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BGA Tilt

Views: 2188

dave

#47399

BGA Tilt | 8 February, 2007

Hi All,

What is the cause of BGA tilt ?

I have a failed board and it seems to have approx 0.25 mm difference in height on one edge of the BGA to the other. It is notable under magnification.

Is this caused by to much time above reflow temp or not enough ?

Dave

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dwelch

#47400

BGA Tilt | 8 February, 2007

Dave, I had the same problem in the past. Use fresh paste and a slightly higher profile. My guess is that you may not be completly reflowing. It worked for me. If that doesn't work you may want to check the bga itself, make sure balls are universal.

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Muhammad Haris

#47423

BGA Tilt checks | 9 February, 2007

CHECKS FIRST that your BGA doesn't tilt from pick & place machine. SECOND lead free paste have some problem that it solder the component whereever pick&place put the component while solder pastes having lead, put the component on its PCB pad like a magnet then reflow it. THIRD follow the specificationS with respect to your REFLOW and SOLDERPASTE both regarding big components like ICs and 240pin QFPs.

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JAX

#47433

BGA Tilt | 9 February, 2007

Has the board been looked at under X-Ray? Have you built more than 1 of the boards in question? Do any of the other boards have the same problem? Have you made any changes to the profile between boards?

One side of the BGA collapsing during reflow while the other side does not reach temp could theorectically cause the problem, but the problem should be seen on more than one board. I would just remove the resistor from under the BGA.

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RDR

#47437

BGA Tilt | 9 February, 2007

Most likely either profile or I was thinking a cap! resistors are to thin to make the part stand up hehehe just a joke.

Do not follow the advice of weighting part, that is ridiculous, poster of that, if you have never done BGA before please do not post.

Russ

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#47448

BGA Tilt | 9 February, 2007

0.25mm tilt? That's pretty small depending on you BGA size. Is it failing? Or just your Q.E. being anal? What size BGA we talking about? What ball count? Just one board? Maybe cheaper to just repair.

Now assuming there is NO part under the BGA:

First check your board. Are all pads the same size? Most board houses will cheat on pad openings. If not check your Gerber to be sure you are asking for same size on all pads.

Next, check your part. Missing balls can cause tilt. Check your balls for coplanarity (on the BGA, not your pants).

Now check your stencil. All ball apertures the same? If so check for clogging. This is prolly the #1 reason for BGA defects (I know, I know, everyone blames the oven but the LAST process isn't always the PROBLEM process).

Check your print next. Getting a clean wipe? Is the print crisp? Got a way to measure it? If not check printer parameters.

Now check you placement. Is it placed on the pads or slightly off? Can you verify through x-ray (use a wet board)? Now if your placement machine is causing a tilt � you better check you board support or your nozzle. Something is seriously wrong if you can tilt-mount a BGA.

And now of course � the EVIL oven. It is possible to partially reflow a BGA. Kinda rare but is possible. Generally you either reflow or you don't. You can x-ray all you want, but unless you have a top of the line x-ray machine it is difficult to determine reflow from cold solder joints. If the BGA is in the middle of a largly populated area, you can just check everything around it. If everything else on the board reflow � then I'd suspect the BGA reflowed as well. Without knowing your board � hard to tell.

Fianally, is this board subject to multiple heat cycles? Two or more reflow solders, a selective solder, wave solder etc? If so it could be caused by a process you�d never suspect or are in charge of.

Now we patiently wait for the reply..........

Who posted to add weights? I gotta see that thread!

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dave

#47458

BGA Tilt | 9 February, 2007

Hi All,

Thanks for all the replies.

I am placing a 672 Pin BGA.

Its the only BGA on the board (Board size 220mmx100mx1.6mm)

We build these in batches of 400. So we have built approx 1200 since transition to Leadfree.

Latest batch had 7 fails - debug have related 1 so far to BGA - when pressure is applied to the BGA it works.

I would be happy enough with the reflow - since reading the thread I might focus in on the Placement on the next batch .

Thanks for all the replies.

Dave

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Wayne

#47545

BGA Tilt | 12 February, 2007

the center part of the BGA balls may not fully reflow or melt and cause BGA tilt, not functioning working (only press then work) and etc..... the simple way to solve this issue is to use low temperature solder paste, it can melt in between 220 to 225 deg C, and will not affect other components surrounding the BGAs, especially the heat sensitive components.

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Joe

#47546

BGA Tilt | 12 February, 2007

yup, current SAC has a lot of problem with large BGA balls. Just like Wayne explained earlier.

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