>
> THANKS Alexandre for the excellent info you
> provided,
> and sorry I didn't reply sooner but I have been busy
> in the workshop. :o)
>
> > > it has good power, high speed and 1/28th mm
> > > resolution is fine for 0805 SMD stuff.
> >
> > How about the repeatability and backslash ?
> Those are the problems I
> > have seem on the printer mechanisms I used. The
> printing head support was
> > too loose without the belts being too tight.
>
>
> It depends on the quality of the printer mechanism.
> I have some 15" NEC Pinwriters from mid 80's that
> are VERY rugged, full steel chassis and 2 large
> steel
> rails. Some of the smaller printers are not good at
> all. One of my 15" printer chassis cost me $5 and
> has a 25mm hardened rail with PB bearings! Don't
> ignore good old printers.
>
> I just chose a chassis to make a CNC PAP (PNP?)
> machine,
> it's a 15" unit with steel cable drive from motor
> to carriage, even less backlash than a belt. Even my
> belt chassis get a lot less than 0.1mm backlash, the
> cable driven unit will be good for 0.05mm
> repeatability.
> How accurate do you need for 0805 placement? I'm
> sure
> even 0.1mm will be ok.
>
> > Do you need just one machine ? I plan to have
> a solution that can scale
> > up with my production. That is another reason to
> go for comercial new parts.
>
> Sure, but you are obviously doing the volumes to
> need
> good machinery. I'm still sticking parts on boards
> with tweezers and a magnifying glass! The thing i'm
> making will do 300mm x 120mm, perfect for pick and
> place on small boards.
>
> > Loctite has some nice solutions in that area
> and you can even use 454
> > gel cyanoacrilate !! It works great !! The only
> problem is that you need a
> > good dispenser for it. Dispensing paste is not
> that critical, specially if
> > you use water at the end of the system. Water does
> not compress so it is
> > easier to control the time and pressure as the
> syringe goes down. You just
> > have to control the time and pressure and it is
> quite repeatable.
>
> OK, you've convinced me to drop the glue idea and
> just dispense solder paste direct to the board. :o)
> How do you mix the water with the paste, what sort
> of applicator nozzle, pump etc are you using?? 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.
>
> > Wave solder is ok if you glue and have a very
> controlled fluxing and
> > cleaning of the board but I would never trust
> dipping a critical board ! You
> > will stress every component over their specs !
>
> Not totally true, but i'm going to trust you and
> stick to the paste and oven method for now as you
> suggested. You helped me so much before with my
> manual toaster oven system. :o)
>
>
> > If the production is too big I would go for
> the comercial machinery or
> > let a factory do it for you. It may not be worth
> the risc. My production
> > levels do not allow sending them out and I cannot
> handle it without some
> > automation, that is the reason I went to the house
> made solution. It is
> > dependable and repeatable but not too fast or
> energy efficient.
>
> My oven system is working well, thanks in part
> to your temperature charts etc. I'm approaching
> that point where it's a pain to tweezer tiny parts
> by hand, and a machine that does the SMD placement
> will be a big help. But I don't need high speeds
> or quantities.
>
>
> > > I have a suggestion here. Get the parts loose,
> > > not on rolls. Sprinkle them on a white tray,
> > > then use a cheap video camera into the PC and
> > > just get the picker to identify the part
> > > orientation and pick it up. You only need a
> video
> > > still capture board,
> >
> > Hey, that is a really cool idea ! The main
> problem would be to correlate
> > the real position of the components to the
> distorted camera view and to
> > solve the problem of refilling the trays and
> making sure that you do not
> > have one component over the other or on the back
> side when using SOT23
> > transistors ! It is pretty hard to get the
> components out of the rolls and
> > not flip half of them on their back side. I am
> really not sure what would be
> > easier, a roll feeding system or the camera.
>
> You don't have to buy on the roll. In 1k
> quantities you can often choose loose or rolled.
> I see the only real work is pouring the parts
> on a tray, making sure they are right side up.
> Parallex error shouldn't be too much problem if
> the camera is 40cm or so from the tray. I can live
> with some manual parts fiddling, anything is much
> better than placing with hand held tweezers. :o)
>
>
> > Believe me on this one :-) It is easier with
> the vaccum tweezer. You
> > just turn the vaccum on and them rotate the
> component to whatever position
> > you need. With the mechanical tweezer you have to
> get the right force and
> > will have to rotate the head 2 times to get the
> job done. The first time to
> > grab the component and the second to put it at the
> right orientation at the
> > board.
>
> Ok, you've sold me on the vacuum tweezer. Are tips
> commonly available? What type of vacuum pump are
> you using? I have a vac solenoid from a bike fuel
> injection system, a high speed one. Any suggestions
> on how to set it up? Does it ever drop parts?
>
> > > Gluing is also safer for
> > > double sided boards??
> >
> > I also thought that way and got glue from
> loctite for the components on
> > the bottom of the board. I still have the glue on
> the fridge and never used
> > it after the first day ! The only components that
> insist on falling once in
> > a while are the AVX surge supressors. They are
> pretty dense and fall once in
> > a while. If you get the right solder paste the
> surface tension is more than
> > enough to hold the components on the bottom side.
>
> Good information, thank you again.
> Any help you can provide on the CNC PNP stuff
> will be very much appreciated. :o)
> -Roman
>
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