Agree with you 2, we use a 300kV Realtime FineFocus monster, all facilities with noise reduction, image processing and such stuff. It's a fantastic machine, really, but it's still hard to define what you see under the BGAs. If there is a short, of course you will see it, but the electric test will also reveal that, and at much shorter time. We have eyed through kilometers of Xray b'n'w film and scratched our heads, because what we want to see is the microworld events under the BGAs, the macro is not a problem. So, best tool is simply to lift off a number of packages and make other forms of analysis....and put an adjusting parameter into the process. OK, I may simplify...but here we are simple people.
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: den 31 maj 2000 03:07
To: [log in to unmask]
Subject: Re: [TN] To X-ray or Not to X-ray.
In a message dated 05/30/2000 5:12:43 PM Central Daylight Time,
[log in to unmask] writes:
> >Help,
> >
> >My company is asking for information leading to the possible purchase of
an
> X-ray machine for BGA s.
> >
> >We are placing some with metal tops such as the ALTERA. ANY info on who,
> what, where, etc. etc. etc.
And then Jerry wrote:
> Having an X-Ray machine just to find shorts on BGA's after soldering is
> overkill. What you may want is the ability to make judgements about the
> amount of solder, the voids, and the wetting. This requires laminography,
> sophisticated image processing, a trained technician, and then you have
> indications which can be used to make logical inferences, not necessarily
> clear cut process measurements. (I've seen my brother arguing with other
> radiologists about the meaning of images, and he wrote a chapter in one of
> the medical texts...)Your mileage may vary, etc.
>
>
> cheers,
>
>
> Jerry Cupples
> Interphase Corporation
Hi Barry!
This is my opinion and I want to express myself in the same terms as Jerry's
caveat. I've just run across a similar situation as you are finding yourself
in with the Altera parts, but my situation is with Texas Instrument parts. It
seems the trend for BGA devices is to use a heatsink in the top of the part
for heat dissapation. The lower powered systems will not penetrate these
devices and give you a decent image.
I will admit that the system we have here was only used for gross defects,
such as bridging, like Jerry said. I have to admit that IS overkill.
Transmission X-Ray (looking straight down) interpretation depends on the
skill of the technition to interpret any detail of the images just like Jerry
said.
There is no way that one can absolutely determine where voids are located
without a LOT of experience and probably a destructive cross section to
validate the images with just straight-through transmission x-ray. Just like
Jerry also said, x-ray laminography (which is at least $500,000, I haven't
priced them lately) or maybe a Fine-Focus machine which has a real-time
rotatable emitter and can get down to the nitty gritty...but you're talking
some money there too.
The next best thing is the ERSA-Scope. This is a really neat tool and I'm
pushing my management to buy it, it's 30K fully loaded. It can look beneath
BGA's and you can actually see the quality of the joints. You can also see
how well you clean beneath them, not something you can do with x-ray. It does
have a problem with staggered-grid arrays, because you won't be able to see
from one side to the other, but I haven't run across a staggered-grid BGA
yet..not to say they're not out there, but I haven't seen one yet. There's
other things the ERSA Scope can do, measure solder paste height, really look
and quantify the heel fillets of gull-wing devices, and much more. I don't
have any interest in ERSA-Scope, just practicing my pitch to management...
hehehe.
Oh, BTW, you can check things out at: http://www.ersa.com/ersascope/index.html
One last thought, how come we started worrying about solder joints that we
couldn't see with BGA's? If I remember correctly, we all were putting
capacitors beneath parts LONG before BGA's that we couldn't inspect...but we
didn't worry about it back then, did we?
-Steve Gregory-
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