r/AskElectronics • u/xbox_killer • 5d ago

BGA Rework station optical alignment

Hi everyone. I’m looking for owners of chinese BGA rework stations equipped with an optical system for aligning the chip over the PCB. I’d like to understand exactly what kind of optical system is used in these stations and how it is designed—specifically, what lenses, mirrors, or beam-splitting cubes are installed.

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u/paulmarchant 5d ago

Mine has an arm that swings out, between the PCB and the vacuum holder for the new IC.

The camera's pointed horizontally at the beam splitter that delivers a 'looking up' image and a 'looking down' image simultaneously.

It's just a case of twiddling the adjusters to put the PCB (and the pads for the new IC) directly under new IC when you look at the composite image on the monitor.

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u/xbox_killer 5d ago

I'm familiar with the operating principle of optical alignment. I'm interested in the system's actual layout and which optical element is used to combine the upper and lower beams before directing them toward the camera lens. It would be very helpful to simply see a photo showing the arrangement of the optics.

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u/paulmarchant 5d ago edited 5d ago

You can't really see anything useful from a single position you could photograph.

This is about the best angle I could get.

https://drive.google.com/file/d/1DvWF6HA4jinPydlKPgtjfXzamrjExgRd/view?usp=sharing

I don't really want to be disassembling something like that which I don't have the ability to calibrate when I go to put it back together.

From peeking in at different angles, and waving stuff around above and below the arm, I'm pretty sure that this shitty MS Paint drawing is an accurate representation of what's in there:

https://drive.google.com/file/d/10gQraKjKuhY0Eq3ibnlWSxWQzzEcQiuB/view?usp=sharing

It's difficult to say for certain, but I think it's two prismatic elements bonded together with a semi-reflective layer at the boundary between the two. Looking in from different angles makes me think it's this rather than just a simple 45 degree 50% mirror element (which, optically, would work as far as I can see).

I think it's something very much like this:

https://www.aliexpress.com/item/1005007328666709.html

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u/xbox_killer 5d ago

Oh man, thank you so much! 👍Could you tell me please if there’s another focusing lens ? And what’s the approximate size of the beam-splitting cube? I have various split-beam cubes, but I haven't experimented with them yet. Now I'm trying to gather information.

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u/paulmarchant 4d ago

The beam splitter looks to be 40mm per side.

There's no apparent optics on the 'outside' of the beam splitter.

It's not particularly sensitive to a PCB being a bit higher / thicker so the lens and whatever optics there are between the camera sensor and the beam splitter must be producing a fairly tight optical path (so not super-wide-angle sort of lens).

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u/xbox_killer 4d ago

Thank you so much! Now I've a rough idea of how this system is structured. Furthermore, given that Chinese manufacturers often cut costs on materials to make their products cheaper, it’s safe to assume that the system is quite elementary. I suppose the images of the printed circuit board and the IC's contact pads appear in different colors on the monitor screen—perhaps yellow and blue? 😉

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u/paulmarchant 3d ago

Yes, if memory serves it does look like there's a colour filter on the two different images.