely on the board being in exactly the same place after the initial setup. Again fully automated machines align every PCB.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 05, 2018, 10:03:22 pm
content: Quote from: SMTech on October 05, 2018, 09:27:50 pm

author: rx8pilot
author_rank: Super Contributor
timestamp: October 06, 2018, 12:18:45 am
content: The majority of trouble for me has been related to solder paste. I have worked to improve my stencil designs, using better paste, electropolished stencils, and much-improved technique on the printing. Those efforts have landed me a fantastic yield on the soldering side.As for placement.....I feel like I am always struggling with one or two parts. My latest problem is the puff-off needs a bit of TLC. Some of the capacitors are sticking to the nozzle and not coming off until the retract which drops the cap off to the side of the pads. Obviously, that is a machine specific problem and it is currently creating a problem every 1,000 placements or so. I think I should see this be in the range of every 100,000 placements.I would be happy if I could manage 10 panels with 1,000 parts each without re-work of some kind. For a commercial assembler, that would be a marginal goal but workable for my in-house needs. If I dial in my machine a bit better....I could probably beat that target fairly well.I inspect PCB's post printing and pre-reflow. It is much easier to fix something at those stages.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 06, 2018, 07:02:06 am
content: Quote from: rx8pilot on October 06, 2018, 12:18:45 amYes, also a similar story. I'm convinced however at least for me, that spending a bit more time ( and money ) on this area will help me even more.QuotePull-off? My machine pushes the part off, ( the vacumn becomes a postive ) and blows it off.. One of the things that i've found needs lots of attention is making sure that all my placment heights are set up just right. needs to be just dropping into the paste but not too much! Having support pins under the board ( and the board being flat) is also important.I would be happy if I could manage 10 panels with 1,000 parts each without re-work of some kind. For a commercial assembler, that would be a marginal goal but workable for my in-house needs. If I dial in my machine a bit better....I could probably beat that target fairly well.I inspect PCB's post printing and pre-reflow. It is much easier to fix something at those stages.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 06, 2018, 01:17:14 pm
content: Quote from: jmelson on October 05, 2018, 07:53:31 pmThermal imager

author: ar__systems
author_rank: Frequent Contributor
timestamp: October 06, 2018, 02:49:37 pm
content: Quote from: jmelson on October 05, 2018, 07:48:15 pmMount the board by the holes on the PCB. Holes are drilled with a better tolerance than the router.

author: coppice
author_rank: Super Contributor
timestamp: October 06, 2018, 03:26:29 pm
content: Quote from: ar__systems on October 06, 2018, 02:49:37 pmMost boards have been broken out of a larger panel. The broken edges are rough, which can be the main source of vagueness in locating the board in downstream tools, like PnP. If you locate the board by a cleanly routed surface it should be better. The precision of both routed slot width or drilled hole size is not that great, though. The best location is normally against the centre location of a hole. A slightly conical locating peg of some kind, pushed into a round hole, works well.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 07, 2018, 02:09:21 am
content: Quote from: mrpackethead on October 06, 2018, 07:02:06 amP-U-F-F O-F-FIt does the same as your machine....a tinypuffof compressed air quickly releases the vacuum. I just need to clean the filter and adjust the pressure a tiny bit to get it right.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 07, 2018, 02:48:02 am
content: Quote from: rx8pilot on October 07, 2018, 02:09:21 amI bought a guage that is central zero, and it displays +/- pressures. Was a really good thing to own. Foruatnly on the yamahas you can manually ( via the UI ) trigger these functions individually. ). It means you can meaure it. Gettig them all consistent really helped.

author: jmelson
author_rank: Super Contributor
timestamp: October 07, 2018, 02:51:14 am
content: Quote from: ar__systems on October 06, 2018, 02:49:37 pmYes, this is the obvious next step. My current setup would not make that easy at all. So, I will have to make some kind of gizmo to do this. Something where I can mount the posts in a slotted piece that then gets mounted under the board. I'll have to work on this.Thanks,Jon

author: mrpackethead
author_rank: Super Contributor
timestamp: October 07, 2018, 03:11:18 am
content: Quote from: jmelson on October 07, 2018, 02:51:14 amWhat is your current system? I've been using a 2mm cut out in the corner of my panels, with quite a lot of sucess. I have some mounts that have 'pins' that are 4mm in diameter, that match them. Its not *perfect* i do sometimes have to make minor adjustmetns for each print. I thought that was just normal. I include a 4mm octogon shape on the tool strip which is 100% the size of a copper ( also octogon ). and use those for the line up. Its a 'manual' fiducial i guess. The reason for the 100% apature there is that you want to be able to see the edge, or its possible to be slightly offset.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 07, 2018, 03:16:19 am
content: Quote from: mrpackethead on October 07, 2018, 02:48:02 amGauge is helpful but may be slow, I wonder if you might have better results with a digital gauge where you can log the pressure on a scope/DAQ. AFAIK, still not perfectly fast, but can be a good deal faster at least.Tim

