Pick and place

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Re: Pick and place

Postby bdring » Fri Nov 30, 2012 9:32 pm

That picture few posts back is a compressed air solder depositor. It gives a programmed pulse of air into a syringe. The nice thing is the syringes and various "needle" sizes are easy to get and pretty cheap. I use the same thing at work, only it is manual. The only automatic thing is the pulse length is controlled. If I want more for a DPAK tab, I just multi-pulse it.
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Re: Pick and place

Postby bdring » Fri Nov 30, 2012 10:03 pm

Here is our machine. The left thingy is the placer. The knob underneath rotates the part.

The right thingy is for the paster. We keep the syringes in the frige when not in use. You can see a few nozzles laying around of various sizes. The red and black thing at the end of the hose snaps to the top of the syringe.

It have foot switches to control the vacuum and parte pulses.

pnp.jpg
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Re: Pick and place

Postby cvoinescu » Sat Dec 01, 2012 11:53 am

Sorry, I did not realize that was a solder paste deposition machine; I thought it was a pick-and-place machine.

So, it's all "just" a matter of getting the software smart enough and unobtrusive enough that it actually helps rather than hinders the process, compared to doing it manually with no computer assistance/interference. That is an interesting challenge.

Trying to get an idea of what the workflow would be. Say, you want to make a few boards. Do you tip out the components you need from larger containers into, say, a shallow tray with compartments? I suppose you don't put all the passives in one pile, because you couldn't tell the capacitors apart anymore, and even the resistors would be a pain. If they are separated by type in compartments with a geometry known to the software, it shouldn't be too difficult to use a camera to locate the parts, turn them the right side up if needed (requires hardware: TBD), identify the polarity or orientation for the parts where that matters, and position them squarely. The user could then manipulate images of the components over the image of the PCB, with the machine following along and doing it for real, and repeating it automatically for any number of boards.

Again, the key is to make this software easy to use -- not necessarily in the sense that anyone could sit down and use it with no previous knowledge, but in the sense that it would allow a reasonably skilled user to work quickly without unnecessary hassle, and it would try to help while being smart enough to know when it doesn't know what to do. Basically, the user should feel they are working with the machine, not against it or despite it. This brings to mind the cheap sets of screwdriver bits that come with a handle. I have one with a plain handle -- it has a fairly thin stem (considering it takes a 1/4" hexagon), about 2" long, and a plastic handle of a decent size and shape. That is the good one, and I use it often when I need a screwdriver of a kind I don't have as a plain old single-piece type, e.g. hex or Torx (I keep 4mm and 6mm flat, Philips #1 and #2, Pozi #2, and stubby Pozi #1 and #2 to hand). Another set has a ratchet handle. It has no stem but a stubby 3/4" thick mechanism, and the ratchet feature is never useful in practice. Even if locked, the mechanism still has enough give to make the handle very annoying to use; and the shape of the mechanism and handle prevents access in many cases. Instead of a magnet, it has a leaf spring with a ball, and it's much harder to change the bits. That's the bad example, where a "feature" hinders much more than it helps. We don't want that. I always try to aim for the set-of-half-dozen-most-frequently-used-standalone-screwdrivers-plus-plain-screwdriver-handle-with-interchangeable-bits type of software, never the let's-add-a-ratchet-and-charge-a-dollar-more-and-make-it-useless-all-round type. :)
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Re: Pick and place

Postby zoominbc » Sun Dec 02, 2012 8:52 am

A prototype pick & place machine doesn't need to be fast but it does need to handle difficult parts like QFN's with a ground slug. It should handle cut tape and loose parts and should probably have a vision system to get part rotation correct. A paste dispenser is a good idea, and perhaps in a prototype machine it might make sense to localize the reflow with a laser or a moving heat block. Good luck with it.
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Re: Pick and place

Postby lasersafe1 » Thu Dec 06, 2012 4:11 pm

Just got an email sales brochure today from a company trying to sell "manual pick and place" machines. I'm sure many of you also received this email today.

They gave the following comparison in their sales pitch:
---------------------------------------------------------------------------------
Rate Comparison (for chip components)
Method Placement Rate @$25.00 hourly
Hand-tool 75-125 components per hour $0.33
Vacuum pencil 100-150 components per hour $0.25
Manual pick & place 600 components per hour $0.04
---------------------------------------------------------------------------------

Do any of you actually believe these numbers? I bought my cheap Chinese vacuum pencil with aquarium pump for around $50 and added my own solenoid controlled by a foot switch. I can easily place a component every 5 seconds when I have a reel on my left and 20 boards on my right. Why in the world would I invest in their "manual pick and place" for $2875.00?
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Re: Pick and place

Postby cvoinescu » Thu Dec 06, 2012 5:27 pm

That sounds like different assumptions for the vacuum pencil and the manual pick-and-place case. As you said, if you're doing the same component over and over, you can do much more than 150 components per hour. If you're doing a complex board with many different components, there's no way the machine would be that fast, not by any useful measurement.
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Re: Pick and place

Postby JeffsInventions » Mon Dec 10, 2012 4:08 am

bdring,
Thanks for the picture of the machine. I hadn't seen one like that before.

You said that one of the reasons that counted towards doing runs less than 20 parts manually was that "It takes time to setup the digital files."

What are the most painful parts of setting up the files? Is there something that we could do that would make it easier? Are there situations where you are making something that you will never draw? What percentage of all situations are those? Do you ever do runs of more than 20, but less than is economical to have done by a third party? If so, how often?


cvoinescu
We plan to add the ability to deposit solder in later versions of the machine.

Your point that the software, and the machine in general, needs to be easy to use is spot on. This is a primary consideration as we make design decisions for the machine.

I have mixed thoughts about your tray dumping idea. While having the operator put the parts in a compartmentalized case would make it easier for the machine to accept them, it runs counter to your idea of making the machine easy to use. Is there a way to make the machine accept parts as folks receive them from manufacturers/distributors, without an extremely complicated mechanism?


zoominbc
Your idea that the machine must must support difficult components is insightful. I was talking to a designer who makes embedded linux boards and he said that the only reason he doesn't do prototypes himself is that he can't hand solder the BGA's.

What is a ground slug? My brief googling seemed to suggest it is the plastic case that the chip fits into. Is that right?

Localizing heating is the leading candidate for reflow. I was thinking of doing it with a heat gun (e.g., http://www.amazon.com/gp/product/B004ZB ... 01_s00_i00). What would the merits of a laser/heat block be over a heat gun?
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Re: Pick and place

Postby cvoinescu » Mon Dec 10, 2012 12:05 pm

JeffsInventions wrote:I have mixed thoughts about your tray dumping idea. While having the operator put the parts in a compartmentalized case would make it easier for the machine to accept them, it runs counter to your idea of making the machine easy to use. Is there a way to make the machine accept parts as folks receive them from manufacturers/distributors, without an extremely complicated mechanism?


I was mainly thinking about the passives that come in arrays of little pill boxes -- you can't really have the machine pick them from the boxes, so you'd have to tip a few of them out somewhere. If the parts are on a strip, that's all the better, all you need is a simple holder for the strip and you can blindly pick them from there.

I'm trying to get a sense of the workflow from the people who do this for work. If all their parts for prototyping come on tape reels, then that's what the machine should use. If they tend to come in loose packs, the easiest solution I could think of was to tip them out on a flat tray and have the machine pick them from there. If it's a mix of both, the machine needs to be able to do both.
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