Jenny,
Many of the larger connectors we place come with a small plastic, disposable
vacuum pad that is clipped into the part prior to being tape and reeled.
After reflow they are removed. This allows a greater surface area to
develop force and is a guaranteed seal. The equipment we use also allows
the programmer to describe the acceleration profile to slow down placement
of difficult to handle components so 3G acceleration may not be required.
Thanks for spending the time up front.
Regards,
Martin
-----Original Message-----
From: Jenny Drake [mailto:[log in to unmask]]
Sent: Tuesday, June 06, 2006 2:03 AM
To: [log in to unmask]
Subject: Re: [TN] Vacuum pick up nozzle area for component weight.
Thanks for the replies so far. A little clarification on why I am asking
the question. We are designing a small surface mount connector, but we
won't be assembling this component ourselves, so I can't test it with
the machines that will be building it. What I am looking for is any
guidance on the flat surface area that will be needed to ensure that it
is unlikely to move about on the pick up tip as it is accelerated across
from the pick to place positions. "As large as possible" isn't very
large on this thing.
If I take the largest flat circular area on the part, take off the
tolerance of the part in the tape, then that gives me a maximum pick up
tip inside diameter. From a reasonable estimate of the vacuum level I
can then get the holding force. If I then guess a coefficient of
friction between nozzle and part I can use the weight of the part to see
if, say, a 3G acceleration is going to be too much for the holding
force. Is this a good approach?
Jenny
-----Original Message-----
From: Jenny Drake
Sent: 05 June 2006 15:49
Subject: Vacuum pick up nozzle area for component weight.
Is there a good rule of thumb for determining the minimum vacuum pick up
nozzle size that will work with a component of a given weight? I am
guessing that the problem is reasonably complex as the component mustn't
move on the nozzle under lateral and rotational acceleration as it is
moved from the tray, or tape, to the PCB. The strength of the vacuum,
the friction between the nozzle and component materials and the centre
of gravity of the component will all affect this for a give component
weight and machine acceleration. Is there a simple rule that people use
that gives good results?
Jen
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