Beginner needs help - video of underside BGA device

[anmb]

Hi
I am a total optics novice and I am trying to design a low cost device to display a video picture of the underside of a BGA chip soldered onto a PCB.

I wondered if I can feed a very small fibre optic(<>1mm) under the chip and with some backlight get the result into a CCD camera.

or use a very small mirror to angle the image upto a CCD camera from the edge of the semiconductor chip.

My question - what is the best way to get a video signal of the underside of a BGA chip that will have a gap of a mm or about ?

Are there any easy to follow newbie guides to light paths, lenses or anything that may help my understanding of the problem.

thanks Roy

 

[IRstuff]

You can't.

You need to describe what you're trying to see, exactly. Looking at an expanse of grey ceramic doesn't strike me as worth the effort. Anything else really requires an X-ray system.

TTFN

FAQ731-376

 

[MacGyverS2000]

A 1mm gap would actually be quite extreme for most large-array BGAs... the balls themselves aren't that large in diameter, and once you heat them up for soldering, well...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

according to:

http://www.dogpile.com/clickserver/_iceUrlFlag=1?rawURL=http://

http://www.senjucomtek.com/images/t...23=0&40=0NUIuF8ZdYgZHIS1A3V9qA==&_IceUrl=true

solder balls go down to 0.1 mm diameter.

TTFN

FAQ731-376

 

[anmb]

Thanks all, for the replies.

I realise that the gap would be smaller than 1mm, I just wondered if it was possible to have some sort of fine fibre that would allow you see the condition of the underneath of a BGA.

I know technology exists to view the underneath by video using a right angled mirror of some sort at the edges of the BGA.

My objective is to find some way of optically seeing underneath a BGA as xray is not feasable for the occassional user, and any help in seeing the general condition of the balls and their alignment would be of benefit.

thanks Roy

 

[ykee]

What are you trying to accomplish?

 

[anmb]

I am trying to see the condition of the balls under the bga and check alignment etc.

thanks Roy

 

[ykee]

There are lots of machines that check chip alignment. this does not have to be done based on the underside of the chip, but rather can use the top. Even if you could get a view of the underside, a visual check may not tell you whether or not you've got cold solder joints.

 

[IRstuff]

You really need to do x-rays.

You are expecting too much from optical. Only the outer row, or two, are visible to any degree. Anything further in, you'd only small portions of the balls.

TTFN

FAQ731-376

 

[anmb]

OK so its looking difficult to achieve visualy without xray.

Assuming a dry/broken joint beneath the BGA, and I remove the BGA, reball it with solder.
I manufacture a device using mirrors and a beamsplitter to combine the 2 images from, below the BGA and above the target pads on the pcb to align it(see attached or

http://www.anmb.co.uk/beamSplitter.jpg)

Would that be the best way to position for resoldering the chip or is there an alternative way ?

If the attached is OK how do I:
1. calculate the size of mirrors
2. calculate magnification needed to zoom in on the corner for example
3. calculate dimensions for positioning the mirrors for a 1/3" CCD with zoom and any BGA ranging from about 9mm upto 40mm
4. how do I focus my combined image for diplay on a monitor
5. what kind of beamsplitter would I need ie. size, type etc.

thanks Roy

 

[MacGyverS2000]

You are trying to solve a problem that was solved many years ago, and your version of the solution adds nothing but complication with no benefit.

Alignment is done through fiducials when installed by machine and by eye when installed by hand. What's the purpose of your huge periscope with multiple mirrors when it has to be moved out of the way long before contact?

Dan - Owner

http://www.Hi-TecDesigns.com