author: rx8pilot
author_rank: Super Contributor
timestamp: October 07, 2018, 04:19:06 am
content: Quote from: T3sl4co1l on October 07, 2018, 03:16:19 amI have never looked at how fast the electronic gauges are. It would be a nice way to optimize the release timing. My machine is rather slow by modern standards, but the vacuum/release is still rather quick. It only takes a tiny shift in the timing to make a mess. The valve and the air pressure combined with the motion control signal all need to be friends. If I have a clogged line or a valve problem....it will take quite an effort to get to them. Fingers crossed it is only the easy stuff.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 07, 2018, 04:23:07 am
content: Quote from: T3sl4co1l on October 07, 2018, 03:16:19 amI guess if you wanted to check the timing out, and see how it ramps up/down it might be good. I've just been using it for so called 'static' measuremnets.. ( turn vacumn on for nozzle, measure, turn it off. Turn on blow air, etc etc. I make a weekly check of it now, as its a good indicator of a problem.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 07, 2018, 08:45:21 pm
content: Spent a good amount of time yesterday looking at the issues that I have seen. ( i've been pretty good at recording them ), and what i can do to improve them and what the likely cost will be. A freind of mine said;"That is the age old problem in manufacturing. Based on 20+ years in the manufacturing automation space, there is a pretty simple rule. Add up your monthly trash, and see what it is costing you. Consider your rework as well. You would not believe how many companies spend more time / money trying to fix a low cost product with high cost labor. In reality 98% first pass yield is not bad for a small operation in simple terms, but the time and labor of finding and possibly fixing the 2% is the costly part. "I've done that and come up with a number of what its costing me. It may not been perfectly accurate, but its given me a budget to work with. The budget is big enough to spend some money on better solder paste application, which is the root cause of the majority of my problems.I had thought that i might be able to compare ourselves to some sort of 'industry' standard, but actually, it does'tn matter. What matters is what we are doing!

author: jmelson
author_rank: Super Contributor
timestamp: October 08, 2018, 07:21:14 pm
content: Quote from: mrpackethead on October 07, 2018, 03:11:18 amOK, what I am doing now is I have a plate with a grid of 10-32 holes on 1" spacing. (Sorry for imperial measurements, but that is what I use.)I have adjustable bars that have a 0.062" step on one edge, so they hold the edge of the PCB, and can be tightened down to the plate.Then, I take the frameless stencil and align it to the PCB, and tape it down with masking tape. The masking tape forms the hinge for the stencil.I think a major cause of the rework issues I'm now having is due to imprecise paste alignment. So, I may have to make up something a lot more sophisticated for stencil alignment. So, maybe a method to put the stencil in an adjustable frame, and then adjust the alignment before printing. I was hoping to avoid that. And, for the low-density stuff with 0805 passives and SOIC, that all works fine. But, when I have SSOP and 0.5mm FPGAs, it just isn't good enough.Thanks,Jon

author: mrpackethead
author_rank: Super Contributor
timestamp: October 08, 2018, 07:36:48 pm
content: Quote from: jmelson on October 08, 2018, 07:21:14 pmIf your stencil is not under tension, you'll have problems, particularly as you get done in finer pitch. There are any number of articles about this topic, just have a little google.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 08, 2018, 10:05:58 pm
content: I'm thinking that buying a big solid printer that is semi-automatic will be a good thing. This has a print area of 500 x 350, weighs 300kg, requires air to drive it. Cost aroudn USD$2500 ex China. Sure its not a DEK, but its also 1/10th of the cost. Trying to get some more info on this

author: mrpackethead
author_rank: Super Contributor
timestamp: October 09, 2018, 03:30:14 am
content: How about one of these, though probably a 500mm one rather than 1200.https://youtu.be/qefgAmsc7zA

author: SMTech
author_rank: Frequent Contributor
timestamp: October 09, 2018, 10:28:35 am
content: Is it not a bit weird thateverysingle Chinese manufacturer of electronic production equipment has a printer that looks like this, but only China. Brand new ones like this all over every website from Neoden to Folungwin as well has the brands that read like hxjinkjhdgf on aliexpress. Oddly the normal square box style printers only seem to appear via proper distribution. Personally I would spend a little more and get an old DEK/Ersa/MPM/Speedprint - if they are easily available from brokers at <£10k in the UK they must be peanuts from China which by all accounts is viable for you.

author: mrpackethead
author_rank: Super Contributor
timestamp: October 10, 2018, 02:21:58 am
content: Quote from: SMTech on October 09, 2018, 10:28:35 amno, its how it is in china. :-) I've seen these in operation aroudn the place though and they do seem to work pretty well.Quoteyes. they do. But there are numerous 'box style' automatic printers as well. but theres a significnat increase in price and with that complexity. At this point Solder Paste is a long way away from my bottle neck.Personally I would spend a little more and get an old DEK/Ersa/MPM/Speedprint - if they are easily available from brokers at <£10k in the UK they must be peanuts from China which by all accounts is viable for you.not really. DK