Electronics > Manufacturing & Assembly

Quad QSA-30A will arrive tomorrow

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jmelson:
Well, the saga continues.  I have done a couple not very demanding boards with quite good results.  Now, I'm doing the top side of the board that started this whole upgrade.  It is a 4" square board with a mix of (for me) fine lead pitch devices.  There a 144-lead FPGA and 8 MSOP10 chips with 0.5 mm pitch, and 5 SSOP24 chips with 0.65mm pitch, and an SSOP16 that I guess is also 0.65mm.  My old Philips machine could not place any of these within half a lead pitch, so I had to put every board under a microscope and poke each chip into alignment.  Thus, the need to upgrade.

So, I knew this was going to be a bit of a stretch for the Quad QSA30.  Well, after just a little tuning, the FPGA is better than 90% accurate enough to require no touchhup.  But, all the other fine pitch parts were getting thrown all over the board.  I played around with the Z adjustments for the heads and for the individual component heights, but really wasn't fixing anything.  But, while watching the assembly, I could see some inductors being forcefully tossed around.
So, I began twiddling the setting for that part, but it didn't help.  Finally, I just told the machine to skip that part, and all the rest of the parts came out pretty good.  not perfect, still had to poke some of them, but WAY better.

Examining the board, I could see depressions in the solder paste that seemed to indicate the parts were initially placed properly, but then got moved.

So, I'm thinking that my solder paste is kaput.  It is way past the expiration date, but hasn't failed me until just now.
Those MSP10 pads don't have very much solder paste on them at all!

I'm going to try some water-soluble paste I have here that is much newer.  I'll have to wash the boards after, but that will tell whether the paste has lost its stickiness.

Jon

Styno:

--- Quote from: jmelson on May 27, 2021, 01:16:05 am ---Examining the board, I could see depressions in the solder paste that seemed to indicate the parts were initially placed properly, but then got moved.

So, I'm thinking that my solder paste is kaput.  It is way past the expiration date, but hasn't failed me until just now.
Those MSP10 pads don't have very much solder paste on them at all!

--- End quote ---
So the part is basically sticking to the nozzle while the nozzle lifts again after placement? Possible causes:
- Blow-off isn't doing it's job. This might be an indication of a clogged nozzle, filter or sticky blow-off valve, or the regulator needs to give just a little more flow.
- The nozzle can be just dirty and sticky with solder paste.

Something else that could cause this:
- The placement height is too low and the board bounces back after placement, launching the part. This is an indication of bad machine calibration, nozzle length setting or wrong component height setting (most likely). I hear a loud *thunk* on each placement when something like this happens with our machine.

Were it not for the indentations then I would also check the camera recognition of the part location/rotation on the nozzle.

I use the slo-mo camera function of my phone to diagnose these sorts of problems.

I'm amazed that such a complex machine has difficulty with 0.5mm pitch components, let alone 0.65. Those are even placed accurately with our simple & old Dima Optimat.

jmelson:

--- Quote from: Styno on May 27, 2021, 08:27:07 am ---So the part is basically sticking to the nozzle while the nozzle lifts again after placement?

--- End quote ---
No, I don't think that is the problem, as NOT placing the inductors allows the fine pitch ICs to be placed accurately.

--- Quote ---Something else that could cause this:
- The placement height is too low and the board bounces back after placement, launching the part. This is an indication of bad machine calibration, nozzle length setting or wrong component height setting (most likely). I hear a loud *thunk* on each placement when something like this happens with our machine.

--- End quote ---
Yes, this seems to be the problem, but I don't think the calibrations and settings are very wrong.  I did have some wrong settings a week ago, and I could easily see the board flex when that component is placed.  Also, if the inductor ended up end-on to the nozzle, it would then plunge too deep and go flying several feet!  (The alignment camera SHOULD have rejected the part in that case.)  Now, I cannot see any flex when the parts are placed, and it doesn't click either.

--- Quote ---Were it not for the indentations then I would also check the camera recognition of the part location/rotation on the nozzle.

--- End quote ---
Again, when the inductors are skipped, the parts are placed quite accurately.  I think the paste is kaput, the fine pitch parts are not adhering to the board.  Also, when the board leaves the machine, the conveyor slams it into the exit stop pretty hard.  That's never been a problem before, but might contribute to parts moving.

I'm going to try different (newer) paste tomorrow.  It is water soluble, so I'll have to wash the boards after reflow.
But, it will verify if the paste is the cause of the issue.

--- Quote ---I use the slo-mo camera function of my phone to diagnose these sorts of problems.

I'm amazed that such a complex machine has difficulty with 0.5mm pitch components, let alone 0.65. Those are even placed accurately with our simple & old Dima Optimat.

--- End quote ---
The head is so big, it covers the whole board.  The only way to see anything is to kneel down and look down the conveyor.  Not the best place to see what is happening.

I don't think the pitch is the problem, just that the paste apertures for the fine pitch parts are REALLY small, to avoid solder bridges.  So, that means the small, fine pitch parts have VERY LITTLE paste to hold the part in place.  The MSOP10 have just 10 TINY dots of paste to adhere them.  Any bounce or banging of the board will displace components.  And, if the paste has separated and most of the flux has already been used up, it won't be sticky enough to hole the parts.  I will find out soon.

Thanks for the comments,

Jon

jmelson:
And more saga!  I was placing some boards, all was going well, then the machine started making HUGE banging noises, like a crash.
I was thinking maybe an encoder cable was going bad, so I tried to examine the issue by manually jogging around the area where it seemed to make the banging.  It would NOT jerk or bang when jogging, only when under control of the placement program.  Also, it would home smoothly.  So, I thought "maybe it is software".  So, I powered down and rebooted it, and the problem totally disappeared!  I made about 8 more of those boards just fine.  Kind of crazy stuff you run into on an old machine.

Jon

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