P&P parts bouncing all over - Page 1
Forum section: electronics / general

author: jmelson
author_rank: Super Contributor
timestamp: May 28, 2021, 10:45:22 pm
content: I am finally doing more of the difficult boards that caused me to go on a one year quest for a better P&P machine.It has everything from a 144-lead FPGA in a 20mm TQFP package down to MSOP10 parts with 0.5mm pitch.The problem I'm having is the really small MSOP10 parts are bouncing off their pads and ending up in a jumble.It all happens so fast, I can't really tell what is going wrong. I did find that mounting some 1008 inductors made it MUCH worse, so I set the machine to skip those. What I see, at least part of the time, is that the MSOP10's have dents in the solder paste right on the pads, indicating the parts WERE placed there correctly, but then got moved later.The big FPGA was placed perfectly, and I guess the 144 pads have enough stick that it did not move.I watched the board closely during placement and was not able to see the board bounce at all, so it is not a case of the board being strongly bounced.I tried changing solder paste, that made no difference.This was a big disappointment, I've done 4 other boards before this one that were less challenging, and they all came out perfectly! I can't figure out what I'm doing wrong.Any hints would be very welcome!Thanks,Jon

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 28, 2021, 11:31:32 pm
content: Some suggestions from my very limited experience.Air pressureor air timing too slow?Different nozzle sizes?Load board in a different order?You sure you're not bouncing the board.Maybe stepper motors too jerky, slow it down?

author: SMdude
author_rank: Frequent Contributor
timestamp: May 29, 2021, 06:29:37 am
content: Pick/place height.Part thickness, getting blown off before it actually contacts the board.Are you using hasl or enig?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 29, 2021, 09:29:05 am
content: Sounds like some combination of paste not tacky enough, and insufficient placement pressure. If you're only seeing small dents in the paste, it's not being pushed into it hard enough

author: jmelson
author_rank: Super Contributor
timestamp: May 29, 2021, 04:51:50 pm
content: Quote from: HackedFridgeMagnet on May 28, 2021, 11:31:32 pmOnly steppers on this machine are for rotation.I think the problem is caused by my vibratory feeder lanes being too high. I got a big click/clack every time the part is picked up. So, I think I set the nozzle to high for a good planting of the part. I will have to lower the vibe feeder and see if I can place the part more firmly. I have some evidence from the tinkering with this that that is going to fix it.Thanks,Jon

author: jmelson
author_rank: Super Contributor
timestamp: May 29, 2021, 04:54:15 pm
content: Quote from: SMdude on May 29, 2021, 06:29:37 amHASL, bit that is not the problem. I was trying to find a happy medium between a too-high pick-up height and the placement height. The RIGHT fix is to correct the pick up height so it is not mashing the parts at pickup.I have one board left, so I can do some testing when I get around to it.Jon

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 29, 2021, 11:24:35 pm
content: Hard to see how it can be anything to do with pickup, as once picked, the part should be set on the nozzle. Component height setting may be off - i.e. machine thinks the part is thicker than it is so doesn't plonk it down far enough

author: jmelson
author_rank: Super Contributor
timestamp: May 29, 2021, 11:28:30 pm
content: Quote from: mikeselectricstuff on May 29, 2021, 11:24:35 pmWell, the vibe feeder was built too high, and the nozzle was mashing the part at pickup. So, I set the nozzle higher to stop that, but that also makes the placement higher. I was trying to fix the wrong thing in the middle of a job that was all set up. Now that I'm done, I can pull the feeder off, take some measurements and put it at the right height.Then, I'll be able to bring the nozzle down so it plants the part properly.Thanks,Jon

author: jmelson
author_rank: Super Contributor
timestamp: May 31, 2021, 04:32:34 pm
content: Actually, the vibe feeder is NOT too high. I am still learning how to use this machine. In the feeder page, you can setthe Z pickup height, in the part profile you can set the thickness, which sets the placement height, and you can set the nozzle home height. I had been doing this all wrong. I did not get it set right in this short run of boards, but now I think I UNDERSTAND how this all interacts, so I can fix it up next time. When the parts don't get bumped, they do seem to align quite well. Way more accurate than my old machine.Jon

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 28, 2021, 02:10:40 am
content: I would start with a reasonable high speed camera.Camera's which can capture several hundreds of frames per second are cheap these days.On top of that you can watch frame for frame and even wind back to just before shit happened.You can also let it run continuously to capture errors that only happen occasionally.

author: ANTALIFE
author_rank: Frequent Contributor
timestamp: June 28, 2021, 03:04:24 am
content: Just to make sure, is this during component placement or paste reflow?

author: Matt-Brown
author_rank: Regular Contributor
timestamp: June 28, 2021, 12:32:19 pm
content: P.SDo you have other parts really close to the msop that are placed first (less than 0.1 or so mm)?If so, the MSOP could be hitting the other parts and preventing it from being placed.