It sounds from this and previous postings "that in view of your demanding application
it might be better to use a higher specification needle than the standard type
normally supplied". Or whatever your present supplier is saying.
Such a higher specification might be one in which the moulding around the steel tube
does not have sudden cross sectional changes and no internal reverse re-entrant
shapings.
You can get these OK from people like EFD. So far as tube length is concerned these
suppliers also make a shorter length, but still long to allow manual access. No
reason why you should not cut them down, provided you can get a good finish. I
suggest a length no greater than 5-6mm.
It just might be worth investigating the type also supplied for solder paste
dispensing. These are made entirely of polysomethingene. And are a conical cross
section from fitting to dispense end. The problem is they can be flexible and may not
give precision placement accuracy.
Reverting to your question on internal finish of needle:
From what little I know about laser machining I suspect you would have great
difficulty making a smooth hole of this size and length. Irrespective of that,
whatever method you use to correct the internal finish it would be especially
difficult to build a tool to hold the needle and get the alignment you require.
So as an alternative you could make your own theoretically perfect ones. These would
consist of a hemisphere internal shape with a projecting tube just long enough to
clear the external body of the hemisphere from the substrate surface to prevent
smearing.
This would be much easier to make.
I now recall visiting a company once that is using these, or at least was about 18
months ago, in high speed component manufacture, I believe they made them themselves
but if you become convinced this is an answer then I will try to remember where and
who they are and see what I can find out.
Mike Fenner
BSP, OX15 4JQ, England
T: +44 1295 722 992
M: +44 789 999 7715
F: +44 1295 720 937
-----Original Message-----
From: Ingemar Hernefjord (EMW) <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 06 September 1999 11:59
Subject: [TN] Clogging dispensers soon...
>Rescuers of going-crazy-dispenser-technicians, Morning to you all,
>I must have a talk with you between 1,600 eyes. Take a chalk go to an airport and
paint two paralell lines, 1000 meters long and 150 meters apart. Then make obstacles
here and there that makes the path only 100 meter wide or even 75 meters. This is
your runway for taking down a Galaxy. Could go, but what if you have some Cessnas att
the same time? That's what the silver flakes have too pass in a 10mm long syringe,
with a nominal diameter on 150um, a minus tolerance upon that plus other obstacles on
the walls. Now,
>
>a ) suggest that you get some flow hindrance near the syringe's outlet, caused by
large flakes agglomeration, what will happen the nearest tenths of seconds after the
auger stopped dispensing? Won't there be a small overpressure on inside of the
syringe? And won't that small overpressure decrease simultaneously with the small
amount of paste that passes the obstacles and comes out of the syringe? Can this be a
reasonable theory why we see small amounts of paste dripping out from the syringe
when the robotic make a secon or two pause?
>
>b) won't it be a problem for all flakes to pass all these 10 mms long syringe in a
80-150um channel, especially if many flakes differ from the paste's medium size, I
mean 30-50um instead om 5um? And won't it be even worse if som flakes agglomerated
already in the pump before coming to the syringe?
>
>c) coming finally to my proposal. If you cut your syringe to, let's say 2mm length
instead of 10mm, won't the whole problem be much smaller? IF there is still some
obstacles, the volume on inside the syringe is much smaller = less leakage of paste
between dots (pauses), because built-up pressure will go down much quicker. And the
clogging risk ought to be much smaller even that, won't it because 4/5ths of the
tunnel is gone.
>
>Aussilek use to be brightest, but there ought to be more with (he-he). Severe
question: am I right? Please, say da. If the theory seems OK, we will make a very
rapid effort in order to get the precision line running /
>
>Ingemar Hernefjord
>Ericsson Microwave Systems
>
>PS. Following question: with a 2mm long syringe, could laser be way to remove
remaining obstacles so that a 150um-minus75um- syringe becomes a true 150um syringe?
Or jetwater? Or sandblast?
>
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