Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Vacuum Delta


Vacuum Delta | 27 February, 2002

This is just a general question. I'm no vacuum expert and I'm curious how pick and place equipment manufacturers are able to turn off and purge their vacuum systems and sense this so fast when they are placing a part on a board. Are they turning it off on the way down? Are they relying on the paste or glue to help pull the part off the nozzle? This seems pretty critical, even now with parts getting smaller. As far as sensing a part on the end of the nozzle, are some machines just assuming that the part was picked (I guess you'll find out with the camera) and then assuming that it was placed on the board?

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Vacuum Delta | 27 February, 2002

Doug, Depending on the machines in question, the release characteristics change. Most of the mechanically driven machines simply stop the vacuum by lowering the nozzle and release the stored vaccum at impact when the nozzle starts to compact back into the head through a spring, etc.. Some of the other Machines use a vacuum "kiss", where the part is actually pushed off of the nozzle. As far as sensing the part on the nozzle machines vary by either reading the vacuum level through out the placement process, Simply checking for availability during vision and/or mechanical alignment ( if this is the case and the part falls off after inspect and prior to placement, the machine will not know ), or some that do not monitor this at all. These are just brief answers to your questions, you should contact some of the different machine vendors for more accurate details and explanations. That's just my opinion, I could be wrong!

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Vacuum Delta | 27 February, 2002

In order to kiss off the components with an air blow, there are two times to consider: 1. reaction time of the solenoid ( to shut off the vacuum and turn on the air ), 5-10 ms 2. time required to fill up an air hose, which leads to the nozzle. Assuming air travels in sound speed, than air travels through a 1,000,000 m long hose within an hour or 16,666 m/sec. At least one air particle should reach the end of an 0.16 m long hose in 0.00001 sec. Travel time of the z-axis is approx. 30 ms in one direction. Measuring vacuum or air pressure is done within nano seconds.

Modern chip shooters locate a separate micro processor into the placement head in order to separate some tasks from the main processor and gain some milli seconds.

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