RE: [CAD_CAM_EDM_DRO] automated "labjack"

Your right Archie, but that’s a different technique.

Wave soldering is normally for conventional through hole components, and
there are insertion machines that crop, preform and automatically place
through hole components in the holes.

Then there is a tank of hot solder which either flows in a down hill line
over a stainless sheet, or is pumped up over a ridge so as to form a moving
wave of solder, it needs to be kept moving to keep it properly fluxed. The
PCB is then suspended above this wave so it laps on the bottom of the
components and solders them.

I haven’t been to close to these machines so my experience is slightly
suspect, but I think that’s about right. I know one company I worked with
there wave solder machine had £18,000 of solder in it, and if you switched
it off you had to dump the solder refill it. Ouch. None of us here have
that kind of money, or the money and turnover to keep one powered all the
time.



There are precision wave soldering machines that use a little pot of molten
solder and small stainless plate they pump the solder over with a stainless
paddle. They then move this around by a CNC machine like an upside down
router table to selectively solder only the areas needed, many of us could
afford to run one of these, and it would be a good project for many of us,
but most of us are trying to move away from through hole components and on
to surface mount.



What we have been discussing today is surface mount soldering technology.
The solder is bought in a paste, it is applied to the PCB either by screen
printing, or by a syringe with the paste in it on a CNC head, normally the
head of a pick n place machine. The pick n place machine then puts the
components onto the PCB, these are what we call surface mount components, no
holes they just sit on the copper pad, and hope the paste is sticky enough
to hold them there. Sometimes they are glued, and sometimes some poor sole
mounts them by hand, did this as a student. Then we put the PCB through an
oven to melt the paste. Some of the ovens have conveyers, some are box
ovens, and some people use modified household toasters, grills and desktop
ovens. There is a special controlled temperature cycle for the oven, you
can’t put heat in too quickly, you have to wait for all the parts to reach a
temperature that they are still safe at, getting as much thermal energy into
the parts as they can stand, then there is a quick cycle to push it up to a
higher temperature for a short period of time, too short to cause any damage
but just enough for the solder to melt and flow. Most then use a set of fans
to cool things down.



I am also new to this technique having just bought all the kit to do it, But
I think I have covered most of it for you correctly.



The only other techniques I know are welding, presently this is a laboratory
technique, or used direct on semiconductor dies, but the equipment is
starting to get cheaper and find it’s way onto ebay. Many of us believe lead
free solder is going to cause us reliability issues, and there are those
that believe welding will be the next circuit production method. Who knows
what the future will bring, I haven’t a clue how to terminate to a slugs
brain.



Hope that helps,



Regs Mark



Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

RSGB DRM111(Cornwall)

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Archie
Sent: 28 March 2007 19:40
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] automated "labjack"



It is my understanding that when boards were soldered commercially the
boards were stationary and a wave was created that deposited the solder
on the boards. But what do I know.
archie =) =) =)

Graham Stabler wrote:

>
> I've been thinking about an idea related to solder/adhesive dispensing
> on PCBs. The idea requires a short stroke z-axis but it would be much
> better if it the PCB itself could be lifted rather than moving the
> head up and down for various reasons.
>
> Lets say you want to move a pcb up and down by about 3mm or so and
> quickly making sure that it all moves by the same amount. Is
> something like a lab jack the best bet or is there something cleverer?
>
> Graham
>
>

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