Mounting SiPMs to PC board

[jmelson]

Last year, I had a project to mount 32 Silicon Photomultipliers to a PC board.  I have a Quad QSA30A pick and place machine.  It should have been able to do this, but the parts weigh just a couple milligrams, and come in a tiny waffle tray.  The problem was that the parts were flying all over the place.  After some thinking, I guessed that the blow-off air from the nozzles was blasting the next over chips out of the tray.  I don't really know how to turn off the blow-off air without affecting other functions of the machine.  I guess one way to solve this is to repack the tray to only have parts in every 3rd pocket.  Maybe that will solve the issue.  Has anyone else run into this sort of issue?  Any good suggestions?
Thanks,
Jon

[jduncan]

Why is your machine doing blow-off above the tray?

[loki42]

What's your board support like?  Any time I've had issues with was with thin boards and insufficient boards support, so the board wasn't at the height of was meant to be. Is your part height programmed correctly?  You might also be able to keep vacuum on during movement if its not getting a good seal.  I do this for a few big parts that have holes or grooves in them. 

[jmelson]

Why is your machine doing blow-off above the tray?

Well, I think the valve for blow-off/vacuum is just a two-way valve, and you either get the blow-off or vacuum, no possibility to get neither of them.
I need to check this in the plumbing diagrams, but I think that is correct.  There are adjustable needle valves to adjust the amount of blow-off air, and maybe that is set too high.
Jon

[jmelson]

What's your board support like?  Any time I've had issues with was with thin boards and insufficient boards support, so the board wasn't at the height of was meant to be. Is your part height programmed correctly?  You might also be able to keep vacuum on during movement if its not getting a good seal.  I do this for a few big parts that have holes or grooves in them.

The board support is not the problem.  I suspected the tray support might be bouncing the tray, so I fly-cut the top of the tray table to make it really flat.  Tapping on the tray does NOT cause the tray to bounce at all.
Jon

[SMTech]

Why is your machine doing blow-off above the tray?

Well, I think the valve for blow-off/vacuum is just a two-way valve, and you either get the blow-off or vacuum, no possibility to get neither of them.
I need to check this in the plumbing diagrams, but I think that is correct.  There are adjustable needle valves to adjust the amount of blow-off air, and maybe that is set too high.
Jon

Are you sure? That would render the machine basically incapable of picking up anything tiny from any carrier type. Maybe they've just hidden this feature somewhere obscure?
An incorrect value for nozzle size or pick height seems much more likely.

[jmelson]

Why is your machine doing blow-off above the tray?

Well, I think the valve for blow-off/vacuum is just a two-way valve, and you either get the blow-off or vacuum, no possibility to get neither of them.
I need to check this in the plumbing diagrams, but I think that is correct.  There are adjustable needle valves to adjust the amount of blow-off air, and maybe that is set too high.
Jon

Are you sure? That would render the machine basically incapable of picking up anything tiny from any carrier type. Maybe they've just hidden this feature somewhere obscure?
An incorrect value for nozzle size or pick height seems much more likely.

Yes, lots of stuff is hidden very well in layers of menu pages.  But, there are only timing values accessible in the vacuum handling page.  The machine does a very good job of picking up small parts from tape, but what I saw was that it would blow away the next-over chip in the waffle tray when it went to pick up the desired part.  The manuals are massively worthless, they just have pictures of the menu pages with minimal description of what the menu entries actually do.
I have to go in there and see how much blow-off air it is using, maybe I need to turn it down.
Thanks,
Jon

[SMTech]

It's not something weird like exhaust or a leak from the divert valve or venturi is it?

[jduncan]

Why is your machine doing blow-off above the tray?

Well, I think the valve for blow-off/vacuum is just a two-way valve, and you either get the blow-off or vacuum, no possibility to get neither of them.
I need to check this in the plumbing diagrams, but I think that is correct.  There are adjustable needle valves to adjust the amount of blow-off air, and maybe that is set too high.
Jon

Never heard of a machine like that. It is somewhat common to have a single valve that turns on vacuum, with backflow when it cuts off used as blow-off. But normal blow-off times are small fractions of a second, I don't see how it could function always-on.

[Doctorandus_P]

  After some thinking, I guessed that the blow-off air from the nozzles was blasting the next over chips out of the tray.

That's some clever thinking, but have you also thought about looking at your PnP to see what is happening?

[jmelson]

  After some thinking, I guessed that the blow-off air from the nozzles was blasting the next over chips out of the tray.

That's some clever thinking, but have you also thought about looking at your PnP to see what is happening?

It is actually hard to get down there and see.  The machine moves a very heavy gantry quickly, getting too close can be QUITE dangerous.  The mounting head is large, so it blocks the light and makes it hard to see exactly what is happening.
Jon