Hi All!

There was a thread the other day about IR rework stations, and I was going to
post, but I got side-tracked. So now I will...

We've got a PDR Lightmaster Pro focused IR light station here, and it's about
the slickest station I've ever worked with. We previously had a OK Systems
(now Metcal) BGA 3000 hot air station, so I've worked with both types. I've
posted some pictures on my web page (http://www.stevezeva.homestead.com) that
will illustrate the things I'm talking about here.

This station does amazingly well in high thermal mass situations. The first
picture is of an assembly that is bonded to a 3/8" thick aluminum heatsink,
and had a 352-pin ceramic QFP bonded to the PCB with loctite 3615. I used
this scrap assembly when we first got the station to see if I could get the
part off the board. It was next to impossible with the hot air station. The
picture speaks for itself. It did take a cycle of about 8-minutes to get the
part off, and I did have to do a little prying. But it came up and I didn't
lift any pads or damage the PCB.

The next picture is a section of an assembly we're going to be building soon.
This picture is of a sample board that I got to help me develop reflow and
rework profiles. This is actually the commercial version, we're ruggedizing
it. But the layout is going to be the same. As you see, getting a nozzle down
around these BGA's is impossible. That's the beauty of this system, no
nozzles are needed, you just open or close the aperture of the lense to fit
the size of the part.

The next picture is of a 625-ball Ceramic BGA that I'm going to remove from
the assembly. I have a thermocouple attached to a center ball in the device
in which I drilled into the bottom of the PCB and attached it.

The next picture shows the application of a thermal conductive tape that
comes with the station. The tape is reusable a number of times. This tape is
needed on devices such as the BGA I'm removing because of the white color.
You would use it also on anything reflective such as a metal slug in the top
of the part...like the gold colored one on the 352-pin CQFP in the picture
earlier.

The next picture is FLAME ON! It is going through the heating prior to
removal cycle now. In the picture you will see two non-contact thermocouples,
one for the PCB temperature, and one for the part temperature. These are
monitored by the software and provide for a closed-loop feedback controlling
the power of both the bottomside heat, and the rework head power to follow
the profile you've set for the part.

The next picture is a screenshot of the software display, this is actually
during the removal cycle. You just click and drag the profile lines for the
part temperature, and PCB temperature to whatever setting you want. You can
also control the times used in each section of your profile by clicking and
dragging the time lines. You will also notice there are three colored lines
on the display, a red for the part, blue for the PCB, and the yellow line is
the wire thermocouple that I have actually embedded inside the BGA. You can
attach up to 6-more wire thermocouples and give them each a different color
on the display to closely monitor temperatures. You will see that there
actually two sets of red and blue lines on the display. The straight ones are
the set points in the profile, the ones that aren't so straight are what the
non-contact thermocouples are seeing and feeding back to the software. The
PCB temperature looks like it's lagging a bit, but it catches-up when it
starts getting into the reflow end of the profile...actually this is pretty
typical. But you can see that the part temperature is following things pretty
good.

The next picture is actual lift-off of the part...about 4 1/2 minutes...

The system has the same sort of vision placement system that a lot of other
systems do. It's a split-prism system where you view the balls and spheres at
the same time, and then use X/Y and Theta micrometers on the workboard holder
to line everything up for placement.

This is a great machine in my humble opinion, and can do some things that a
hot air system can't...

-Steve Gregory-

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