Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


BGA rework

Vijay

#27530

BGA rework | 7 March, 2004

Hello , Can any body help in solving the problem of PCB warpage during BGA rework. I am using IR heating system. No problem found in reworking BGA's size less than 30mmx30mm but for 35 mmx35mm and above BGA get solder short due to PCB warpage. Note this warpage is just like a buldging of the PCB at the BGA area. Thanks,

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#27533

BGA rework | 8 March, 2004

Sounds like you have some delamination problems. How hot is the board getting? Try baking the board prior to rework. Is the quality of the board good? Goog Luck.

MrMaint

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#27534

BGA rework | 8 March, 2004

Good Morning Vijay,

It sounds like the PCB is getting too hot at rework. Is there any way to attach a thermocouple to check actual temps? This would give you an idea if it is your process or your PCB.

Good Luck

Chris

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RDR

#27536

BGA rework | 8 March, 2004

Is this problem really related to the size of the BGA OR the size/thickness of the PCB? Would I be correct in assuming that your pre-heater is small in size? Usually a board warps like this when the ramp is to great at the localized area. the immediate area gets very hot and as you go outward the board ends up at ambient temp. So you have the local area expanding at a much greater rate than the rest of the PCB. Try slowing down the pre-heat to allow for better heat dissipation through the board. Sometimes it also helps to raise the nozzle off the board surface anywhere from .05" to .25" depending on what you see. Also, if the board is layed out with a large copper plane that is not symetric to the area this can give you fits forever.

My thoughts

Russ

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Bryan

#27559

BGA rework | 9 March, 2004

I never met such a issue.I use SRT1100&Freedom2000,and they works well with BGA larger than 3.5x3.5cm.

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#27580

BGA rework | 9 March, 2004

Vijay: Questions are: * Where are the shorts occuring? * Would you please describe your preheat / underside heating methods?

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Vijay

#27584

BGA rework | 9 March, 2004

The shorts happen at corner of the BGA. The PCB thickness is 1.6mm, It is a PC motherboard with all thru hole connectors mounted on.The preheating is done using IR heater and the temp is 120-160 for about 70-80 sec.I am using ERSA IR550A

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Vijay

#27585

BGA rework | 9 March, 2004

The shorts happen at corner of the BGA. The PCB thickness is 1.6mm, It is a PC motherboard with all thru hole connectors mounted on.The preheating is done using IR heater and the temp is 120-160 for about 70-80 sec.I am using ERSA IR550A

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#27586

BGA rework | 9 March, 2004

Warping BGA are the usual cause of shorts in the corners and are usually caused by the reflow profile. BGA have a natural tendency to warp due to CTE and package thermal mismatch, as you have seen at rework.

The PBGA will go from a bowl shape to an upside down bowl shape as the various components in the BGA reach their Tg and their respective CTE change. CTE is temperature dependent and not temperature changing rate dependent, so you are pretty much hosed by the physics.

However, we do like trying like hell to get the top and bottom of the BGA the same temperature before entering reflow. Moving into reflow slowly so the paste has time to become liquid before the BGA begins to dance. This means a long soak before reflow. Although, we will admit this is probably wishful thinking since the physics of CTE doesn't care about the rate of temperature change.

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Ken

#27591

BGA rework | 9 March, 2004

Is this a PBGA? If yes. run a flat steel rule or edge across the top of the PBGA. Is it flat or cupped?

Is this a TBGA (super bga). I have seen issues with a suppliers heat spreader design that actually will deflect the corners down and raise the center of the device. I actually shot a video of this happening in the reflow process (at 360 mag.) because my supplier thought I was an incompetent Manufacturing Engineer that had just fallen off the truck!

Make sure your board is not warping upwards and pressing the part into the nozzle- causing bridges.(done that)

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#27599

BGA rework | 10 March, 2004

We have the expertise of mounting and rework of all types of bga without facing any problem. If you want or you can give us one oppurtunity.

K S Walia Xo Infotech Ltd. India

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Steven

#27634

BGA rework | 12 March, 2004

Sorry for the late reply, I am an ersa dealer may I suggest mounting an alternative thermocouple attached to a DMM in close proximity to the BGA. See what the differences are in your readings from the DMM and the Digital temp reading on the IR550A. It may be that the Ersa display is not accurate. If this is the case have the system checked. If not then abide by the above suggestions.

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Jed Johnson

#27658

BGA rework | 18 March, 2004

A few good points have been made here: The profile could be ramping too fast. The profile could be gettting too hot. The profile may need to have more "soak" time before reflow to allow the board temperatue to equalize and the board to "relax" and stop "reacting" to the heat being applied. The thermocouple could be giving incorrect readings due to being out of calibration.

I have seen a couple of examples where heating up the board up to reflow and then "shutting off the heat" can cause warpage in the BGA package itself. This is because the package and the board both "react" to the rapid change in temperature, but they react differently. In these cases I have added an additional process step after reflow which reduces the heat being applied to control the cool down until the package is at or near the solder melting point. Granted, I am suing convection, not IR, but the effect of the profile should be very similar.

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george

#27664

BGA rework | 19 March, 2004

Vijay: If you are still having difficulty or are frustrated with your yields try http://www.solder.net. They work on the most difficult packages and boards.

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