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

#28287

BGA Rework | 28 April, 2004

Hello All, I am having trouble with bridges under my BGA's.I am using paste flux. The compresion on the component appears to be good but i am seeing bridges every 1 out of 5 reworked. The alignment before it starts reflowing the part is fine. Dont under stand how a bridge can form without the application of paste. Help!!!!!

Thanks

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RDR

#28290

BGA Rework | 28 April, 2004

Where are your bridges at?

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#28291

BGA Rework | 28 April, 2004

Are your solder balls after reflow a perfect sphere or are they oblong, like chushed. I know a heavy bga or incorrect reflow profile could cause bridging. Also too much flux paste. Sometimes what we do is brush the flux paste onto the pcb pads instead of pasting it in a machine.

Paul

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#28294

BGA Rework | 28 April, 2004

Russ, The bridges tend to be on the 2 outside rows. But we have seen a few near the center.

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#28295

BGA Rework | 28 April, 2004

Paul, It is hard to tell with the bridge the shape of the shere. The balls that are not bridged look very symetrical as far as the sphere. It does not appear to be over compressed.

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#28296

BGA Rework | 28 April, 2004

How are you applying the flux paste? Stencil or my hand, brush or dot? Are you balling the BGA's or are they already pre-balled?

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#28297

BGA Rework | 28 April, 2004

Paul, We are applying the paste flux to the bga. We have a plate that has a 4mil step that we squeege flat and then dip the BGA into the flux.The BGA's that we are using are new components.

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#28300

BGA Rework | 28 April, 2004

Paul, We are applying the paste flux to the bga. We have a plate that has a 4mil step that we squeege flat and then dip the BGA into the flux.The BGA's that we are using are new components.

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RDR

#28302

BGA Rework | 28 April, 2004

This could be a long shot but here goes. I have found that if flux is applied in excess that it will actually "move the solderballs" during reflow. I have actually seen where the balls are completely outside the package and oviously there are shorts everywhere. I am going to assume that these parts are baked out and your profile does not have any excesseive ramp rates.

Try this lightly flux the PCB with a brush and see what happens.

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#28303

BGA Rework | 28 April, 2004

In rework, your thermal recipe needs to better mimic the recipe that your use in your reflow oven. Oh, that and proper preheating of the board and BGA. [Yano, if you get bored fighting this, rereflowing the board is within reason.]

That you are hitting on four of five cylinders indicates that you are not too far from the balance point. The different materials used in your BGA cause it to act like a bimetallic strip during the run-up heat during your recipe.

Prove that we're correct by setting your BGA on a piece of tempered glass [you can get it at a glass shop or fireplace store] and watch it jump around while you proceed through your recipe. At one time, Bob Willis posted a vid of the ball side of a BGA. In this vid, the balls "magically" joined together and bridged themselves. Nothing up the sleeve, no mirrors, nuthin'.

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mk

#28366

BGA Rework | 2 May, 2004

Use solid solder deposit for GGA's and you will not have shorts, opens, voids or need cleaning. Simple as that.

mkehoe@sipad.net www.sipad.net

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mk

#28367

BGA Rework | 2 May, 2004

Use solid solder deposit for BGA's and you will not have shorts, opens, voids or need cleaning. Simple as that.

mkehoe@sipad.net www.sipad.net

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