Alexandre Guimar=E3es wrote:

> > How accurate do you need for 0805 placement? I'm sure
> > even 0.1mm will be ok.
>=20
>     Absolutely... Even 0.5 mm should be ok if it is repeatable and not
> cumulative.


>     You are using mechanical tweeezers because you like to suffer !!!! =
:-)
> Just get an aquarium pump and get you vacuum tweezers done with some ho=
t
> glue !!! It is very easy.. Many aquarium pumps can be altered to make
> vacuum. You will need very little vacuum and the needles can be bought =
in
> any dimension you want from www.smallparts.com . You can also use a
> hipodermic needle number 8. works as a charm if you cut it carefuly wit=
h
> small pliers and sand it afterwards. For the handle go to the medical
> equipament store and by some "silicon tubing". You do not even need to =
turn
> the vacuum on and off ! Just use the right vacuum and it will pick up t=
he
> parts without solder paste and not pick up after they are put over the
> solder paste !!! It works and is fast and easy. You just have to play a=
round
> to make the "right vacuum" and a comfortable handle.

You are a legend Alexandre. :o) I have an aquarium
air pump and some needles I bought to use with
the solder paste syringe. Are these the right
type? So you just use the metal tube needle,
filed flat on its end, as the bit that touches
the SMD? I thought it had to be rubber or something
but your way sounds very easy to make. The aquarium
pump hose will match up to my vacuum solenoid too,
same size rubber hose.

> > How do you mix the water with the paste, what sort
> > of applicator nozzle, pump etc are you using??
>=20
>     DO NOT MIX the paste with water !! You can put water behind the syr=
inge
> and after your solenoid air valve ! I do not use it because my people p=
refer
> to control the dispensing time by hand and I just use a solenoid air va=
lve
> and a pressure regulator set to about 20 PSI. The water will help when =
you
> are doing automatic timed dispensing and you need as little variation a=
s
> possible. If you are dispensing by hand it is not needed.

Ok, I understand now. With regulated pressure and
controlled time you can get fairly exact quantity
of paste dispensed. But is this suitable for the
repeated tiny paste spots needed to use 0805 SMD
parts?? And does the consistency of the solder
paste change over time and cause problems with
dispensing an accurate spot each time?

> > I thought
> > of standard size rubber hose in a simple peristaltic
> > pump turned by a stepper motor. That should dispense
> > dots and also lines of paste quite well.
>=20
>     I use a paiting air compressor. They are cheap and work very well. =
Just
> have a big air cylinder and you can turn the compressor on just once or
> twice a day. I live the air line with just 40 PSI on it so I have very =
low
> risk. I tried many small pumps and they all make too much noise and end=
 up
> costing more than a good membrane pump. Just go to the hardware store. =
For
> the cylinder to hold air I use disposable freon cylinders. Very cheap (=
 free
> most of the time) and reliable enough for 40 PSI ! The solenoid air val=
ves
> should not be hard to find also.

It is so great to hear from someone actually
doing it. Experience is quality. :o)

>     We should talk off list about this.... Sound like a very good idea =
to
> make the mechanical problems smaller.

Will do. :o) But i'm hoping that people aren't
objecting too much to this SMD CNC topic? I would
think there must be a lot of us doing small
quantity manufacturing that would like a cheap
SMD pick and place machine.
-Roman

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